Patagonian glacier-climate changes during the Holocene based on 10Be (and 14C) dating

REYNHOUT, SCOTT; ARAVENA, JUAN CARLOS; RODRIGO VILLA MARTINEZ; GARCIA, J. L.; KAPLAN, M.R.; SAGREDO, ESTEBAN; MATEO MARTINI; PELTIER, C.; SCHAEFER, J.M.; STRELIN, J.A.; MORENO, PATRICIO; SOTERES, RODRIGO L.

Dublin

Congreso; INQUA Congress 2019; 2019

International Union for Quaternary Research (INQUA)

Mountain glaciersrespond sensitively to changes in Earth's atmosphere such that records of theirhistory serve as a useful proxy for past climates. The record of glacierbehavior around Patagonia reflects former climates that affected the cryosphereat the middle to high latitudes of the Southern Hemisphere. Recently, in situ 10Becosmogenic nuclide dating, combined with detailed geomorphic mapping, has beenapplied to Holocene-age moraines in southern and central Patagonia. Wesummarize at least three areas where we are focusing: there are in the drainageareas of Lago Argentino and Lago Viedma, and around the San Lorenzo massif. Onthe one hand, the findings indicate, in general, an early Holocene warm periodwith reduced glacier extents. This finding is strongly supported by otherproxies, which collectively indicate a swath of warmth from the middle to highlatitudes. On the other hand, observations so far indicate that smallerglaciers do register relatively brief cool periods that punctuated thegenerally warm early Holocene interval. By 8,000-6,000 years ago, climaticconditions favored cooling and recurrent glacier expansions for much of theremaining Holocene. At least one temporal exception of limited glacierexpansion occurred from 4,000 to 2,500 years ago, which agrees with other proxyrecords for a relatively warm dry period. Several advances occurred during the LittleIce Age interval in Europe; however, in all areas we have worked in Patagonia ?these are generally not the largest expansions of the Holocene.We compare 10Be (and 14C) glacierchronologies with recent reconstructions of SAM-like conditions since LateGlacial time, based on other proxy types including of past vegetation changes.Positive and negative SAM-like conditions are associated with warm/dry andcool/wet climates in central/southern Patagaonia, which are favorable forreduced and expansive glaciers, respectively. We conclude that millennial andcentennial intervals of generally reduced ice − from the middle to highlatitudes − occur when positive Southern Annular Mode (SAM)- like conditionsare persistent. We infer these intervals are times of weakening and/or polewardexpansion of the Southern Hemisphere westerlies, and they are associated withreduced sea ice. Conversely, persistent negative SAM-like conditions, increasedsea ice, and perhaps equator-ward focus of the westerlies are favorable forglacier expansions in Patagonia.