ABSTRACTS OF PRESENTATIONS FROM PACLIM2007
(May 13-16, 2007)
CHARACTERIZING REGIONAL MODES OF CLIMATE VARIABILITY IN
CALIFORNIA
JOHN T. ABATZOGLOU, KELLY T. REDMOND, AND LAURA M. EDWARDS
Western Regional Climate Center, Desert Research Institute,
Reno NV 89512
John.Abatzoglou@dri.edu
A novel approach is presented to identify regional patterns of climate variability in
California. Coherent regions of climate variability across the state are identified using principal
component analysis of monthly precipitation and temperature data from a wide network of
climate stations and the gridded PRISM dataset. This multivariate analysis results in the division
of California into 11 homogeneous regions with respect to variations in climate. Although largescale modes of climate variability dominate patterns statewide, the complex interplay between
circulation patterns and maritime and topographic influences leads to a number of important
regional modes of variability. These climate regions are useful in exploring mechanisms for
regional climate variability as well as for tracking variations in climate from 1895 to the present.
THE COLD EVENT 8,200 YEARS AGO: COSMOPOLITAN CONSEQUENCES OF A
PROVINCIAL PERTURBATION
DON BARBER
Geology Department, Bryn Mawr College, Bryn Mawr, PA 19010
dbarber@brynmawr.edu
NO ABSTRACT SUBMITTED
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SANTA BARBARA BASIN DIATOM RECORD SUGGESTS COINCIDENCE OF
COOLER SST WITH WIDESPREAD OCCURENCE OF DROUGHT IN THE WEST
DURING THE PAST 2,200 YEARS
JOHN A. BARRON
U.S. Geological Survey, MS 910, 345 Middlefield Road, Menlo Park, CA 94025
jbarron@usgs.gov
Diatom assemblages from the upper 4.50 m of sediment from Ocean Drilling Program
Hole 893A in the Santa Barbara Basin were studied every 5 cm. The varve chronology of Arndt
Schimmelman (written comm., 2006) suggests that this interval covers the period from ca. 2,240
cal yr B.P. to A.D. 1880 with sampling intervals ranging between 12 and 43 years. The diatom
assemblages in these 1-cm-thick samples are assumed to represent a composite of between 2.5
and 8 years of deposition. The ratio of the subtropical diatom Fragilariopsis doliolus to the
more cosmopolitan diatom Thalassionema nitzschioides (Fd/Tn) has been used successfully as a
sea surface temperature (SST) proxy in Holocene paleoclimatic studies off northern California.
Cooler intervals probably represent times when spring upwelling conditions were dominant over
summer conditions during the interval sampled. In the ODP 843A record Fd/Tn generally varies
between 0.0 and 0.5 with cooler intervals (< 0.20) more common than warmer (> 0.30) intervals.
Throughout the record of the past 2,200 years, a strong correspondence exists between lower
Fd/Tn (< 0.20) values and heavier oxygen isotope values in the Globigerina bulloides record of
Kennett and Kennett (2000), suggesting that diatoms and planktonic foraminifers record periods
of enhanced upwelling. These cooler intervals, including the Medieval Warm Period between
ca. A.D. 1000 and 1250, correspond with intervals of wider geographic occurrence of long-term
drought in the West, according to the tree ring studies of Cook and others (2004). The
relationship between cooler SST in the Santa Barbara Basin and more widespread drought in the
West is consistent with the hypothesis that long-term drought in the West is associated with La
Niña-like conditions in the Pacific Ocean.
Cook, E.R., Woodhouse, C.A., Eakin, C.M., Meko, D.M., and Stahle, D.W., 2004, Long-term aridity changes in the
western United States: Science, v. 306, p. 1015-1018.
Kennett, D.J., and Kennett, J.P., 2000, Competitive and cooperative responses to climatic instability in coastal
southern California: American Antiquity , v. 65, no. 2, p. 379-395.
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THE RELATION OF GREAT BASIN LATE QUATERNARY HYDROLOGIC AND
CRYOLOGIC VARIABILITY TO NORTH ATLANTIC CLIMATE OSCILLATIONS
L.V. BENSON (1), R.J. SPENCER (2), D. RHODE (3), L. LOUDERBACK (4),
AND R. RYE (5)
(1) U. S. Geological Survey, 3215 Marine Street, Boulder, CO 80303
(2) Department of Geology and Geophysics, University of Calgary, Alberta
T2N 1N4, Canada
(3) Division of Earth and Ecosystem Sciences, Desert Research Institute, 2215 Raggio Parkway,
Reno, NV 89512
(4) Anthropology Department, University of Nevada,1664 North Virginia Street, MS 096,
Reno, NV 89557
(5) U.S. Geological Survey, MS 963, Denver Federal Center, Lakewood, CO 80225
lbenson@usgs.gov
New data from the Lake Bonneville basin and previously published data from four
western Great Basin lakes indicates that some Heinrich events were associated with periods of
relative aridity in Great Basin lake basins and that Dansgaard-Oeschger stades were associated
with periods of alpine glacier advance in the Sierra Nevada. The climatically induced highstands
of Lake Bonneville, Mono Lake, and Pyramid Lake terminate shortly after Heinrich event 1.
Glacial recession in the Sierra Nevada and Wasatch Mountains appears to have occurred during
the climate warming that began at the end of Heinrich event 1 and that culminated in the
Bølling-Allerød warm period. Lake level oscillations occur in the Bonneville and Owens Lake
basins during the Preboreal oscillation and Younger Dryas interval; however, the wet period
does not appear to occupy the entire Younger Dryas interval. In general, a clear correlation
between the hydrologic balances of Great Basin lakes and Dansgaard-Oeschger (DO)
oscillations can not be made; however, the δ18O records for Lake Bonneville and Pyramid Lake,
in a smoothed sense, resemble the GISP2 δ18O record. This suggests the possibility, that
whatever the nature of the climate mechanism involved in producing DO oscillations, it also
affected the hydrologic balances of some, if not all, Great Basin lakes. The lack of obvious
coherence between the GISP2 and Great Basin hydrologic records suggests that the DO signal
was shifted in time and(or) space when it reached the Great Basin. We offer the hypothesis that
the change in size and shape of the Laurentide ice sheet associated with a Heinrich event caused
a shift in the mean position of the polar jetstream away from the catchment areas of some of the
Great Basin lakes. The coherence of Sierra Nevada glacial oscillations with DO events also
suggests the existence of a teleconnection between the western Great Basin and the North
Atlantic.
ON TELECONNECTIONS OF THE TREE RING RECORD IN THE TORREY PINE:
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ENSO, NAO, AND DROUGHT IN THE SOUTHWEST
W. H. BERGER
Scripps Institution of Oceanography, La Jolla, CA 92093-0244
wberger@ucsd.edu
The Torrey pine (Pinus torreyana) in northern San Diego County is restricted to a small
area along the coast, near Del Mar, with one other population existing on Santa Rosa Island. The
reasons for the restricted distribution is not known. Likewise, the history of the connection
between the two populations is obscure. What is known is that the tree-ring record of the San
Diego population largely reflects winter precipitation in southern California, which is in turn
informed by southwestern precipitation patterns that are linked to sea surface temperatures in the
tropical eastern North Pacific through (El Niño – Southern Oscillation) ENSO variations (Biondi
and others, 1997). Also, and rather surprisingly, southwestern patterns of precipitation are linked
to sea surface temperatures in the northern North Atlantic Ocean (Cayan and others, 1998); that
is, to the dynamics of the North Atlantic Oscillation (NAO). The dual linkage implies that the
Torrey pine record – and indeed all such records in the southwest – should bear a combination
signal from ENSO and (North Atlantic Oscillation) sources. If the ENSO and NAO contain
periodicities that are well defined (e.g., through linkage to astronomical forcing) the tree-ring
records should show the appropriate interference patterns in addition to the primary stimulation
periods. Thus, it should be possible to obtain some notion of the relative importance of the
ENSO and NAO linkage through history, as concerns the precipitation patterns in the southwest.
Clearly, such changes in linkage patterns greatly influence shifts in the distribution of floras and
faunas; that is, the ‘migration’ of plants and animals.
Biondi, F., Cayan, D.R., and Berger, W.H., 1997, Dendroclimatology of Torrey Pine (Pinus torreyana Parry ex
Carr.): American Midland Naturalist, v. 138, p. 237-251.
Cayan, D.R., Dettinger, M.D., Diaz, H.F., Graham, N.E., 1998, Decadal variability of precipitation over western
North America: Journal of Climate, v. 11, p. 3148-3166.
AN EXTREME TURN-OF-THE-CENTURY HYDROLOGIC EVENT RECORDED IN
δ18O FROM BRISTLECONE PINE TREE-RING CELLULOSE
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MAX B. BERKELHAMMER and LOWELL D. STOTT
Department of Earth Sciences, University of Southern California, Los Angeles 90089-0740
berkelha@usc.edu
The bristlecone pine chronology from the White Mountains of California has provided
important insight into the climate of the last two millennia. Ring-width chronologies from the
species have been shown to record subtle changes in climate, showing a strong correlation with
the Palmer Drought Severity Index, an integrated climate index incorporating both changes in
temperature and humidity. Previous studies have shown that the D/H and δ13C in the tree-ring
cellulose of bristlecone pines respond to low frequency changes in temperature (Feng and
Epstein, 1994) and soil moisture (Leavitt, 1994), respectively. This demonstrates the potential to
reconstruct climate characteristics otherwise hidden in the integrated ring-width data. Due
perhaps to the diminutive size of its rings, no previous study has attempted to create an annually
resolved stable oxygen isotope chronology for this species. Some studies suggest that at midlatitude locations tree cellulose δ18O can record changes in atmospheric circulation patterns that
influence the source of precipitation. Such a reconstruction from the bristlecone pines would be a
useful tracer of environmental history in California. Here we present preliminary δ18O (cellulose)
results from bristlecone pines from the White Mountains. The δ18O chronology follows a
distinctive bidecadal oscillation throughout the 20th century with peak excursions being on the
order of 4‰. This trend gives way to a dramatic enrichment of approximately 10‰ that began in
the latter part of the nineteenth century and continued in a stepwise fashion until it stabilized at
approximately 1860. The δ18O values were stable throughout the rest of the 18th and 19th
centuries. Previous studies of climate patterns in the western United States have also purported
to see a bidecadal hydrologic cycle. The phasing of the δ18O oscillation indicates a relationship
with Pacific-wide ocean-atmosphere systems that modulate the hydrologic cycle in the western
United States. Geochemical modeling of the cellulosic δ18O indicates that the only likely
candidate to explain the magnitude of the excursions could be changes in source water. This
provides further credence to the conclusion that the isotopic pattern is controlled by regional
hydrologic changes. The magnitude of the extreme event at the beginning of the 20th century is
unequaled in the record and suggests a major regime change that is consistent with the results of
other proxy records that show major environmental changes occurred during this time interval.
Feng X, and Epstein, S., 1994, Climatic implications of an 8,000-year hydrogen isotope time series form bristlecone
pine trees: Science, v. 265, no. 5175, p. 1079-1081.
Leavitt, S.W., 1994, Major wet interval in White Mountains Medieval Warm Period evidenced in δ13C of
bristlecone-pine tree-rings: Climatic Change, v. 26, no. 2-3, p. 299-307.
THE MAAR LAKES OF GUANAJUATO, MEXICO: HIGH RESOLUTION ARCHIVES
OF HOLOCENE CLIMATE CHANGE
ROGER BYRNE (1), JUNGJAE PARK (1), JAMES JOHNSTON (1), HARALD BOHNEL (2)
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LYNN INGRAM (3), WENBOW PARK (3), AND ULRIKE KIENEL (4)
(1) Department of Geography, University of California, Berkeley, CA 94720
(2) Centro de Geociencias, Campus UNAM Juriquilla, 76230 Queretero, Mexico
(3) Department of Earth and Planetary Science, University of California,
Berkeley, CA 94720
(4) GeoForschungsZentrum Potsdam, Section 3.3 Climate Dynamics and Sediments,
Telegrafenberg Haus C, D-14473 Potsdam, Germany
arbyrne@berkeley.edu
There are seven maar craters in the Valle de Santiago area of Guanajuato, Mexico. Two
of them, Rincon de Parangueo and La Alberca, had deep (50 m+) lakes until recent (post-1970)
lowering of the regional water table caused them to desiccate. The desiccation, which was due to
groundwater exploitation for irrigation, has made it possible to recover core samples directly
from the exposed lake floors. Since 2001 we have recovered numerous piston cores from both
Rincon and Alberca; the longest core from Rincon has a basal date of 9,000 cal years B.P., and
the longest core from Alberca a date of ca. 6,000 cal years B.P. Here we report on the pollen,
magnetic susceptibility, sediment chemistry, and stable isotopic composition of the Rincon
cores. The pollen record is rather complacent and is dominated by pine and oak pollen, both of
which reach the lake via long-distance dispersal. Changes in sediment chemistry reflect
alternating periods of drier and wetter climate, which in part are also evident in the pollen
record. The stable isotope records (oxygen and carbon) also indicate changes in precipitation
and evaporation throughout the Holocene. Of particular interest is a high resolution (subdecadal) isotope record that covers the last 2,000 years. This record provides new evidence of
solar forcing of climate in Central Mexico during the late Holocene.
RAPID BUT VARIABLE RESPONSES OF SIERRA NEVADA GLACIERS TO ABRUPT
CLIMATE CHANGE
DOUGLAS H. CLARK (1) AND NICOLE D. BOWERMAN (2)
(1) Geology Department, Western Washington University, Bellingham, WA 98225
(2) North Cascades National Park, Marblemount, WA 98267
Doug.Clark@wwu.edu
Detailed analyses of lake sediments below glaciers in the Sierra Nevada demonstrate that
the small glaciers are highly sensitive to changes in climate, but that their responses may not be
simple and monotonic (i.e., advances during cooling). Whereas moraines offer “snapshots” of
maximum glacier positions, proglacial lakes provide more complete records of glacier ebb and
flow. The lakes act as efficient sediment traps for rock flour emanating from the glaciers and
provide continuous, datable, high-resolution proxy records of extent and timing of glacier growth
and degradation. The moraines then provide a means to quantify the climate changes driving
these fluctuations.
