Evolution of stratification over the New England shelf during the Coastal Mixing and Optics study, August 1996–June 1997

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Abstract
To investigate the processes influencing the evolution of stratification over continental shelves a moored array was deployed on the New England shelf from August 1996 to June 1997. Temperature, salinity, and current observations spanning the water column were obtained at four midshelf sites, along with meteorological measurements at a central site to estimate the wind stress and the surface heat and freshwater fluxes. Four processes contributed to the seasonal evolution of the stratification. (1) The breakdown of the seasonal thermocline in fall was primarily due to wind forcing, not surface cooling, and occurred in four discrete steps associated with westward, along‐coast wind stress events. Eastward wind stress events of similar magnitude did not reduce the stratification. (2) The water at midshelf remained stratified throughout most of the winter due to saltier shelf‐slope front water displaced onshore by anomalously strong and persistent eastward alongcoast wind stresses. (3) The gradual redevelopment of the thermocline, beginning in April, was primarily a one‐dimensional response to increasing surface heat flux. (4) Stratification in early April and throughout May was substantially enhanced by low‐salinity water associated with river runoff from southern New England that was driven eastward and offshore by upwelling‐favorable (eastward) wind stresses.