A CLIMATOLOGY OF THE SHELFBREAK FRONT IN THE MIDDLE ATLANTIC BIGHT

Description of the shelfbreak front in the Middle Atlantic Eight is ha mpered by the extreme variability of the front. In order to gain insig ht into both the seasonal variability and regional variations in the m ean frontal structure and associated baroclinic jet, historical data a re used to produce two-dimensional climatological fields of temperatur e and salinity for the region south of Nantucket shoals, along the sou th flank of Georges Bank, and off the coast of New Jersey. Associated cross-shelf fields of density and geostrophic velocity are also comput ed. The climatological temperature and salinity are consistent with pr evious descriptions of the frontal hydrography. The temperature contra st across the front varies seasonally between 2 degrees and 6 degrees C. The salinity contrast is 1.5-2, with little seasonal variation. The near-surface density gradients are strongest during the winter and we akest during the summer, when the seasonal thermocline is established. The cross-frontal density gradients are strongest near the foot of th e front, Despite the inherent smearing of frontal gradients incurred b y averaging over large temporal and spatial scales, the geostrophic ve locity field south of Nantucket shows a strong (0.2-0.3 m s(-1)) baroc linic jet associated with the frontal density gradients. The core of t he jet, having a width of 15-20 km, is located near the 150-m isobath, Transport calculations for the flow over the outer shelf and slope ar e in the range of 0,2-0.3 Sverdrups (Sv) to the west. This is comparab le to the estimated transport (0.4 Sv)shoreward of the 100-m isobath.