The archetypal extreme climate event, the Younger Dryas, has spawned abundant
research efforts, and even a Hollywood disaster film. Although the event had a remarkable
effect on climate and glaciation in the circum-North Atlantic region, its effects elsewhere around
the globe were more subtle. In the Sierra Nevada, the Younger Dryas chronozone (YD) does not
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show as a significant glacial advance. Instead, lake records indicate that it was a cold, dry period
following closely on the heels of a small but regionally significant late glacial advance, the
Recess Peak event (~12,200-11,200 14C yr B.P.; 14,200-12,200 cal yr B.P.) Glaciers during the
YD, if extent, were smaller than those related to Neoglaciation because no YD moraines have
been identified in the range. This finding is consistent with sediment records from the east
(playas) and west (Santa Barbara Basin), which indicate cold and dry conditions elsewhere in
California during the YD. Glacial deposits from farther a-field (Cascade Range, Rocky
Mountains) indicate minor local glacier advances during the YD, but at a scale on par with those
related to Neoglaciation (~ 1-2 C).
Most mountains of the western US appear to have been glacier-free following the YD
until the late Holocene. Beginning about 3,200 14C yr B.P. (~ 3400 cal yr B.P.), cirque glaciers
began to reform in the Sierra Nevada and the CascadeRange, culminating with maximum
advances late in the Little Ice Age (LIA). In the Sierra Nevada, the Palisade Glacier appears to
have reached progressively greater maxima at ~ 2,800, ~ 2,200, ~ 1,600, ~ 700 and 250-170 cal
yr B.P. Since the last maximum, the lakes below the Palisade Glacier have experienced a
substantial decline in rock flour flux, despite the fact that the glacier was not actually retreating
for most of this period. Instead, this decreased rock flour flux appears to record the thinning of
the glacier. With such small glaciers, even minor thinning or shrinking related to ice loss
(negative mass balance) will reduce the flow velocity, which in turn reduces the production and
delivery of rock flour to the downstream lakes. The glaciers and adjoining lakes are thus highly
sensitive recorders of net snowfall in the mountains.
The combined records of moraines and alpine lake sediments provide clear constraints on
abrupt climate events in the western U.S. During the YD, glaciers throughout the region were
only locally slightly larger than during the height of the LIA, indicating a substantially
diminished climate event compared to that in the North Atlantic. Conversely, during the late
Holocene, glaciers in the Cordillera repeatedly expanded and contracted after 3,400 cal yr B.P.,
reaching their Holocene maxima during the past 150-200 years. Since then, glaciers throughout
the west have retreated significantly.
POST-YOUNGER DRYAS WARMING: AN ANALOG FOR THE NEXT 100 YEARS?
KENNETH L. COLE
U.S. Geological Survey, Southwest Biological Science Center, P.O. Box 5614,
Northern Arizona University, Flagstaff, AZ 86011
ken_cole@usgs.gov
Recent paleotemperature data from northern Arizona indicating a rapid temperature
increase at end of the Younger Dryas correlate well with global records . The δ13C values and
presence of Utah Agave in fossil packrat middens from the Grand Canyon suggest that winter
temperatures increased by at least 4 oC between ca. 11,700 and 11,500 years ago. The timing of
this rapid warming at the end of the Younger Dryas is indistinguishable from similar increases
observed in the better-dated records from Greenland ice cores and eastern Pacific Ocean cores.
The rate and magnitude of this warming is similar to that projected for the next century.
Previous studies have noted unusual, anomalous plant communities typical of the very
early Holocene immediately follow this rapid temperature increase. Packrat midden records
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suggest that species diversity was lower during this time and that plant communities were
dominated by mid-seral species typical of substrates that are several hundred years in age, such
as Acacia greggi at low elevations and Fraxinus anomala at middle elevations. Higher-elevation
pollen records from this time are often poorly constrained by radiocarbon dates, yet some
contain higher levels of some early successional species such as Artemisia spp., Poaceae, and
Asteraceae. Earlier interpretations of these anomalous assemblages have focused on such things
as the high levels of summer insolation during this period. More precise chronological control
suggests that because of the rapid temperature warming just prior to this period, a successional
perspective on this vegetation change may allow a more robust understanding. If plant
successional dynamics did cause these unique early Holocene assemblages, then similar changes
should be expected in the future due to the continuing effects of global warming.
DYNAMIC SIMULATION MODELING OF MOSQUITO POPULATIONS WITH
CLIMATE DATA
ANDREW C. COMRIE AND CORY MORIN
Department of Geography and CLIMAS Project, University of Arizona, Tucson, AZ 85721
comrie@arizona.edu
Climate is an important control on populations of mosquito disease vectors such as Aedes
aegypti. Improved understanding and modeling of climate effects on mosquito populations is
needed to help predict disease epidemics, and to understand the impacts of climate on
mosquitoes as disease vectors. There is a surprisingly limited number of mosquito models with a
climate component reported in the literature. The majority of these are empirical and statistical,
and in particular, there are no dynamic simulation models. In this study we report on the
development of a dynamic mosquito population model driven in part by climatic data. Model
inputs include temperature, precipitation and relative humidity that influence mosquito
population development through maturity and mortality in relation to temperature, population
density, and water availability. These factors are considered through all phases of mosquito life
cycle development from mosquito ovulation though each larval stage to pupae and finally adult.
Temporal resolution is daily, and the model can be calibrated for specific mosquito species and
locations. We use the model to evaluate the role of climate variability in mosquito populations,
using Tucson, Arizona as a case study. Using different versions of the model we examine the
relative behavior of the species of mosquito most likely to dominate the mosquito population
given a specific area and climate. We also provide model results on the effects of different types
of climate change and variability, including abrupt change and ENSO impacts.
RAIN-FED FLOOD RISKS IN A WARMING WEST
MICHAEL DETTINGER (1), DANIEL CAYAN (1), AND JESSICA LUNDQUIST (2),
(1) U.S. Geological Survey, Scripps Institution of Oceanography, La Jolla, CA 92093
(2) University of Washington, Seattle, WA 98195
mddettin@usgs.gov
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In recent decades, western North America has warmed significantly with far-reaching
hydrological and landscape consequences. For example, precipitation falls more often now as
rain rather than snow, springtime snowpacks are smaller, the annual hydrographs of snow-fed
streams now rise earlier in the year, plants are greening and blooming earlier, and wildfire risks
have increased. One important aspect of the western landscape that does not appear to have
trended in statistically significant ways is the occurrence of floods. Documentation of flood-risk
responses to recent warming, to the extent that such responses may exist, is difficult because
floods are extreme and infrequent events and thus many decades of warming may be required
before the changes can be confidently detected, even under the best conditions. Another factor
that makes detection of flood-risk changes difficult is that we do not yet know what kinds of
changes we should be looking for: Will western floods become more common or less, more
severe or less, different in origins from historical floods or more of the same?
A well-documented flood in Yosemite National Park on 16 May 2005 provides an
example of one way that floods may be expected to change in a warmer world, because the flood
generation was driven directly by unusually warm storm-time conditions, rather than by extreme
precipitation amounts (only ~ 2.5 cm of precipitation fell) and without deriving much of its flow
from melting snowpacks (which may not be as large in a warmer world). A Pacific storm drew
warm, wet subtropical air into the Sierra Nevada, causing moderate rains and major flooding
(ninth largest flood peak in 90 years of record) in Yosemite Valley. The flood derived its runoff
mostly from high-altitude rainfall on soils already wet due to the onset of spring snowmelt a few
days earlier. No significant snow-water content changes were measured. Flooding occurred
because, although the average storm in Yosemite provides rain—rather than snow—to only
about 15% of the park’s river-basin areas, this storm was warm enough to blanket 85% of the
park with rain, vastly increasing the area and runoff volumes contributing to the flood.
This flood is an example of one way that flood generation and risks are likely to change
in a warmer world: The flood was caused by warmer, rainier than normal conditions rather than
by intense precipitation. The flood did not result from rain that melted snow, which will
presumably be less common in a warmer world. The flood was made possible because the soils
were already wet from earlier snowmelt. To the extent that snowpacks still blanket western
mountains in a warmer climate, they are likely to form from warmer, wetter snows and to remain
warmer and wetter until they melt (earlier). Thus soils are likely to receive more frequent
replenishments during the winters and springs of a warmer world, so that flood facilitation by
wetter soils may become more common in the warmer world.
From our growing cache of temperature observations in the high country of Yosemite
National Park, we have learned that storm-time temperature lapse rates tend to conform to moistadiabatic conditions, cooling fairly regularly by about -6.5 ºC for every kilometer of elevation
rise. Thus the 90 year historical record of wet-day temperatures measured in Yosemite Valley
can be extrapolated over the topography to estimate, on a storm-by-storm basis, what fractions of
the river basins received rain rather than snow. This exercise shows that the May 2005 storm was
quite unusual in terms of the large basin area that received rain rather than snow. Such raincontributing areas have been encountered during only about 0.6% of all historical storms
yielding more than 2.5 cm of precipitation, or four times in 95 years. If a modest +3 ºC warming
is imposed on the historical record — to represent the simplest form that continued warming
trends could take--such runoff-contributing areas are encountered much more often, occurring in
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about 5% of storms or in about one year in three, thereby increasing the opportunities for this
type of flooding dramatically, even if the intensities or frequencies of precipitation extremes do
not change. Notably, a comparison of how often the day of each year’s maximum flow in the
Merced River were wet or dry historically indicates that annual-flood peaks on wet days became
considerably more common as the 20th century progressed. Decadal counts of the numbers of
wet- vs dry-day flood peaks rose from no wet-day floods, or 100% dry-day snowmelt-fed flood
peaks, in the 1920s to about 60% wet-day, rainfed flood peaks in the 1990s.
These results from Yosemite rivers can be extrapolated to other rivers in the Sierra
Nevada and across the conterminous U.S., and when this is done, a sobering picture emerges:
The Sierra Nevada, together with the Cascade Range, are by far the most susceptible to increased
flood risks due to increases of rainfed basin areas with warming. With a +3 ºC warming, the
number of opportunities for rain-fed flood generation to occur might be expected to increase by
as much as 5-10 additional flood opportunities per year in broad swathes of the Sierra Nevada
and Cascade Range; while in most of the rest of the west (as in the rest of the country),
opportunities for such rain-area driven floods do not increase by more than a couple
opportunities per decade. Thus, whether or not storms become larger or more frequent, and with
or without future snowpacks, the Pacific Coast states should expect their flood risks to increase
significantly if recent warming trends continue.
AIR TEMPERATURE, COLD AIR DRAINAGE, AND TOPOCLIMATIC
EFFECTS IN THE LAKE TAHOE BASIN
SOLOMON Z. DOBROWSKI (1), JONATHAN GREENBERG (2), GEOFF SCHLADOW (1)
(1) Tahoe Environmental Research Center, University of California, Davis, CA 95616
(2) Center for Spatial Technologies and Remote Sensing, University of California,
Davis, CA 95616
szdobrowski@ucdavis.edu
Air temperature exhibits complex spatial and temporal patterns in mountain
environments. Spatial estimates of air temperature in these environments are often estimated at
coarse spatial grains while more fine-grained estimates often rely solely on elevation-based lapse
rates. We provide a case study of the development and interpretation of fine-scale and
physiographically informed spatial temperature estimates within the Lake Tahoe Basin. As a
reference, we characterize daily elevation-based lapse rates for the study area over a 10 year
period for minimum, maximum, and average temperatures using data from 14 SNOTEL stations.
We then employ a regional regression modeling approach that utilizes a single, domain wide,
multivariate regression function between temperature and elevation, solar insolation, topographic
convergence, latitude, and longitude. To drive this model, we utilize GIS terrain analysis
techniques to model topographic convergence as a proxy for cold air drainage, and a mechanistic
solar radiation model. Our results demonstrate that for minimum temperature, approximately
40% of the daily observations exhibited positive lapse rates, the majority of which occurred
through the summer months (May- September). In contrast, 4% of the maximum and average
temperature lapse rates were positive, the majority of which occurred during the winter months
(November-March). This latter group showed concomitant positive minimum temperature lapse
rates suggesting temperature inversions that persisted over the course of a day or over multiple
10
days. Results from the regional regression model show that elevation has little explanatory
power when characterizing minimum temperatures. In contrast, topographic convergence (a
measure of cold air drainage) has substantial explanatory power. Average temperatures show
sensitivity to elevation, topographic convergence, and solar insolation. Our results demonstrate
that spatial modeling of air temperature estimates in mountain environments greatly benefit from
physiographically informed modeling techniques. Moreover, our results have direct implications
on the use of spatial temperature estimates for climate change impact assessments.
ANALYSIS AND SUMMARY OF JULY 2006 RECORD-BREAKING
HEAT WAVE IN CALIFORNIA
LAURA M. EDWARDS (1) AND DANIEL R. KOZLOWSKI (2)
(1) Western Regional Climate Center, Desert Research Institute, 2215 Raggio Parkway,
Reno, NV 89512-1095
(2) California-Nevada River Forecast Center, 3310 El Camino Avenue,
Sacramento, CA 95821-6373
laura.edwards@dri.edu
A record-breaking heat wave affected much of the state of California during the period
from Sunday, July 16 through Wednesday, July 26, 2006. Although numerous daily maximum
temperature records were set, the aspect that made this event unique was the elevated overnight
minimum temperatures at several reporting stations. This was especially true in the southern
Sacramento Valley and much of the San Joaquin Valley. Along with the intensity of this heat
wave, the duration of abnormally high maximum and minimum temperatures was particularly
noteworthy. Previous studies have shown that the duration of a heat episode is an important
factor to consider when determining its impact. These factors, along with the meteorological
synoptic situation, local effects and impacts, were addressed in this study of the July 2006
California event.
