Physical and Biological Exchange Processes and Lagrangian Pathways of Eel Larvae Between Deep Ocean and Shelf Regions of the Northwestern Atlantic
Exchange between waters over the continental shelf or slope and the deeper ocean offshore is important for understanding the distribution of temperature, salinity and other physical, chemical, and biological water properties in the ocean. Despite their importance and the extensive number of previous studies, these exchange processes are not well understood. This is because they occur over short scales in time and space, which makes it a challenge to resolve them with field measurements or numerical models. This comprehensive study will make use of state-of-the-art realistic ocean circulation models in combination with novel dynamical system tools to better understand and quantify these exchanges. The study area will extend from Gulf of Maine and the Mid-Atlantic Bight to the Gulf Stream and the Sargasso Sea, which is the spawning site for the American eel, a species of great scientific interest and economic value. This fish undertakes a remarkable spawning migration from freshwater habitats along the North American coast to the Sargasso Sea, and its larvae then have to return to coastal nursery habitats that predominantly occur along the eastern seaboard of North America. Since the larvae have only limited swimming ability, they have to navigate ocean circulation features to complete their migration. This study will also explore how they achieve this remarkable feat. The project will support three early-career scientists and will promote collaboration between physical oceanographers and biologists. The project will also contribute to K-12 educational programs, including class visits and field trips targeting mostly minority students. It will also continue efforts to bring science to the public through art and dance. The overarching goal of the proposed study is to characterize and quantify, from a Lagrangian viewpoint, water mass exchanges and property fluxes between the continental shelf and the open ocean. Several physical mechanisms are expected to influence the exchange processes in this region. These include topographic steering, wind forcing, instabilities and meanders of the shelfbreak jet, and Gulf Stream meanders and rings impinging on the shelf, each of which will be investigated and quantified. Specific regions and features of interest for the proposed study include the Mid-Atlantic Bight, the Gulf of Maine, the Slope Sea, the Gulf Stream and its extension, and the Sargasso Sea. A focused application of the proposed effort will be devoted to investigating the dispersal of eel larvae as an example of semi-Lagrangian, biologically relevant particles. The study will be based on a high-resolution regional model and a data-assimilative global model, and would compare Eulerian flux estimates with their Lagrangian counterparts and combine conventional statistical techniques with novel dynamical systems analysis. By its interdisciplinary nature, this project will have impacts across a variety of fields, including physical oceanography, marine biology, and dynamical systems. The PIs will also collaborate with colleagues at the NOAA Northeast Fisheries Science Center. Participation in K-12 educational programs will include (1) efforts with established partner schools to introduce project results into their earth science module, and (2) class visits and field trips for East Boston High School (>80% minority students) students. PIs participating in the MIT/WHOI Joint Program in Oceanography will incorporate the study's findings into their graduate courses.