Transcript 884K PPT - Sealevel

Arctic catastrophes: sea ice changes and impacts in the Eastern Arctic during the past 4,000 years
Mudie, P.J.1, Levac, E.2 , and Rochon, A.3
1 Geological
•
SUMMARY
Climate warming and reduction
of sea ice in the last 30 years has
forced major changes on the
traditional way of living for Inuit
people of the Eastern Canadian
Arctic. Large breaks in archaeological records also suggest that
drastic climate changes forced
abandonment of settlements and life
style shifts in Paleo- and Neoeskimo societies. However, the low,
century-scale time resolution of
these records does not allow testing
of this hypothesis of climate-driven
cultural changes (Mudie et al.
2005).
In this study, we looked at
decadal-scale paleoclimatic changes
recorded by palynological data in
unbroken 6,500 year records from
Coburg Polynya near sites on the
North Devon Lowlands (Panel A),
and from the North Water Polynya
near S.E. Ellesmere Island (Panel
B). Paleotransfer function data from
dinoflagellate cyst assemblages
provide estimates of changes in
surface temperature (SST) and sea
ice cover (SIC) with a precision of
+/- 1C and 1 month, respectively.
The proxy-data for both marine
sites show that abrupt temperature
changes of 2 – 4oC correspond to
major shifts in hunting modes of
Paleo- and Neo-Eskimo peoples and
to occupation-abandonment cycles
recorded for Devon and Ellesmere
Islands by Helmer (1991; 1992) and
Schledermann (1990). From ~6500
to 2600 BP, there were large swings
in summer SST from 2-4oC cooler
than now to 6oC warmer. Annual
variations in SIC ranged from times
of a 2-month longer pack ice season
to intervals with a 4-month longer
open water season. The warmer
times were when the pre-Dorset
Palaeoeskimos hunted mostly land
animals: muskox, caribou and fox.
The switch to marine-based hunting
(seal, whale, bear) by the later
Dorset and Neo-Eskimo people
corresponds to progressively cooler
intervals with more sea ice. These
past climate warming events took
~50-200 years to reach peak
temperatures: this is only about half
as fast as the current global
warming.
Survey Canada Atlantic, 2 St. Mary’s University, Halifax; 3 IFREMER, Rimouski
Study Areas
Location Map
Arctic dinoflagellates
A) RESULTS: JONES SOUND-DEVON ISLAND CORE 6
Fig. 1
B) RESULTS: NORTH WATER- ELLESMERE ISLAND
Fig. 2
Core 6 is from eastern Jones Sound,
about 10 km SE of the northermost
Inuit village at Grise Fiord (Fig. 1). Six AMS radiocarbon ages were used to date the 11 m
core of marine mud. Abundant dinoflagellate cysts, the organic walled resting spores of
phytoplankton and sea ice algae, were used to quantify past winter and summer temperatures (red fill), and amount of sea ice cover (blue fill), using the 607 coretop databases
of Mudie and Rochon (2001) and De Vernal et al. (2001). Grey shading shows the
intervals when summer temperatures were warmer than now, up to 6oC. The green bars
show occupation times of land-based hunters; blue bars show marine-based hunters.
CONCLUSIONS: Forecasts of future Arctic climate change predict an increase of +4 to 6
ºC and summer open channels by year 2030 C.E., and there has already been a temperature
rise of 1.5ºC in the past 30 years, while sea ice has shrunk by 14%. Some of the recent
change is part of the natural long-term cycles that Arctic people have adapted to for 4,000
years. But the change is much faster now than the natural warming rate of 50-200 years, and
the big question is “Can traditional hunting ways survive such rapid climate change?”
Two cores were obtained
from the North Water
(Levac et al., 2001), about
50 km south of Alexandra
Fiord, Bache Peninsula
(Fig. 2). Nine radiocarbon
ages were used to date the
8 meter-long section, and
dinoflagellate cysts were
used to reconstruct SST
and SIC, as for Core 6 (see
Panel A). Temperature
changes at this more
northern location are
smaller than off Devon
Island, but the alternating
warmer and colder periods
roughly coincide. In S.E.
Ellesmere, however, we
see slightly earlier
evidence of the marine
hunters (blue bars) and an
earlier start of more severe
sea ice conditions.
REFERENCES: De Vernal et al., 2001. J. Quaternary Science 16: 681698; Helmer, ,JW, 1991, Arctic 44:301-317; Ibid, 1992. J. Field Archaeology 19: 291313; Levac, E. et al., 2001. J. Quaternary Sci. 16:353-363; Mudie & Rochon,
2001. J. Quaternary Sci 16: 603-620; Mudie et al., 2005. Environmental
Archaeology 10 (2); Schledermann, P., 1990. Crossroads to Greenland, AINA,
Calgary, 364 pp.