Marine Heatwaves on the Patagonian Shelf

The SouthWestern Atlantic Ocean (SWA) is undergoing significant changes as a result of climate change, including progressive sea surface warming, altered wind patterns, the poleward migration of western boundary currents, and an increase in the frequency and intensity of climate-driven variability events. Within the SWA, the Patagonian Shelf (PS), extending from the southern tip of South America (~55°S) to the Brazil/Malvinas Confluence (~38°S), stands out as one of the most biologically productive regions and a globally relevant carbon sink. Marine heatwaves (MHWs) have doubled in frequency over recent decades, lasting longer and becoming more severe. The consequent abrupt temperature shifts can significantly impact phytoplankton community structure and productivity while disrupting essential marine biogeochemical processes such as oxygen production and respiration, carbon sequestration, and nutrient cycling. However, knowledge on MHWs in the PS is scarce.

The present study focuses on characterizing MHWs in the PS by analyzing their spatial and temporal variability. Two methodologies were applied to four daily sea surface temperature (SST) datasets to determine the most suitable approach to identify MHWs in the study area. Key metrics for MHW characterization included the frequency of occurrence (MHW/year), mean intensity (SST anomaly, °C), and duration (number of days). These metrics were analyzed in relation to regional climatology, seasonality, and long-term trends. Notably, within the PS, where SST anomalies are relatively modest, both MHW identification approaches proved to be effective. Our results reveal an increasing trend in MHW days, particularly in the northern PS, where a strong correlation between MHWs and ENSO events is observed.