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

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°-55°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 Ocean-SWW 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, 13,600-14,600 cal yr BP), followed in turn by a deeper lake and modest warming during Younger Dryas time (YD, ∼11,800-13,000 cal yr BP), superseded by terrestrialization and forest expansion at the beginning of the Holocene.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 ∼10,000 and 11,500 cal yr BP causing a precipitation decline throughout Patagonia, concurrent with peak mid- and high-latitude temperatures and atmospheric CO2 concentrations.