Deglacial changes of the southern margin of the southern westerly winds revealed by terrestrial records from SW Patagonia (52°S)

Abstract

Much of the ongoing discussion regarding synchrony or bipolar asynchrony of paleoclimate events has centered on the timing and structure of the last glacial termination in the southern mid- latitudes, in particular the southwestern Patagonian region (50 e55 S). Its location adjacent to the Drake Passage and near the southern margin of the southern westerly winds (SWW) allows examining the postulated links between the Southern OceaneSWW coupled system and atmospheric CO2 variations through the last glacial termination. Results from two sites located in the Última Esperanza area (52 S) allow us to infer SWW-driven changes in hydrologic balance during this critical time interval. These findings indicate peatland development under temperate/wet conditions between 14,600 and 14,900 cal yr BP, followed by cooling and a lake transgressive phase that led to a shallow lake during the early part of the Antarctic Cold Reversal (ACR, 13,600e14,600 cal yr BP), followed in turn by a deeper lake and modest warming during Younger Dryas time (YD, w11,800e13,000 cal yr BP), superseded by terrestrialization and forest expansion at the beginning of the Holocene. We propose that the SWW (i) strengthened and shifted northward during ACR time causing a precipitation rise in northwestern and southwestern Patagonia coeval with mid- and high-latitude cooling and a halt in the deglacial atmospheric CO2 rise; (ii) shifted southward during YD time causing a precipitation decline/increase in NW/SW Patagonia, respectively, high-latitude warming, and invigorated CO2 release from the Southern Ocean; (iii) became weaker between w10,000 and 11,500 cal yr BP causing a precipitation decline throughout Patagonia, concurrent with peak mid- and high-latitude temperatures and atmospheric CO2 concentrations.