Sea surface temperature and marine heatwave variability in interconnected basins: The Black-Marmara-Aegean Seas

Sea surface temperature (SST) is a crucial parameter affecting marine ecosystems and has risen dramatically in recent decades due to climate change. This warming has led to an increase in the frequency and intensity of marine heatwave (MHW) events, prolonged periods of extreme SSTs, which have severe ecological consequences. This study investigates the spatiotemporal variability of SST and MHW characteristics across the interconnected Black, Marmara, and Aegean Seas using satellite-derived daily SST data from 1982 to 2021. Our findings indicate a significant SST increase across all three basins, with the most pronounced warming observed in the Black Sea, followed by the Marmara Sea. SST trends reach 0.8 °C/decade in the eastern Black Sea and 0.3 °C/decade in the Aegean Sea. Since the 2000s, SST warming has accelerated, with the long-term spatial mean trend of 0.57 °C/decade increasing to 0.68 °C/decade. This warming trend has driven a sharp increase in MHW frequency and duration, particularly in the last decade. The highest trend in MHW frequency is observed in the Marmara Sea, with an increase of 1.56 events/decade which further intensified after the 2000s. Beyond long-term trends, MHWs exhibit interannual variability, which correlates with the Eastern Atlantic (EA) and Eastern Atlantic/Western Russia (EAWR) climate indices. Given the rising frequency and duration of MHW events, we also examined mucilage outbreaks in the Marmara Sea during 2007 and 2021. Our analysis suggests that mucilage blooms correspond to years with intense and prolonged MHW events, highlighting MHWs as a potential driver of mucilage formation.