motions in the surface and bottom boundary layers. And, of course, the fluxes also are effected by the possible interactions among all of these phenomena and in their relationships with the large-scale circulation and stratification. In the general circulation models, these fluxes are represented by parameterizations of well-known equations, and they are designed and evaluated on the basis of theory, measurement, and fine-scale simulation. To further improve ocean parameterizations, there are two ocean mixing CPTs in addition to the aforementioned cloud-feedbacks CPT—one studies the interaction of eddies and the surface boundary layer, and the other studies the bottom boundary layer as a gravity current. A recent essay (Schopf et al., 2003) commissioned by U.S. CLIVAR in developing a plan for these CPTs surveys the relevant processes and the status of their understanding and parameterization.

The oceanic and terrestrial ecosystems are important functional elements of Earth’s system. For instance, the ocean’s biogeochemical cycling of nitrogen, carbon, oxygen, and so forth is carried out by the lower trophic levels from viruses through plankton. In large-scale models this is represented as transport, reaction, and population dynamics. For the most part, the model rules for these ecosystem dynamics are acts of imagination, usually involving abstraction of actual organisms to hypothesized generic forms but guided by overall conservation principles. Such constructs are exceedingly difficult to evaluate except at the gross level of chemical distributions and fluxes, both because of their organismic unreality and the technical measurement challenges of highly variable compositions with quite heterogeneous distributions.

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