CHANGES IN RAINFALL AND WATER AVAILABILITY ON ISLA ISABELA, GULF
OF CALIFORNIA
AMY ENGLEBRECHT (1), LYNN INGRAM (1), ROGER BYRNE (2), ULRIKE KIENEL (3),
HARALD BOEHNEL (4), AND GERALD HAUG (3)
(1) Department of Earth and Planetary Science, University of California, Berkeley, CA 94720
(2) Department of Geography, University of California, Berkeley, CA 94720
(3) Department 3.3 Climate Dynamics and Sediments, GeoForschungsZentrum
Potsdam, Potsdam Germany
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(4) Centro de Geociencias, Universidad Nacional Autonoma de Mexico
Campus Juriquilla, Querétaro Mexico
aenglebrecht@berkeley.edu
Here we use the stable isotopic composition (oxygen and carbon) and pollen content of
seasonally laminated lake sediments from Isla Isabela (21 52’ N, 105 54’ W) to reconstruct
the history of recent climate change in northwestern Mexico. Isabela crater lake is located
approximately 30 km offshore the state of Nayarit, in the precipitation region of the Mexican
Monsoon (also called North American Monsoon). Work on a short core indicates coherent
periodicities in δ13C and δ18O values from bulk inorganic carbonate throughout the past two
centuries. Most notably, strong excursions in δ13C and observable sedimentological changes
occur at depths in the core corresponding to the 1780s, 1810s, 1860s, 1950s, and 1973-74 —
recognized periods of historical drought in Mexico. Further downcore work reveals additional
periods of reduced water availability that may correspond to variations in the Mexican Monsoon.
CAN HYDROGEN ISOTOPE RATIOS IN PLANT LIPIDS PROVIDE A
QUANTITATIVE PROXY FOR ARIDITY?
SARAH J. FEAKINS AND ALEX L. SESSIONS
California Institute of Technology, Mail Stop 100-23, Pasadena, CA 91125
feakins@gps.caltech.edu
Hydrogen isotopic fractionation within the hydrological cycle respond strongly to
climatic variables, including evaporation. We are investigating whether the D/H ratios of leafwax lipids can provide a quantitative proxy for aridity. Under low precipitation, high
evaporation climate regimes, differences in water uptake, conservation, and biosynthesis
between plant species may exert a significant control on the hydrogen isotopic composition of
plant leaf waxes. We measure the D/H ratios of environmental waters, xylem water, leaf water,
and leaf wax lipids in order to quantify the isotopic enrichment within individual plants. We
survey a diverse range of species and floristic regions across an aridity gradient in southern
California in order to assess the range of isotopic compositions of plant leaf waxes and
enrichment factors associated with ecological and climatic differences. Preliminary data from
this sampling program will be presented at the meeting.
SEA SURFACE TEMPERATURE, DROUGHT, AND DROUGHT PREDICTION
IN CALIFORNIA
IAN FERGUSON (1,2) AND JOHN DRACUP (1)
(1) Department of Civil and Environmental Engineering, University of California,
Berkeley, CA 94720
(2) Lawrence Livermore National Laboratory, Livermore, CA 94550
iferguson@berkeley.edu
Droughts are complex ocean-atmosphere phenomena, with impacts on virtually all
12
human and environmental systems at timescales ranging from seasonal to inter-decadal. Since
1863, eleven droughts have affected California, with lengths ranging from two to six years. The
last major drought in California occurred from 1987 to 1992; water managers are anxious that
the low 2006-07 Sierra Nevada snowpack is the beginning of California’s next drought.
While several studies have shown that ocean-atmosphere interactions influence seasonal
and longer scale climate variability, the physical mechanisms that lead to drought events are not
well understood. Here we evaluate seasonal-to-interannual drought characteristics in the
Sacramento and Colorado River basins, which together supply most of California’s municipal,
industrial, and agricultural water. Using a global sea surface temperature (SST) dataset, we
evaluate the relationship between SST anomalies and drought in both basins. While a simple
correlation analysis shows that 20th century streamflow variability is significantly correlated with
SST anomalies over several ocean regions—most notably the tropical Pacific—a composite
analysis of individual drought events shows only a weak relationship between SST anomalies
and droughts. Results are discussed with respect to the physical mechanisms of drought and the
potential for long-lead drought prediction.
FLOOD VARIABILITY IN RESPONSE TO CLIMATE VARIABILITY,
SACRAMENTO-SAN JOAQUIN RIVER SYSTEM, CALIFORNIA
JOAN L. FLORSHEIM (1) AND MICHAEL DETTINGER (2)
(1) Geology Department, University of California, Davis, CA 95616
(2) U.S. Geological Survey, Scripps Institution of Oceanography, La Jolla, CA 92093
florsheim@geology.ucdavis.edu
Climate variability governs river discharges and flood variability and thus modulates a
river’s ability to accomplish geomorphic work. We explore the propensity of climate
phenomena such as El Niño and La Niña phases of the ENSO cycle, positive and negative phases
of the PDO, and seasonal “pineapple-express” storms to initiate river discharges and floods
capable of causing geomorphic change in California’s Sacramento-San Joaquin River system.
Historical levee breaks serve as a metric of the potential for geomorphic change and dangerous
flood damage, representing an important way that the anthropogenically altered system currently
responds to floods. Time series analysis of post-dam discharge and flood records from three
representative stations shows a signal with a period of ~10-15 years with slight differences from
north to south. In this decadal context, strong relations exist between levee breaks and annual
peak discharge normalized by the mean of the peaks over the period of record (Qpeak/Qmean(pk)).
Qualitatively, it appears that high flows caused by pineapple-express storm conditions generate
levee breaks. As suggested by the non-standard 10-15 year time scale noted above, on multiyear time scale, relatively poor relations exist between annual numbers of levee breaks and
phases of cyclic climate phenomena such as ENSO and PDO. The history of levee breaks
through the 20th century does not indicate that the presence of flood control infrastructure such as
dams and levees has reduced the frequency of breaks. A better understanding of the influence of
climate variability on floods and their geomorphic consequences in the modern fluvial system
will aid in improving hazard-risk assessments.
CLIMATE CHANGE’S INFLUENCE ON SUDDEN OAK DEATH
13
SUSAN J. FRANKEL
U.S.D.A. Forest Service, Pacific Southwest Research Station, Albany, CA 94710
sfrankel@fs.fed.us
Sudden Oak Death, caused by the exotic invasive plant pathogen Phytophthora ramorum,
was first recognized in California in the mid-1990s. Over the past decade, millions of tanoak
(Lithocarpus densiflorus) and coast live oak (Quercus agrifolia) have been killed from Big Sur
(Monterey County) north to Curry County, in southwest Oregon. The pathogen also causes nonlethal, sporulating infections on camellia, rhododendron, and other popular ornamental nursery
plants which can serve as vehicles for long-distance spread. Phytophthora ramorum was new to
science upon its discovery in 2000. Researchers are just now unraveling the biology and ecology
of this pathogen in coastal redwood/tanoak and mixed evergreen forest ecosystems. Extremes in
climate appear to be increasing tree mortality and inoculum levels in California’s infested
forests. The global risk of pathogen establishment is also being influenced by changes in
climate.
LAKE TAHOE AND THE WORLD WATER CRISIS
CHARLES R. GOLDMAN
Distinguished Professor of Limnology, Environmental Science and Policy, University of
California, Davis, CA 95616
crgoldman@ucdavis.edu
The World Water and Climate Network (WWCN) was established to assemble the best
possible information on inland water problems associated with climate change. The effects of
climate change and variability on the thermal structure of Lake Tahoe were studied over a 32year period. The changes in thermal structure were related to an upward trend in air temperature
since 1970 and a four-year decline, probably due to volcanic activity, followed by recovery in
solar radiation. Thermal structure changes in Lake Tahoe included a long-term warming trend,
the expected increase in resistance to mixing, and a trend toward decreasing depth of the October
thermocline. The implications of these and other changes studied over almost a half-century at
Lake Tahoe and Castle Lake in northern California have direct application for anticipating the
impact of climatic change and global warming on the world’s surface water supplies.
HOLOCENE FIRE HISTORY OF CONIFER FORESTS IN THE SIERRA NEVADA OF
CALIFORNIA, SOUTHERN BRITISH COLUMBIA, AND COASTAL ALASKA, AND
ITS CONNECTION TO ABRUPT CLIMATE CHANGE
DOUGLAS J. HALLETT (1), R. SCOTT ANDERSON (2),
AND DANIEL G. GAVIN (3)
(1) Department of Geography and School of Environmental Studies, Queen's University,
Kingston, Ontario, K7L 3N6 Canada
(2) Center for Environmental Sciences & Quaternary Sciences Program, Box 5694,
Northern Arizona University, Flagstaff, AZ 86011
(3) Department of Geography, University of Oregon, Eugene, OR 97403-1251
14
hallettd@post.queensu.ca
Synchrony of forest fire activity between independent lake sites can be tested using welldated millennial-scale records of sedimentary charcoal. Paleo-fire records have the potential to
demonstrate large-scale climatic control of crown fire response across forest ecosystems. Fire
episodes recorded at three sites in the Sierra Nevada show significant synchrony across 100 to
1,000-year windows for the overlapping portions of the record (8,500 cal yr B.P. to present).
Frequent fire episodes tend to cluster during portions of the middle and late Holocene and may
indicate a response to the onset of enhanced ENSO activity. The 13,500-year-long charcoal
record from Swamp Lake, Yosemite National Park displays frequent fire activity during the early
Holocene and an increasing, but periodic, trend in fire episode frequency from 8,000 cal yr B.P.
to present. This trend in fire episode frequency and the raw charcoal data corroborate well with
other proxy records that reconstruct century-scale variability of ENSO frequency during the
Holocene. Synchronous fire response occurs during the Mediaeval Climatic Anomaly (1,000700 cal yr B.P.) at all the Sierra Nevada sites and supports other paleoenvironmental records in
the region. Long-term fire history records from southern British Columbia and Alaska show a
response to Neoglacial climate change and the advance of regional glaciers in the late Holocene.
Significant synchrony between fire episodes at five British Columbian lake sites (7,000 cal yr
B.P. to present) also occurs across 100 to 800-year windows. Synchronous forest fire response
at these independent sites is another important test linking large-scale circulation features to
ecosystem disturbance. We suggest that century-scale climate variability is an important control
on forest fire response across 50° N and future changes in climate will produce abrupt shifts in
disturbance regimes across Pacific states and provinces.
CHANGING PERIODIC BEHAVIOR OF THE HOLOCENE NORTH AMERICAN
MONSOON FROM VARVED SEDIMENTS IN THE
GULF OF CALIFORNIA
ANN MARIE HARRIS AND ROBERT E. KARLIN
Department of Geological Sciences, University of Nevada, Reno, NV 89519
thelite@ix.netcom.com
Laminated sediments from DSDP Site 480 in the central Gulf of California yield a
virtually continuous sedimentation record of monsoonal circulation down to a sub-annual scale
for the interval from 11,500 to ~1,800 years ago. Site 480 lies under the influence of the North
America Monsoon (NAM) with seasonally reversing winds resulting in winter upwelling with
high diatom productivity and summer deposition of aeolian terrigenous material. An annually15
resolved paleoclimate history of the Holocene was extracted from digital images of radiographs
of the Site 480 Cores by identifying and counting annual and sub-annual units and measuring
their thicknesses. The varve chronology agrees very closely with the independent chronology
constructed from available radiocarbon and isotopic ages. This suggests that the varve record is
complete and that seasonal monsoonal circulation has persisted over the Gulf throughout the
Holocene.
Holocene sedimentation on annual and seasonal scales is somewhat chaotic, but has ~50to 500-year long intervals with characteristic patterns showing quasi-periodic behavior. Both the
annual and seasonal proxies have periodicities which wax and wane throughout the Holocene.
The most significant periodicities falling within the decadal (10-11 year) and bi-decadal (18-22
years) solar cycles and the Pacific Decadal Oscillation (PDO) (20-50 years). The fewest and
shortest annual and seasonal periodicities are in the bi-decadal to ENSO range and occur in the
early Holocene from 11,500 to 10,400 and 9,400 to 8,900 cal yr B.P. Predominant annual
periodicities shift back and forth between bi-decadal to PDO range to the decadal to bi-decadal
range on a millennial-scale until 4,100 cal yr B.P. Annual patterns are less persistent from
4,100 cal yr B.P. to ~1,800 cal yr B.P. Seasonal patterns are similar to the annual ones in about
half of the intervals. Dissimilarities between the varve and both seasonal records are primarily
due to the weakness of one or both of the seasonal signals. Persistent decadal and bi-decadal
signals in summer sedimentation from 6,500 to 7,700 cal yr B.P. and a coincident summer
insolation maximum suggest a solar influence on the strength of the summer monsoon. There is
little to no periodicity the summer sedimentation from 4,200 to 2,400 cal yr B.P. associated with
overall lower and highly variable sedimentation. Periodicities in winter sedimentation are not as
persistent and undergo abrupt shifts on a centennial to millennial scale. In general, fewer
periodicities and lower frequencies tend to be associated with intervals of lower winter
sedimentation. Low overall sedimentation at 9,300-9,000, 8,850-8,700, and 8,100-8,000 cal yrs
B.P. appear to indicate weak monsoonal circulation.
DROUGHT AND FAILURE OF PACIFIC-NORTH AMERICAN MONSOON DURING
THE HOLOCENE FROM VARVED SEDIMENTS AT DSDP SITE 480 IN THE GULF
OF CALIFORNIA
ANN MARIE HARRIS AND ROBERT E. KARLIN
Department of Geological Sciences, University of Nevada, Reno, NV 89519
thelite@ix.netcom.com
Laminated sediments from DSDP Site 480 in the central Gulf of California contain a
virtually continuous sedimentation record of monsoonal circulation down to a sub-annual scale
and multidecadal- to centennial- scale summer droughts for the interval 11,500 to ~1,850 cal yr
B.P. Site 480 lies under the influence of the Pacific-North America Monsoon (PNAM) with
seasonally reversing winds, resulting in winter upwelling with high diatom productivity and
16
summer deposition of aeolian terrigenous material. Varve counts and laminae width
measurements were made using densiometry of x-radiographs of sliced and half core sections to
create a varve chronology and sedimentation history. An independent chronology was
constructed from available radiocarbon and isotopic ages. The age model was refined by
comparing paleosecular variation records at Site 480 with well-dated inclination records from
Saanich Inlet, British Columbia. The varve chronology agrees very closely with the age model,
suggesting that the varve record is complete and that seasonal monsoonal circulation has
persisted over the Gulf throughout the Holocene.
