WHEN THE CANADIAN ARCTIC WAS 5°C WARMER THAN TODAY

WHEN THE CANADIAN ARCTIC WAS 5°C WARMER THAN TODAY

Quaternary Research. Volume 65, Issue 3 , May 2006, Pages 431-442

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A multi-proxy lacustrine record of Holocene climate change on northeastern Baffin Island, Arctic Canada

Jason P. Briner a), Neal Michelutti b), Donna R. Francis c), Gifford H. Miller d), Yarrow Axford d), Matthew J. Wooller e) and Alexander P. Wolfe b)

a) Geology Department, University at Buffalo, Buffalo, NY 14260, USA

b) Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB T6G 2E3, USA

c) Department of Geosciences, University of Massachusetts, Amherst, MA 01003, USA

d) Department of Geological Sciences and the Institute of Arctic and Alpine Research, University of Colorado, Boulder, CO 80303, USA

e) Alaska Stable Isotope Facility, Water and Environmental Research Center and School of Fisheries and Ocean Sciences, University of Alaska, Fairbanks, AL 99775-5860, USA

Abstract

Reconstructions of past environmental changes are critical for understanding the natural variability of Earth's climate system and for providing a context for present and future global change. Radiocarbon-dated lake sediments from Lake CF3, northeastern Baffin Island, Arctic Canada, are used to reconstruct past environmental conditions over the last 11,200 years. Numerous proxies, including chironomid-inferred July air temperatures, diatom-inferred lakewater pH, and sediment organic matter, reveal a pronounced Holocene thermal maximum as much as 5°C warmer than historic summer temperatures from 10,000 to 8500 cal yr B.P. Following rapid cooling 8500 cal yr B.P., Lake CF3 proxies indicate cooling through the late Holocene. At many sites in northeastern Canada, the Holocene thermal maximum occurred later than at Lake CF3; this late onset of Holocene warmth is generally attributed to the impacts of the decaying Laurentide Ice Sheet on early Holocene temperatures in northeastern Canada. However, the lacustrine proxies in Lake CF3 apparently responded to insolation-driven warmth, despite the proximity of Lake CF3 to the Laurentide Ice Sheet and its meltwater. The magnitude and timing of the Holocene thermal maximum at Lake CF3 indicate that temperatures and environmental conditions at this site are highly sensitive to changes in radiative forcing.

Introduction

Information on past environmental change provides a context for present and future global change and informs our understanding of the underlying mechanisms of natural climate variability. High latitude regions have experienced the greatest climatic and ecological changes since the last deglaciation, and they are expected to be exceptionally susceptible to anthropogenic warming due to cryosphere-albedo feedbacks involving changing sea ice, boreal forest, and glacier extents (Overpeck et al., 1997, CAPE Project Members, 2001, Moritz et al., 2002 and Smol et al., 2005). Quantitative records of past climate change can provide constraints on the magnitude of future changes in the Arctic (e.g., Bigler et al., 2002 and Kerwin et al., 2004). Although recent progress has been made toward obtaining spatially dense records of Holocene climate change (Kaufman et al., 2004), quantitative records are relatively few and far between.

Despite relatively stable climate forcings compared with glacial periods, the Holocene interglacial experienced dramatic environmental changes. These include, for example, temperature changes significant enough to cause the collapse of Norse settlements on Greenland (Barlow et al., 1997) and periodic changes in ocean sedimentation that may follow the cycle of solar variability (Bond et al., 2001). Lake sediments are valuable archives of environmental changes, because lakes are geographically widespread and their sediments are often continuous and datable (e.g., Wolfe et al., 2004). In addition, multiple physical, chemical and biological proxies can be analyzed from lake sediment cores, which can provide reliable indicators of past environmental and climatic change (e.g., Wolfe et al., 2000, Rosén et al., 2001, Bigler et al., 2002 and Larocque and Bigler, 2004).

Although records of Holocene conditions in the Baffin Bay region (Fig. 1) exist from western Greenland (Kelly, 1985, Willemse and Törnqvist, 1999 and Bennike, 2000) and Baffin Bay itself (Dyke et al., 1996 and Levac et al., 2001), high-resolution records (sub-centennial scale) from Baffin Island are lacking. Ice cores provide important insights of Holocene climate variability for selected sites on southern Baffin, Devon, and Ellesemere islands (Fig. 1; e.g., Fisher et al., 1995 and Fisher et al., 1998), but Holocene lake sediment records from Baffin Island thus far are either coarsely resolved or do not encompass the entire Holocene. This study provides a multi-proxy reconstruction of Holocene (11,200 cal yr B.P. to present) climate change from a lake sediment core from eastern Baffin Island. Multiple physical, chemical, and biological proxies all register a well-defined period of warmer-than-present conditions between 10,200 and 8500 cal yr B.P. followed by cooling during the middle and late Holocene. [...]

Conclusions

Multiple proxies in Lake CF3 sediments indicate an early HTM 5°C warmer than present, which ended 8500 cal yr B.P. in a rapid cooling followed by more gradual cooling that continued until the last century. This finding is strengthened by several independent chemical and biological proxies that indicate the same overall trend. The high correlation between percentages of organic matter and chironomid-inferred summer temperatures indicates that the %C (%CTOC or approximation by LOI) may be a potentially sensitive recorder of past summer temperature in lakes similar to Lake CF3. Given the many lakes with similar morphological and limnological characteristics to Lake CF3 on eastern Baffin Island, this finding has implications for the potential use of %C measurements to increase the spatial coverage of Holocene climate reconstructions from this region.

Lake CF3 sediments register an HTM earlier than in many other records from northeastern North America (Kaufman et al., 2004). Middle Holocene warmth recorded in many arctic regions has been attributed to delayed warming due to the influence of the decaying Laurentide Ice Sheet during the earliest Holocene. This influence may be most important for proxies responding to oceanic conditions, such as ocean floral and faunal assemblages. On the other hand, lacustrine proxies such as organic matter, chironomids and diatoms, which primarily record local summer conditions, likely reflect insolation-driven warmth in the early Holocene despite the proximity of waning ice sheets.

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doi:10.1016/j.yqres.2005.10.005

Copyright © 2005 University of Washington Published by Elsevier Inc.