WHOI PO

Identifying Fronts In Energetic Flows Through Remotely-Sensed Ocean Velocity Data: spatiotemporal patterns and ecological consequences
 
Coastal oceans and upwelling areas are complex with influences from three-dimensional movements. This complexity makes it difficult to elucidate patterns in observed circulation important to our understanding of marine ecosystem processes. This study used a Lagrangian diagnostic tool to characterize patterns of transport within the coastal Mid-Atlantic Bight (MAB). The MAB experiences some of the most pronounced seasonal and long-term oceanographic variability, fueling a dynamic ecosystem that sustains many economically important fisheries. This region has also been continuously observed by a MARACOOS High Frequency Radar (HFR) array for over 10 years, providing temporally resolved maps of surface currents across the region. 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 (surface ocean fronts) from 2013-2022. 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 more strong 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. Results have also inspired new work in the Antarctic Circumpolar Current (ACC), where a similar Lagrangian diagnostic tool has been applied to satellite altimetry derived geostrophic flows to understand the role of ACC in the Southern Ocean biological carbon pump.