Evolution of winter and summer marine heatwaves in Antarctica and its surroundings since 1981

Marine heat waves (MHWs; events of at least 5 consecutive days that exhibit sea surface temperature, SST, above a threshold corresponding to each location) record changes in frequency and intensity in various regions of the world. Their impacts can be severe since they generate alterations in the biodiversity and dynamics of the oceans. In the high latitudes of the southern hemisphere, MHWs have been reported during the austral summer (November to March, NM) in different locations (among others, the Tasman Sea). However, the MHWs during the autumn to spring months (May to October, MO) and summer still need to be better understood, particularly in Antarctica and its surroundings. We used daily SST data based on the ERA5 reanalysis to evaluate decadal-scale trends of MHWs during 1981-2022 for MO and 1981-2023 for NM. The 90th (P90), 95th (P95), and 99th (P99) percentiles have been defined as SST intensity thresholds, calculated from the period 1981-2010. MHWs were evaluated using different durations, from 5 to 60 consecutive days. Our results indicate, for MHWs defined from the P90 and P95 percentiles during the MO, when using periods of 5 to 10 days, an increase of up to 1 consecutive MHW event per decade in the Amundsen-Bellinghausen Sea (AB ) and north of the Antarctic Peninsula. Similar trends are also found in NM using the three percentiles, accounting for a similar increase in MHWs observed in the AB, Ross, and Davis Sea.