AUTHOR=Baetge Nicholas , Graff Jason R. , Behrenfeld Michael J. , Carlson Craig A. 

TITLE=Net Community Production, Dissolved Organic Carbon Accumulation, and Vertical Export in the Western North Atlantic

JOURNAL=Frontiers in Marine Science

VOLUME=7

YEAR=2020

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2020.00227

DOI=10.3389/fmars.2020.00227

ISSN=2296-7745

ABSTRACT=<p>The annual North Atlantic phytoplankton bloom represents a hot spot of biological activity during which a significant fraction of net community production (<italic>NCP</italic>) can be partitioned into dissolved organic carbon (<italic>DOC</italic>). The fraction of seasonal <italic>NCP</italic> that is not respired by the heterotrophic bacterial community and accumulates as seasonal surplus <italic>DOC</italic> (Δ<italic>DOC</italic>) in the surface layer represents <italic>DOC</italic> export potential to the upper mesopelagic zone, and in the North Atlantic this is facilitated by winter convective mixing that can extend to depths &gt; 400 m. However, estimates of Δ<italic>DOC</italic> and vertical <italic>DOC</italic> export for the western North Atlantic remain ill-constrained and the influence of phytoplankton community structure on the partitioning of seasonal <italic>NCP</italic> as Δ<italic>DOC</italic> is unresolved. Here, we couple hydrographic properties from autonomous <italic>in situ</italic> sensors (ARGO floats) with biogeochemical data from two meridional transects in the late spring (∼44–56°N along ∼−41°W) and early autumn (∼42–53°N along ∼−41°W) as part of the North Atlantic Aerosols and Marine Ecosystems Study (NAAMES). We estimate that 4–35% of seasonal <italic>NCP</italic> is partitioned as Δ<italic>DOC</italic> and that annual vertical <italic>DOC</italic> export ranges between 0.34 and 1.15 mol C m<sup>–2</sup> in the temperate and subpolar western North Atlantic. Two lines of evidence reveal that non-siliceous picophytoplankton, like <italic>Prochlorococcus</italic>, are indicator species of the conditions that control the accumulation of DOC and the partitioning of <italic>NCP</italic> as Δ<italic>DOC</italic>.</p>