Biogeochemical regimes in the oceanic Southeastern United States: Deep-sea black corals and exported primary production

Deep-sea proteinaceous corals are sessile, benthic animals that preferentially consume surface-derived particulate organic matter, which is eventually integrated into the coral’s proteinaceous skeleton. As a result, this provides a direct connection between the geochemistry of the corals’ skeleton and primary production in the euphotic zone. This relationship has prompted the expansion of deep-sea coral proxy development to explore the biogeochemical regimes of the surface ocean. In the Southeastern United States, nutrient mixing between the euphotic zone and Gulf Stream is the primary driver of photosynthesis off the continental shelf. However, questions remain as to whether plankton regimes exporting organic material to benthic ecosystems have been constant through time. Sea surface temperature, Gulf Stream transport, and anthropogenic activity are all external influences that could impact biogeochemical regimes over the last several hundred years. Here, we use bulk isotope and compound-specific isotope amino acid analysis from a Leiopathescoral to examine this question. Located offshore of the Southeastern United States, our study site is directly underneath the influence of the Gulf Stream, and offers a prime location to investigate nutrient dynamics. Preliminary evidence from bulk isotope analysis (δ¹³C) indicates a relatively consistent plankton regime during over the last several hundred years, with rapid and cyclical fluctuations of approximately 1‰. Isotopic fingerprinting with compound-specific data corroborates this finding, with all samples traced to eukaryotic algae (rather than prokaryotes) as the primary source of exported organic carbon. By expanding these initial findings to additional sites, we can gain further information about biogeochemical regimes along the Southeastern United States.