Abstract
A recent study of currents, sea level and temperatures in the Chesapeake Bay found interannual to decadal variability and a significant trend in outflow from the bay toward the Atlantic Ocean, suggesting influence on the dynamics of the bay from both- local river discharges as well as large scale climate variability. This study expands the previous findings in one bay into three major U.S. East Coast bays: the Chesapeake Bay (CB), the Delaware Bay (DB) and the New York Bay (NB). Monthly surface currents at 2 km resolution near the mouths of these bays were obtained from high-frequency radars (Coastal Ocean Dynamics Application Radar, CODAR) during 2012–2024. The contribution to flow variability from local and remote forcing is evaluated by comparing surface currents with (a) river discharges into each bay, (b) with winds, and (c) with the North Atlantic Oscillation (NAO). The results show that flow variability in the bays is significantly correlated with all three driving factors. The three bays often show similar flow patterns not only of the seasonal cycle, but also during extreme weather events. For example, increased inflow into the bays from the Atlantic Ocean is seen when hurricanes are observed offshore in the fall, and increased outflow from the bays is seen during winter storms. During positive NAO phases, outflow from all three bays increased due to intensified westerly winds, while during negative NAO phases outflow decreased with weakening winds in the region. Increased river discharges over the record length resulted in increased outflows from DB and NB of about 4 cm/s per decade. However, in CB extremely large river discharges into the bay in 2018–2019 resulted in a change in the outflow from a significant upward trend before 2018 to a significant downward trend after 2019. The results demonstrate the complex nature of the outflow from bays since multiple drivers contribute to the observed variability.