Attractive Lagrangian Features in the Mid‐Atlantic Bight: Using Lagrangian Coherent Structures to Describe Seasonal and Interannual Changes in Circulation

Abstract Coastal ocean dynamics are complex with influences from freshwater input, alongshore flows, offshore slope water intrusions, and overlapping mixing and stratification processes. This complexity makes it difficult to elucidate patterns in observed coastal circulation important to our understanding of natural and anthropogenic marine ecosystem processes. This study used a Lagrangian diagnostic tool to characterize patterns of transport within the coastal Mid‐Atlantic Bight (MAB) off the eastern coast of the United States. The MAB is home to some of the largest seasonal and long‐term oceanographic variability that drives an equally dynamic ecosystem that supports many economically important fisheries. This region has also been continuously observed by a Mid‐Atlantic Regional Association Coastal Ocean Observing System high frequency radar (HFR) array for over 10 years, providing temporally resolved maps of surface currents. With these data as input, we developed a multi‐year seasonal analysis of Lagrangian coherent structures using Finite Time Lyapunov Exponent (FTLE) to map attracting features from 2013 to 2022. Spatial patterns showed areas of year‐round attracting features along the continental shelf break and south of Cape Cod where tidal amplitudes are large. Seasonal differences were found with more attracting features and higher within‐season variability in summer and spring stratified seasons compared to the winter and fall “mixed” seasons. A potential regime shift was also identified, with stronger FTLE features after 2017 especially in the northern half of MAB in fall and winter. Results from this study provide new insights to coastal circulation in the MAB and create opportunities for future work to investigate the ecological importance of these dynamics.