A modelling reconstruction of the last glacial maximum ice sheet and its deglaciation in the vicinity of the northern patagonian icefield, south america


A time-dependent model is used to in- vestigate the interaction between climate, extent and fluctuations of Patagonian ice sheet between 45° and 48°S during the last glacial maximum (LGM) and its subsequent deglaciation. The model is applied at 2 km resolution and enables ice thick- ness, lithospheric response and ice deformation and sliding to interact freely and is perturbed from present day by relative changes in sea level and equilibrium line altitude (ELA). Experiments imple- mented to identify an LGM configuration compati- ble with the available empirical record, indicate that a stepped ELA lowering of 750 to 950 m is required over 15 000 years to bracket the Fenix I–V suite of moraines at Lago Buenos Aires. However, 900 m of ELA lowering yields an ice sheet which best match- es the Fenix V moraine (c. 23 000 a BP) and Calden- ius’ reconstructed LGM limit for the entire modelled area. This optimum LGM experiment yields a highly dynamic, low aspect ice sheet, with a mean ice thickness of c. 1130 m drained by numerous large ice streams to the western, seaward margin and two large, fast-flowing outlet lobes to the east. Forcing this scenario into deglaciation using a re-scaled Vostok ice core record results in an ice sheet that slowly shrinks by 25% to c. 14 500 a BP, after which it experiences a rapid collapse, loosing some 85% of its volume in c. 800 years. Its margins stabilize dur- ing the Antarctic Cold Reversal after which it shrinks to near present-day limits by 11 000 a BP.

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