PICES XV
S1-2894
Oral
Synchronous ecological regime shifts in the Kuroshio and Humboldt Currents
Juergen Alheit
Baltic Sea Research Institute, Seestr. 15, 18119 Warnemuende, Germany. E-mail: juergen.alheit@io-warnemuende.de
Decadal-scale dynamics of the Kuroshio and Humboldt Current ecosystems are controlled by shifts between
alternating sardine and anchovy regimes that restructure the entire ecosystem. The transition from an anchovy
to a sardine regime occurred in both systems between 1969 and 1971. The reversal back to an anchovy regime
was observed in both systems in the mid-1980s. The causes for these dramatic, abrupt changes of major
biological components in both ecosystems and their striking synchrony are a puzzle. However, the synchrony of
events in both systems might be the key to solving the regime shift problem as it points to an external forcing
mechanism which drives both systems. Recent work has drawn attention to subsurface processes which might
be involved in the regime shift mechanisms. Changes in mixed layer depth in the Kuroshio Current Extension
(KCE) region and associated changes in biological production coincide with the population changes observed in
the KCE. Similarly, interdecadal changes of thermocline depth off the coast of Peru and Chile which are well
correlated with interdecadal SST anomalies occurred at the time of transitions from anchovy to sardine and back
to anchovy regimes. The coincidence of the timing of physical processes and ecosystem regime shifts in both
ecosystems which are thousands of miles apart from each other raises the question whether both systems are
governed by basin-wide climatic teleconnection patterns. This contribution will describe the ecological regime
shifts in the two Pacific ecosystems and discuss commonalities, differences and possible teleconnection patterns.
PICES XV
S1-3054
Oral
Intraseasonal wind oscillations and their influence on northern California Current
coastal ecosystems
John A. Barth1 and John M. Bane2
1
2
College of Oceanic and Atmospheric Sciences, Oregon State University, 104 COAS Admin. Bldg., Corvallis, OR, 97331-5503, U.S.A.
E-mail: barth@coas.oregonstate.edu
Department of Marine Sciences, University of North Carolina, Chapel Hill, NC, 27599, U.S.A.
Intraseasonal oscillations (ISOs) are fluctuations in the atmosphere-ocean-climate system with periods between
20 and 40 days which is longer than the typical 2- to 6-day “weather-band” wind fluctuations that drive coastal
upwelling and downwelling. We show how wind ISOs directly influence the coastal ocean ecosystem in the
northern California Current System, the eastern boundary current of the North Pacific. During summer 2001 in
the Oregon coastal upwelling system, ecosystem variations were due to 20-day ISOs in wind stress. Upperocean temperature, phytoplankton and zooplankton varied principally on the 20-day time scale and correlated
with the stress, showing the importance of the stress ISOs in driving the oceanic ecosystem. The stress ISOs
were driven by variations in the north–south position of the atmospheric Jet Stream, which were generated by an
interaction between the Jet Stream and the western U.S. mountain ranges. In 2005, the spring transition to
upwelling-favorable wind stress was delayed by over a month in the northern California Current Large Marine
Ecosystem by 20- to 40-day wind ISOs associated with a southward shift of the Jet Stream. Early in the
upwelling season (May–July) off Oregon, the cumulative upwelling-favorable wind stress was the lowest in 20
years, nearshore surface waters averaged 2°C warmer than normal, surf-zone chlorophyll-a and nutrients were
50 and 30% less than normal, respectively, and mussel and barnacle densities were reduced by 83 and 66%,
respectively. The negative impact of these changes propagated up the marine food web.
PICES XV
S1-2820
Invited
The Northern California Current Ecosystem: Variability, indicator development, and
an ocean condition index for fishery management
Edmundo Casillas and William T. Peterson
Northwest Fisheries Science Center, NOAA-Fisheries, 2725 Montlake Blvd. E., Seattle, WA, U.S.A. E-mail: edmundo.casillas@noaa.gov
Since 1997, we have been monitoring the coastal ocean environment of Washington and Oregon, including an
assessment of the Columbia River plume, its interaction with the California Current, and how it affects the
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abundance, distribution, and growth of juvenile salmon as a means to assess their survival as they enter the
marine landscape. Our observations indicate the northern California Current is a dynamic large marine
ecosystem whose features vary widely at daily to decadal time scales. The ocean conditions we have observed
are a measure of the interaction of the physical forces (e.g., temperature, winds, water mass) and the biological
features and responses to these physical drivers (e.g., food resources, predator populations). The result of these
physical-to-biological interactions is that growth, abundance and survival of fish in the pelagic ecosystem varies
each year. Fisheries experts recognize that our ability to manage fishery resources will depend in part on
forecasting the impact of changing ocean conditions as a result of the natural variability inherent in the
ecosystem and the directed change as a function of impending global climate change. However, until now the
region has lacked a clear set of tools that provide this information. I will discuss the physical and biological
metrics we have evaluated and our results to date. Our goal is to communicate the status of the Northern
California Current Ecosystem annually through a technical report, and in real time by posting the state of the
California Current to our website for managers to use.
