Impact of the Elemental Composition of Exported Organic Matter on the Observed Dissolved Nutrient and Trace Element Distributions in the Upper Layer of the Ocean

Systematic regional variations in the ratio of nutrient depth gradients of dissolved inorganic carbon (Delta DIC):nitrate (Delta NO3):phosphate (Delta PO4) in the upper layer (300 m) of the Pacific Ocean are observed. Regional variations in the Delta DIC/Delta NO3/Delta PO4 are primarily the result of three processes, that is, the C/N/P of organic matter (OM) being exported and subsequently degraded, nitrogen fixation, and air-sea CO2 gas exchange. The link between the observed dissolved Delta DIC/Delta NO3/Delta PO4 and the C/N/P of exported OM is established using surface layer dissolved DIC, NO3, and PO4 budgets. These budgets, in turn, provide a means to indirectly estimate the C/N/P of OM being exported from the surface layer of the ocean. The indirectly estimated C/N/P of exported OM reach maxima in the subtropical gyres at 177/22/1, that is, significantly greater than the Redfield ratio and a minimum in the equatorial ocean at 109/16/1 with both results agreeing with available observed particle C/N/P and ocean biogeochemical models. The budget approach was applied to a bioactive trace element (TE) using the measured dissolved Cadmium (Cd) to PO4 gradients to estimate the Cd/P of exported OM in the Pacific Ocean. Combining the budget method with the availability of high-quality dissolved nutrient and TE data collected during the GOSHIP and GEOTRACES programs could potentially provide estimates of the C/N/P/TE of exported OM on global ocean scales which would significantly improve our understanding of the link between the ocean's biological pump and dissolved nutrient distributions in the upper ocean.