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A state estimate of the routes of the upper branch of the Atlantic Meridional Overturning Circulation
  • Louise Rousselet,
  • Paola Cessi,
  • Gaël Forget
Louise Rousselet
Scripps Institution of Oceanography, University of California, San Diego
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Paola Cessi
Scripps Institution of Oceanography, University of California, San Diego

Corresponding Author:[email protected]

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Gaël Forget
Massachusetts Institute of Technology
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Abstract

The origins of the upper branch of the Atlantic Meridional Overturning Circulation (AMOC) are traced with backward-in-time Lagrangian trajectories, quantifying the partition of volume transport between different routes of entry from the Indo-Pacific sector into the Atlantic. Particles are advected by a three-dimensional, incompressible velocity field from a recent release of “Estimating the Circulation and Climate of the Ocean’ (ECCOv4). This time-variable velocity field is a dynamically consistent interpolation of over one billion oceanographic observations collected between 1992 and 2015. Of the 13.6 Sverdrups (1Sv = $10^6$ m$^3$/s) of upper and intermediate water flowing northward across 6\mdeg S, 15% enters the Atlantic from Drake Passage, 35% enters from the straits between Asia and Australia, termed the Indonesian Throughflow, and 49% comes from the region south of Australia, termed the Tasman Leakage. The salinity budget shows that the AMOC exports freshwater out of the Atlantic.