Projections of future rates of mass loss from the Greenland Ice Sheet are highly uncertain because its sensitivity to warming is unclear. Geologic reconstructions of Quaternary interglacials can illustrate how the ice sheet responded during past warm periods, providing insights into ice sheet behavior and important tests for data-model comparisons. However, paleoclimate records from Greenland are limited: Early Holocene peak warmth has been quantified at only a few sites, and terrestrial sedimentary records of prior interglacials are exceptionally rare due to glacial erosion during the last glacial period. Here, we discuss findings from a lacustrine archive that records both the Holocene and the Last Interglacial (LIG) from Greenland, allowing for direct comparison between two interglacials. Sedimentary chironomid assemblages indicate peak July temperatures 4.0 to 7.0 °C warmer than modern during the Early Holocene maximum in summer insolation. Chaoborus and chironomids in LIG sediments indicate July temperatures at least 5.5 to 8.5 °C warmer than modern. These estimates indicate pronounced warming in northwest Greenland during both interglacials. This helps explain dramatic ice sheet thinning at Camp Century in northwest Greenland during the Early Holocene and, for the LIG, aligns with controversial estimates of Eemian warming from ice core data retrieved in northern Greenland. Converging geologic evidence for strong LIG warming is challenging to reconcile with inferred Greenland Ice Sheet extent during the LIG, and the two appear incompatible in many models of ice sheet evolution. An increase in LIG snowfall could help resolve this problem, pointing to the need for hydroclimate reconstructions from the region.
|Original language||English (US)|
|Number of pages||6|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|State||Published - Jun 19 2018|
Bibliographical noteFunding Information:
ACKNOWLEDGMENTS. We thank the people and government of Greenland for site access (sample export permit 028/2014). M. Bigl, G. Bromley, M. Jackson, G. E. Lasher, E. Roy, J. Thompson, L. Corbett, E. Lutz, and A. Taylor assisted with field work; and the Thule Air Base, Air Greenland, the United States Air Force, J. Hurley, K. Cosper, and Polar Field Services provided logistical support. C. Carrio, G. Schellinger, and T. Stilson helped in the laboratory at Northwestern. LacCore, the Woods Hole Oceanographic Institution National Ocean Sciences Accelerator Mass Spectrometry facility, the Center for Accelerator Mass Spectrometry at Lawrence Livermore National Laboratory, and J. P. Brown and the Field Museum provided additional analytical support. Maps were created using The Generic Mapping Tools. J. Townsend, C. Kuzawa, and two anonymous reviewers provided thoughtful comments on the manuscript. This work was funded by the National Science Foundation (NSF) Division of Polar Programs (Awards 1108306 and 1107411), the NSF CAREER Program (Award 1454734), an NSF Graduate Research Fellowship, the Geological Society of America, and the Institute for Sustainability and Energy at Northwestern.
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Copyright 2018 Elsevier B.V., All rights reserved.
- Holocene thermal maximum
- Last Interglacial
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