WHOI PO

The Northeast U.S. continental shelf is a highly productive and economically important region that has experienced robust changes in upper-ocean properties in recent decades. Warming rates exceed the global and North Atlantic average and in particular several episodes of anomalously warm temperatures, so called marine heatwaves (MHWs), have had devastating impacts on regional fisheries over the past decade. Due to the lack of subsurface observations, the depth-extent of MHWs is not well-known, which hampers the assessment of impacts on pelagic and benthic ecosystems. We utilized a global ocean circulation model with a high-resolution (1/20°) nest in the Atlantic to investigate the depth structure of MHWs and associated drivers on the Northeast U.S. continental shelf. The highest intensities are found around 100m depth with temperatures exceeding the climatological mean by up to 7°C, while surface intensities are typically smaller (around 3°C). Distinct vertical structures are associated with different spatial MHW patterns and drivers. Two case studies provide insight into opposing MHW patterns at the surface and at depth, being forced by anomalous air-sea heat fluxes and Gulf Stream warm core ring interaction, respectively. The results highlight the importance of local and regional ocean processes, which is my work expanded to a more general interest in understanding the ocean variability in the region from seasonal to multi-decadal scales. I will further talk about observational analyses of spatio-temporal salinity signals on the shelf, including mid-depth salinity intrusions, using remotely sensed sea surface salinity and Coastal Pioneer Array data, as well as in-situ data from two research cruises. River discharge along the eastern U.S. and Canadian coast drives a seasonal freshening on the shelf, while shelf break exchange driven by the interaction of Gulf Stream warm core rings drive an onshore flux of heat and salt. Furthermore, large-scale forcing associated with latitudinal shifts of the Gulf Stream can impact the along-shelf advection of Artic-originating freshwater. Connecting local and larger-scale processes is crucial to improve our understanding of the observed recent changes.