Small‐scale physics of the ocean

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Abstract
Four years ago, we noted that, although there was a widespread belief that the key to many ocean processes must be the communication of energy by internal waves, there had been little progress in definitely relating small‐scale processes to internal waves (Caldwell, 1983a). For example, although it seemed plausible that the energy that supplies spots of turbulence in the thermocline is delivered to those spots by internal waves, the process had neither been directly observed nor shown theoretically in a verifiable calculation. In the past four years there has been some progress; observations have been made which render such connections more plausible and some theoretical ideas have been advanced, but we've seen no breakthrough in this direction.Instead, progress has come on other fronts. Our picture of turbulent processes in the upper ocean, especially in the equatorial ocean, is becoming more clear (and more complicated). Strong downdrafts in the mixed layer have been discovered. Dissipation in the convective mixed layer has been found to scale very much as it does in similar layers in the atmosphere. The dynamics of intrusions have drawn attention because they may contribute a good deal of the mixing of the oceans. Although significant laboratory experiments are now available, controversy remains concerning the application of laboratory turbulence concepts to the ocean. Bottom‐layer flows have now been carefully defined. One notable development is the increased interest in the effect of mixing conditions on biological activity. Our instrumentation is becoming more routinely deployable, an important step toward obtaining the large amount of sampling required to form a reasonably accurate picture of small‐scale processes in the ocean.