AUTHOR=Selden Corday R. , Einarsson Sveinn V. , Lowry Kate E. , Crider Katherine E. , Pickart Robert S. , Lin Peigen , Ashjian Carin J. , Chappell P. Dreux 

TITLE=Coastal upwelling enhances abundance of a symbiotic diazotroph (UCYN-A) and its haptophyte host in the Arctic Ocean

JOURNAL=Frontiers in Marine Science

VOLUME=9

YEAR=2022

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2022.877562

DOI=10.3389/fmars.2022.877562

ISSN=2296-7745

ABSTRACT=<p>The apparently obligate symbiosis between the diazotroph <italic>Candidatus</italic> Atelocyanobacterium thalassa (UCYN-A) and its haptophyte host, <italic>Braarudosphaera bigelowii</italic>, has recently been found to fix dinitrogen (N<sub>2</sub>) in polar waters at rates (per cell) comparable to those observed in the tropical/subtropical oligotrophic ocean basins. This study presents the novel observation that this symbiosis increased in abundance during a wind-driven upwelling event along the Alaskan Beaufort shelfbreak. As upwelling relaxed, the relative abundance of <italic>B. bigelowii</italic> among eukaryotic phytoplankton increased most significantly in waters over the upper slope. As the host’s nitrogen demands are believed to be supplied primarily by UCYN-A, this response suggests that upwelling may enhance N<sub>2</sub> fixation as displaced coastal waters are advected offshore, potentially extending the duration of upwelling-induced phytoplankton blooms. Given that such events are projected to increase in intensity and number with ocean warming, upwelling-driven N<sub>2</sub> fixation as a feedback on climate merits investigation.</p>