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: The overflow of dense water from the Nordic Seas through the Denmark Strait is one of the primary sources of the deep water in the world’s oceans. In 1998, a rapid high-resolution survey on the F/S Poseidon with expendable profilers (XCP/XCTD) collected velocity, temperature, and salinity data from the region of the Denmark Strait sill to study the initial descent of the overflow into the deep North Atlantic. The major results from this and an earlier, more modest, survey in 1997 on the R/V Aranda, along with additional analysis of satellite and current meter data, can be summarized as follows: - The flow near the sill is characterized by a strongly barotropic structure associated with a nearly-vertical temperature front. As the denser water descends the Greenland slope, it develops the bottom-intensified structure characteristic of a gravity current. - Initial transport of sq 〉 27.8 water at the sill is measured by the synoptic sections to be 2.7 ± 0.6 Sv, essentially identical both in mean and variability to that measured in 1973 by a 5-week current meter array deployment. - Despite large spatial and temporal variability in velocity, thickness, and transport, the overflow’s pathway and descent with distance from the sill are remarkably steady. - Measurements of near-bottom shear stress (from logarithmic velocity fits) confirm the importance of bottom friction in controlling the rate of overflow descent. - Satellite sea-surface temperature images confirm the birth and downstream propagation of cyclonic eddies starting at approximately 125 km southwest of the sill. This same point is also marked by a change in the rate of overflow entrainment and a maximum in overflow speed. Σ The presence of subsurface eddies upstream of the appearance of the surface features suggests a geographical separation between the region of flow instability and the site of eddy generation and vortex stretching. These two distinct processes occur in the approach to the sill and over the steepest descent, respectively.

Description: The mean trophic level (TL) of fish landed in fisheries on the east and west coasts of Canada is declining by 0.03–0.10·decade–1, similar to global trends. This finding is based on data from United Nations Food and Agriculture Organization and the Canadian Department of Fisheries and Oceans and other Canadian sources for the period 1873–1997. Significant rates of decline in mean TL were obtained even when key species — Atlantic cod (Gadus morhua) on the east coast and Pacific herring (Clupea pallasi) and Pacific hake (Merluccius productus) on the west coast — were omitted from the analysis. Fish taken in inland water fisheries did not exhibit a decline in mean TL. Two models were developed, based on length and age, respectively, for correcting TL estimates of individual species for the effects of changes in body size due to changes in fishing mortality. Both produced corrections that were small relative to changes in mean TL that resulted from changes in species composition of the catch over time. Overall, these results suggest that the mean TL of fish landed can be used as an index of sustainability in ultispecies fisheries and that its reliability will depend on the quality of the data and length of the time series available for analysis.