PICES XV
S1-2812
Oral
Decadal changes of the Oyashio and Kuroshio affected spatio-temporal variation of the
copepod community in the western North Pacific
Sanae Chiba1, Hiroya Sugisaki2 and Toshiro Saino1,3
1
2
3
Frontier Research Center for Global Change, JAMSTEC, 3173-25 Showa-machi, Kanazawa-ku, Yokohama 236-0001, Japan
E-mail: chibas@jamstec.go.jp
Tohoku National Fisheries Research Institute, 3-27-5 Shinhama-cho, Shiogama, Miyagi 985-0001, Japan
Hydrospheric Atmospheric Research Center, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan
The KOE region, consisting of the Kuroshio, Oyashio and Transition zone, shows the highly variable, complex
environments, where dynamics of those currents greatly influence biological production. We report the decadal
change in geographical distribution pattern of copepods in the Oyashio and Transition zone using the historical
zooplankton collection (Odate Collection). Temporal variation of the copepod community was examined by the
principal component analysis (PCA). PC1 time-series mirrored interannual variation of the abundance of
“Oyashio assemblage.” The “jumps” of the PC1 value were detected in 1976 and 1988, both of which coincided
the years of the major and minor climatic Regime Shifts in the North Pacific. On the other hand, PC2 timeseries mirrored the variation of small-sized, warm-water species, defined as the “Transition zone assemblage”
copepods, and a jump year was observed in 1982. The distribution of the Oyashio assemblage shifted
southwestward after 1976, responding to the southern intrusion of the Oyashio. It further shifted west toward
the Japanese coast after the 1988, presumably due to the northern intrusion of the Kuroshio. Although there was
no clear change in the geographical distribution of the Transition zone assemblage before and after 1982,
increase in its abundance was manifest. Considering that geostrophic transport of the Kuroshio increased in the
early 1980s, several years after the southward shift of the Oyashio, it is suggested that distribution pattern of the
copepod community was determined by the combined effects of lagged and un-lagged hydrographic variations,
which are closely related to the Pacific Decadal Oscillation.
PICES XV
S1-3055
Oral
The North Equatorial Countercurrent: An anomalous boundary current with
biologically significant upwelling and a predictable response to climate forcing
James Christian
Fisheries and Oceans Canada; Canadian Centre for Climate Modelling and Analysis, University of Victoria, P.O. Box 1700, STN CSC,
Victoria, BC, V8W 2Y2, Canada. E-mail: jim.christian@ec.gc.ca
The North Equatorial Countercurrent (NECC) forms the southern boundary of the North Pacific Ocean.
Meandering ocean currents are known to generate significant upwelling, but the biological significance of this
upwelling is not well understood. In the NECC during the 1997-98 El Niño event, satellite images showed a
“river of dark water” formed by phytoplankton blooms in a narrow meandering current against a backdrop of
oligotrophic waters. These blooms are closely related to the basin-scale dynamics of ENSO (El Niño Southern
Oscillation), i.e., the chlorophyll anomaly is predictable from real-time observations of e.g., tropical Pacific sea
surface temperature, or from an ENSO prediction model if the model itself has predictive skill. This region
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contains some of the world’s largest underexploited oceanic fish populations and is a prime candidate for using
satellite data and climate models to engineer a sustainable fishery in an underdeveloped region.
PICES XV
S1-3093
Oral
Intrinsic oceanic decadal variability in the North Pacific generated in the Eastern
Boundary Current System
Emanuele Di Lorenzo1 and Niklas Schneider2
1
2
School of Earth and Atmospheric Sciences, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, GA, 30332-0340, U.S.A.
E-mail: edl@gatech.edu
International Pacific Research Center, University of Hawaii at Manoa, 1680 East West Road, Honolulu, HI, 96822, U.S.A.
