A climatology of salty intrusions over the continental shelf from Georges Bank to Cape Hatteras

Abstract

Intrusions or lens of anomalously salty slope water (Smax intrusions) are often found over the continental shelf of the Middle Atlantic Bight (MAB). Salty intrusions were identified in 11% of 10,652 historical hydrographic profiles. Intrusions occurred primarily in summer, were observed across the entire shelf, but were most common over the outer shelf, and were concentrated at the depth of the seasonal pycnocline. The percentage of profiles with intrusions increased linearly along the MAB shelf from Georges Bank (3%) to Chesapeake Bay (15%), suggesting either a north to south increase in generation or an along-shelf accumulation associated with a decay timescale of 90 days or longer. Intrusions were typically less than 30 m thick, with a salinity anomaly of less than 0.5, though 10% of the anomalies were greater than 1. The thickness increased as the stratification decreased in a manner consistent with double-diffusively driven lateral intrusions. Intrusions did not preferentially occur during certain wind conditions. Salty intrusions increase the average salinity of the MAB shelf during summer by 0.3 or more, depending on how rapidly intrusions mix with the surrounding shelf water.