Pycnocline development and its consequences in the Middle Atlantic Bight

Sciences Seasonal pycnocline development in the shelf and slope waters of the Middle Atlantic Bight is investigated numerically using a one‐dimensional, two‐layer, bulk‐mixing model. The model considers the buoyancy budget of the system and includes both turbulent diffusion and entrainment across the pycnocline that separates the layers as well as a parameterization for mixed‐layer shallowing. Climatic estimates of the surface buoyancy and energy inputs drive the model. The shelf and slope water regimes, however, experience different inputs: freshening, due to river runoff, and a larger net heat gain, due to a more positive air‐sea temperature difference, both contribute to a larger buoyancy input to the shelf water regime; and the wind stress is larger over the slope. Numerical computation of vernal pycnocline development results in the formation of a shelf water pycnocline that is both shallower and more intense than that over the slope. A consequence of this mismatch is a reversal of the offshore density gradient at intermediate depths and an intrusion of slope water into the shelf water pycnocline, called the pycnocline salinity maximum. It is possible that interannual variations in the timing and magnitude of the heating and freshwater input from rivers can cause concomitant variations in salt input via the pycnocline salinity maximum.