A Comparison of Pinus albicaulis Tree-Ring Chronology and
Summer Temperatures as a Basis for Reconstructing Glacial
Mass Balance in the North Cascades
Rebecca Franklin Laboratory of Tree-ring Research, Department of Geosciences, University of
Arizona, Tucson, Arizona 85705, USA
ABSTRACT
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nhIOehto enoiwehro ihnoieah;oAnoweih ioaoi oIfaoihyolhieao’ihsl
hah nlnhlh
Figure 1 Map of North Cascade
glaciers. Glaciers used in mass
balance
reconstruction
are:
C=Columbia, F=Foss, LC=Lake
Curtis, R=Rainbow, D=Daniels,
IW=Ice
Worm,
L=Lynch
and
Y=Yawning
an idea of climate conditions to expect in the future
INTRODUCTION
An increasing interest in the effects of
(Watson and Luckman, 2004).
global warming, especially as seen in the retreat of
Annual mass balance is the difference
temperate-zone glaciers is prevalent in both the
between total accumulation and total loss, or
scientific
ablation, of snow for a glacier.
and
public
communities.
Glacier
This specific
fluctuation records of sufficient length can be used
measurement can quantify how a glacier is
as indicators of past climate conditions. Examining
responding to climate change in its region (Pelto
these long term records can give researchers today
and Reidel, 2001).
GEOLOGY May 2005
1
Few mass balance records of sufficient
However, in addition to trees in the
length are currently available, with the lengthiest
immediate vicinity being able to reproduce the
records not usually exceeding the past few decades.
climate signal affecting glacial mass balance,
For extending glacial mass balance records into the
attention needs to be paid to broad regional scale
past, many proxies for mass balance have been
climate signals, as glacial mass balance is highly
used. Nicolussi and Patzelt, 1996 and Luckman,
correlated
2000, have used lichonometric, dendrochronologic
correlation values of up to 0.98 over a ~8000 km2
and historical records for reconstructing glacial
area (Pelto and Reidel, 2001).
across
region
scales,
with
cross-
mass balances. Historical repeat photography is a
The North Cascades Glacier Climate Project
valuable resource but rare, and lichenometric
has recorded mass balances of 8 different glaciers
studies yield results that are not annual in
(Fig.1) since 1984 (Pelto and Reidel, 2001). With
resolution, as needed for annual mass balances
this record, I will see how significant of a
(Winchester and Harrison, 2000).
reconstruction of past glacial mass balance I can get
record
with
tree-ring
by using both a local climate proxy (tree-ring
chronologies are often used (Cook and Kairiukstis,
records) and regional proxies (summer average
1990), as trees with strong climate signals are
maximum temperatures and total snowfall).
ubiquitous in regions of boreal-zone glacial activity.
North Cascades are located in climate Region 5 of
Using
annual
To obtain a
resolution,
dendrochronology to
reconstruct
Washington state.
The
Climate information for this
glacial mass balance and other glacial processes
region can be retrieved from the National Oceanic
such as glacial advance and oscillations in length
and
has given fruitful results as in the cases of
National Climatic Data Center using “NNDC
LaMarche and Fritts in the Austrian Alps, 1971 and
Climate Data Online”.
Atmospheric
Administration’s
(NOAA)
in the Patagonian Ice Field by Villalba et al, 1990.
This region lies in an area that receives
These and others have found that radial growth
heavy precipitation, lying on the west side of the
variations of high elevation trees are highly
precipitation divide of Washington state. This and a
correlated to local glacial activity.
2 GEOLOGY May 2005
moderate maritime climate and high mountain
peaks (with glaciers at ~2500 meters) allow for the
existence of both glaciers and forests in the same
METHODOLOGY
To reconstruct a history of glacial mass
balance for a region ~8000 km2 in area, I used the
location.
