Southern Ocean surface pressure and winds during the 20th century from proxy-data assimilation

Abstract Winds and pressure over the Southern Ocean are critical to many aspects of the climate system, including ocean circulation and carbon uptake, sea ice extent, and the mass balance of Antarctica. However, reliable climate data around Antarctica begin only in 1979. Here, we reconstruct sea level pressure and zonal surface wind anomalies over the Southern Ocean through the 20th century, using data assimilation with a global database of paleoclimate proxy records. There is very good agreement between the reconstructions and satellite-based reanalysis products both at the large scale and in the smaller Amundsen Sea, a key region of West Antarctica where rapid glacier retreat has occurred in recent decades. The reconstructions show insignificant trends in the zonal-average circumpolar westerlies, but a significant strengthening in mid-latitude Pacific westerlies, associated with a deepening of the Amundsen Sea Low, beginning well before the satellite era. The mean zonal-wind trend along the continental shelf break in the Amundsen Sea is easterly through the 20th century, contrasting with previous results that have suggested that glacier change in this region can be attributed to strengthening westerlies. Our reconstructions underscore the value of using paleoclimate data assimilation methods in assessing historical changes in Southern Hemisphere climate and suggest that zonally asymmetric features of atmospheric circulation may be key for understanding high-latitude climate and associated ice-sheet changes.