DEVELOPMENT OF A COUPLED C-N-P-O-S MODEL OF MARINE BIOGEOCHEMISTRY FOR PALEOCEANOGRAPHIC APPLICATIONS

Abstract

A model of marine carbon, nitrogen, phosphorus, oxygen, and sulfur biogeochemistry is developed for use on one-thousand year to multi-million year time scales. It includes simple plankton population dynamics and explicit representation of nitrogen fixation, nitrification, denitrification, anammox, and thiodenitrification. The biogeochemistry module is coupled to a new intermediate-complexity box model representation of global ocean circulation, which includes representation of high-latitude, gyre, and coastal upwelling regions. A separate version of the circulation model is developed for the Black Sea, allowing the same biogeochemistry model to be tested under anoxic conditions. Careful validation of the of the simulated circulation and biogeochemistry for the modern Global Ocean and Black Sea was carried out using temperature, salinity, natural and bomb radiocarbon, chlorofluorocarbon, and a wide variety of tracer profiles and major biogeochemical fluxes. When coupled to an appropriate circulation model, the same biogeochemical model is capable of accurately simulating observed component profiles and fluxes in both the modern Global Ocean and Black Sea. For the Global Ocean, it is demonstrated that the new box model is capable of avoiding many of the artifacts found in simpler box model representations of ocean circulation, including excessive high-latitude sensitivity and the need to assign component-dependent eddy diffusivities. It is anticipated that this new model will have many applications for problems linking coupled nutrient cycling and changes ocean redox. Efficient numerical integration (1 My/hour) and modular program design make it relatively easy to modify existing processes or add entirely new processes and components. A copy of model source code (in MATLAB) is available from the author upon request.