The Meridional Oceanic Transports of Heat and Nutrients in the South Atlantic

Jürgen Holfort (1) and Gerold Siedler (2)

Institut für Meereskunde, Kiel, Germany
1 Now at Institut für Meereskunde, Hamburg, Germany.
2 Presently at Instituto Canario de Ciencias Marinas, Telde, Gran Canaria, Spain.

Abstract:

Meridional transports of mass, heat, nutrients and carbon across coast-to-coast WOCE and pre-WOCE sections between 11░S and 45░S in the South Atlantic are calculated using an inverse model. Usually salt preservation is used as a condition in the inverse model, and only in the case of heat transport the condition of zero total mass transport is taken instead. Other constraints include silica conservation, prescribed southward fluxes of salt and phosphate, and transports in the southward Brazil Current and in the northward Antarctic Bottom Water flow obtained from WOCE moored current meter arrays. The constraints set the underdetermined system of linear equations of the inverse model whose solutions depend on weights, scales and matrix ranks. The discussion emphasizes the sensitivity of the fluxes to changes in the model input. The transports given in the following are obtained as the means of ``reasonable'' solutions at 30░S. The error numbers in parentheses include uncertainties due to wind stress and temporal variability, the numbers without parentheses do not contain these terms. 0.53 ± 0.03 (0.09) Tg/s mass to the south, 0.29 ± 0.05 (0.24) PW heat to the north, 15 ± 120 (500) kmol/s oxygen to the south, 121 ± 22 (75) kmol/s nitrate to the south, 64 ± 110 (300) silica to the north and 1997 ± 215 (600) kmol/s dissolved inorganic carbon to the south. The above errors in transports are obviously dominated by uncertainties in wind stress and temporal variability. The divergence in meridional heat and mass transport is consistent with integral surface flux changes between corresponding zonal bands. The mass compensation of southward flowing North Atlantic Deep Water occurs to a greater extent in the warm surface waters than in the Antarctic Intermediate Water below. If one follows the arguments of earlier authors on the relation between meridional fluxes and the significance of the two possible pathways for the global thermohaline circulation, the warm water path south of Africa seems to be somewhat more important than the cold water path through Drake Passage.

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