Abstract
The Greenland Ice Sheet is a major component of the Arctic cryosphere and the magnitude of its response to future climate changes remains uncertain. Longer-term records of climate near the ice sheet margin provide information about natural climate variability and can be used to understand the causes of past changes in the Greenland Ice Sheet. As a proxy for Holocene climate near the ice sheet margin, we reconstruct the fluctuations of Bregne ice cap in the Scoresby Sund region of central east Greenland. Bregne is a small ice cap (2.5km2 in area) and responds sensitively to summer temperatures. We employ a multi-proxy approach to reconstruct the ice cap fluctuations using geomorphic mapping, 10Be ages of boulders and bedrock and lake sediment records.Past extents of Bregne ice cap are marked by moraines and registered by sediments in downvalley lakes. 10Be ages of bedrock and boulders outboard of the moraines indicate that Bregne ice cap was within ~250m of its present-day limit by at least 10.7ka. Multi-proxy data from sediments in Two Move lake, located downvalley from Bregne ice cap, indicate that the ice cap likely completely disappeared during early and middle Holocene time. Increasing magnetic susceptibility and percent clastic material from ~6.5 to ~1.9calkaBP in Two Move lake sediments suggest progressively colder conditions and increased snow accumulation on the highlands west of the lake. Laminated silt deposited at ~2.6calkaBP and ~1.9calkaBP to present registers the onset and persistence of Bregne ice cap during the late Holocene. 10Be ages of boulders on an unweathered, unvegetated moraine in the Bregne ice cap forefield range from 0.74 to 9.60ka. The youngest 10Be age (0.74ka) likely represents the age of the moraine whereas older ages may be due to 10Be inherited from prior periods of exposure. This late Holocene moraine marks the second largest advance of the ice cap since deglaciation of the region at the end of the last ice age. The oldest moraine in the forefield dates to ≤2.6calkaBP. The fluctuations of Bregne ice cap were likely influenced by Northern Hemisphere summer insolation throughout the Holocene and abrupt late Holocene cold events.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 357-368 |
| Number of pages | 12 |
| Journal | Quaternary Science Reviews |
| Volume | 92 |
| DOIs | |
| State | Published - May 15 2014 |
Bibliographical note
Funding Information:We thank C. Smith and B. Goehring for assisting with fieldwork and S. Hammer for conducting lake sediment analyses. J. Chipman provided Geographic Information System expertise, O. Bennike helped identify macrofossils for radiocarbon dating and A. Giese offered helpful comments on the manuscript. S. Funder and an anonymous reviewer gave valuable comments that improved the manuscript. POLOG and CHM2Hill Polar Field Services and Air Greenland provided field logistics. The Greenland Bureau of Mines and Petroleum offered permits to conduct this research. D. Kaufman and K. Sides measured biogenic silica. We thank NOSAMS for radiocarbon measurements and R. Finkel and D. Rood at LLNL CAMS for beryllium measurements. The LRC staff assisted with sediment core shipping and processing. This project was funded by National Science Foundation (NSF) grants ARC-0909270 (Kelly), ARC-0909285 (Lowell), ARC-0908081 (Hall). L. Hempel was funded by a Stiffler Family Undergraduate Grant at Dartmouth College. The 2006 field season was supported by the Comer Science and Education Foundation and an NSF grant ( ANT-0527946 to Kelly).
Copyright:
Copyright 2014 Elsevier B.V., All rights reserved.
Keywords
- Greenland
- Greenland Ice Sheet
- Holocene
- Lake sediment cores
- Scoresby Sund