What do I hope to find out with this
mass balance record recorded by the North
research? What seem to be the controls on glacial
Cascades Glacier Climate Project (NCGCP). Their
mass balance for the North Cascades region of
record is of 8 glaciers located in the North Cascades
Washington?
Can glacial mass balance be
between 120o and 122o W longitude and between
reconstructed using a tree-ring chronology or would
49o and 48o N latitude. These are the Columbia,
climatic factors be a more precise way to
Foss, Lake Curtis, Rainbow, Daniels, Ice Worm,
reconstruct mass balance? Of the climate variables
Lynch and Yawning glaciers (Fig. 1). Their mass
in the region which- temperature or precipitation
balances as recorded by the NCGCP can be seen in
will more closely follow along with the activity of a
Figure 2.
glacier’s mass balance?
Figure 2.
.
Glacial Mass Balances as recorded by NCGCP for 8 North cascade glaciers, 1984-2000
GEOLOGY May 2005
3
I then took an average of the 8 glaciers to
and longitude a set of tree-ring chronologies were
get one regional average. Since all 8 glaciers are
obtained that were sampled at the proper elevations
highly cross-correlated (Pelto and Reidel, 2001) this
(~2500 meters) to capture the same temperatures
average can be seen as representative of the entire
and precipitation signals as would the NCGCP
region (Fig 3.).
glaciers. I selected chronologies that had sample
sizes larger than 30 to make sure a significant signal
2.5
Annual Mass Balance in Meters of Water
2
1.5
1
Cloumbia
Foss
Daniels
Ice Worm
L Curtis
Rainbow
Lynch
Yawning
was being captured.
already been standardized but were in Tucson
0.5
Decadal Form so I fed them through the program
0
-0.5
“Yuxtoponer”
(also
from
the
WDC
for
-1
-1.5
Paleoclimatology, ITRDB) to be able to read them
-2
-2.5
1984
in a two-column year/value and be able to
1986
1988
1990
1992
1994
1996
1998
2000
Year
Figure 3. Annual Mass Balances of 8 North Cascade
Glaciers (monitored by the NCGCP), 1984-1991.
The average annual mass balance is what I
used for the calibration of several regression
functions that would later be used to reconstruct a
period of mass balances reaching back to 1722 for
the tree-ring proxy and to 1958 for the climate
proxies.
TREE-RING METHODOLOGIES
A tree-ring record for this region was found
on the World Data Center for Paleoclimatology by
searching in the International Tree Ring Data Base
(ITRDB). By selecting the required area by latitude
4
These chronologies had
GEOLOGY May 2005
manipulate them statistically.
The four chronologies extracted were of
Abies
lasiocarpa
ABLA),
Pinus
(subalpine
albicaulis
fir,
abbreviated
(whitebark
pine,
abbreviated PIAL), Picea engellmenii (Engellmen
spruce, abbreviated PCEN), and Larix lyallii
(subalpine larch, abbreviated LALY).
I then plotted, using MINITAB pageplot the
four chronologies next to their average and the
average of the 8 glacial mass balances (Fig 4.).
1986
1987
1988
1989
1990
1991
Avg TR index
1985
0.5
PCEN index
1984
0.4
y = 2.7071x - 2.6489
R2 = 0.6638
Avg Mass Bal.
PIAL index
ALBA index
Glacial Mass Balance
LALY index
0.3
1984
1985
1986
1987
1988
1989
1990
1991
0.2
0.1
0
-0.1
-0.2
-0.3
Figure 4. Comparison of Average Mass Balances and both
individual and average tree-ring indices for four species, P.
albicaulis, A. lasiocarpa, L. lyalii and P. engellmenii, 1984-1991.
-0.4
-0.5
0.6
In examining the plotted time series, I found
that the chronology that most closely approximated
the average annual mass balance was the PIAL. A
correlation of .38 (Fig. 5.).
