Late Quaternary glacial history of the South Patagonian icefield at Torres del Paine, Chile
The principal aim of the thesis is to determine the Late Quaternary glacial history of the South Patagonian Icefield at Torres del Paine (51°S, 73°W), Chile. The secondary aim is to compare this glacial history with palaeoclimatic records from elsewhere to test the theory that climate change over the last glacial-interglacial cycle was synchronous between the two polar hemispheres. Synchronous climate change cannot be explained as an atmospheric response to insolation changes unless fundamental ocean-atmosphere reorganisations occurred (Broecker and Denton, 1990). Empirical glacial-geologic data from southern South America is therefore used to test recent models of global climate change. The global pattern of climate change over the last glacial-interglacial cycle is assessed by reviewing proxy palaeoclimate records including isotope records from polar ice cores and deep sea sediment cores, and glacial geologic records from the southern Andes. Conclusions from this review form the basis for hypotheses about what 'should' have happened at Torres del Paine. To test these hypotheses glacial geologic investigations were undertaken on site. Geomorphological evidence is used to define eight icesheet, deglaciation and valley glacier stages; ice extended ca.50km east of the modern South Patagonian Icefield margin during the last glaciation. Basal dates from peat bogs provide dating control for some glacial stages. Pumice fragments associated with glacial deposits were derived from an eruption of Volcan Reclus ca.12,000 yr BP and therefore constrain the Lateglacial depositional sequence. Models of the glacial history are constructed. Evidence that climate change at Torres del Paine was synchronous with other sites is equivocal. However, significant results are: (a) evidence of a Late-Lateglacial ('Younger Dryas') advance - the first such site in Patagonia; (b) evidence that deglaciation occurred slowly; and (c) evidence that the greatest extent of ice did not necessarily coincide with the coldest part of the last glaciation.