BGC-09 Biogeochemistry in Subtropical Oceans
Comparative surface ocean DOC:DON:DOP stoichiometry between the Atlantic and Pacific Oceans
Zhou Liang* , Department of Earth, Ocean and Atmospheric Science, Florida State University, Tallahassee, FL, USA
Robert T. Letscher, Earth Sciences & Ocean Process Analysis Laboratory, University of New Hampshire, Durham, NH, USA
Angela N. Knapp, Department of Earth, Ocean and Atmospheric Science, Florida State University, Tallahassee, FL, USA

Dissolved organic matter in the ocean plays an important role in the global carbon cycle, both as a product of and substrate for primary production. Individually, dissolved organic nitrogen (DON) and dissolved organic phosphorus (DOP) can be assimilated by phytoplankton in the ocean when inorganic nutrients are limiting. Together, the stoichiometry of dissolved organic carbon (DOC):DON:DOP concentration ratios in the global surface ocean can be used to infer patterns of DON and DOP production and consumption, especially to support primary production and nitrogen fixation. Here we use recently updated databases of DOC, DON, and DOP concentrations in the global ocean to present DOC:DON:DOP concentration ratios in different biogeochemical and geographical regions in the global surface ocean, mainly in the Pacific and Atlantic Oceans. We also explore relationships between satellite-derived rates of net primary productivity (NPP) and surface ocean DOC, DON, and DOP concentrations. Surface bulk DOC, DON, and DOP concentrations are significantly positively correlated with rates of NPP but with decreasing R2 for DOC, DON and DOP, consistent with utilization of DON and DOP by phytoplankton. We calculate global mean labile and refractory DOC:DON:DOP concentration ratios of 173:16:1 and 920:56:1, respectively, according to their relationships with rates of NPP. Our results show that bulk surface ocean DOC:DON:DOP concentration ratios are higher than the canonical Redfield ratio and that bulk DOC:DON concentration ratios exhibit a narrower range than DOC:DOP and DON:DOP concentration ratios. Lower bulk and labile DOC:DOP and DON:DOP concentration ratios are found in the equatorial region than in the subtropical gyres. We also find increasing bulk DOC:DOP and DON:DOP concentration ratios from east to west zonally across the Pacific, and increasing bulk DOC:DOP and DON:DOP concentration ratios from south to north meridionally in the Atlantic, with a maxima at 30˚N. Our work presents patterns of DOC:DON:DOP concentration ratios in the global surface ocean whose variability can be explained by DON and DOP production and consumption in the ocean.