On the importance of intermediate water flows for the global ocean overturning

rschlitzer [ at ] awi-bremerhaven.de


A steady state inverse global ocean model is used together with theavailable original, historical hydrographic database to study andquantify the large-scale global ocean circulation. The model has avariable resolution grid with grid sizes as small as 2.5\degree\longitude by 2\degree\ latitude along boundaries, straits or oversteep topography and a default resolution of 5\degree\ by 4\degree\ in``quiet'' open ocean regions. The model has 26 vertical levels with 60m resolution near the surface. The adjoint method is applied to drivethe model to the hydrographic data and to optimize horizontal flows,air-sea heat fluxes, and mixing coefficients in an iterative way.Mass, heat, and salt budgets are satisfied exactly by the model.After assimilation, both simulated temperature and salinity fields arein good agreement with observations. Sensitivity experiments showthat different circulation patterns with varying relative importanceof intermediate water versus warm water transports and varying warmwater inflow from the Indian Ocean into the Atlantic are consistentwith the hydrographic data. However, for all solutions we find thatthe water mass that dominates the compensation of North Atlantic DeepWater export is Antarctic Intermediate Water. The northward transportrates of intermediate water in the South Atlantic and South Pacific inour model solutions range between 10 and 15 Sv in each ocean and areconsiderably larger than previously published values.

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Heras, M. d. l. and Schlitzer, R. (1999): On the importance of intermediate water flows for the global ocean overturning , Journal of geophysical research-oceans, 104, 15, 515 .

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