Shrinking glaciers, melting permafrost, and reduced sea ice all indicate rapid contraction of the Arctic cryosphere in response to present-day climate warming, a trajectory that is expected to continue, if not accelerate. The reaction of the Arctic cryosphere to past periods of climate variation can afford insight into its present and future behavior. Here, we examine a ∼12,000 year record of glacier fluctuations and meltwater variation associated with the Renland Ice Cap, East Greenland, that extends from the early Holocene thermal optimum through the cooling of the Little Ice Age to present. Sediment records from glacially fed lakes indicate rapid early Holocene deglaciation, with ice extent likely slightly smaller than at present by ∼9500 yr BP. Glacial activity resulted in occasional deposition of rock flour in the studied lakes in the early Holocene until at least ∼7500 yr BP. Rock flour is absent for much of the period ∼7000-4000 yr BP, suggesting ice extent generally was smaller than at present. However, thin layers of blue-gray clay throughout this period may indicate millennial-scale ice expansions, with Renland Ice Cap briefly reaching extents during cold phases that may have been similar to today. Glacial sediment deposition occurred again in the late Holocene at ∼3200–3400 yr BP and was followed by a brief glacial episode at ∼1340 yr BP and then a major event beginning shortly after ∼1050 yr BP. We infer that rock flour deposition in the lakes in the last millennium corresponds with advance of Renland glaciers to their Little Ice Age positions, marked by a fresh, gray drift limit. Radiocarbon dates of in situ plant remains adjacent to the present ice cap indicate a short relatively warm period ∼500 yr ago, when ice was within its AD 2011 limit, followed by glacier readvance. The general pattern of ice fluctuations in Renland is similar to that at other ice caps in the region, but also has important differences, including the preservation of a possible mid-Holocene record at times when lower-elevation ice caps in the Scoresby Sund region may have been absent. This finding reinforces the concept that examination of multiple geographic and geomorphologic settings is necessary for a full understanding of ice variations in a region. © 2021 Elsevier Ltd
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Although apparently smaller than present for much of the Holocene, from at least 9490 until the onset of the late Holocene glaciation about 1050 yr BP, Renland Ice Cap may have undergone periodic fluctuations, as represented by clay layers (Fig. 15). The most prominent event in terms of sediment thickness and spatial extent was at ?7200?7600 yr BP and may have been coeval with the R?defjord moraines (?7600 yr BP; Funder, 1978), which were deposited by GIS outlet glaciers in the fjords adjacent to Renland. Whether this timing is coincidental or the result of a common climatic forcing of local ice caps and GIS outlet glaciers remains unknown, as the significance of the R?defjord moraines is uncertain (Funder, 1978).Insect assemblages at Last Chance Lake in Milne Land indicate warmer summer temperatures than today throughout the early and most of the middle Holocene (Axford et al., 2017), in good agreement with our records. The temporary migration of dense dwarf shrub heath northward into the Scoresby Sund region ?8800-5500 yr BP also suggests warmer temperatures than at present (Funder, 1978). Moreover, the period ?7800-4100 yr BP also corresponds to a time of minimum Holocene ice extent in southeast Greenland (Balascio et al., 2015).This work was funded by the Arctic Natural Sciences Program of the United States National Science Foundation (Kelly: ARC-0909270; Lowell: ARC-0909285; Hall: ARC-0908081). We thank CM2Hill, the Danish Polar Center, and Air Greenland for logistical support, and the staff at the Limnological Research Center at the University of Minnesota for assistance with core transport and initial processing. We especially wish to thank two anonymous reviewers for thoughtful, detailed comments.
This work was funded by the Arctic Natural Sciences Program of the United States National Science Foundation (Kelly: ARC-0909270; Lowell: ARC-0909285; Hall: ARC-0908081). We thank CM2Hill, the Danish Polar Center, and Air Greenland for logistical support, and the staff at the Limnological Research Center at the University of Minnesota for assistance with core transport and initial processing. We especially wish to thank two anonymous reviewers for thoughtful, detailed comments.
© 2021 Elsevier Ltd
- Glacier variations
- Lake sediments
- Renland ice cap
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