Abstract

Atmospheric circulation around Antarctica is critical to many aspects of the climate system and influences the stability of the Antarctic ice sheet. In the Amundsen Sea region, wind-driven upwelling of warm circumpolar deep water enhances glacier retreat. The paucity of climate data around Antarctica before 1979 makes it challenging to interpret recent climate activity. We use a proxy-data assimilation framework to reconstruct atmospheric circulation over the Southern Ocean, with a focus on the Amundsen Sea region. We use four different climate model priors and a global database of proxy records. The reconstructions show good agreement with available verification data, and reveal strengthening Southern Hemisphere westerlies and a deepening Amundsen Sea Low through the 20th century. The reconstructions agree with a subset of ensemble members in the historical “Pacemaker” and “Large ensemble” simulations from the CESM climate model, allowing us to make inferences about the relative contributions of tropical variability and anthropogenic forcing in the Amundsen Sea region. The reconstructions also suggest that individual large westerly events in the Amundsen Sea region, such as that associated with the large 1939-1941 El Niño event, may have played an important role in the initiation of glacier retreat. Ongoing work includes high resolution regional ocean modeling, which can help us understand how ocean circulation responds to events and trends revealed by the reconstructions.