Both monsoonal intensity and summer precipitation generally have increased since the
early Holocene as evidenced by increasing annual and seasonal sedimentation toward the
present. The long-term trend does not appear to be due to compaction. Superimposed on the
long-term linear trend are several large-scale, episodic fluctuations 500-1,000 years in length.
Weaker winter upwelling and lower summer terrigenous sedimentation rates occur during the
intervals from 11,500-10,400, 9,400-9,000, and 3,850-3,100 cal yr B.P. The interval from 8,2006,700 cal yr B.P. also averages less than the long-term linear trend and includes two abrupt,
multi-centennial-scale drops in sedimentation, suggesting drought conditions. The 8,200-8,000
yr B.P. drought correlates with a high latitude 8,200 yr B.P. cold event observed elsewhere. A
similar drought present at ~7,200 yr B.P. may be more regional in nature. Most multi-decadal to
centennial-scale declines in sedimentation at DSDP Site 480 correspond to periods of intense
drought along the northern border of the PNAM region.
THE RESPONSE OF THE CALIFORNIA MARGIN TO RAPID CLIMATE CHANGE:
INFLUENCES OF CHANGING ATMOSPHERE AND OCEAN CIRCULATION ON
THE MARINE ENVIRONMENT
INGRID L. HENDY
Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48109-1063
ihendy@umich.edu
The discovery of large abrupt submillennial scale climate change in ice cores
fundamentally altered our perception of climate change. Paleoclimate research objectives
following this discovery have focused on identifying the forcing mechanisms behind these
profound changes. ODP Site 893, Santa Barbara Basin (SBB) produced the first rapid climate
change record outside the Atlantic. The impact of this discovery was twofold. First, it
demonstrated a possible global influence of these events, and second, amplification of forcing
17
mechanisms had to have occurred to produce the magnitude of changes identified in this key
record. In recent years, research along the California Margin has focused on further
understanding aspects of local atmosphere and ocean circulation and their response to
submillennial climate variability. Our understanding of the California Margin marine
environmental response to submillennial scale climate variability during Marine Isotope Stage
(MIS) 3, the deglaciation and the late Holocene is summarized.
The warm climatic events of MIS 3 in SBB were characterized by sea surface
temperatures (SSTs) warmer than 12 C and a planktonic foraminiferal assemblage dominated
by dextral (right coiling) Neogloboquadrina pachyderma and Globigerina bulloides. Along with
these foraminiferal assemblage changes, the isotopic differences suggest a stable, strong
thermocline. The oxygen minimum zone (OMZ; 400 and 1000 m water depth) was present and at
~ 400 m water depth subsurface water was warm (~ 6 C). The Point Conception upwelling cell
was active, and the high nutrient content of upwelled water stimulated G. bulloides blooms and
marine snow production. Cool intervals of MIS 3 in comparison were < 8 C and associated with
an isothermal water column (no apparent thermocline) demonstrated by a sinistral (left coiling)
N. pachyderma, Globigerina quinqueloba, and Globigernita glutinata assemblage and the
isotopic similarity between G. bulloides and N. pachyderma. Subsurface water was cool (~ 3
C) and well-oxygenated, suggesting the production of an intermediate water mass in the North
Pacific. The transition between warm and cool intervals was rapid (< 50 years), but more abrupt
during cooling. The sequence during warming was as follows: Gradual warming of intermediate
waters occurred 60 to 200 years prior to abrupt surface waters warming and reduced ventilation.
A further reduction in subsurface ventilation and increased productivity then followed surface
warming.
Deglaciation was for the most part similar to MIS 3 with the rapid warming of the
Bølling-Ållerød resembling the warm intervals of MIS 3, and the Younger Dryas akin to the cool
intervals. Several distinct differences occur however: First, productivity during the Bølling was
more pronounced than any other interval of the last 60,000 years. Second, productivity dropped
during the Ållerød and Younger Dryas, however, oxygen concentrations increased only during
the Younger Dryas. This is the strongest evidence yet for changes in North Pacific Intermediate
Water (NPIW) production ventilating the California Margin OMZ. Climate change during the
last two millennia follow some of the patterns that occurred during the last glacial. During the
Medieval Warm Period (A.D. 800 to 1200) surface waters were warmer than 10 C and well
stratified as indicated by an assemblage dominated by dextral N. pachyderma and isotopic
differences between G. bulloides and N. pachyderma. In contrast, during the Little Ice Age (LIA;
A.D. 1300 to 1700) SSTs rapidly cooled (> 8 C for a portion of the year) and the water
column became isothermal. Differing to MIS 3, these warming and cooling trends are not
apparent in the planktonic foraminiferal isotope record and upwelling increased during the LIA.
The bi-modal shift between dextral N. pachyderma-G. bulloides and sinistral N.
pachyderma-G. quinqueloba assemblages has been associated with atmospheric pressure system
changes in the Pacific. A strong North Pacific high pressure system during warm intervals
intensified upwelling and strengthened the California Current System (CCS) such that the
California Countercurrent advected warm water into SBB. During cool intervals, a strong
Aleutian Low resulted in subpolar characteristics of water advected into the CCS. Cooling of the
North Pacific also led to greater NPIW production in the Sea of Okhotsk, and subsequent
ventilation of the OMZ along the North American margin. In contrast to the last glacial, cooling
18
during the LIA may be related to strengthening of global atmospheric circulation rather than
relative changes in the North Pacific High and Aleutian Low.
A HYPOTHESIS FOR THE 1976-1977 WESTERN DROUGHT
JAMES JOHNSTONE
Department of Geography, University of California, Berkeley, CA 94720
jajstone@berkeley,edu
During the winter of 1976-77, the western U.S. experienced the most severe
meteorological drought in over a century of instrumental records. The anomalous circulation
pattern surrounding this drought is discussed, and a hypothesis is presented for its occurrence,
based on the connection of related biennial and decadal global oscillatory waves. The nature of
the cycle coupling tended to inhibit severe drought winters during most of the 20th century; the
anomalous conditions of 1976-77 are attributed to a temporary alteration of the long-term phase
relationship.
THE 20,000 YEAR LAKE RECORD OF THE SALTON BASIN: APPLICATIONS OF
AMS 14C, δ 18O, δ13C AND δ87Sr ON THE LAKE TUFA DEPOSITS
HONG-CHUN LI (1,2)
(1) Department of Earth Sciences, National Cheng-Kung University, Tainan, Taiwan 701
(2) Department of Earth Sciences, University of Southern California, Los Angeles,
CA 90089-0740
hli@usc.edu
Investigation of δ18O and salt content of surface waters in the Salton Basin, California,
shows that there is a strongly positive correlation between δ18O values and salt contents and that
the δ18O of Salton Sea is much heavier than that of its input waters due to strong evaporation.
The 87Sr/86Sr ratio of Salton Sea is very close to that of the Colorado River input, but much
lower than that of Whitewater River which is another major tributary.
During the past four years, we have made 37 AMS 14C measurements on samples
including lake tufa, mollusk shell and charcoal from the ancient Lake Cahuilla, Salton Basin.
Three tufa slabs, LC-1 (64-cm thick), SST-1 (19-cm thick) and SST-5 (38-cm thick), reveal 14C
ages of 1,7840±80 to 1,310±30 yr B.P. (15 dates), 4,790±25 to 1,365±20 yr B.P. (5 dates) and
7,080±20 to 1,265±15 yr B.P. (9 dates), respectively. All age results show minor influence of
reservoir effect and are in stratigraphic order. These dates indicate that Lake Cahuilla in the
Salton Basin had a continuous history during 20,500-800 yr B.P. when the tufas grew
continuously in the lake. Between 18,000 and 1,300 yr B.P., Lake Cahuilla level was above 24m a.s.l. which was at least 50 m higher than modern Salton Sea. Between 7,000 and 1,300 yr
B.P., the lake stayed at the highest level — 12 m a.s.l. which was 87 m higher than Salton Sea.
During these periods, Colorado River was connected with the Salton Basin. After 1,300 yr B.P.,
the lake dropped its level rapidly, probably due to both arid climates and a change in course of
Colorado River. Salton Basin became a part of Sonora Desert after 1,300 yr B.P. Human
occupation on the lake shore below 12m a.s.l. should be before 7,000 yr B.P. or after 1,300 yr
19
B.P.
The Sr isotope measurements made on LC-1 and SST-1 exhibit relatively constant
Sr/86Sr ratios throughout the past 20,000 years and the average is very close to that of the
Colorado River input. This means that the Colorado River input was the dominant water source
for Lake Cahuilla at least during 20,500-800 yr B.P. Hence, the paleoclimatic proxies retrieved
from the Lake Cahuilla tufas in the Salton Basin can decipher the discharge and flood history of
the Colorado River under the influence of climate variability in the Colorado River drainage
basin.
Theδ18O and δ13C values of LC-1 and SST-1 indicate that the lake experienced closed
and/or overflowed conditions between 20,500 and 800 yr B.P. The variations in δ18O and δ13C
values reflect changes in the relative humidity in Salton Basin and variations in the Colorado
River inflow and hence climatic conditions in the Colorado River drainage basin. The tufa
records exhibits palaeoclimates of Salton Basin as follows: (1) Relatively dry climate between
20,000 and 18,000 yr B.P. was followed by a wet climate between 18,000 and 17,000 yr B.P.. (2)
Decreasing effective moisture (precipitation − evaporation) from 17,000 to 16,000 yr B.P.
corresponded to Heinrich 1 event, whereas effective moisture increased at ca.15,500 yr B.P.
during the Trans-US Wet Period. (3) From 15,200 to 14,500 yr B.P., the effective moisture
decreased, and followed by a strongly increased effective moisture until 14,000 yr B.P. probably
corresponding to the Bølling-Ållerød interstadial. (4) Climate in Salton Basin during the
Younger Dryas was wet/cold. (5) Wet/warm early Holocene corresponding to the Maximum
Effective Moisture Period perhaps brought about by the strengthening of North American
monsoon. (6) Toward 2,000 yr B.P., the climate became dryer, apparently resulting from
weakening of the monsoons, especially around 6,200 and 2,500 yr B.P. (7) A wet regime
occurred in the basin during the Medieval Warm Period.
87
CHANGES IN SEDIMENT SOURCE AND CLIMATE IN THE NORTHERN REACH OF
SAN FRANCISCO BAY OVER THE PAST MILLENNIUM
F. MALAMUD-ROAM (1) AND B. LYNN INGRAM (2)
(1) Department of Geography, University of California, Berkeley, CA 94720
(2) Department of Earth and Planetary Sciences, University of California, Berkeley, CA 94720
fmalamud@eps.berkeley,edu
The geochemistry of inorganic sediments (silts and clays) from a sediment core from
Petaluma marsh (the northern reach of San Francisco Bay) were analyzed in order to assess the
changes in sediment source over time. These sediments were carried in suspension and deposited
on the marsh surface. The main sources for these sediments are local rivers (Petaluma), the
Sacramento River, draining the northern central valley watershed, and the San Joaquin River,
20
draining the southern central valley watershed. Changes in the relative proportion of sediments
from each watershed reflects overall climatic variability over the entire watershed region of the
San Francisco Bay estuary. Sediment flux history of Petaluma marsh in the northern reach of the
San Francisco Bay indicates considerable variability over the last ca. 900 years, and that
variability has increased over the last 200 years. The sedimentary record from Petaluma indicates
that detrital sediment influx was generally high from about 450 to 150 cal yr B.P., corresponding
to the Little Ice Age, a period shown in other California climate records to have been cool and
wet. The San Joaquin River appears to account for the majority of sediments for the early part of
this period of high sediment influx (450 – 300 cal yr B.P. The Sacramento River became
increasingly dominant as a source of sediments after 300 cal yr B.P. During the Medieval
Climate Anomaly (1,000 – 600 cal yr B.P., a period shown to be warm and dry by many proxy
climate records in California, including several records in San Francisco Bay, sediment flux from
the Sacramento River to Petaluma marsh was reduced during most of this time, while the San
Joaquin was generally moderately high. Local sediment flux was variable, though generally
more often high during this time. The recent 200 years of sediment flux to Petaluma marsh
shows considerably more variability than the prior 700-year period. In general, the Sacramento
River’s contribution to the sediment load was greater, possibly reflecting human disturbance in
the watershed, particularly hydraulic gold mining activity that flushed huge volumes of sediment
through the Sacramento River system.
JOINT VARIABILITY OF GLOBAL RUNOFF AND GLOBAL SEA-SURFACE
TEMPERATURES
GREGORY J. MCCABE (1) and DAVID M. WOLOCK (2)
(1) U.S. Geological Survey, P.O. Box 25046, Denver, CO 80225
(2) U.S. Geological Survey, 4821 Quail Crest Place, Lawrence, KS 66049
gmccabe@usgs.gov
A monthly water-balance model is used with global monthly temperature and
precipitation data (at a 0.5 grid resolution) to compute time series of annual runoff for 19052002. The global runoff is aggregated to a 5o grid resolution and is analyzed jointly with global
SST data (at a near10o grid resolution) using principal components analysis (PCA) with varimax
rotation to identify the primary modes of variability in these data sets. The first three components
from the rotated PCA explain almost 30% of the total variability in the combined runoff/SST
data. The first component explains 13% of the total variance and primarily represents long-term
21
trends in the data. The long-term trends in SSTs are most evident as warming in the Atlantic and
Indian oceans. The associated long-term trends in runoff suggest increasing flows for much of
North America and Australia, and in parts of South America and Eurasia; decreasing runoff is
most notable in Africa and southern Asia. The second component explains 11% of the total
variance and reflects variability of the El Niño-Southern Oscillation (ENSO) and its associated
influence on global annual runoff patterns. The third component explains 6% of the total
variance and indicates a response of global annual runoff to variability in tropical Atlantic SSTs.
The association between runoff and tropical Atlantic SSTs appears to explain an apparent steplike change in runoff that occurred around 1970 for a number of continental regions.
