Departmental Seminar

In spite of inorganic nutrient concentrations that approach detection limits, oligotrophic gyres support a significant fraction of new production globally. Organic nutrients are thought to contribute to this new production in oligotrophic gyres, but identifying and quantifying where these nutrients originate, as well as where they are consumed, remain open challenges. Here I discuss new geochemical tools used to identify the production and consumption of organic nutrients in surface waters where inorganic nutrients are scarce. Specifically, I review a new marine dissolved organic phosphorus (DOP) concentration database my lab has generated, and how we have used that with complementary databases of marine dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) concentration to generate novel DOC:DON:DOP concentration ratio maps of the global ocean. These efforts demonstrate that organic nutrients are produced in ratios close to Redfield, i.e., 106:16:1, stoichiometry, but the preferential consumption of DON and especially DOP by autotrophs in the surface ocean result in elevated DOC:DON:DOP concentration ratios in oligotrophic gyres. We further link surface ocean DOC:DON:DOP concentration ratios to surface ocean iron availability, denitrification in the Eastern Pacific, and atmospheric dust deposition in the North Atlantic. Finally, I discuss how the isotopic composition ("δ15N”) of DON can be used to identify DON production and consumption in surface waters. Measurements of the δ15N of DON provide insight into DON production and consumption patterns that DOC:DON:DOP concentration ratios cannot because of the relatively narrow dynamic range in surface ocean DON concentration compared to DOP.