Variability and Trends of the Amundsen Sea Low since the Early Twentieth Century from Seasonal-Station-Based Reconstructions

The Amundsen Sea is dominated by a quasi-stationary low-pressure region, the Amundsen Sea Low (ASL). ASL variability impacts on regional weather and the basal melting of ice shelves, an important contributor to sea-level rise. To understand trends and variability of the ASL, it is important to have data for a long time period. However, the shortness of the satellite record starting in 1979 and the sparseness of Antarctic observational data prior to this, makes understanding variability on decadal scales challenging. Century-long reanalyses are available but have well-known pressure biases, meaning that trends cannot be reliably quantified. Other reconstructions are available at annual resolution, but mask important seasonal differences. Here we reconstruct the ASL at seasonal resolution from 1905, using Southern Hemisphere weather station sea-level pressure data, which takes advantage of well-known teleconnections between the tropics and Antarctica, although the strength of these is seasonally dependent and varies decadally. We compare our reconstructions with two centennial reanalyses and ERA5. Our reconstruction captures early 20 th century variability associated with ice-shelf melting and retreat, and places recent ASL trends in a longer-term context. We find that recent deepening of the ASL across all seasons is unprecedented since 1905 and there is increased uncertainty in the ASL index during the mid 20 th Century. We also assess the stationarity of association between station data and the ASL by using data from a Pacific Pacemaker climate model experiment. The stationarity assumption for our ASL reconstruction is valid, except for austral autumn due to insufficient data availability.