EPISODIC 20TH CENTURY RECRUITMENT OF LIMBER AND BRISTLECONE
PINES IN THE WHITE MOUNTAINS, CALIFORNIA
CONNIE MILLAR, BOB WESTFALL, AND DIANE DELANY
U.S.D.A. Forest Service, Sierra Nevada Research Center, Albany, CA 94710
cmillar@fs.fed.us
Subalpine forests are assumed to respond to warming temperatures by shifting upslope
relative to their current elevational zones. Given that minimum temperatures in the Sierra
Nevada have increased by > 1 C over the 20th century, we might expect a gradual recruitment
upslope of conifer forests paralleling temperature trends. In the White Mountains of California,
subalpine forests comprise bristlecone pine (Pinus longaeva, PiLo) and limber pine (P. flexilis,
PiFl); current PiLo treeline is higher than PiFl by ~ 200 m, especially on dolomitic soils, which
are thought to competitively exclude PiFl. Lower treeline elevation of both species is similar,
although PiLo extends lower than PiFl on calcareous soils. We aged recruitment (trees < 100
years) along transects in three elevational zones: above upper treeline, middle elevations, and
below lower treeline. PiFl exceeded PiLo in abundance of recruits at all sites. At lower
elevations, recruitment was limited to narrow, west- and north-facing ravines; at middle
elevations, recruitment occurred within the general forest zone and also into sagebrushdominated depressions and basins of the mid-elevation plateaus. Greatest abundance of
recruitment was at high elevations above current treeline. Surprisingly PiFl abundance exceeded
PiLo by > 400%. On dolomite substrates, PiFl was often the only recruiting species at the
highest elevations -- as much as 100 m above current PiLo treeline and 300 m above current PiFl
treeline. While some recruitment occurred early in the 20th century, over 80% occurred as an
episodic pulse between 1965 and 1992; a smaller pulse occurred in 1995-2001. The negative
phase of the AMO correlates strongly with the larger recruitment pulse. Highest positive
monthly correlations between climate and recruitment are with September precipitation, winter
maximum temperature, and summer minimum temperature. Recruitment is also greater under
high annual minimum temperature and higher precipitation. Combinations of these conditions
may contribute to successful episodic seedling establishment above treeline at these very high
elevations. While we are unclear why the species differ in response, PiFl appears to be
advancing episodically in dominance over PiLo in the White Mountains, and particularly in leapfrog fashion above current PiLo treeline.
HOLOCENE LANDSCAPE RESPONSE TO SEASONALITY OF STORMS IN THE
22
MOJAVE DESERT
DAVID M. MILLER (1), SHANNON A. MAHAN (2), JOHN P. MCGEEHIN (3), JOHN A.
BARRON (1) AND LEWIS OWEN (4)
(1) U.S. Geological Survey, 345 Middlefield Road, Menlo Park CA 94025
(2) U.S. Geological Survey, P.O. 25046, Denver Federal Center, Denver, CO 80225
(3) U.S. Geological Survey, 12201 Sunrise Valley Drive, Reston, VA 20192
(4) Department of Geology, University of Cincinnati, Cincinnati, OH 45221
dmiller@usgs.gov
Ongoing research in Quaternary landscape evolution of the Mojave Desert is advancing
the understanding of geology-ecosystem links, climate history, and earth-surface processes.
High-resolution geochronology allows us to map deposits at time scales that connect the history
of landscape response to distinctive climate periods. Widespread alluvial fan deposits present a
significant challenge for dating due to lack of suitable organic material for radiocarbon dating.
To overcome this problem, we use luminescence and U/Th series methods to date these deposits.
We find that the Mojave Desert depositional record during the Holocene is similar to previously
determined climate-landscape records of the region. Evidence from ephemeral rivers and lakes
indicates periods of sustained stream flow during the Little Ice Age (ca. A.D. 1300-1800) and
during a brief cool interval within the Medieval Warm Period at about 1050 A.D. Periods of
alluvial fan aggradation across the desert are approximately 15,000-11,000 and 6,000-3,000
years ago, corresponding to nearby Gulf of California marine records of dominance by tropical
diatoms and silicoflagellates. We suggest that periods of increased sea surface temperatures in
the Gulf of California experience more frequent and more intense summer and fall monsoons and
hurricanes. Sustained alluvial fan aggradation may be driven by these periods of intense storms.
The position of the Mojave Desert near the Pacific coast may promote a partitioning of
landscape process responses to climate forcings that vary with seasonality of the dominant
storms. Winter Pacific frontal storms create river flow and ephemeral lakes, whereas periods of
intense summer monsoons cause alluvial fan aggradation. Ecosystem effects of the two
proposed landscape processes are poorly known; however, wood rat midden studies could target
periods of climatic transition and possibly isolate vegetation response to different landscape
processes. River and lake expansion may promote integration of formerly separate riparian and
aquatic habitats. Alluvial fan aggradation may greatly increase the landscape occupied by early
successional species and decrease connections among older parts of the landscape.
HISTORICAL TRENDS IN MOSQUITO POPULATIONS IN RESPONSE TO CLIMATE
DATA IN THE WESTERN UNITED STATES
CORY MORIN AND ANDREW C. COMRIE
Department of Geography, University of Arizona, Tucson, AZ 85719
coryWM417@aol.com
Climate is an important control on populations of disease vectors such as Aedes aegypti
and Culex quinquefasciatus mosquitoes. Improved understanding and modeling of climate
23
effects on mosquito populations is needed to help predict and mitigate disease epidemics. This
study reports on the development of a dynamic mosquito population model driven in part by
climatic data. Model inputs include daily temperature, precipitation, and evaporation rates that
influence mosquito population development and mortality in relation to temperature, population
density, and water availability. These factors are considered through all phases of the mosquito
life cycle from ovulation, though the larvae and pupae stages, and finally emergence into an
adult mosquito. In this study, the model is utilized in order to construct historical predictions of
A. aegypti and C. quinquefasciatus populations in select areas throughout the western United
States. In addition, data of future climate projections are input into the model in order to assess
the affect that climate change may play on the distribution of these vectors. Using this method
produces both a geographic and historical analysis of the ecological factors affecting population
patterns of these mosquitoes. Ultimately, this study seeks to evaluate the role climate variability
has had and will have on the distribution of important disease vectors in the western United
States.
TIMING AND SPATIAL EXTENT OF MIDDLE HOLOCENE ABRUPT
CLIMATE CHANGE
CARRIE MORRILL
National Climatic Data Center, Paleoclimatology Branch, Boulder, CO 80305
carrie.morrill@noaa.gov
A number of recently-published paleoclimate records suggest that the middle Holocene
(about 6,000 to 4,000 cal yr B.P.) was a period of particularly widespread abrupt climate change.
These changes punctuated long-term trends in temperature and precipitation through the
Holocene and could have been a rapid response of the climate system to steadily decreasing
summer insolation. Detecting abrupt climate changes in individual records is difficult, however,
because the time-series also reflects thresholds and non-linearities that are inherent to the
proxies. To assess the evidence for abrupt climate change during the middle Holocene, a
compilation of more than a hundred previously published proxy records from around the globe is
used in this research. The records include all types of proxies (i.e., pollen, ice cores, lake
sediments, marine sediments, loess, peat, speleothems). All records have a resolution of 150
years or better, well-defined age models, and clear proxy interpretations. Abrupt climate changes
are identified objectively through the use of several statistical tests. Some coherent regional
24
abrupt changes are apparent, but evidence for globally-synchronous changes is not currently
strong. These results will be used to discuss hypotheses for the causes of middle Holocene
abrupt climate change.
CALIFORNIA FISHERIES AND ECOLOGICAL RESPONSES TO ABRUPT OCEAN
CLIMATE CHANGES
JERROLD G. NORTON (1), JANET E. MASON (1), AND SAMUEL F. HERRICK (2)
(1) Environmental Research Division, S.W.F.S.C., N.O.A.A. 1352 Lighthouse Avenue,
Pacific Grove, CA 93950
(2) Fisheries Research Division, S.W.F.S.C., N.O.A.A. 8604 La Jolla Shores Drive,
La Jolla, CA 92037
jerrold.g.norton@noaa.gov
The responses of California fish populations and their ecosystems processes to abrupt
ocean climate changes can be rapid, delayed, or both. The delay in response depends on the
mobility, life cycle and abundance of each species when climate change occurs. Rapid responses
may be observed within a year in mobile short lived dolphinfish (Coryphaena hippursus). Less
rapid responses may not be apparent for 5 to 10 years in sedentary long-lived rockfish (Sebastes
sp.) populations. The impact of the responses of commercially important species to abrupt
climate changes on the fisher's income and influence on local economies depends on the value of
the fisheries. The revenue produced by a fishery comes from the abundance of an available
species and from the revenue generated per unit harvested. California fisheries have produced
the greatest revenue when both abundant lower value and less abundant higher value fisheries
have been available. Market squid (Loligo opalescens), accounted for 44% of the total
commercial weight landed and 25% of the total exvessel revenue in 1999; this squid is a high
abundance and relatively low value species that has a short life cycle and a conspicuous and
rapid fisheries response to climate changes. Swordfish (Xiphias gladius) have contributed less
than 5% of the total landings weight, but have high unit value and contributed more than 10% of
the total California landings revenue in 1986. Swordfish have a longer generation time and
prolonged response to environmental changes, but their mobility and their ability to feed over a
wide range of temperatures influence the response of the swordfish fishery to environmental
changes. When physical environmental changes are multi-decadal, ecological adjustments
accumulate and species that are commercially abundant in one phase may be absent in
commercial quantities in the cycle's reverse phase (e.g. Sardinops sagax, Thunnus alalunga).
The 20th century has seen alternating cool and warm periods, with cool periods before 1920 and
between 1960 and 1975. Although the California fisheries were not fully developed before
1940, it appears from our analysis of commercial species harvested throughout the 20th century
that the warm periods and the cool periods both present characteristic ecosystems associated
with characteristic fisheries opportunities.
SIERRA NEVADA SPELEOTHEMS: POTENTIAL FOR HIGH-RESOLUTION
ARCHIVES OF CHANGES IN ATMOSPHERIC CIRCULATION OVER
WESTERN NORTH AMERICA
25
JESSICA L. OSTER (1), ISABEL P. MONTAÑEZ (1), AND WARREN D SHARP (2)
(1) Geology Department, University of California, Davis, CA 95616
(2) Berkeley Geochronology Center, Berkeley, CA 94709
oster@geology.ucdavis.edu
Speleothems from caves developed in limestone and marble terranes of the western
Sierra Nevada from 37o to ~41° N allow reconstruction of high-resolution paleoprecipitation
records for western North America near the boundary between Hadley and Ferrel atmospheric
circulation cells. Global circulation models and paleoclimate proxy records suggest that the polar
cell expanded during northern hemisphere cold periods of the last glacial cycle and the
Holocene, pushing the polar jet stream southward over the southwestern United States. We plan
to test this long-standing hypothesis by using these speleothems to track changes in temperature
and precipitation amounts that are expected to accompany latitudinal movement of the polar jet
stream since the last glacial maximum (LGM). Existing paleoclimate records from Sierra Nevada
lake sediments provide insight into the past hydrologic balance of the region, but do not reveal
the specific causes of effective moisture change or their link to modified ocean-atmosphere
circulation.
An actively forming stalagmite from Moaning Cave (38° N) precipitated without visible
discontinuity for the last 18,000 years based on 230Th/U dating. Analyses of O and C isotopes
indicate that modern speleothem and drip water are in isotopic equilibrium. The O and C
isotopes display large variations (~2‰ for O and ~5‰ for C) along the speleothem’s growth
axis. These variations correlate with substantial changes in Mg and Sr concentrations.
Comprehensive evaluation of modern cave conditions and water chemistry will delineate
seasonal and inter-annual variations in source water and fluid-rock interaction, and further test
for kinetic isotopic fractionation in the modern speleothem. Preliminary results suggest that
carefully calibrated, high-resolution records from Sierra Nevada speleothems can help test the
hypothesis of polar jet stream migration since the LGM and clarify the environmental parameters
recorded by geochemical proxies in speleothems.
A POSSIBLE COSMOCLIMATOLOGICAL DRIVER OF OBSERVED
CYCLIC HOLOCENE CLIMATE CHANGE AND MARINE
PRODUCTIVITY IN THE NORTHEASTERN PACIFIC
R. TIMOTHY PATTERSON (1), ANDREAS PROKOPH (2), ALICE CHANG (3), HELEN M.
ROE (4), NATALIA VAZQUEZ RIVEIROS (1), AND ANDREW WIGSTON (1)
(1) Department of Earth Sciences, Carleton University, Ottawa, ON, K1S 5B6 Canada
(2) SPEEDSTAT, Ottawa, ON, Canada
(3) School of Earth and Ocean Sciences, University of Victoria, Victoria, BC, V8W 3P6 Canada
(4) School of Geography, Archaeology and Palaeoecology, Queen’s University of Belfast,
Belfast, BT7 1NN United Kingdom
tpatters@earthsci.carleton.ca
Annually deposited laminated sediment couplets deposited under anoxic conditions in
fjords along the British Columbia coast provide a high-resolution archive of Holocene climate
variability and marine productivity. In the Seymour-Belize Inlet Complex (SBIC) on the
26
mainland coast and in Effingham Inlet, Vancouver Island, diatom-dominated laminae are
deposited when marine productivity is higher in the spring to fall, and darker clay-dominated
laminae are laid down under higher precipitation conditions during winter. Wavelet transform
and other time series analysis methods were applied to sediment color (i.e. gray-scale values)
line scans obtained from x-ray images of cores and compared with global records of cosmogenic
nuclides (14C and 10Be), as well as the Ice Drift Index (hematite-stained grains) record to detect
cycles, trends and non-stationarities in the sedimentary record. We carried out similar analyses
on foraminifera, diatom, dinoflagellate, and fish scale records recovered from these same cores.
