Spatial variability of marine heatwaves in the Chesapeake Bay

The Chesapeake Bay is the largest estuary in the continental United States. Extreme temperature events, termed marine heatwaves, are impacting this ecologically important zone with increasing frequency. Although marine heatwaves evolve across space and time, a complete spatial picture of marine heatwaves in the Bay is missing. Here we use satellite sea surface temperature to characterize marine heatwaves in the Chesapeake Bay. We consider three products: NASA MUR, NOAA Geo-Polar, and Copernicus Marine OSTIA, and validate their effectiveness using in situ data from the Chesapeake Bay Program. We find that Geo-Polar SST is the most suitable dataset for marine heatwave analysis in this location, with an root mean squared error of 1.6°C. Marine heatwaves occur on average of 2.3 times per year and last 10.8 days per event. A north-south (along estuary) gradient is identified as a common pattern of spatial variability. Seasonally, summer marine heatwaves are shorter, more frequent, and have a more consistent duration, with an inter-quartile range of 6-11 days (median=8 days). December marine heatwaves have a much larger inter-quartile range of 6-28 days (median=13 days). Marine heatwaves are increasing at a rate of 4 events/year in the upper Bay and 2 events/year in the main stem of the lower Bay. Our analysis suggests that the major observed spatial patterns are a result of long term warming, not shifts in the spread of the temperature distribution. Overall, the qualitative character of marine heatwaves in the Chesapeake Bay is not changing but they are becoming more frequent.