Turbulent Mixing Under Drifting Pack Ice in the Weddell Sea

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Science  14 Jan 1994:
Vol. 263, Issue 5144, pp. 218-221
DOI: 10.1126/science.263.5144.218


By providing cold, dense water that sinks and mixes to fill the abyssal world ocean, high-latitude air-sea-ice interaction is the main conduit through which the deep ocean communicates with the rest of the climate system. A key element in modeling and predicting oceanic impact on climate is understanding the processes that control the near surface exchange of heat, salt, and momentum. In 1992, the United States—Russian Ice Station Weddell-1 traversed the western Weddell Sea during the onset of winter, providing a platform for direct measurement of turbulent heat flux and Reynolds stress in the upper ocean. Data from a storm early in the drift indicated (i) well-formed Ekman spirals (in both velocity and turbulent stress); (ii) high correlation between mixed layer heat flux and temperature gradients; (iii) that eddy viscosity and eddy thermal diffusivity were similar, about 0.02 square meters per second; and (iv) that the significant turbulent length scale (2 to 3 meters through most of the boundary layer) was proportional to the wavelength at the peak in the weighted vertical velocity spectrum. The measurements were consistent with a simple model in which the bulk eddy viscosity in the neutrally buoyant mixed layer is proportional to kinematic boundary stress divided by the Coriolis parameter.