The timing, dynamics and palaeoclimatic significance of ice sheet deglaciation in central Patagonia, southern South America

Robust reconstructions of glacial retreat are required to elucidate controls on ice-sheet deglaciation and (a)synchronicity in the climate system. Such reconstructions can be derived through detailed geological investigations of glacial landforms and sediments. Patagonia, in southern South America, contains a well-preserved glacial record and occupies an important location regarding major Southern Hemisphere climate systems. However, resolving the history of ice-sheet deglaciation has proven problematic, owing to generally low-resolution geomorphological mapping, and a paucity of high-precision dating control. This thesis explores the deglacial history of the Lago General Carrera–Buenos Aires (LGC–BA) and Lago Cochrane–Pueyrredón (LC–P) ice lobes (46–48°S) of the former Patagonian Ice Sheet (PIS). The region is chosen because there are uncertainties associated with: (i) the deglacial configuration and evolution of retreating ice lobes and proglacial lake systems; and (ii) the sub-millennial timing of deglacial
events.

A new glacial geomorphological map is produced to reconstruct the spatio-temporal evolution of ice lobes and proglacial lakes. The elevation(s) of relict lake shorelines are examined to quantify glacio-isostatic adjustment and accurately assign former lake levels, lake outflows, and ice-margin positions, through the last deglaciation. These new reconstructions are used to target sites for high-resolution dating. A ~1000-year varve chronology is developed at LGC–BA after examining the sedimentary properties of laminated glaciolacustrine sequences. Tephrochronology anchors this record to the calendar-year timescale. The chronology indicates that PIS retreat commenced at 18,086 ± 214 cal a BP, and accelerated from 5 to 18 m yr-1 over the next ~1000 years. The new timing for deglaciation at LGC–BA allows an exploration of climate forcing mechanisms. Comparisons with palaeoclimatic records reveal a hemisphere-wide warming influence on LGC–BA deglaciation. Moreover, spectral analyses of varve thickness time-series demonstrate a likely teleconnection with tropical Pacific climate oscillations, and PIS sensitivity to short-term variations in melt-season temperature.