Characterising Marine Heatwaves in the Svalbard Archipelago and Surrounding Seas

Marine heatwaves (MHWs) have become a major concern due to their impact on marine ecosystems. In the Arctic Mediterranean, largely based on sea surface temperature from satellite data, the annual intensity, frequency (events per year), duration, and areal coverage of MHWs have increased significantly in recent decades. In particular, a high frequency of MHWs has been shown around the Svalbard Archipelago. Based on this, we investigate patterns in MHWs around Svalbard both at the surface and subsurface, using a regional reanalysis from TOPAZ for the period 1991-2022. Overall, we find a shift in the frequency and duration around the Svalbard Archipelago, with higher values in 2011-2022 compared to 1991-2010. Analysis of eight individual summer (June-September) MHW events lasting longer than 10 days on the western side of Svalbard indicated the presence of four shallow (≤50m) and four deep (≥200m) MHWs. All events occurred after 2010. Deep MHW events were associated with an increase in ocean heat content (down to 300m), potentially connected to changes in the temperature of Atlantic Water inflow in the region. The mean duration of each event was 29 days. In terms of spatial extent, some events extended not only along the west of Svalbard but also across the Barents Sea, covering a broader area. Understanding the characteristics of MHW events including their spatial and vertical distribution, as investigated in this study, is crucial for identifying their driving mechanisms and assessing their ecosystem impact. Furthermore, as MHWs increase, it will become essential to be able to predict such events. Hence, we also present plans to use the Norwegian Climate Prediction Model (NorCPM) to evaluate the predictive skill for MHWs in the Arctic Mediterranean.