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The global overturning circulation and the importance of non-equilibrium effects in ECCOv4r4
  • Tatsu Monkman,
  • Malte Friedrich Jansen
Tatsu Monkman
The University of Chicago

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Malte Friedrich Jansen
University of Chicago
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Abstract

We quantify the volume transport and watermass transformation rates of the global ocean circulation using the Estimating the Circulation and Climate of the Ocean version 4 release 4 (ECCOv4r4) reanalysis product. Our results support large rates of intercell exchange between the mid-depth and abyssal cells, in agreement with modern theory and observations. However, the present-day circulation in ECCO cannot be interpreted as a near-equilibrium solution. A dominant portion of the apparent diapycnal transport of watermasses within the deep ocean is not associated with irreversible watermass transformation. Instead up- and down-welling is associated with isopycnal volume changes, reflecting trends in the deep ocean density structure. Our results reveal disagreement between ECCO’s representation of the overturning circulation and associated watermass transformations, and prevailing equilibrium theories of the overturning circulation.