Collaborative Research: Exchange and Dispersion Across the Inner Shelf: Understanding the Importance of Spatial Variability

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This study seeks to understand spatial variability in the flow field over the inner part of the continental shelf at scales of 100s of meters to 10s of kilometers, its contribution to exchange and dispersion, and its implications for coastal systems. Recent observations of the coastal ocean south of Martha's Vineyard, MA have documented startling examples of spatially-variable flows with the potential to drive focused lateral exchange across the shelf rivaling that due to the frequently-examined along-shelf uniform response to upwelling or downwelling. Yet, we know almost nothing about the characteristics of the flow field at these scales because conventional observational techniques and typical realistic shelf models do not adequately resolve these scales. This will likely be the first comprehensive study of current variability in the coastal ocean at scales from 100s of meters to 10s of kilometers by employing a unique combination of high-resolution HF radar surface currents, dense observations of subsurface velocity and hydrography, and mass drifter releases along with comparisons to realistic and idealized numerical models. The proposed work will quantify the total flux of water masses across the shelf, the relative importance of spatial variability in the wind, stratification, and bathymetry on exchange, and the role of spatially-variable dispersion.Previous efforts to quantify the rates of exchange in the coastal ocean have generally focused on the transport due to along-shelf uniform, wind-driven dynamics. While evidence of additional transport due to major capes or headlands, bathymetric irregularities, or non-uniform wind fields has been found in most coastal areas, the relative impact of these sources of variability on exchange and dispersion across the shelf have not been quantified. Additionally, the effects of small-scale and/or transient features, potentially important sources of spatially-dependent exchange or dispersion, have never been resolved. This comprehensive view of exchange across the coastal ocean south of Martha's Vineyard, including the use of Lagrangian trajectory analyses in addition to the Eulerian-based transport studies, will enable a much broader range of spatial variability to be captured and will quantify the occurrence of transient events, their drivers, and their importance for coastal systems.The movement of water masses from the shallow waters adjacent to the coast to the larger coastal ocean offshore controls the flux of heat, salt, nutrients, and pollutants between the nearshore and the global ocean. By providing a holistic look at across-shelf transport, the results of this work will document the potential effects of spatial variability on coastal systems. This effort will improve our ability to quantify and predict the exchange critical to assessing the productivity of coastal areas and the dispersion rates critical to monitoring the fate of harmful algal blooms, pollutants, and search and rescue operations. The PIs are actively involved in teaching and mentoring at WHOI and UMASS Dartmouth as well as interacting with coastal managers and planners. In collaboration with the NOAA's Northeast Fisheries Science Center, a broad educational program will entrain K-12 students in the region into the science being conducted through additional drifter deployments