0.8
0.9
1
1.1
1.2
Tree Ring Index
Figure 5. Regression of Pinus albicaulis Tree-Ring
Indices and Average Glacial Mass Balance of 8 N
Cascade Glaciers, 1984-1991.
bivariate scatter showed one outlier; when the
outlier was removed they were found to have a
0.7
I used the regression equation of Mass
Balance = 2.701*(Tree-Ring Indices)-2.6489. This
gave the following Mass Balance reconstruction in
Figure 6, and Figure 7 shows the reconstruction
versus the calibration period.
1.6
1.5
P. Albicaulis Chronology
Reconstructed Mass Balance
Pinus albicaulis Chronology
1
1.2
0.5
1
0.8
0
0.6
-0.5
0.4
-1
0.2
0
Reconstructed Average Mass Balance
1.4
-1.5
1
51
101
151
201
251
Years after 1722
Figure 6. Comparison of Pinus albicaulis chronology and Reconstructed Average Glacial Mass Balance, 17221991.
GEOLOGY May 2005
5
that starting in April and extending through
0.6
Reconstructed
September,
Actual
0.4
temperatures
were
consistently over (by ~15oF) the melting point for
0.2
Mass Balance
maximum
0
the glaciers, thus able to impact glacial mass
-0.2
balance.
-0.4
Precipitation, in the form of snow also has a
-0.6
-0.8
1984
large effect on glacial mass balance even though
1985
1986
1987
1988
1989
1990
1991
glaciers in the Cascades at the last glacial maximum
Year
Figure 7. Reconstructed v. Actual Average Annual
Mass Balances of 8 N Cascade Glaciers, 1984-1991,
reconstructed using PIAL chronology.
maintained themselves with decreased precipitation
(Hostetler and Clark, 1996).
Precipitation data as total snowfall was also
CLIMATE METHODOLOGIES
found on NOAA’s NCDC Climate Data Online site.
As Davi et al (2003) found in a study
inferring boreal temperature variability from treering width data, warm season temperatures correlate
highly with boreal-zone trees and nearby glacial
activity.
Washington Region 5 climate zone have data
For those five
stations, Carson Fish Hatchery, Peterson’s Ranch,
Longmire Rainier NPS, Rainier Paradise Ranger
Station and Ross Dam I averaged warm season
maximum temperatures, which were chosen April
through September. These months were selected
because upon analyzing the climate data I found
6
GEOLOGY May 2005
(October through September of the proceeding year)
was being used rather than the secular year. The
NCGCP measured the mass balance of the glaciers
starting from mass balance minimum and ending at
Five of the climate stations that comprise the
reaching down to the present.
I adjusted the years so that the hydrologic year
the next mass balance minimum. These minima did
not always come at the same time but were, on
average, late September/early October.
This falls
right at the onset of the hydrologic year, allowing
for a consistent basis for comparison. The values
that I used to correlate were total snowfall
accumulation over the whole hydrologic year.
I
chose these instead of monthly averages because of
the accumulatory nature of the mass balance of
750
glaciers (Hostetler and Clark, 1996).
Figure 8 is a comparison of the contrasting
effects on the mass balance of a glacier. The post1976 shift in climate patterns attributed to the shift
in the El Nino/Southern Oscillation index seems to
Temperature, Tenths of a Degree F
700
650
600
550
500
450
1955
1960
1965
1970
1975
1980
1985
1990
1995
2000
Year
be apparent in these graphs, though unfortunately
our glacial mass balance record here does not
extend far back enough in time to also capture this
Figure 8. Upper graph: Average total snowfall in
tenths of inches. Lower graph: Average maximum
April-September temperature in tenths of a degree
Fahrenheit. Both for Washington Region 5, 19552004.
shift. This would have been an excellent test of the
When I ran a correlation between average
power of the regression equations used in this
total snowfall and mass balance I found that for the
reconstruction.
period of overlap with the tree-ring record, 1984-
12000
1991,
Snowfall, Tenths of Inches
10000
and
even
for
the
period
of
mass
8000
balance/snowfall record overlap, 1984-2000, there
6000
were no significant correlation.
