Date of Award

2011

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Earth Sciences

Advisor

Brenda L. Hall

Second Committee Member

George H. Denton

Third Committee Member

Daniel F. Belknap

Abstract

Greenland, along with the rest of the Arctic, is displaying a significant reaction to warming climate, resulting in considerable ice loss and consequent sea-level rise. Reconstruction of Greenland ice masses during former warm periods can afford context for present-day conditions and allow better predictions for the effects of future warming. Small ice caps respond quickly to climate change and therefore are sensitive indicators of past climate. As part of an effort to determine if the current warming is unique in the Holocene and to provide long-term context for present-day events, I identified Holocene fluctuations of Istorvet Ice Cap in east Greenland from sediment cores taken from three glacially fed lakes and one non-glacial control lake. Bone and Round Lakes are closest to the ice margin; they are distal to a fresh, unvegetated, icecored moraine that marks the Little Ice Age (LIA) limit. Emerald Pond is fed through a channel from Round Lake. Snowbank Lake was chosen as a control lake, which allows identification of non-glacial (i.e., flood) events. I used sedimentological characteristics of the cores to identify past glacier fluctuations. In general, gray, inorganic, high magnetic susceptibility, clay-rich sediment indicates more meltwater input to the lake than brown, organic, silt-rich sediment. The same stratigraphic pattern occurs in all three glacially-fed lakes and consists, from the base of the sediments, of: 1) lower gravel and gray clay from early Holocene deglaciation; 2) thick, brown, organic silt relating to an extended period of restricted ice; 3) upper, inorganic, gray clay dating to the LIA; and 4) soupy, organic, brown silt at the surface. Snowbank Lake contained only the basal clay and gravel and the thick, brown, organic section. Radiocarbon dating of an organic mat near the base of Snowbank Lake afforded a minimum age for deglaciation of ~10.5 kyr BP, suggesting that the area probably became ice-free at the end of the Milne Land Stade (of late-glacial age) in east Greenland. Organic remains at the base of the upper clay unit in Bone Lake date to ~785 and 819 cal yr BP (AD ~1100) and date the start of the LIA. The lack of glacial input to the lakes for most of the Holocene, combined with data from prior studies, indicates that this area of Greenland experienced a climate that was as warm as, if not warmer, than present from the early Holocene to the end of the Medieval Warm Period. Therefore, the current warming and ice recession in Greenland, whatever their cause, have not surpassed average Holocene conditions. Our data also indicate that the LIA advance was the largest of the Holocene, a finding in agreement with some other records from the North Atlantic region. The relationship between this pattern of Northern Hemisphere climate and that of the Southern Hemisphere, necessary to address the origins of Holocene climate change, is not yet clear. Some existing data suggest an out-of-phase relationship between climate events in the two hemispheres, but any firm conclusions require additional high-resolution data.

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