The results indicate that the marine productivity and sedimentary record of the northeast Pacific
responded to abrupt changes and long-term variability in climate that can be linked to external
forcing (e.g. variations in cosmic ray influx due to solar magnetic activity). For example, a
strong cooling in the NE Pacific at ~ 3,550 yr B.P. that is correlated with widespread
neoglaciation in the region can be correlated to a weakening of high-frequency (50-150) year
pulses at the Gleissberg solar cycle band. Episodes of low sun activity are characterized in the
sedimentary record (e.g. 3,350, 2,750, and 2,350 yr B.P.) of the cores by intervals of clay-rich
and thick laminae that were deposited under unusually wet conditions. These intervals of higher
precipitation may have been related to a regional intensification of the Aleutian Low (AL)
caused by an eastward migration of the center of action (COA) of the AL, which occurs during
intervals of solar minima, similar to what occurred during the “Little Ice Age” (e.g. Spörer,
Maunder, and Dalton minima). Dryer conditions prevail in the region when the COA of the AL
migrates westward and the COA of the North Pacific High (NPH) migrates northward during
intervals of solar maxima. These NPH and AL COA changes greatly impact the influence of
open ocean upwelling in Effingham Inlet and estuarine circulation in the SBIC.
EVIDENCE OF THE DIFFERENTIAL RESPONSE OF LAKES IN THE SIERRA
NEVADA, CALIFORNIA DURING THE YOUNGER DRYAS CHRONOZONE
DAVID F. PORINCHU (1), GLEN M. MACDONALD (2), KATRINA A. MOSER (3),
AARON P. POTITO (4), AND AMY M. BLOOM (5)
(1) Department of Geography, The Ohio State University, Columbus, OH 43210
(2) Department of Geography, University of California, Los Angeles, CA 90095
(3) Department of Geography, University of Western Ontario, London, ON, N6A 5B7 Canada
(4) Department of Geography, NUIG, Galway, Ireland
(5) Department of Geography-Geology, Illinois State University, Normal, IL 61790-4400
porinchu.1@osu.edu
Sub-fossil midge stratigraphies were developed for five small lakes in the eastern Sierra
Nevada, California. Application of a midge-based inference model for surface water temperature
provided quantitative estimates of the thermal conditions that existed during the Younger Dryas
chronozone (12,900 – 11,600 cal yr B.P.; YD). The sediment sequences were recovered from
lakes spanning an elevation gradient of approximately 800 m, with the low elevation site
surrounded by Jeffrey pine woodland, mid-elevation sites situated in upper Montane forest and
the high elevation sites characterized by sub-alpine vegetation. The chironomid-based
reconstructions suggest that post-glacial climate amelioration was spatially and temporally
27
complex within the Sierra Nevada. All sites experienced a warming immediately following deglaciation, with water temperatures increasing approximately 2-3 oC between 14,000 and 13,000
cal yr B.P. Surface water temperatures at mid-elevation sites were depressed ~ 3 oC during the
YD. However, it appears that surface water temperatures at high elevation sites increased
slightly or remained stable during this interval; whereas, the low elevation site experienced
greater variability in surface water temperature. Temperatures at all lakes stabilized during the
early Holocene. Paleohydrological changes inferred from diatom and stable isotope records
developed for the mid-elevation sites will also be discussed.
THE WEATHER AND CLIMATE OF PACLIM YEAR 2006-2007
KELLY REDMOND
Western Regional Climate Center, Desert Research Institute, 2215 Raggio Parkway, Reno, NV
89512-1095
kelly.redmond@dri.edu
After an auspicious and even exceedingly soggy or white start in parts of the West, the
main feature of the 2006-07 winter turned out to be a major deficiency in mountain snowpack,
and an extremely dry winter in the Southwest. In southern California this driest winter on record
follows only two years after the wettest on record. In the Sierra Nevada, the effects of two
immediately prior significantly wet winters greatly alleviated water angst, at least for summer
2007. The summer heat wave of 2006 was outstanding in several aspects, and more mundane in
others, with some very dramatic differentials along the coast. The snowfall deficit encompassed
much of the drainage of the upper Colorado River, and the longstanding and major drought there
once again intensified after a brief increase two years ago. Reservoir storage on Lake Powell
and Lake Mead now stands just about half full. Reminiscent of 2004, a warm and dry March in
the interior West produced a rapid loss of snowpack, and the inflow forecast to Lake Powell fell
steadily to 50 percent of average. Spring months have been warming over the past two decades,
but the last few years have brought cool episodes along the West Coast. Arizona remained dry
all winter, but parts of New Mexico experienced significant precipitation later in the winter.
Western and Colorado Basin temperatures in 2006 continued their rising trend, and the period
2000-2006 shows decidedly different temperature anomalies for the eastern and western United
States. Recent papers have fueled speculation as to the nature of the Southwest drought: Is this
"just another typical large drought" or is this "a new type of drought"? Hemispheric patterns will
be discussed briefly. The national fire acreage in 2006 was the greatest on record, and
expectations for 2007 are for another active year. The wet north / dry south precipitation pattern
in the West occurred despite a mild El Niño that many widely presumed would produce the
opposite effect. This later gave way to a nascent La Niña whose prospects for winter 2007-08
are not fully clear, but would portend yet another dry winter in the southern West.
IMPACTS OF CLIMATE CHANGE AND LAND USE ON THE NAVAJO NATION IN
THE SOUTHWESTERN UNITED STATES
MARGARET HIZA REDSTEER
U.S. Geological Survey, Flagstaff Science Center, Flagstaff, AZ 86011
28
mhiza@usgs.gov
Native Americans of the southwest, including the people of the Navajo Nation, live in an
ecologically sensitive arid to semi-arid region with limited resources. In this region, as on other
Native lands, traditional people live a subsistence lifestyle that is closely tied to, and dependent
upon landscape conditions. Global change, with regard to climate, includes significant changes
in long-term average temperature and precipitation. Many studies have shown that in the past
couple of decades, average temperatures have risen (compared to historic averages) in many
parts of the world, including the southwestern United States. During this past decade, the
southwestern United States, including the Navajo Nation, has also been experiencing a major
drought. Global warming may already be contributing to drought severity on the Navajo Nation
and adjacent lands. The dual effects of increased temperatures and changing patterns of
precipitation are likely to have profound effects (both geologic and biologic) on this semiarid
landscape. For the region of the Navajo Nation and those lands at a similar latitude, the amount
of effective precipitation, the moisture not lost to evaporation, decreases by approximately 5 cm
for every 1 oC increase in temperature. These calculations highlight the clear connection
between climate change and drought severity for the western United States. Annual rainfall in
many parts of the Western Navajo Nation averages between 12.7 and 18 cm in “normal” years,
but has been as low as 2.5 to 5 cm in many areas during recent drought years. In addition,
average annual snowfall for the Navajo Nation has decreased significantly since the early part of
the 20th century. Snowfall and snow pack are important for their contribution to recharge of
aquifers and water storage in reservoirs. Our work has found that some land use practices, such
as importing weedy hay during periods of drought, and off-highway vehicle use, are
compounding the sobering effects of drought and climate change to mobilize surface sediment
and degrade rangeland. Sand dunes that cover approximately two-thirds of rangeland on the
Navajo Nation have become partly active to active in many areas in recent years. These changes
can be attributed to changing climatic factors.
EXAMINATION OF DROUGHT TOLERANCE IN PINYON PINE USING
ANCIENT DNA
BETHANY RIGGINS (1), AMY WHIPPLE (1), KRIS HASKINS (1), AND
KENNETH COLE (2)
(1) College of Engineering and Natural Science, Northern Arizona University, AZ 86011
(2) U. S. Geological Survey, Southwest Biological Science Center, P.O. Box 5614, Northern
Arizona University, AZ 86011
bmr34@nau.edu
Due to a recent drought in Arizona, thriving pinyon forests have turned into sparse
forests. The purpose of this study is to discover why many pinyon trees lived, while many others
died. This study specifically focuses on the aspect of genetic adaptations to drought by
examining drought tolerance genes through time. Comparing ancient and recent DNA will allow
us to look for patterns between genetic variation and climate. It is expected that genes specific to
drought tolerance have changed as surrounding climate has changed. Packrat middens were the
source of needle tissue from trees which have been dead for hundreds of years. Twenty-two
29
drought specific genes will be sequenced to study how and if pinyon drought genes have
significantly changed over time. The genes have been selected but not yet. We expect to see
variation between genes, but the cause of that variation is unknown at this time. In addition to
genetic change detection, a second goal is to test if the genetic change is the result of neutral
variation or natural selection.
POSTGLACIAL RELATIVE SEA-LEVEL AND CLIMATIC HISTORY OF THE
SEYMOUR-BELIZE INLET COMPLEX, BRITISH COLUMBIA:
BIOSTRATIGRAPHIC EVIDENCE FROM ISOLATION BASINS
HELEN M. ROE (1), CHRISTINE T. DOHERTY (1), R. TIMOTHY PATTERSON (2), AND
GLENN A. MILNE (3)
(1) School of Geography, Archaeology and Palaeoecology, Queen’s University of Belfast,
Belfast, BT7 1NN, United Kingdom
(2) Department of Earth Sciences, College of Natural Sciences, Carleton University, Ottawa,
ON, K1S 5B6, Canada
(3) Department of Earth Sciences, Durham University, Durham, DH1 3LE,
United Kingdom
h.roe@qub.ac.uk
The late glacial and Holocene relative sea-level (RSL) history of the sparsely populated
central mainland coast of British Columbia is poorly understood, yet this area remains critical for
testing models of post-glacial rebound following deglaciation of the Cordilleran ice sheet and for
assessing residual crustal movements. This paper presents the results of a recent study of the late
glacial and Holocene RSL history of the Seymour-Belize Inlet Complex (SBIC) of central
British Columbia, approximately 50 km north of Vancouver Island. Detailed sedimentological
and biostratigraphic analyses of sediment cores from three coastal isolation basins (Woods Lake,
Two Frog Lake, and Tiny Lake), ranging in sill elevation from 2.13-3.59 m MTL, provide new
data from an area previously devoid of RSL information. Diatom analysis reveals that the lake
basins were inundated by the sea and subsequently isolated during the late glacial at ca. 11,800
14
C yr B.P. The RSL rose during the early Holocene and breached the 2.13 m sill at Woods Lake
at ca. 8,000 14C yr B.P. Brackish conditions existed in the basin between 7,000-2,400 14C yr
B.P. The RSL rose to 1.49 m MTL at ca. 2,400 14C yr B.P. Subsequently, RSL fell, with the
final isolation of Woods Lake at ca. 1,900 14C yr B.P. The results have been used to produce a
RSL curve for the SBIC for the late glacial and Holocene and draw comparisons with RSL
estimates derived from geophysical models. The diatom record also includes evidence of
regional cooling during Neoglacial times. The late glacial and Holocene RSL history recorded
in this region compares well to that recorded in eastern Vancouver Island.
WY 2007: ARE THE GOOD YEARS OVER?
MAURICE ROOS AND MICHAEL ANDERSON
California Department of Water Resources, P.O. Box 219000, Sacramento, CA 95821-9000
mroos@water.ca.gov
30
Both water year 2005 and 2006 were wet in northern California, mainly due to wet
springs. Last year was sixth wettest of record (101 years) for the Sacramento River basin and
ninth wettest on the San Joaquin River system. Statewide runoff was estimated to be 170% of
average, quite a contrast to the 67% for the Colorado River inflow to Lake Powell.
So far (as of mid-March), water year 2007 seems to be heading for a dry designation with
projected runoff in the 60% range. Northwestern California seasonal precipitation has been near
average, sharing somewhat in the bounty of the Pacific Northwest. But southern California has
been extremely dry in spite of the El Niño year, with brush fires even in the winter. So far,
February was the only month with above average in precipitation. December was fairly good,
mostly in the north. January, which is our wettest month on average, was extremely dry.
Downtown Sacramento had only 0.18 cm, compared to an average of about 10.7 cm, less than
the previous record monthly low of 0.38 cm in 1889, more than a century ago.
1994 was the last “critically” dry year, although 2001 and 2002 were “dry”, the next
category up. In spite of rainfall deficits, we don’t expect 2007 to be “critically” dry although it
may well be dry. Carryover reservoir storage on October 1 from the last water year was 20%
above average and that will save most of us this year from water shortages this year. Next year
could be another story.
Temperature was also an important factor this winter with an extended cold spell in
January. The freeze caused major damage to Central Valley citrus crops and to winter
vegetables in the southland desert areas, with losses estimated to be over $ 1 billion. Some San
Joaquin Valley stations saw lows under 20 º F, especially on the west side with lows of 15 º F at
Lemoore and Kettleman City.
Looking at past years which had extended cold spells in winter, a wet or normal
December followed by a dry January, there is a suggestion that the following year will also be
quite a bit below average. This happened in 1932, 1948, 1949, and 1991. I am not sure if this is
my selective imagination or whether it would be an explainable response to a strong mid-winter
perturbation of the atmosphere. If so, it does not bode well for next year’s water supply. I leave
it to you research folks to see if there is any dependable long range forecast potential in this in
northern California for next year.
HIGH RESOLUTION STUDY OF PYRITE FRAMBOID DISTRIBUTION IN SANTA
BARBARA BASIN SEDIMENTS AND IMPLICATIONS FOR WATER-COLUMN
OXYGENATION
JUERGEN SCHIEBER AND ARNDT SCHIMMELMANN
Department of Geological Sciences, Indiana University, Bloomington, IN 47405-1405
aschimme@indiana.edu
Monitoring of the concentration of dissolved elemental oxygen (i.e., ‘oxygenation’) of
sub-sill waters in the Santa Barbara Basin (SBB) over the last few decades has consistently
demonstrated sub-oxic bottom water conditions. However, anoxic conditions and hydrogen
sulfide (H2S) are present below a few millimeters depth in the sedimentary column. The absence
of euxinic conditions (i.e., anoxic-sulfidic: no free O2 but free H2S) in any part of the modern
SBB water column makes this basin geochemically distinct from the Black Sea and other more
oxygen-depleted basins.