4000
scatterplot confirmed this visually and led me to
A bivariate
2000
abandon the use of total snowfall as a basis for mass
0
1955
1960
1965
1970
1975
1980
Year
1985
1990
1995
2000
balance reconstruction for this part of the Cascades.
The correlation between temperature and
mass balance yielded better results. Again, I chose
the period of correlation to match that of the period
in common for the tree-ring series so all correlations
could be suitable for comparison.
This gave a
correlation of .84 as seen in Figure 9.
GEOLOGY May 2005
7
0.6
RESULTS
0.4
y = -0.0167x + 10.903
R2 = 0.8457
Glacial Mass Balance
0.2
The highest correlation with glacial mass
0
balance comes from the average maximum summer
-0.2
temperature record from Washington Region 5
-0.4
climate zone with an R2 of .84. The whitebark pine
-0.6
-0.8
620
630
640
650
660
670
680
690
chronology yielded an R2 of 0.38 while the snowfall
700
Temperature, Tenths of a degree F
record had a negligible correlation of at the highest
Figure 1. Correlation between Washington Region 5
Average March -September Temperature, Tenths of a
degree Fahrenheit and Average Annual Glacial Mass
Balance for 8 N. Cascade Glaciers, 1984-1991.
R2 = 0.11 for the period of overlap of snowfall
record and mass balance, and an R2 of .0002 for the
With the regression
equation,
Mass
period of concern, (the overlap of mass balance and
Balance = -0.0167*(temperature) + 10.903, I
tree-ring record) 1984-1991.
reconstructed the mass balance for the period 19582000.
An excellent representation of how the
Temperature, because of its highest
reconstructions compare to one another is in Figure
correlation value seems to be the most promising of
10.
the three proxies used so far.
Actual Mass Balance
Reconstructed by Chronology
Reconstructed by Temperature
2
1.5
1
Mass Balance
0.5
0
1
3
5
7
9
11
13
15
17
19
21
23
25
27
29
31
33
35
37
39
41
43
-0.5
-1
-1.5
-2
-2.5
-3
Years After 1958
Figure 2. Periods of Positive and Negative Glacial Mass Balance, 1958-1991. Note how reconstructions may not
reproduce actual values but do reproduce the shifts in positive to negative mass balance.
8
GEOLOGY May 2005
It can be seen that while not reconstructing exact
values for mass balance, as can be seen in the
validation section of the graph (the yellow value is
actual glacial mass balance) both reconstructions
0.9
reproduce the shifts from negative to positive mass
0.8
0.7
balance quite well. Chart1 is a quick reference for
R2 values.
0.6
PIAL
Chronology
0.5
Figure 12 provides another quick
Total Snowfall
0.4
0.3
reference to see how each of the proxies compares,
Max Summer
Temp
0.2
0.1
over the period in common, to the actual average
0
R^2
mass balance. It is quite apparent that there is a
direct
negative
correlation
between
summer
temperature and actual mass balance.
Chart 1. R2 values for calibration period 1984-1991
for each reconstruction method.
1985
1986
1987
1988
1989
1990
1991
1984
1985
1986
1987
1988
1989
1990
1991
Actual Mass Bal
PIAL Chron
Snowfall
Temperature
1984
Figure 12. A comparison of the actual values for average mass balance, whitebark pine chronology, total snowfall
and average maximum summer temperatures, from 1984-1991.
GEOLOGY May 2005
9
possibly be because both the tree ring record and
DISCUSSION
In this research project I found that summer
the mass balance record are a synthesis of different
maximum temperatures were a much stronger driver
processes and are not governed totally by one
for glacial mass balance than was winter snowfall
climatic process.
accumulation. It is interesting that in such a snowy
parametric model for mass balance would be more
region, snowfall had such a slight effect on mass
appropriate, with different factors operating at
balance. This could be due to the fact that while on
certain thresholds.
