Nutrient Streams and the Subduction process: their effect on global nutrient distributions

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Biological production leads to an export of organic matter from the surface, sunlit ocean, which is important in transferring carbon within the ocean and in providing a biological drawdown of carbon dioxide from the atmosphere. This export can only be sustained over several years if there is a compensating supply of new nutrients to the upper ocean. Traditionally, this nutrient supply has been explained in terms of a vertical advective or diffusive transfer. In this proposal, we instead explore how the horizontal transfer of nutrients acts to maintain the surface nutrient concentrates and, thus, sustain export production. We propose to examine the following scientific questions: 1. How do boundary currents (through nutrient streams) and the subduction process (the exchange of fluid between the mixed layer and thermocline) control surface nutrient distributions over ocean basins? 2. How does interannual variability in mode water formation and spreading affect the nutrient reservoir of the upper thermocline for subtropical gyres? 3. How do fine-scale eddies sustain nutrient concentrations within the upper thermocline? These questions are addressed through a combination of data analyses and coupled isopycnic circulation and nitrogen model experiments.