Dissolved Organic Carbon Accumulation and Export Potential in the Western North Atlantic

The annual North Atlantic phytoplankton bloom represents hot spot of biological activity during which a significant fraction of net community production (NCP) can be partitioned into dissolved organic carbon (DOC). DOC that is not respired by the heterotrophic bacterial community and accumulates in the ocean’s euphotic zone after escaping rapid microbial remineralization has the potential to be exported into the upper mesopelagic zone provided there is sufficient deep convective mixing. The fraction of seasonal NCP that is partitioned and accumulates as surplus DOC within the euphotic zone represents DOC export potential in regions of the North Atlantic where winter convective mixing can extend to depths >400 m. However, estimates of DOC accumulation and export for the western North Atlantic remain ill-constrained. Furthermore, the influence of phytoplankton community structure on the partitioning of NCP as seasonally accumulated DOC remains unresolved. Here, we couple hydrographic properties from autonomous in situ sensors (BioARGO floats) with biogeochemical data from two meridional ship transects in the late spring (~ 44 – 56˚N along ~ -41˚W) and late summer (~ 42 – 53˚N along ~ -41˚W) as part of the North Atlantic Aerosols and Marine Ecosystems Study (NAAMES). We estimate that 9% to 35% of NCP is partitioned as DOC and that the upper-bound of DOC export potential ranges between 0.3 and 1.2 mol C m^-2 in the western North Atlantic. Analyses reveal that non-silicifying picophytoplankton, like Prochlorococcus, are indicator species that can be used to identify regions of disproportionate partitioning of NCP as net DOC accumulation and export potential.