The thermal structure of the Upper Ocean

G̀iulio Boccaletti, Ronald C. Pacanowski, S. George H. Philander, Alexey V. Fedorov

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Abstract

The salient feature of the oceanic thermal structure is a remarkably shallow thermocline, especially in the Tropics and subtropics. What factors determine its depth? Theories for the deep thermohaline circulation provide an answer that depends on oceanic diffusivity, but they deny the surface winds an explicit role. Theories for the shallow ventilated thermocline take into account the influence of the wind explicitly, but only if the thermal structure in the absence of any winds, the thermal structure along the eastern boundary, is given. To complete and marry the existing theories for the oceanic thermal structure, this paper invokes the constraint of a balanced heat budget for the ocean. The oceanic heat gain occurs primarily in the upwelling zones of the Tropics and subtrupics and depends strongly on oceanic conditions, specifically the depth of the thermocline. The heat gain is large when the thermocline is shallow but is small when the thermocline is deep. The constraint of a balanced heat budget therefore implies that an increase in heat loss in high latitudes can result in a shoaling of the tropical thermocline; a decrease in heat loss can cause a deepening of the thermocline. Calculations with an idealized general circulation model of the ocean confirm these inferences. Arguments based on a balanced heat budget yield an expression for the depth of the thermocline in terms of parameters such as the imposed surface winds, the surface temperature gradient, and the oceanic diffusivity. These arguments in effect bridge the theories for the ventilated thermocline and the thermohaline circulation so that previous scaling arguments are recovered as special cases of a general result.

Original languageEnglish (US)
Pages (from-to)888-902
Number of pages15
JournalJournal of Physical Oceanography
Volume34
Issue number4
DOIs
StatePublished - Apr 1 2004

All Science Journal Classification (ASJC) codes

  • Oceanography

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    Boccaletti, G., Pacanowski, R. C., Philander, S. G. H., & Fedorov, A. V. (2004). The thermal structure of the Upper Ocean. Journal of Physical Oceanography, 34(4), 888-902. https://doi.org/10.1175/1520-0485(2004)034<0888:TTSOTU>2.0.CO;2