Decadal variations in the North Pacific have profound implications on the marine ecosystems, which are
characterized by nonlinear, and regime-like, responses to changes in the physical environment. Previous studies
of the mechanism of North Pacific decadal variability focus on the existence of midlatitude coupled ocean–
atmosphere modes, or on the ocean response to atmospheric stochastic variability. However, sources of intrinsic
ocean variability, which arise from ocean internal dynamics without atmospheric coupling and stochastic
forcing, have not been explored.
In this study we investigate the role of the Eastern Boundary Current System in generating intrinsic decadal
variations in the North Pacific. Specifically we show how the intrinsic mesoscale eddy field that develops in the
California Current leads to decadal variations in the temperature (T) and salinity (S) properties of the eastern
subtropical mode waters (ESMW). The subducted TS anomalies are density compensated and may ultimately
lead to a delayed feedback on the tropical coupled ocean–atmospheric system when the ESMW are ventilated by
equatorial upwelling.
The findings of this study rely on a multi-century long integration of an eddy-resolving ocean model of the
Northeast Pacific. The model is forced either with monthly climatological forcing or with a 50 year-long
forcing cycle derived from the National Center for Environmental Prediction (NCEP) reanalysis. A comparison
of the model output with the long-term California Cooperative Fisheries Investigations (CalCOFI) TS dataset is
also presented. Surprisingly, the model intrinsic variations capture the amplitude and periodicities of the
CalCOFI salinity time series, which have been previously unexplained.
PICES XV
S1-3164
Invited
The response of North Atlantic boundary currents and their ecosystems to climate
change and variability - Contrasts and comparisons with the North Pacific
Kenneth F. Drinkwater and Svein Sundby
Institute of Marine Research, Box 1870, Nordnes, N5817 Bergen, Norway. E-mail: ken.drinkwater@imr.no
Like the North Pacific, the North Atlantic is surrounded by numerous boundary currents (e.g., Gulf Stream,
Labrador Current, West Greenland and East Greenland Currents, Norwegian Atlantic Current, Norwegian
Coastal Current, etc.) with a diversity of ecosystems. Also, like the North Pacific, these ecosystems have been
shown to respond to changes in climate from short-term events such as wind storms to long-term multidecadal
oscillations and climate warming trends. The responses depend in large degree on the frequency of forcing and
various examples from the North Atlantic will be given to highlight these differences. Future climate scenarios
will be discussed in terms of the possible changes to these boundary currents and their implications for the
marine ecosystems. Discussion will also be presented on the effects of fishing on the sensitivity of fish species
to climate forcing. Finally, we ask the question, can we obtain additional insights into the effects of climate
forcing on marine ecosystems by comparing and contrasting responses between the North Atlantic and North
Pacific?
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PICES XV
S1-2999
Invited
The biophysical oceanography of the Leeuwin Current, a poleward-flowing eastern
boundary current off the west coast of Australia
J. Anthony Koslow, Ming Feng, Stéphane Pesant and Peter Fearns
CSIRO Marine & Atmospheric Research, Private Bag 5, Wembley, Western Australia 6913, Australia. E-mail: tony.koslow@csiro.au
The Leeuwin Current is a uniquely poleward-flowing eastern boundary current (EBC) off the west coast of
Australia. Because it is driven by a pressure gradient established by the Indonesian Throughflow, the primary
link between the Pacific and Indian Oceans, its dynamics are closely coupled with variability in the North
Pacific circulation, notably the El Niño Southern Oscillation (ENSO) cycle. But unlike other EBCs, the
Leeuwin is a warm, nutrient-poor current that suppresses upwelling. As a consequence, the waters off Western
Australia are generally oligotrophic. Interestingly, however, recruitment to the region’s (and Australia’s) most
valuable single-species fishery, the western rock lobster (Panulirus cygnus), is positively correlated with
interannual variability in the flow of the Leeuwin Current. The annual phytoplankton bloom also coincides with
the period of strongest Leeuwin flow in late autumn, when the current spins up eddies just beyond the shelf
break. The eddy kinetic energy of the Leeuwin is greater than that of other EBCs. Recent biogeochemical
studies have generated several hypotheses that link the dynamics of the Leeuwin with regional productivity.
These hypotheses suggest a mechanism underlying the apparently paradoxical correlation between the strength
of the Leeuwin Current and western rock lobster recruitment.
