Study Reveals Unexpected Findings on Subsurface Effects Of Marine Heatwaves In Estuaries…to help us better understand climate change and its consequences

Led by School of Marine Science Ph.D. student Nathan Shunk, the new study builds on 2022 research conducted by Piero Mazzini and Cassia Pianca that resulted in the first comprehensive study of climatological aspects of marine heatwaves in the Chesapeake Bay.

A dearth of data that is both at the right frequency and over a long enough period means that little is known globally about temperatures below the water’s surface during marine heatwaves. For this study, Shunk and his co-authors Mazzini and Ryan K. Walter (Cal Poly) explored data combined from three different monitoring programs in the Chesapeake Bay — the National Data Buoy Center, the Center for Operational Oceanographic Products and Services and the Chesapeake Bay National Estuarine Research Reserve in Virginia — covering a period from 1986 to 2021.

Subsurface temperature data and other variables such as dissolved oxygen, available through the Chesapeake Bay Program, allowed the team to identify subsurface anomaly profiles during marine heatwave events. Ultimately, they identified approximately 760 marine heatwave vertical profiles for use in their analysis.

“First of all, this study would not have been possible without thirty years of steadfast efforts by the various monitoring programs that collected the data we explored. So, I would like to thank the researchers and staff that make the use of these datasets possible,” said Shunk. “The most surprising aspect of this analysis was that warming reached the bottom during the winter. We expected the effects of these events to be limited to the surface, like we found in the summer.”

The research shows that marine heatwave events have very different impacts in the subsurface depending on the season. Two regimes are documented: a “Homogeneous Season” and a “Stratified Season.” During the “Homogeneous Season,” taking place in the fall and winter, warming during marine heatwaves occurs throughout the entire water column, influencing bottom organisms. During marine heatwaves in the spring and summer “Stratified Season,” on the other hand, warming is only seen in the near-surface and not the bottom.

Reflecting on the value of the data used for the study, Mazzini said, “We are very fortunate to have such a wealth of information provided through decades of immense effort of data collection by the different monitoring programs in the Chesapeake Bay. I hope the important results from our research inspire the creation of monitoring programs in other estuaries worldwide. Long term data sets like those now available in the Bay are crucial to help us better understand climate change and its consequences, and guide future management actions that will help to protect our marine and estuarine environment for future generations.”