MASS, HEAT, OXYGEN AND NUTRIENT FLUXES AND BUDGETS IN THE NORTH-ATLANTIC OCEAN

Hydrographic, oxygen and nutrient data from two transatlantic sections at 24-degrees and 36-degrees-N are used to estimate physical and chemical fluxes and overall budgets. Nutrients carry significant information independent of temperature and salinity, with silicate being particularly useful. Accurate estimates of nutrient fluxes are found to require very detailed estimates of the circulation. The zonally integrated meridional cell carries a poleward heat flux of 1.3 +/- 0.2 x 10(15) W and an equatorward oxygen flux of 2900 +/- 180 kmol s-1 across both latitudes. The net flux of silicate is 138 +/- 38 kmol s-1 and 152 +/- 56 kmol s-1 equatorward at 36-degrees and 24-degrees-N, respectively, and is sensitive to the details of the horizontal circulation as well as the strength of the overturning cell. The nitrate flux is 119 +/- 35 kmol s-1 to the north across 36-degrees-N and is indistinguishable from zero at 24-degrees-N, leading to a net divergence of nitrate between these two latitudes. This divergence, and the net convergence poleward of 36-degrees-N, can be accounted for by a shallow cell in which the northward flow of inorganic nitrogen (nitrate) in the Gulf Stream is balanced by a southward flux of dissolved organic nitrogen in the recirculation gyre. Oxidation of the dissolved organic matter during its transit of the subtropical gyre supplies the required source of regenerated nitrate to the Gulf Stream and consumes oxygen, consistent with recent observations of oxygen utilization in the Sargasso Sea.