Baltic Sea surface temperature analysis 2022: a study of marine heatwaves and overall high seasonal temperatures

Abstract

Abstract. In 2022, large parts of the Baltic Sea surface experienced the third-warmest to the warmest temperatures over the summer and autumn months since 1997. Warm temperature anomalies can lead to marine heatwaves (MHWs), which are discrete periods of anomalous high temperatures relative to the usual local conditions. Here, we describe the overall sea surface temperature (SST) conditions observed in the Baltic Sea in 2022 and provide a spatiotemporal description of surface MHW events based on remote sensing, reanalysis, and in situ station data. The most MHWs, locally up to seven MHW events, were detected in the western Baltic Sea and the Inner Danish Straits, where maximum MHW intensities reached values of up to 4.6 °C above the climatological mean. The northern Baltic Proper and the Gulf of Bothnia were impacted mainly by two MHWs at maximum intensities of 7.3 and 9.6 °C, respectively. Our results also reveal that MHWs in the upper layer occur at a different period than at the bottom layers and are likely driven by different mechanisms. Reanalysis data from two exemplary stations, “Lighthouse Kiel (LT Kiel)” and “Northern Baltic”, show a significant increase in MHW occurrences of +0.73 MHW events per decade at LT Kiel and of +0.64 MHW events per decade at Northern Baltic between 1993 and 2022. Moreover, we discuss the expected future increased occurrence of MHWs based on a statistical analysis at both locations.