In this case, perhaps a multi-
the west side of the precipitation divide, the glacier
A strong feature of my reconstruction is the
sites were relatively close to the divide and could be
ability of the regression equation to reproduce the
experiencing a slight continental effect. This would
shift from negative to positive mass balance. This
explain why summer temperatures influenced the
can be especially noted in Figure 11 for the period
mass balances of the glaciers.
of overlap of all three series, 1984-1991.
It thought it would be interesting to see how
The shift to more negative mass balance
well the whitebark pine chronology correlated to
values that comes at 1985 is interesting and looking
summer temperatures and snowfall accumulation.
back to Figure 8 which has snowfall accumulation
Surprisingly,
higher
and summer temperatures from 1955 to present, it
correlation with snowfall (R2 of .66) than with
can be seen that while before 1985 temperature
temperature (R2 of .34).
Both of these had the
were quite a bit lower and snowfall was definitely
outlier year taken out (this was not done for the
higher. Possibly this shift in snowfall (which is
regression equations).
more
the
chronology
had
a
extreme
than
the
shift
in
summer
Another interesting point is that although
temperatures) is what has allowed for there to be
summer temperatures were more highly correlated
such a negligible effect of the snowfall record on
with mass balance, it looks as though the tree rings
glacial mass balance.
show evidence of the higher variance that goes
Although summer temperatures have a
along with the mass balance record. This could
higher correlation, the tree-ring index has the
10 GEOLOGY May 2005
combination of climatic factors that parallels the
Davi, N.K., Jacoby, G.C. and Wiles, G.C., 2003,
combination of factors that are likely influencing
Boreal temperature variability inferred from
mass balance. Again I point to the fact that the
maximum latewood density and tree-ring width
reconstructions based on the tree-ring chronology
data,
exhibits the higher variance that the mass balance
Quaternary Research, v. 60, p. 252-262.
record does.
Wrangell
Mountain
region,
Alaska:
If it is true that the tree rings are
Hostetler, S.W., and Clark, P.U., 1996, Climatic
actually a better representation of mass balances
controls of western U.S. glaciers at the last
then perhaps Figure 6 is an accurate reconstruction
glacial maximum: Quaternary Science Reviews,
of mass balance.
v. 16, p. 505-511.
When reconstructing any time
series based on such a long record as tree-rings
Pelto, M.S., and Reidel, J., 2001, Spatial and
provide, however, it is wise to find out if there have
temporal variations in annual balance of North
been any major shifts in climate patterns that would
Cascade
change how the trees react to either temperature or
Hydrological Processes, v. 15, p. 3461-3472.
precipitation.
glaciers,
Washington
1984-2000:
Villalba, R., Leiva, J.C., Rubulls, S., Suarez, J., and
Another constraint on this reconstruction is
Lenzano, L., 1990, Climate, tree-ring, and
the short time span of the calibration period. This
glacial fluctuations in the Rio Frias Valley, Rio
reconstruction has a much lower significance than
Negro, Argentina: Arctic and Alpine Research,
one done on a calibration period of 25 years or
v. 22, p. 215-232.
longer. This is just one more reason why more
Watson, E. and Luckman, B., 2004, Tree-ring-based
funding needs to go into high elevation/high latitude
mass-balance estimates for the past 300 years at
climate monitoring stations.
Peyto Glacier, Alberta, Canada: Quaternary
Studies like these
depend on high spatial and temporal depth to
achieve meaningful results.
REFERENCES CITED
Research, v. 62, p. 9-18.
Winchester,
V.
and
Dendrochronology
Harrison,
and
S.,
2000,
lichenometry:
colonization, growth rates and dating of
GEOLOGY May 2005
11
geomorphological events on the east side of the
North
Patagonian
Icefield,
Geomorphology, v. 34, p. 181-194
12 GEOLOGY May 2005
Chile: