This work was stimulated by conversations with E. Firing, W. Kessler, J. McCreary, D. Rowe, and, as always, L. Thompson. E. Firing, W. Kessler, J. McCreary, and an anonymous review all helped to improve the manuscript. K. McTaggart helped with calibration and processing of CTD data. This work was funded by the NOAA Office of Oceanic and Atmospheric Research, the NOAA Office of Global Programs, and the NASA Physical Oceanography Program.
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