The rate at which turbulent kinetic energy is dissipated influences growth, encounter probability, coagulation rates and vertical distribution of plankton. In this study we quantified the effectiveness with which boundary (wall) layer theory represents turbulent dissipation rates (E, W m-3) measured within natural surface mixing layers. This model explained 58 "/o of the variance in 818 literature-derived estimates of turbulent dissipation rates measured at 11 different geographic sites. The residual mean square error (RMSE) associated with the regression of loglo observed dissipation rate vs log,o predicted dissipation rate showed that ca 68 % of surface layer dissipation rates observed in nature were within a factor + 5.2-fold of dissipation rates estimated using boundary layer theory.Dissipation rates in more complex mixing environments, where turbulence was known to be caused by additional hydrographic phenomena (free convection, breaking of waves in the upper 1.5 m of the water column, current shear, upwelling), exceeded the boundary layer prediction by 1.5-to 26-fold depending on the mechanism associated with turbulence-generation. We found no evidence that turbulence near the surface (0 to 5 or 0 to 10 m) during high winds (27.5 or 2 10 m S -' ) was higher than the boundary layer prediction. When all data were combined into one data set, n = 1088), a multlple regression model having wind speed (W) and sampling depth ( 2 ) as inputs (log F = 2 6881og W -1.3221ogz -4.812) explained 54 % of the variance in surface layer turbulent dissipation rates (RMSE = + 5.5-fold). The potential for developing more precise empirical models of mixlng layer turbulent d~ssipation rates is h~g h and can be achieved by reporting wind conditions prior to, and during, turbulence measurements more thoroughly, and by collecting replicate turbulence profiles. The existing theoretical and empirical models are, however, adequate for many biological applications such as estimating the nature and magnitude of interactions among, and distributions of, many plankton taxa a s a result of wind forcing.
The energetics of six harbor seals in air at temperatures from 25 °C to −20 °C and in water from 25 °C to 0 °C was studied in animals acclimatized to summer conditions at Woods Hole, Mass. Over the above temperature range, the temperature of skin of the back cooled from about 35° to 1° with lowering temperature of the medium. Temperatures of the flippers were less dependent upon the surroundings than those of the body skin. The dependence of metabolism upon temperature was operative below 2 °C in air and below 20 °C in water (the critical temperatures), but the body skin temperature at these critical temperatures was the same, viz. 21 °C. Metabolism in air and in water was the same over the range of comparable skin temperatures. Body insulation was equal in air and in water at the respective critical temperatures. The insulation index of the air was approximately 20 times that of the water. Heat conductivity of living blubber to water averaged 2.5 cal/cm2/hr/°C, which exceeded that reported for dead blubber by about 50%.When compared with seals tested at St. Andrews during December, summer seals had a higher critical temperature, a lower body insulation index at the critical temperature, and a warmer body skin temperature for the same metabolic rate. No seasonal changes were found in thermoneutral metabolic rate, and no discernible changes in skin temperatures or in thermal gradients in the blubber.
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