Annina Margreth

Ph. D. Thesis

CLIMATE SENSITIVITIES OF POLYTHERMAL ICE SHEET, ICE CAP, AND ALPINE ICE DYNAMICS AND RELATED EPISODIC EROSION ON CUMBERLAND PENINSULA, BAFFIN ISLAND, NUNAVUT

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The sensitivity of glaciers to climate and the resulting landscape changes has not been fully evaluated because of difficulties in extracting records of glacial advance, comparing sensitivities of different glacier types (ice sheets, ice caps, and alpine ice) for the same location, and measuring rates of episodic processes, which are common to glacial systems. This thesis applied innovative strategies to Cumberland Peninsula, Baffin Island, Arctic Canada, to achieve these objectives by i) radiocarbon dating currently exhuming, subfossilized bryophytes to test the sensitivity of cold-based ice cap growth to short-lived Holocene cooling events; ii) analysing the climate-sensitivities of all three glacier types by mapping and comparing their coeval ice margin extents during three short-lived but significant post-Last Glacial Maximum (LGM) climate changes (Heinrich Event-1, Younger Dyras, and the cooling associated with the regionally extensive Cockburn moraines); iii) quantifying the landscape evolution of upland plateaus by a novel approach, which couples the measurement of two cosmogenic radionuclides in pairs of tor surfaces to a Monte Carlo method to establish long-term rates of subglacial episodic erosion. The radiocarbon results indicate that cold-based ice caps advanced instantaneously (within years) of major volcanic eruptions and also suggest that bryophytes may re-grow after thousands of years of ice entombment. The high-resolution ice-margin map coupled with the first glacial chronology through the interior of the peninsula, reveal that the three glacier types responded differently to post-LGM climate changes. Asymmetric retreat pattern of alpine glaciers indicates a first-order control by precipitation, possibly as a manifestation of sea-ice cover extent. Except for narrow, high-elevation coastal ridges, upland surfaces were covered by cold-based ice during Pleistocene glaciations that caused lowering of the landscape at an-order-of-magnitude slower rates than adjoining glacially-deepened valleys. The results suggest that most of the peninsula was covered by a relatively climate-sensitive polythermal alpine glacier system, while the Laurentide Ice Sheet was restricted to the westernmost part of the peninsula where it coalesced with an expanded Penny Ice Cap. This and the quantification of episodic erosion rates provide a significant improvement of the conceptual model of paleo-ice dynamics on Cumberland Peninsula and the resulting Quaternary landscape evolution.

Keywords: glacial dynamics, Cumberland Peninsula, Nunavut, cosmogenic nuclide, exposure dating, episodic erosion, landscape evolution, climate sensitivity, polythermal ice
Pages: 474
Supervisor: John Gosse