Description: The Joint Global Ocean Flux Study (JGOFS) has completed a decade of intensive process and time-series studies on the regional and temporal dynamics of biogeochemical processes in five diverse ocean basins. Its field program also included a global survey of dissolved inorganic carbon (DIC) in the ocean, including estimates of the exchange of carbon dioxide (CO2) between the ocean and the atmosphere, in cooperation with the World Ocean Circulation Experiment (WOCE). This report describes the principal achievements of JGOFS in ocean observations, technology development and modelling. The study has produced a comprehensive and high-quality database of measurements of ocean biogeochemical properties. Data on temporal and spatial changes in primary production and CO2 exchange, the dynamics of of marine food webs, and the availability of micronutrients have yielded new insights into what governs ocean productivity, carbon cycling and export into the deep ocean, the set of processes collectively known as the "biological pump." With large-scale, high-quality data sets for the partial pressure of CO2 in surface waters as well for other DIC parameters in the ocean and trace gases in the atmosphere, reliable estimates, maps and simulations of air-sea gas flux, anthropogenic carbon and inorganic carbon export are now available. JGOFS scientists have also obtained new insights into the export flux of particulate and dissolved organic carbon (POC and DOG), the variations that occur in the ratio of elements in organic matter, and the utilization and remineralization of organic matter as it falls through the ocean interior to the sediments. JGOFS scientists have amassed long-term data on temporal variability in the exchange of CO2 between the ocean and atmosphere, ecosystem dynamics, and carbon export in the oligotrophic subtropical gyres. They have documented strong links between these variables and large-scale climate patterns such as the El Nino-Southern Oscillation (ENSO) or the North Atlantic Oscillation (NAO). An increase in the abundance of organisms that fix free nitrogen (N-2) and a shift in nutrient limitation from nitrogen to phosphorus in the subtropical North Pacific provide evidence of the effects of a decade of strong El Ninos on ecosystem structure and nutrient dynamics. High-quality data sets, including ocean-color observations from satellites, have helped modellers make great strides in their ability to simulate the biogeochemical and physical constraints on the ocean carbon cycle and to extend their results from the local to the regional and global scales. Ocean carbon-cycle models, when coupled to atmospheric and terrestrial models, will make it possible in the future to predict ways in which land and ocean ecosystems might respond to changes in climate.

Description: A means of assimilating simulated satellite ocean color data with a coupled physical-biological model of the North Atlantic Ocean is implemented, allowing the relative sensitivities of different biological parameters to those data to be investigated. The model consists of an eddy-permitting general circulation model derived from the WOCE Community Modeling Effort and a nitrogen-based, four-compartment NPZD marine ecosystem model. Many of the parameters in marine ecosystem models are poorly known and via assimilation, we hope to better constrain their values. The control parameters chosen for the variational assimilation are the model parameters involved in parameterizations of recycling as these are the most poorly known. Simulated observations are taken while following several floats seeded in varying dynamical biogeochemical provinces of the North Atlantic model domain over a six-month period. Twin experimental results show that, for the given functional forms of growth, mortality and grazing, the following parameters can be successfully recovered from simulated satellite ocean color data: nitrate and detrital recycling parameters in the trade wind domain, zooplankton parameters at higher latitudes (westerly wind and polar domains), and the phytoplankton mortality rate in all regions. By simultaneously assimilating ocean color data in different biological provinces, it becomes possible to successfully constrain all ecosystem parameters at once.