Date of Award

Spring 1-1-2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Gifford H. Miller

Second Advisor

Robert Anderson

Third Advisor

Jason Briner

Fourth Advisor

Rebecca Flowers

Fifth Advisor

Scott Lehman

Abstract

Arctic temperatures are increasing faster than the Northern Hemisphere average due to strong positive feedbacks unique to polar regions. However, the degree to which recent Arctic warming is unprecedented remains a topic of debate. Because Arctic glacier dimensions are dominantly controlled by summer temperature, records of past glacier activity can provide context for the magnitude of modern warming. The modern-day east coast of Baffin Island, Arctic Canada, is characterized by deep fiords separated by low-relief, high elevation uplands that support numerous thin, cold-based ice caps that are frozen to the underlying surface and thus minimally erosive. As these ice caps retreat under a warming climate, they reveal dead tundra plants, still in their growth position, that have been entombed by ice since the time ice expanded over that site. Radiocarbon dates from such plants thus constrain the timing of ice cap growth. Additionally, recently exposed uneroded rock surfaces contain a long-term record of ice cover in their cosmogenic radionuclide inventoies. In this dissertation, I have incorporated radiocarbon ages of preserved plants and cosmogenic nuclide inventories of adjacent rock surfaces into 1D and 2D numerical models to constrain ice cover histories over the Quaternary. This approach reveals that Baffin Island ice caps grew gradually over the past ~2000 years, prior to rapid retreat during the last century. These data-constrained models also suggest that peak warmth during the Holocene occurred ~2000-5000 years earlier than the 8 to 5 ka suggested by biologic records, and that modern warming exceeds that early Holocene warmth, despite present-day Northern Hemisphere summer solar insolation being ~9% lower. Furthermore, some settings yielded plant ages and cosmogenic nuclide inventories indicative of ice cover for >40,000 years; these sites have likely been continuously ice-covered since the Last Interglacial period. The implication of this continuous cover is that summer temperatures on Baffin Island are now, on average, warmer than they have been for the past ~115,000 years. Finally, measurement and inversion modelling of longer-lived cosmogenic radionuclides from the same preserved landscapes indicate that the Laurentide Ice Sheet transitioned from more uniformly erosive to selectively erosive as fiord systems became more mature through successive Quaternary glacial cycles.

Comments

Additional adviser: Kurt Refsnider

Included in

Geology Commons

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