The Late-glacial in south Patagonia and Tierra Del Fuego

STRELIN, JORGE; DENTON, GEORGE; MARTINI, MATEO ANTONIO; KAPLAN, MICHAEL

Cordona

Congreso; XIX Congreso Geológico Argentino; 2014

Asociación Geológica Argentina

The late-glacial advance in the Lago Argentino Basin (Strelin et al. 2011) corresponds in magnitude and age with other events detected in nearby Seno Última Esperanza (Sagredo et al. 2011), Torres del Paine (Garcia et al. 2012), Lago Viedma (Caldenius 1932), and Lago San Martín (Glasser et al. 2011). Morphostratigraphic and geochronologic studies, carried out by these authors, show that after a major retreat from their LGM moraine positions, the outlet-glaciers readvanced again even beyond their cordilleran limits. These advances correlate well with the Antarctic Cold Reversal (ACR) from14.8 to 13.0 ka BP (Pedro et al. 2011). However, such large advances did not occur north and south of this Central Sector (Fig. 1), where the outlet-glaciers of Lago Buenos Aires and Lago Pueyrredón (Turner et al. 2005) - to the north - and between Seno Skyring and Beagle Channel (Killian et al. 2007, Boyd et al. 2008, Hall et al. 2013) ? to the south - were subjected to rapid and deep ice recession, and thus their existing late-glacial moraines did not abandon the cordilleran fjords and valleys. This recent findings disagree with earlier interpretations of glacier behavior in the Southern Sector (Fig. 1), which postulate the existence of large ice-masses occupying the occidental part of the Magellan Strait during the ACR (McCulloch et al. 2005) and the Beagle Channel until at least 11.8 ka BP (Rabassa et al. 2008). It is worthy to attempt some consideration about the reason of these particular and differing glacier behaviors during the last deglaciation. An important point is that the large outlet lobes show water-facing fronts during the last deglaciation, which could have influenced their flow dynamic, and accordingly their sensitivity and response time to the climate signals. Considering the most recent data (Boyd et al. 2008, Hall et al. 2013), the glaciers of the Southern Sector experienced a marked warming during the deglaciation, which caused collapse of their large ice tongues. This warming occurred in coincidence with the Heinrich Stadial 1 (HS1, 18.0 to 14.6 ka BP) of the Northern Hemisphere and an important southward displacement of warm climatic belts and oceanic currents (Denton et al. 2010). Accordingly, the ACR signal affected glaciers in a pronounced withdrawn situation, and thus their lateglacial moraines have to be sought inboard of the mountain valleys, close to the Neoglacial moraines (Menounos et al. 2013). On the other hand, the main outlet-glaciers of the Central Sector clearly interrupted their deglacial recession, and they readvanced in a major way during the ACR, in coincidence with the Northern Hemisphere Bølling-Allerød interstadial (Denton et al. 2010). Their particular behavior might be related with their catchment area location in the Southern Patagonian Icefield (SPI in fig. 1), which was certainly the largest ice reservoir of the Southern Hemisphere (except Antarctica) during HS1 warming, thus allowing a major glacier advance during the ACR. Finally the glaciers located in the Northern Sector, which are linked with the present Northern Patagonian Icefield, also receded deep in the cordilleran domain during deglaciation and were only subjected to a still-stand or relatively short advance during the ACR (Turner et al. 2005). Probably this occurred due to their lower latitude location and high accumulation and ablation rates, which determined a rapid climate response, favoring the deep recession of these glaciers. As a consequence, like in the Southern Sector, these glaciers did not readvance much during the ACR.