Oxygen Utilization and Nutrient Remineralization Rates in the Pacific Ocean (Supplement to Continuation of Models of the Pacific Basin Circulation Based on WOCE-era Observations)

Woods Hole Oceanographic Institution, Woods Hole MA

Investigators

Abstract

ABSTRACT OCE-0326162 Biogeochemical cycling will be studied in a multi-box inverse model of the Pacific Ocean with focus on oxygen utilization and nutrient remineralization rates. The inverse model was developed under previous grants incorporating for the first time all the main WOCE hydrographic sections collected in the Pacific Ocean to determine zonal and meridional transports within density layers as well as diapycnal fluxes and air-sea exchange fluxes. Biogeochemical fluxes will be added in the model to investigate, on basin-scale, the depth-dependent rates at which oxygen is consumed and nitrate, phosphate, silicate, and total alkalinity (TA) are produced below the euphotic zone. The formulation of this inverse model differs from previous models in that the biogeochemical source/sink terms are explicitly included as unknowns. Through the incorporation of these terms, it is possible to put constraints on the biogeochemical rates. We propose to perform a set of model experiments to explore this approach including coupling of oxygen utilization and phosphate and nitrate remineralization rates through Redfield ratios, introducing non-zero initial guesses for the biogeochemical rates, and imposing positivity/negativity constraints. In addition, experiments will be conducted with varying the weights of the model equations, predefining the vertical diffusivities, and evoking top-to-bottom nutrient conservation. The best estimates of oxygen utilization and nutrient/TA. remineralization rates, from which organic matter, opal, and calcium carbonate (CaCO3) export rates can be inferred, will be compared to results from tracer age based approaches and other studies in the literature. Broader Impacts: This work forms an interdisciplinary component of the ongoing synthesis of the data collected during the international WOCE program. It also represents a novel application of inverse methods (widely used in physical oceanography) to the inference of biogeochemical rates. The resulting estimates of organic carbon and CaCO3 remineralization rates will benefit the study of the oceanic component of the global carbon cycle. The funds will support a postdoctoral investigator who is in the process of establishing herself in interdisciplinary research and is interested in further combining physical and biogeochemical approaches.