Covariability of the Southern Westerlies and atmospheric CO2 during the Holocene

Abstract

A suite of mechanisms has been proposed to account for natural variations in atmospheric CO2 during the Holocene; all of which have achieved limited success in reproducing the timing, direction, and magnitude of change. Recent modeling studies propose that changes in the latitudinal position and strength of the Southern Hemisphere Westerly Winds (SWW) can greatly infl uence large-scale ocean circulation and degassing of the deep ocean via changes in wind-driven upwelling in the Southern Ocean. The extent to which the hypothesized SWW– Southern Ocean coupled system could account for changes in atmospheric CO2 is uncertain, because of a lack of observations on the behavior of the SWW in the past, the paucity of appropriate records of productivity changes in the Southern Ocean, and our limited understanding of the sensitivity of the Southern Ocean biological and/or physical system to SWW forcing. Here we report a reconstruction of the behavior of the SWW during the past 14 k.y. based on terrestrial ecosystem proxies from western Patagonia, South America. The reconstructed variations in the intensity of zonal fl ow correspond to the timing and structure of atmospheric CO2 changes, and are consistent with the modeled magnitude of CO2 changes induced by varying strengths of the SWW. The close match between data and models supports the view that the SWW–Southern Ocean coupled system underpins multimillennial CO2 variations during the current interglacial and, possibly, during glacial cycles over the past 800 k.y.