Abstract
The Southern Westerly Winds (SWW) are the surface expression of geostrophic winds that encircle the southern mid-latitudes. In conjunction with the Southern Ocean, they establish a coupled system that not only controls climate in the southern third of the world, but is also closely connected to the position of the Intertropical Convergence Zone and CO2 degassing from the deep ocean. Paradoxically, little is known about their behavior since the last ice age and relationships with mid-latitude glacier history and tropical climate variability. Here we present a lake sediment record from Chilean Patagonia (51°S) that reveals fluctuations of the low-level SWW at mid-latitudes, including strong westerlies during the Antarctic Cold Reversal, anomalously low intensity during the early Holocene, which was unfavorable for glacier growth, and strong SWW since ~7.5 ka. We detect nine positive Southern Annular Mode-like events at centennial timescale since ~5.8 ka that alternate with cold/wet intervals favorable for glacier expansions (Neoglaciations) in southern Patagonia. The correspondence of key features of mid-latitude atmospheric circulation with shifts in tropical climate since ~10 ka suggests that coherent climatic shifts in these regions have driven climate change in vast sectors of the Southern Hemisphere at centennial and millennial timescales.
Highlights
Southern South America (Patagonia, between 40° and 56°S) is the only continuous continental landmass that intersects the core of the Southern Westerly Winds (SWW), extending south into the SO at the latitude of the Drake Passage
In this study we extend the high-resolution analysis from Lago Cipreses (LC) to examine past changes in the SWW since local deglaciation (Supplementary Figures 1 and 2; Supplementary Table 1), and their relationships with Holocene records of atmospheric CO2 concentrations, ENSO variability in the eastern tropical Pacific, and Neoglacial activity in southern Patagonia
The LC record suggests a virtually treeless landscape with muted fire activity dominated by cold-resistant herbs and shrubs (Poaceae, Ericaceae, Asteraceae, Acaena) between 14.6 and 12.7 ka commonly found in modern high Andean environments and the forest-steppe ecotone
Summary
One important item of discussion is whether the SWW influence was anomalously high[20] or low[21] in southwestern Patagonia (between 51° and 53°S) during the early Holocene (between 10.5 and 7.5 ka) and, for deciphering whether the core of the SWW shifted southward[20] or whether its strength diminished below modern values[21] over this interval in the southern hemisphere Resolving this divergence is important and the strategic location of southwestern Patagonia can be used to test hypotheses stressing the role of changes in the position/intensity of the SWW at the critical latitude of the Drake Passage on variations in SO upwelling, ocean productivity and ventilation of deep-water CO2.
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