The scientific objective of R/V Endeavor cruise 400 is to determine the subsurface hydrographic structure of oceanic fronts on the continental shelf south of New England. Fronts in the ocean are boundaries between distinct water masses of differing temperature and/or salinity. The rate of exchange of water across these boundaries is thought to control the degree to which materials such as land-derived pollutants and organisms such as fish larvae are mixed horizontally in the ocean. Because fronts are also locations where fish accumulate, it is important to understand the physical processes occurring at these locations.

The focus of the expedition will be the newly discovered mid-shelf front that is found in water depths of approximately 50 meters. This front has recently been identified in surface temperature maps derived from satellite measurements, but its subsurface characteristics and the mechanism underlying its formation are unknown at present.

Measurements of water temperature and salinity from a towed undulating sensor package along with observations of ocean currents from the moving ship will provide basic information as to the strength of the front and whether there is an ocean current jet flowing along the front as is often observed at other fronts. In addition to the physical oceanographic observations, measurements of the concentration of natural chemical tracers present in land derived freshwater will provide estimates of the speed of mixing of these waters with open ocean waters.

Also joining the expedition are GSO marine research specialist Sandra Fontana, GSO marine research associate Roger Kelly, and University of Massachusetts postdoctoral scholar Takeyoshi Nagai. Also, GSO graduate students Joe Kuehl, Yongsheng Xu and Elly Speicher.