Change in environmental conditions of the Southern Ocean observed by satellites and data-assimilating models between 1981 and 2019

We provide a summary of environmental change in the Southern Ocean over the period of satellite observaton (1981 to present). The environmental data we consider are: (1) chlorophyll-a concentration from merged observation of SeaWiFS and MODIS-Aqua (1987–2019); (2) sea-surface temperature (SST) from the AVHRR series of NOAA satellites (1981–2019); (3) spatial gradient of SST (as an indicator of ocean fronts) from the same AVHRR observations; (4) sea ice concentration from microwave satellite sensors (SMMR, SSM/I); (5), net primary productivity (NPP) using the vertically-generalised productivity model (VGPM); (6) estimates of mixed layer depth from the data-assimilating US Navy hindcast model HyCOM (GLBu0.08); and (7) incident light intensity at the sea-surface. The data show heterogenous patterns of environmental change across the Southern Ocean over the last 4 decades. Key results are: (1) warming of the ocean surface north of the southern limit of the ACC and slight cooling to the south; (2) evidence of movement north of the Subantarctic Front; (3) increasing chl-a and NPP in the Subantarctic Front and around the southern limit of the ACC except in the Ross Sea region; (4) decreasing chl-a and NPP in the Ross Sea sector and on the Antarctic continental shelf; (5) gradual loss of sea-ice in the Amundsen Sea and increasing sea-ice in the Weddell, Bellingshausen and Ross Seas; (6) deepening of the mixed-layer near the Polar Front, contrasting with shallowing in the Ross Sea region, and both increases and decreases in different parts of the Weddell Sea; (7) increasing trends in incident light intensity in Subantarctic waters and generally decreasing trends near the Antarctic continent.