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When we measure the Fresh Water Content of the ACC, we are measuring the combined effects of the coastal FWD, the wind mixing and any possible effects of Ekman transport. If you'll imagine a box that contains the coastal region, including the front, with the bulk of the fresh water sitting against the coast. This box extends 40 km offshore and from the surface to the bottom: this is our integration region. Downwelling winds offshore will tend to move fresh surface water onshore into our coastal box in the Ekman layer and this flow will be compensated by return flow at depth from the box to the offshore region. We have made annual estimates of the gain/loss of fresh water to our coastal current with three experiments, depending on where the return flow is taking place:

  1. Onshore Ekman transport is balanced by return flow in the middle of the water column at the outer edge of the front.
  2. Onshore flow is balanced by return in the bottom boundary layer at the outer edge of the front.
  3. Onshore flow is balanced by return subsurface flow inshore of the front.

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