Aaron Medford

Date of Award

5-2013

Level of Access Assigned by Author

Open-Access 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

The Arctic is responding to the modern increase in temperature, resulting in ice loss and consequent sea-level rise. In order to understand present-day changes, we need to understand how the Arctic has reacted in the past to natural variations in climate forcing. To begin to identify the mechanisms behind climate change, I produced a Holocene glacial and climate record for the Renland Ice Cap, Scoresby Sund, East Greenland, from sediments in glacially fed lakes. I cored Rapids and Bunny Lakes, which are fed by meltwater from the Renland Ice Cap, as well as Raven Lake, which does not receive glacial influx at present. The presence or absence of glacial sediments in Rapids and Bunny Lakes gives information on the size of the Renland Ice Cap.

I studied multiple sediment characteristics in the cores, including magnetic susceptibility (MS), grain size, organic and carbonate content, and color intensity. In general, I identified glacial sediment as grey, inorganic, and with high MS. Non-glacial material was black or brown with high organic content and low MS. Chronology for the cores came from radiocarbon dating of macrofossils and sieved organic fragments.

My results suggest that the region may have deglaciated as early as ~12.5 ka. The high organic content in all three lakes suggests that the early- to mid-Holocene was warm with periods of limited ice extent, consistent with the Holocene thermal maximum, which has been documented elsewhere. After this warmth, the area cooled during the Neoglaciation that culminated in the largest glacial event of the Holocene during the Little Ice Age. Superimposed on the long-term climate change were multiple centennial-to-millennial-scale glacial advances at ~ 9.4, 8.6-8.8, 8.1-8.3, 7.6-7.8, 7.0-7.5, 5.8-6.0, 4.7-5.0, 3.7-4.0, 3.0-3.6, and ~1.0 (AD 600 and 900) cal. kyBP.

My reconstruction of variations in the Renland Ice Cap matches well with other glacial records from Scoresby Sund and from the wider Northern Hemisphere. In addition, comparison with other glacial records from the Scoresby Sund region suggests that elevation exerts a strong control on the timing, size, and number of glacial advances exhibited at each site. This highlights the need for caution when comparing glacial records from large geographic areas.

The Renland record, along with other Northern Hemisphere data, indicates pervasive millennial-scale climate change throughout the Holocene, with the largest magnitude glacial advance occurring during the Little Ice Age. This pattern favors a cyclical forcing mechanism, such as solar variability or a 'wobbly ocean conveyor,' rather than unique events, such as volcanic eruptions or outburst floods, as a cause of millennial-scale climate change.

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