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Biogeochemistry in oligotrophic ocean gyres
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The ecology and biogeochemistry of nitrogen-fixing microorganisms in the subtropical North Pacific
Tuesday 8th @ 1350-1410, Multifunction Hall
Matthew J. Church* , Flathead Lake Biological Station, University of Montana
Presenter Email: matt.church@umontana.edu |
| Nitrogen-fixing microorganisms (termed diazotrophs) play key roles in plankton ecology and biogeochemistry in the subtropical North Pacific. Through their physiological activities, diazotrophs influence cycling of key bioelements, rates of new production, and export of material from the upper ocean to the interior waters of the sea. Based on a combination measurements at Station ALOHA, the field outpost for the Hawaii Ocean Time-series (HOT) program, approximately half of the material export to the deep sea in the subtropical North Pacific is supported by diazotroph supply of nitrogen to the upper ocean. Distinct groups of cyanobacteria appear to dominate diazotroph assemblages in this region, including both small unicellular and larger filamentous microorganisms. Time series measurements of abundances indicate seasonally-variable contributions of several of these cyanobacterial diazotrophs to plankton biomass. In particular, members of unicellular cyanobacteria termed UCYN-A appear most dominant in the winter and spring, while members of the genus Crocosphaera display punctuated increases in abundance during the late summer and early fall. Time-variable changes in diazotroph abundance co-vary with changes in upper ocean temperature and appear partly regulated by mesoscale physical variability. This presentation will highlight on-going research exploring the ecology and biogeochemistry of diazotrophs in the oligotrophic waters of the North Pacific Ocean. |
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