Geographically-dependent coastal marine heatwaves: Insights from coastal seas around a semi-enclosed bay

Coastal seas connecting the open ocean and land are highly impacted by local terrestrial weather and climate systems. However, there is a lack of research focus on the distinct coastal geographical features, which may locally contribute to the spatiotemporal pattern and associated drivers of coastal marine heatwaves (MHWs). MHW metrics defined using the Climate Change Initiative Sea Surface Temperature (SST) dataset during 1981‒2020, including event-averaged cumulative intensity, duration and frequency, show significant spatial correlations (| R | > 0.92) with each other at Shark Bay, Western Australia, which also have distinct high correlations ( R > 0.73) with bathymetry. Mixed-layer heat budget analyses using the Bluelink ReANalysis (BRAN2020), analogues to the interpretation of results from a simplified atmospheric-forced experiment, further confirm the possibly nonnegligible contribution of geographical features to the warming and cooling effects caused by atmospheric and oceanic drivers during the onset and decline phase of major events. All major events illustrate a constrained contribution of the entrainment process over bay-entrance areas (<0.01°C/d). Events in the out-bay (bathymetry > 25m) and bay-entrance (bathymetry ≤ 25m) areas experience different magnitudes of net cooling or net warming effects of horizontal advection and mixing processes. By evaluating the geographically separated MHWs over the last 40 years, it was found that MHWs over the shallow in-bay areas are typically frequent (approximately once per year) but less intense and short, while events in the deep out-bay areas are less frequent (approximately interannual) but more intense and prolonged when concurrent with anomalous ENSO-sensitive warm water advection. We suggested that a global assessment of these differences is necessary to identify qualified coastal seas associated with higher resilience to sudden and prolonged ocean warming.