Centennial-scale variability of the Southern Hemisphere westerly wind belt in the eastern Pacific over the past two millennia

B G Koffman,A V Kurbatov,D A Winski,K J Kreutz,M J Handley,S D Birkel,D J Breton,E J Kane

doi:10.5194/cp-10-1125-2014

Abstract

Abstract. We present the first high-resolution (sub-annual) dust particle data set from West Antarctica, developed from the West Antarctic Ice Sheet (WAIS) Divide deep ice core (79.468° S, 112.086° W), and use it to reconstruct changes in atmospheric circulation over the past 2400 years. We find a background dust flux of ~4 mg m−2 year−1 and a mode particle size of 5–8 μm diameter. Through comparing the WAIS Divide record with other Antarctic ice core particle records, we observe that coastal and lower-elevation sites have higher dust fluxes and coarser particle size distributions (PSDs) than sites on the East Antarctic plateau, suggesting input from local dust sources at these lower-elevation sites. In order to explore the use of the WAIS Divide dust PSD as a proxy for past atmospheric circulation, we make quantitative comparisons between both mid-latitude zonal wind speed and West Antarctic meridional wind speed and the dust size record, finding significant positive interannual relationships. We find that the dust PSD is related to mid-latitude zonal wind speed via cyclonic activity in the Amundsen Sea region. Using our PSD record, and through comparison with spatially distributed climate reconstructions from the Southern Hemisphere (SH) middle and high latitudes, we infer that the SH westerlies occupied a more southerly position from circa 1050 to 1400 CE (Common Era), coinciding with the Medieval Climate Anomaly (MCA). Subsequently, at ca. 1430 CE, the wind belt shifted equatorward, where it remained until the mid-to-late twentieth century. We find covariability between reconstructions of El Niño–Southern Oscillation (ENSO) and the mid-latitude westerly winds in the eastern Pacific, suggesting that centennial-scale circulation changes in this region are strongly influenced by the tropical Pacific. Further, we observe increased coarse particle deposition over the past 50 years, consistent with observations that the SH westerlies have been shifting southward and intensifying in recent decades.

Highlights

The Southern Hemisphere (SH) westerly winds (SWW) are a major driver of regional and global climate (Thompson and Solomon, 2002; Toggweiler et al, 2006)
Because the snow accumulation rate at West Antarctic Ice Sheet (WAIS) Divide was relatively constant during the late Holocene, it appears to have had little to no influence on the dust concentration or flux (Figs. 2e, 3)
Considering the lack of relationship seen between dust concentration and accumulation rate, we infer that a combination of dry and wet deposition occurs at this site

Summary

Introduction

The Southern Hemisphere (SH) westerly winds (SWW) are a major driver of regional and global climate (Thompson and Solomon, 2002; Toggweiler et al, 2006). A growing number of publications point to the SWW as the primary control on atmospheric CO2 variability on glacial–interglacial timescales because wind stress on the Southern Ocean controls the rate of deep water ventilation around Antarctica (Toggweiler et al, 2006; Anderson et al, 2009; Burke and Robinson, 2012). The Southern Ocean is the only region in the world’s oceans where water of 2– 3 km depth can upwell to the surface, coming into direct contact with the atmosphere (Russell et al, 2006).

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