Spatio-Temporal Oceanographic Variability at Deep-Sea Coral Sites along the U.S. Atlantic Margin

In recent years, several collaborative projects under the ASPIRE campaign have sought to enhance our understanding of the occurrence of deep-sea corals within U.S. waters and the factors that govern their distribution. Notably, fieldwork conducted by both the DEEPSEARCH program and the Okeanos Explorer has resulted in the repeated collection of oceanographic data at multiple locations across a deep-sea coral province along the southeast U.S. margin at depths to approximately 1000 m. Since 2018, six cruises have visited sites in the region between April and October, with each making CTD deployments and sampling water to characterize the water column structure overlying the deep-sea coral province. Coupled with long-term deployments (>6 months) of benthic landers, our understanding of the oceanographic influences on the benthos has significantly increased. Generally, deep-sea coral sites within the region are heavily influenced by Western North Atlantic Central Water (100-500 m depth) and Western Atlantic Subarctic Intermediate Water (500-1500 m depth). However, variability in several oceanographic properties, including temperature, salinity, and dissolved oxygen was observed over daily to seasonal scales. Notably, deep-sea coral sites in the region experience considerable variation in oxygen saturation, ranging from a high of >300 µmol·kg^-1 in the spring months (April-May) to a low of 160 µmol·kg^-1 in the summer (August); furthermore, the coral sites are influenced by strong currents and large fluctuations in temperature (±6°C) were observed down to 800 m depth during events (days-weeks). This variability is likely due to several factors, including meandering of the Gulf Stream, potential intrusion of fresh groundwater, and the influence of Arctic Intermediate Water on the Blake Plateau. Ultimately, the results of this study contribute to our understanding of the niche in which deep-sea corals thrive and emphasizes the significance of interdisciplinary collaboration to collect repeated datasets in deep-water habitats.