PICES XV
S1-3059
Invited
Long-term changes in the climate of the California Current, with biological impacts
Arthur J. Miller
Scripps Institution of Oceanography, La Jolla, CA, 92093-0224, U.S.A. E-mail: ajmiller@ucsd.edu
The CalCOFI dataset in the southern California Current reveals a significant surface-intensified warming and
stratification (buoyancy frequency) change across the 1976-77 climate regime shifts. However, the average
depth of the thermocline, defined as the maximum gradient of temperature, did not change significantly across
the regime shift. But as the surface heating changed the strength of stratification, it also changed the slope of
the nitrate-temperature relation for the mid-depth waters (roughly 30m to 200m). This may have affected the
quality of upwelled water and the depth from which it is drawn. These historical changes can be useful in
anticipating the potential impact of global warming on the oceanic circulation off the coast of California. For
example, an eddy-permitting ocean model forced with wind stresses, heat fluxes and open boundary conditions
obtained from a global climate model forced by increased greenhouse gases predicts increased upper-ocean
temperatures, and increased stratification along the coast. The vertical structure of the thermal response is
similar to recent studies of global warming trends.
PICES XV
S1-3121
Oral
Kuroshio and Oyashio boundary currents: Critical foraging habitat for the short-tailed
albatross (Phoebastria albatrus), one of Japan’s natural monuments
Robert M. Suryan1, Fumio Sato2, Gregory R. Balogh3, Noboru Nakamura2, Paul R. Sievert4 and Kiyoaki Ozaki2
1
2
3
4
Oregon State University, Hatfield Marine Science Center, 2030 S.E. Marine Science Dr., Newport, OR, 97365, U.S.A.
E-mail: rob.suryan@oregonstate.edu
Yamashina Institute for Ornithology, 115 Konoyama, Abiko, Chiba 270-11, Japan
U.S. Fish and Wildlife Service, 605 W. 4th Ave., G-61, Anchorage, AK, 99501, U.S.A.
U.S. Geological Survey, Massachusetts Cooperative Fish and Wildlife Research Unit, Department of Natural Resources Conservation,
University of Massachusetts, Amherst, MA, 01003, U.S.A.
The Kuroshio-Oyashio current region is a physically dynamic system supporting rich biological productivity
and important foraging habitat for upper trophic level predators, including the short-tailed albatross
(Phoebastria albatrus). We integrated satellite tracking of albatrosses and oceanographic remote sensing data to
identify physical and biological features important to albatross foraging habitat. Nineteen albatrosses were
tracked from their breeding colony on Torishima (Izu Islands) for three years, between 2002 and 2006. Primary
foraging areas included prominent chlorophyll and sea surface temperature fronts, generally within the 17 oC
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isotherm off the continental shelf break and slope domains. Geographically, these areas were off the northern
Izu-Ogasawara Ridge, northeastern Honshu, eastern Hokkaido, and the Kuril Islands. In particular, a cool water
tongue of the Kuroshio-Oyashio convergence off northeastern Honshu (35º–40ºN) was a consistent foraging
destination for albatrosses in all years. Albatrosses foraged progressively northward with the warm water
intrusion of the Kuroshio Current during spring and summer. Most satellite-tagged albatrosses had migrated out
of the Kuroshio-Oyashio current region by August. Despite the well documented eddy formation and elevated
productivity of the Kuroshio extension and bifurcation regions, short-tailed albatrosses made relatively little use
of these areas, other than transiting its northern boundary en route to the Aleutian Islands, Alaska. Our results
identify prominent features of this boundary current system that are important to foraging for an upper trophic
level marine predator, an endemic breeder, and designated natural monument of Japan.
PICES XV
S1-2788
Invited
The Kuroshio and Oyashio current system: Variability and impact on the ecosystem
Ichiro Yasuda
Ocean Research Institute, University of Tokyo, 1-15-1 Minamidai, Nakano-ku, Tokyo 164-8639, Japan. E-mail: ichiro@ori.u-tokyo.ac.jp
Recent studies are changing our view of the Kuroshio and Oyashio current system and water-mass formation in
the western boundary currents. Large diapycnal tidal mixing expected around the Kuril and the Aleutian Straits
enhances sinking in the Okhotsk Sea, and diapycnal upwelling could promote Oyashio and North Pacific
Intermediate Water formation. These processes may have an influence on the Kuroshio and the Kuroshio
Extension. Furthermore, large diapycnal mixing changes in the 18.6-year period because the diurnal tidal flow
amplitude changes up to 20%. Sea surface temperatures (SSTs) around the Kuril and Aleutian Straits, and the
surface to intermediate waters in the North Pacific subarctic region, show evidence of ocean-originated bidecadal variability. This process may influence atmospheric bi-decadal variability. We also find long-term
variability in zooplankton in the Oyashio waters and species replacement of small pelagic fishes among
Japanese sardine and Pacific saury. We discuss possible mechanisms behind these long-term changes.
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