Collaborative Research: Observations of the Structure and Dynamics of Mid-Shelf Fronts

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A field program including remotely sensed, shipboard, moored, and autonomous vehicle measurements is proposed to obtain basic observational data on the structure and variability of the front in the mid-Atlantic Bight. Although detected in SST, from a dynamical perspective this feature is a salinity front that separates cool, lower salinity inner shelf water from warm, saltier outer shelf water. The vertical structure of this front is poorly known and the mechanism of formation has not been described.The objectives of the project are to test two competing theories for the formation of the mid-shelf front, determine the vertical structure and variability of the front, and to evaluate whether the front acts as a barrier to cross-shelf exchange of dissolved and particulate materials. Concurrent observations of satellite SST, HF radar surface currents, and autonomous glider sections will be analyzed to determine the relationship between the surface velocity jet, if present, the surface thermal front, and the subsurface hydrographic structure. A towed undulating vehicle will be used to obtain multiple high-resolution cross-frontal sections of hydrography and velocity to elucidate how the frontal structure varies on tidal and subtidal time scales. Measurements of the activities of short-lived radium isotopes will be used to infer crossshelf mixing rates. Moored observations of velocity and hydrographic profiles over a 3-month period will allow estimation of the cross-shelf buoyancy flux and its divergence.Improving our understanding of mid-shelf fronts, which are ubiquitous in the coastal ocean, will contribute to the broader scientific thrust of determining the role of the coastal ocean in the carbon cycle. It is also of interest to researchers studying larval and juvenile fish, as it likely impacts recruitment of organisms with widely separated spawning and nursery areas (such as bluefish).Collaboration is planned with the URI Office of Marine Programs in their outreach efforts to give K-12 teachers exposure to sea-going oceanographic. A partnership with the Mid-Atlantic Center for Ocean Science Education Excellence will be developed by making data available to educators. Curricula describing the impact and generation of ocean fronts will be added to existing projects already posted on the COOLClassroom [http://www.coolclassroom.org]. The project will provide research opportunities for undergraduate students and will include the training of a graduate student.