Centennial-scale dynamics of the Southern Hemisphere Westerly Winds across the Drake Passage over the past two millennia
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2018 Geological Society of America. The Southern Hemisphere Westerly Winds (SHWW) exert important controls on regional and global climate. Instrumental and reanalysis records indicate strengthening and poleward contraction of the SHWW belt since the late twentieth century. Such changes also have implications for Southern Ocean upwelling and CO2 degassing. Therefore, a better understanding of the long-term SHWW behaviors and dynamics beyond recent decades is critical for projecting future changes. Here, we applied isotope analysis of Sphagnum moss cellulose from a peat bog in southernmost Patagonia (~54S) to reconstruct changes in oxygen isotope composition of precipitation (18Op) that could elucidate past shifts in moisture sources and trajectories. We interpreted the positive shifts in 18Op to indicate weaker SHWW and, importantly, more frequent easterly flows that enhance moisture supply sourced from the Atlantic Ocean. In contrast, negative shifts in 18Op indicate stronger SHWW and intensification of the Andean rain shadow. Our data, along with other evidence from southernmost Patagonia and the Antarctic Peninsula, suggest a coherent pattern of centennial-scale variability in SHWW strength on either side of the Drake Passage over the past two millennia, probably as a teleconnection response to El Nio-Southern Oscillation-like variability. Our study implies that investigations of past changes in the SHWW and associated teleconnection mechanisms should consider synoptic-scale atmospheric circulation patterns, rather than seeing SHWW as a simplistic west-to-east (zonal) wind-flow pattern, particularly on the time scales over which the SHWW express zonal asymmetry among different sectors of the Southern Ocean.