31
The varved sediment record from the central SBB has been used extensively for highresolution paleoceanographic reconstructions. The SBB and other oxygen-depleted basins are
considered modern analogs for black shales. Geochemical proxies for paleo-redox conditions in
black shales need to be tested against modern, well-constrained depositional systems like the
SBB. Pyrite framboids are a common component in many anoxic marine sediments and are
deemed to carry paleoceanographic information. Observations from modern Black Sea sediment
yielded the hypotheses that (i) abundant small framboids below 5 µm diameter indicate euxinic
(anoxic-sulfidic) bottom waters, and (ii) mean framboid sizes above 5 µm indicate suboxic or
normally oxygenated bottom waters. We are using scanning electron microscopy to compile a
detailed inventory of framboid occurrence in A.D. 1983-2004 SBB varves and compare framboid
size distribution against the known history of SBB water column oxygenation.
Our ground-truthing effort has shown that framboids in modern SBB sediment
dominantly are in the 2-4 µm range and thus show closely similar size distributions to those
measured in Black Sea sediments underlying an euxinic water column. Of course, the lower SBB
water column is suboxic, and therefore we conclude that the framboid size distribution in modern
sediment and in black shales has no diagnostic value for paleo-water column oxygenation. Our
data further indicate significant variability in mean framboid size between successive varves that
do not correlate with historic changes in SBB water oxygenation. We are evaluating other
potential factors that could affect framboid size, for example (i) the availability of iron from
clastic terrestrial input from the continent, (ii) the availability of freshly deposited organic matter
nourishing the microbial community and influencing the redox profile near the sediment-water
interface, and (iii) the depth of burial within the near-surface sediment that fosters the
precipitation of framboids. The generally lower abundance of framboids in the youngest,
uppermost varves suggests that it takes several years of mineralization before framboid
formation goes to completion in a given sediment layer. After about five years framboid
abundance appears to stabilize, providing further support of the view that framboids do not form
in the water column and should not be considered recorders of water column oxygenation.
VEGETATION RESPONSES TO CLIMATE CHANGE: 11,000 YEARS AGO, 6,000
YEARS AGO, AND 21ST CENTURY VEGETATION SIMULATIONS FOR BERINGIA
SARAH L. SHAFER (1), PATRICK J. BARTLEIN (2), MARY E. EDWARDS (3),
AND STEVEN W. HOSTETLER (1)
(1) U.S. Geological Survey, Corvallis, OR 97333
(2) Department of Geography, University of Oregon, Eugene, OR 97403
(3) School of Geography, University of Southampton, UK and
Alaska Quaternary Center, University of Alaska-Fairbanks, AK 99775
sshafer@usgs.gov
Future climate changes are projected to be particularly large for northern hemisphere
high latitudes. Coupled atmosphere-ocean general circulation model (AOGCM) simulations
produced for the recent Intergovernmental Panel on Climate Change Fourth Assessment Report
(IPCC AR4) indicate warmer and wetter conditions for Beringia (eastern Siberia, Alaska, and
northwestern Canada) at the end of the 21st century. The magnitude of these climate changes
would significantly affect the vegetation of this region. To understand the climate-forced
32
dynamics of vegetation in Beringia, we compare paleovegetation simulations for 11,000 and
6,000 years ago with those for the future. We examine a variety of variables, including effective
moisture and atmospheric CO2 concentrations, to explain the simulated differences in vegetation
response for the three time periods. Paleoclimatic data for the vegetation simulations are derived
from model experiments conducted with a regional climate model, RegCM2, which was run with
time-varying boundary conditions from Genesis 2.0, an atmospheric general circulation model
with a mixed-layer ocean. Future climate data are derived from AOGCM simulations for the 21st
century (2001-2100) downscaled to a 5-minute grid over Beringia. Vegetation is simulated with
BIOME4, an equilibrium vegetation model, and LPJ-GUESS, a dynamic ecosystem model. For
both 11,000 years ago and 6,000 years ago, areas of Beringia are simulated to have had warmer
summer temperatures and slightly more summer precipitation than present. These paleoclimate
anomalies are of the same magnitude and direction as those simulated for Beringia in the future.
The simulated paleovegetation data are compared with paleovegetation proxy data (e.g., pollen
from lake sediments) for 11,000 and 6,000 years ago from the region.
PROJECTING CLIMATE CHANGES AND ECOLOGICAL RESPONSES
GARY D. SHARP (1), LEONID KLYASHTORIN (2),
AND DOUGLAS McLAIN (1)
(1) Center for Climate/Ocean Resources Study, Salinas, CA 93907
(2) V.N.I.R.O., Moscow, Russia
gsharp@redshift.com
Climate change has long been documented in many locations as being responsible for
major ecological responses in regional ocean ecosystems. Unfortunately, due to reluctance by
many agency policy makers to fund the necessary monitoring of both physical and ecological
components, and the dominant presumption that underlying all ecology there are fundamental
equilibrium processes that determine the System State – ‘surprises’ keep occurring. In recent
decades there have been many gross simplifications and analyses of particularly undependable
data sets, from limited time series of species landed catch data, various local temperature series,
and some in situ sampling of plankton, etc., and thus the potential for any dependable projections
have been minimal, and those that have been made are for the most part, quite gloomy. However,
in the 1970-80 period when biological oceanography was the basis for many powerful efforts to
understand the fundamental requirements for successful year class production in many ocean
species, it became obvious that wind speed and direction, incident sunlight and temperature were
the fundamental factors that determine which species would thrive, and by tracking these and the
subsequent production patterns, useful forecasts of likely species-specific survival changes could
be made. Given these insights, the long-term insights from old cultures about atmospheric
cycles, and consequent species dynamics, it is now possible to focus on when and where to
monitor various properties that will enhance the benefits of both system monitoring and resource
management. We provide examples for future reference.
33
ELEVATIONAL AND TEMPORAL TRENDS IN SALIX-FEEDING BEETLES AND
ASSOCIATED INSECTS ALONG THREE SIERRA NEVADA,
CALIFORNIA DRAINAGES
JOHN T. SMILEY (1), NATHAN E. RANK (2), ELIZABETH P. DAHLHOFF (3)
(1) University of California White Mountain Research Station, 3000 E. Line Street,
Bishop, CA 93514
(2) Department of Biology, Sonoma State University, 1801 East Cotati Avenue,
Rohnert Park, CA 94928
(3) Department of Biology, Santa Clara University, 500 El Camino Real,
Santa Clara, CA 95053
jsmiley@wmrs.edu
We have been studying the ecology, evolution, and physiology of the willow leaf beetle,
Chrysomela aeneicollis, in the eastern Sierra Nevada, California, since the early 1980's. By
examining changes along three elevation gradients, Big Pine (BP), Bishop Creek (BC), and Rock
Creek (RC) we hoped to discover asymmetrical or unidirectional shifts that might be predicted in
a warming climate regime. Foliage air temperature measurements since 2000 revealed that
daytime temperatures experienced by the beetles were reduced at higher elevations with a lapse
rate of approximately 10 oC/1,000 m of elevation. In contrast, nighttime low temperatures were
often coldest at lower elevations, with reduced (BP) or no elevation effects (BC and RC).
Beginning in 1982 in BP, C. aeneicollis beetle populations expanded and contracted their
elevational range, but also shifted upwards by about 300 m so that in 2006 the highest elevation
populations are at timberline (3,550 m). A concomitant 300 m upward shift also occurred in
populations of one of the beetles’ principal predators, the wasp Symmorphus cristatus.
Beginning in 1998 we sampled C. aeneicollis beetles in BC and RC. They did not appear to shift
their ranges upward until the summer of 2006, at which time beetles colonized several timberline
sites. The pre-2006 data are consistent with measurements of temperature physiology which
suggest that nighttime low temperatures constrain beetle distributions. However, the 2006
upward shift, along with some new physiology and genetics findings, suggest a more complex
relationship between foliage air temperatures and beetle survival. The overall results suggest
that beetle populations may be moving upward in elevation, and we hope to continue to
characterize the underlying ecology, physiology, and genetics of this process.
CORRELATING LATE GLACIAL AND HOLOCENE MARINE AND LACUSTRINE
CLIMATE RECORDS IN NORTHERN CALIFORNIA
SCOTT W. STARRATT AND JOHN A. BARRON
U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025
sstarrat@usgs.gov
Evidence of long-distance connections between the marine and terrestrial realms along
the northern California margin is affected by both latitude and elevation. In this study, the late
glacial and Holocene history of the California Current derived from a marine core is compared
34
with the records from two lakes.
The 16,000-year-long marine record (ODP Site 1019) is based on the analysis of the
diatom and pollen assemblages, alkenones, sediment geochemistry, and physical properties
(density, biogenic silica, and environmental magnetism). The terrestrial record at Medicine
Lake, located on the Modoc Plateau in northeastern California at an elevation of more than 2,000
meters, contains an 11,400-year-long record derived from diatom and pollen assemblages,
sediment geochemistry, and physical properties. The 19,000-year-long record from Swamp
Lake, located near the northern boundary of Yosemite National Park at an elevation of about
1500 meters, includes pollen (Smith and Anderson, 1992) and diatom assemblages, biogenic
silica, loss-on-ignition, and magnetic susceptibility. The extent of the record in both of the lakes
is limited by late Wisconsin glaciation.
The marine and Swamp Lake records indicate
cooler temperatures and decreased productivity during the transition from the Bølling-Allerød to
the Younger Dryas, followed by warmer conditions prior to the end of the Younger Dryas. This
interval was not covered at Medicine Lake.
The early Holocene (11,500-8,000 cal yr B.P.) is characterized by a transition from
warmer and wetter to cooler and drier conditions along the coast and in inland areas, indicating
declining July insolation. This interval was characterized by warm winter sea surface
temperatures and a California Current of moderate strength. Warmer winters led to earlier
snowmelt and an increase in the volume of both lakes. Biogenic silica levels in Swamp Lake
increase during this time as does the abundance of oligotrophic planktonic taxa. Clastic input
decreased in both lakes during this period, suggesting increases vegetation in the watershed. The
pollen record indicates that along the coast, the warmest temperatures occurred early in this
interval, followed by cooling and increased moisture. At Medicine Lake, conditions were
relatively stable whereas the warmest temperatures were reached toward the end of the early
Holocene at Swamp Lake.
The early part of the middle Holocene (8,000-3,000 cal yr B.P.) was characterized by
weaker, less regular El Niño events, and more sustained La Niña-like conditions resulting in
lower coastal sea surface temperatures and drier conditions inland. Gradual strengthening of the
California Current due to a stronger thermal gradient led to increased seasonal (spring-summer)
coastal upwelling and associated fog along the coast during the latter half of this interval. At
Swamp Lake, biogenic silica values leveled off after reaching their highest values in the record,
and pollen suggests an increase in effective moisture. However, the record is equivocal, because
it suggests this increase in moisture may have been seasonal; there appears to be a hiatus of
several thousand years in the shallower part of the lake. The pollen record from Medicine Lake
also indicates an increase in effective moisture.
The late Holocene (3,000-0 cal yr B.P.) is distinguished by increasing winter
precipitation and enhanced ENSO cycles. The marine record suggests warmer winter sea surface
temperatures and a stronger seasonal gradient. The pollen records at both lakes show an increase
in effective moisture. However, the productivity in Medicine Lake decreases to levels recorded
in the earliest Holocene, while the productivity in Swamp Lake remains at middle Holocene
values. This may reflect not only the difference in latitude and elevation, but also the
characteristics of the watershed. During the late Holocene, marine and lacustrine records show
several extended periods of lower precipitation, alternating with wetter periods.
Smith, S.J., and Anderson, R.S., 1992, Late Wisconsin paleoecologic record from Swamp Lake, Yosemite National
35
Park, California: Quaternary Research, v. 38, p. 91-102.
TOO CUNNING TO BE UNDERSTOOD: THE RECORD OF LATE HOLOCENE
CENTRAL CALIFORNIA CLIMATE FROM SAN FRANCISCO
BAY MARSH SEDIMENTS
SCOTT W. STARRATT
U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025
sstarrat@usgs.gov
Sediment cores collected from three marshes on the northern margin of San Francisco
Bay provide differing records of late Holocene climate variation in central California. The
timing of changes in the diatom floras illustrates the complex interaction between local and
regional climatic processes.
Results from Rush Ranch and Petaluma marsh suggest that conditions along the central
coast became drier prior to the Medieval Climatic Anomaly and that fresh water became
increasingly abundant during the transition from the Medieval Climate Anomaly (A.D. 8001300) to the Little Ice Age (A.D. 1300-1900). In contrast, the Benicia State Park site is
dominated by a freshwater flora during the Medieval Climate Anomaly, and conditions become
brackish at the beginning of the Little Ice Age.
The Rush Ranch site shows periods of increased salinity between 3,000 to 2,700 cal yr
B.P., 1,750 to 750 cal yr B.P., and from about A.D. 1930 to the present. The 3,700 year-long
Benicia State Park record shows a rapid decrease in salinity around 3,200 cal yr B.P. Fresher
conditions continue until 500 cal yr B.P., after which salinity increases. During this later period,
sediment deposition occurred in the summer and fall when river flow rates were lower, resulting
in a more brackish diatom flora.
Differences in the timing and duration of the fresher and more saline intervals at Rush
Ranch and Benicia State Park are largely controlled by proximity to the main channel of the
Sacramento-San Joaquin River system. The short (about 15 km) distance from the mouth of the
tidal channel to Rush Ranch appears to have a dampening effect on the signal of climate
variation. For example, the transition from brackish to fresher conditions takes place between
3,200 and 3,100 cal yr B.P. at Benicia State Park, but does not occur until several hundred years
later at Rush Ranch. The subsequent transition from fresher to more brackish conditions occurs
150 to 200 years earlier at Rush Ranch.
The record at Petaluma marsh is strongly controlled by precipitation in the Coast Ranges.
Beginning about 1,550 cal yr B.P., conditions become more saline, and, with the exception of a
200-year period from ~700 to 500 cal yr B.P., continued to increase in salinity to the present.
This shift in the diatom flora may be influenced by marsh accretion, resulting in longer periods
of exposure during the summer and fall.
