Neoglacial fluctuations of two contrasting Southern Patagonian Icefield glaciers (49°S)

RUIZ, L.; PONCE, JUAN; DELINE, PHILIP; LE ROY, MELAINE; GEIGER, ALESSA,; VILLALBA, RICARDO.; SCHIMMELPFENNIG, IRENE; ZORZUT, VALENTINA.

Dublin

Congreso; INQUA 2019; 2019

Direct constraints on the timing of Neoglacial glacier advances remain sparse in the South American mid-latitudes. Classical schemes ? based on limiting 14C ages ? indicate several steps of Neoglaciation with the most extensive reached during the mid-Holocene, around 5 ka (Porter, 2000). Here we investigate the timing of Neoglacial extent of two contrasting east-flowing outlet glaciers of the Southern Patagonian Icefield (SPI) through 10Be exposure dating of moraine boulders. The studied glaciers show different size, slope and tongue grounding environment. Viedma glacier is one of the largest SPI outlets (~900 km²) whose tongue calved into lake Viedma during most of the Holocene, whereas Marconi glacier (~ 50 km²) ? whose tongue was grounded during the intervening period ? merged with another major SPI outlet (Chico glacier; ~300 km²) during Holocene highstands. We show that the Viedma and Marconi glacier experienced their Neoglacial maxima around 7 ka and that at least two other advances quite similar in size occurred before 4 ka. Then, two other Neoglacial stadials of decreasing magnitude occurred around 2 ka and during the Little Ice Age, from 0.5 ka. Our chronology is consistent with growing evidence of a prominent change in the regime of the Southern Westerly Winds (SWW) at 7 ka, as indicated by proxy records (Moreno et al, 2018)