EVALUATING ISOTOPE TRACERS OF PALEOSALINITY, FRESHWATER INPUT,
AND ENVIRONMENTAL CHANGE AT
CELESTUN LAGOON, YUCATAN
JOSEPH H. STREET (1), MEGAN B. YOUNG (2), MICHELLE GOMAN (3),
36
JORGE HERRERA-SILVERIA (4) AND ADINA PAYTAN (1)
(1) Department of Geological and Environmental Sciences, Stanford University 94305-2115
(2) Stable Isotope Tracers Project, U.S. Geological Survey, Menlo Park 94025
(3) Department of Earth and Atmospheric Sciences, Cornell University, Ithaca NY 14853-1504
(4) Departmento de Recursos del Mar, CINVESTAV, Merida, Yucatan, Mexico
jstreet@stanford.edu
Several studies have attempted to reconstruct Quaternary climate variability in MesoAmerica and the Caribbean region (e.g., Hodell and others, 1995; Hughen and others, 2004).
Interest in this region has been driven in part by evidence that changes in tropical ocean
conditions may drive climate on a global scale and by the realization that the region is wellplaced to track past shifts in the average position of the Intertropical Convergence Zone (ITCZ),
which is a major control on precipitation and drought cycles in tropical and sub-tropical areas of
the world (Hoerling and others, 2001). With this in mind, we seek to develop a new record of
regional paleoprecipitation and environmental change based on the Sr, O, and C isotopic
compositions of benthic foraminiferal tests recovered from estuarine sediment cores collected in
Celestun Lagoon, on the northwestern Yucatan Peninsula. In addition, we have measured
foraminiferal assemblages and the C and N isotope composition of sedimentary organic matter
from these cores. The groundwater that dominates freshwater input into Celestun is recharged
over a large area of the Yucatan, suggesting that a record of paleosalinity and groundwater
discharge to Celestun will integrate a regional signal. Along a present-day, head-to-mouth
transect, estuarine salinity is strongly correlated to 87Sr/86Sr of both water and core-top
foraminifera. The relationship between salinity and δ18O is more complex, though foraminifera
appear to faithfully record δ18O water, with little temperature effect, and may provide a means of
tracing the relative importance regional and local groundwater sources to the lagoon in the past.
Preliminary downcore results suggest that the estuary has experienced pronounced
environmental changes over the course of the late Holocene. We will compare the utility of the
various tracers for estuarine paleoclimate reconstruction and evaluate our results in the broader
regional context.
Hodell, D.A., Curtis, J.H., and Brenner, M., 1995, Possible role of climate in the collapse of Classic Maya
civilization: Nature, v. 375, p. 391-394.
Hoerling, M.P., Hurrell, J.W. and Xu, T., 2001, Tropical origins for recent North Atlantic climate change: Science,
v. 292, p. 90-92.
Hughen, K.A., Eglinton, T.I., Xu, L., and Makou, M., 2004, Abrupt tropical vegetation response to rapid climate
changes: Science, v. 304, p. 1955-1959.
OCEANS AND CLIMATE, AND THEIR EFFECT ON FOREST-INSECT
INTERACTIONS
ALAN J. THOMSON
Pacific Forestry Centre, Victoria, BC, V8Z 1M5, Canada
athomson@pfc.cfs.nrcan.gc.ca
37
The earliest recorded outbreaks of western spruce budworm (Choristoneura occidentalis
Freeman) on its principal host, Douglas fir (Pseudotsuga menziesii (Mirb.) Franco), in British
Columbia occurred on southern Vancouver Island. Outbreaks have increased in extent in British
Columbia since that time, yet there have been no outbreaks on southern Vancouver Island since
the 1930s. When outbreaks occur, bands of defoliation occur at different positions along
topographic gradients from year to year as the insects respond to changes in weather. However,
this adaptive capacity was insufficient for outbreaks to reoccur on Vancouver Island. Using a
web-based program for exploring budworm-host phenology, we have recently found that over
the last 90 years for which records are available, warming winter temperatures on southern
Vancouver Island, linked to a rise in sea temperature, promoted earlier larval emergence while
the timing of bud flush has remained constant. This differential response to changed climate has
resulted in a significant departure from optimal phenological synchronization that would explain
the outbreak history. Changing phenological relationships along topographic gradients due to
climate change will have significant consequences for the interactions between herbivorous
insects and their host plants. Studies of such relationships have generally focused on changes in
growing season of the plants. However, as the mode of action of the effect in our present study
was through the insect in the off-season, rather than through the plant during the growing season,
will alteration of inter-species relationships by climate change through this route result in more
surprises than those resulting though changes in plant growing seasons?
ABRUPT CLIMATE CHANGE AND ECOSYSTEM RESPONSE: A 2,000 YEAR
HISTORY OF SEVERE DROUGHTS, EXTREME TEMPERATURES, AND STANDREPLACING FIRES IN THE SIERRA NEVADA IN RESPONSE TO ABRUPT
CLIMATE CHANGE
STEPHEN F. WATHEN
Department of Plant Sciences, University of California, Davis, CA 95616
sfwathen@ucdavis.edu
Climate change is increasingly seen as a serious threat to modern environments and yet
little is known about the environmental effects of abrupt climate change during the Holocene. I
investigated the environmental effects of abrupt climate change over the past 2,000 years at
Coburn Lake, California to test the hypothesis that Coburn Lake charcoal peaks represent standreplacing fires that occurred within the Coburn Lake watershed in response to abrupt climate
change. I compared the timing of Coburn Lake charcoal peaks with both the timing of the onset
of droughts and the presence of temperature extremes in the Sierra Nevada. Charcoal peaks,
with associated proxies for erosion, occurred at the beginning of all ten droughts, and only then,
in the northern Sierra Nevada over the last 1,900 years. The environmental stress caused by the
onset of severe droughts was made all the more severe due to severe cold temperatures, or abrupt
shifts in temperatures, at the beginning of most droughts in the Sierra Nevada over the last 1,900
years. These results suggest an “abrupt climate change-severe fire hypothesis,” that implies that
abrupt climate change during the late Holocene caused vegetation and mountain slopes around
Coburn Lake, and perhaps more widely, to be seriously out of balance with changing climates;
resulting in forest die-off, stand-replacing fires, and severe soil erosion. Taken together, this
38
study provides a rare detailed history of abrupt climate and environmental change in the Sierra
Nevada over the past 2,000 years.
CLIMATE CHANGE AND WILDFIRE
ANTHONY L. WESTERLING (1,2), HUGO HIDALGO (2),
DANIEL R. CAYAN (2,3) AND THOMAS W. SWETNAM (4)
(1) Sierra Nevada Research Institute, University of California, Merced, CA 95344
(2) Climate Applications Program, Scripps Institution of Oceanography, La Jolla, CA 92093
(3) U.S. Geological Survey, La Jolla, CA, 92093
(4) Laboratory for Tree-Ring Research, University of Arizona, Tucson, AZ 85721-0058
awesterling@ucmerced.edu
Western U.S. forest wildfire regimes shifted abruptly in the mid-1980s, with larger, more
frequent, longer-burning fires occurring in many fire seasons since then. The greatest increases
occurred in mid-elevation forests of the northern Rocky Mountains. Other forests of the west
have seen increased wildfire, but the change has varied greatly with location. Wildfire regimes
in other, non-forested ecosystems of the western U.S. have not changed dramatically in recent
decades. The increase in forest wildfire is strongly associated with warming and earlier springs.
Why have some ecosystems responded so dramatically to these changes in climate, while others
have not?
Climatic impacts on wildfire regimes are the result of complex, nonlinear responses of
ecosystems and wildfire to changes in climate and other factors. The same climatic influences
that limit the kinds of vegetation that can grow in a specific location also affect fire regimeecosystem interactions and their responses to changes in climate. We use documentary wildfire
histories and climate records, models and proxies from the western U.S. to demonstrate some
important climate-vegetation-wildfire interactions, from which we infer causes of the observed
variability in wildfire regime responses to recent climate change, and extrapolate impacts of
future climate changes.
TREE RINGS INDICATE SUMMERTIME STRATUS CLOUDS AS IMPORTANT
SOURCES OF PRE-DAWN WATER AND AFTERNOON SHADE FOR COASTAL
VEGETATION IN CALIFORNIA
A. PARK WILLIAMS (1), CHRISTOPHER J. STILL (1), DOUGLAS T. FISCHER (1)
39
AND STEVEN W. LEAVITT (2)
(1) Department of Geography, University of California, Santa Barbara, CA 93101
(2) Laboratory of Tree-Ring Research, University of Arizona, Tucson, AZ 85721-0058
williams@geog.ucsb.edu
The coast of California is home to many rare, endemic conifers and other plants that are
drought sensitive and generally not well adapted to the summer-dry Mediterranean climate that
prevails across most of the state. Ecologists have long assumed that coastal pines survived the
early-Pleistocene transition to a warmer and drier environment because they benefit from
frequent fog and low stratus clouds that provide water and shade during the rainless summer.
Here, we report evidence for the importance of summer cloud cover to a stand of Torrey pines
(Pinus torreyana) on Santa Rosa Island in Channel Islands National Park. We developed a treering width chronology (1920-2004) and quantified the effects of summer cloud cover by
comparing ring widths to airport cloud-frequency records. Summertime cloud frequency
correlated significantly and positively with ring widths after we removed the effect of wetseason precipitation. Correlation with cloud frequency at altitudes low enough for fog to
inundate the entire pine stand was strongest in July early mornings (03:00 PST, R2 = 0.262).
Correlation for clouds high enough to provide shade but not water was strongest in July late
afternoons (16:00 – 18:00 PST, R2 = 0.148). These relationships were substantially stronger in
years when the early part of the rainy season was relatively dry and/or the bulk of the rainy
season was relatively wet, suggesting that these pines do not grow during every summer. This
may be due to an adaptive growing season length with a termination date dictated by water
availability, and possibly an upper limit on growing-season length. A decrease in fog activity
along the California coastline, which is apparent in various local climate records, would likely
impact relict stands of species that depend, in part, on frequent and predictable summertime
stratus-cloud cover.
Unfinished research focuses on comparing modeled vs. actual stable isotope (carbon and
oxygen) ratios in Bishop pine tree rings from Santa Cruz Island to further evaluate the
relationship between growth and cloud cover. We are also compiling a daily record (2000-2006)
of spatially continuous cloud cover, as observed via satellite (MODIS). We will compare the
spatial distribution of cloud-cover frequency to the spatial distributions of various endemic plant
species on the U.S. west coast to further evaluate where and for which species regular cloudiness
is crucial. We will also compare this spatial record of coastal cloud cover to other daily climate
records such as spatial distributions of atmospheric pressure, sea surface temperature, and wind
direction to improve our understanding of what causes low stratus and fog to develop in specific
locations.
MAGNITUDE OF OCEAN WARMING DURING THE PALEOCENE-EOCENE
THERMAL MAXIMUM
JAMES C. ZACHOS
Department of Earth and Planetary Science, University of California, Santa Cruz, CA 95064
jzachos@pmc.ucsc.edu
The Paleocene-Eocene Thermal Maximum (PETM) provides a unique opportunity to
40
observe the global climate sensitivity to a rapid and large increase in greenhouse gas levels.
Although the approximate changes in atmospheric CO2 levels have yet to be determined, carbon
isotope and deep-sea carbonate accumulation records confirm the rapid release of several
thousand gigatons of carbon (<10,000 years). Such a massive release over such short time scales
should have raised pCO2 by hundreds of ppm. In response, sea surface temperatures should have
risen uniformily over most of the planet. Such a response is supported by more than a dozen
SST anomaly records from pelagic and shallow marine sections which show a 5 to 9 C
increase. Most of these SST anomaly records are based on oxygen isotopes analyses of
planktonic foraminifera, and a few are based on Mg/Ca and TEX86. In locations where multiple
proxies are available, there is generally good agreement on the magnitude of SST change. The
few exceptions are primarily in tropical pelagic cores where it appears the oxygen isotope based
anomalies are damped. Reliable reconstructions of absolute SST, on the other hand, are far more
limited. Nevertheless, the few available points consistently show 5-8 C of warming with peak
PETM temperatures well above modern, as high as 33 C in the mid-latitudes and 22 C in the
Arctic. Along the Pacific Coast of North America, new data from the Toomey Hills in central
California indicate that SST over the shelf peaked at 27 C. The pattern of global warming is
consistent with greenhouse forcing in the absence of ice-albedo feedbacks. However, the peak
temperatures appear to be higher than can be achieved with just CO2 forcing alone (using current
climate models) implying that other trace gasses may have contributed as well.
MONO BASIN CLIMATE CHANGES CORRELATIVE WITH NORTH ATLANTIC
DANSGAARD-OESCHGER OSCILLATIONS
SUSAN ZIMMERMAN (1, 2), CORINNE HARTIN (3,4), CRYSTAL PEARL (3),
STEPHANIE SEARLE (1), SIDNEY HEMMING (1), AND N. GARY HEMMING (1,3)
(1) Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964
(2) now at Lawrence Livermore National Laboratory, Livermore, CA 94550
(3) Queens College, City University of New York, New York, NY 11367
(4) now at Rosentiel School of Marine and Atmospheric Sciences,
University of Miami, Miami, FL 33149
herrzim@gmail.com
Lakes are highly sensitive recorders of climate processes, but can be extremely difficult
to correlate precisely to ice core and marine records, especially beyond the range of radiocarbon
dating. Mono Lake, California (38 N, 119 W) preserves high-elevation strandlines and
multiple exposures of deep-lake silts of the late Pleistocene Wilson Creek Formation, indicating
that the lake level was high and variable in the past. Revision of the Wilson Creek Formation age
model, based on relative paleointensity (RPI) of Earth’s magnetic field, allows independent
correlation of paleoenvironmental changes in the Mono Basin to global climate records at
millennial timescales.
Comparison of relative lake level changes, based on mapping of facies in the Wilson
Creek Formation, with high-resolution bulk-sediment carbonate records reveals correlation of
high carbonate concentration with high lake level. Application of the new age model to the
carbonate record shows that during times of high local spring insolation the Mono Basin was
generally wetter, with high-amplitude, short-duration fluctuations in lake level correlative to the
41
Dansgaard-Oeschger (D-O) events of Greenland. Such regional expressions of the D-O events
have now been found globally, which the currently-favored hypothesis suggests may be related
to changes in the mean position of the Intertropical Convergence Zone.
42