Flow and Mixing in the Rift Valley of the Mid-Atlantic Ridgeстатья из журнала
Аннотация: High levels of diapycnal mixing and geothermal heating near midocean ridges contribute to the buoyancy fluxes that are required to close the global circulation. In topographically confined areas, such as the deep median valleys of slow-spreading ridges, these fluxes strongly influence the local hydrography and dynamics. Data from a segment-scale hydrographic survey of the rift valley of the Mid-Atlantic Ridge and from an array of current meters deployed there during an entire year are analyzed in order to characterize the dominant hydrographic patterns and dynamical processes. Comparison with historic hydrographic data indicates that the temporal variability during the last few decades has been small compared to the observed segment-scale gradients. The rift valley circulation is characterized by inflow from the eastern ridge flank and persistent unidirectional along-segment flow into a cul-de-sac. Therefore, most of the water flowing along the rift valley upwells within the segment with a mean vertical velocity >10−5 m s−1. The observed streamwise hydrographic gradients indicate that diapycnal mixing dominates the rift valley buoyancy fluxes by more than an order of magnitude, in spite of the presence of a large hydrothermal vent field supplying several gigawatts of heat to the water column. Hydrographic budgets in the rift valley yield diffusivity values of order 5 × 10−3 m2 s−1, consistent with estimates derived from statically unstable overturns, the largest of which were observed downstream of topographic obstacles in the path of the along-segment flow. This suggests vertical shear associated with cross-sill flows as the dominant contributor to the mechanical mixing in the rift valley.
Год издания: 2002
Авторы: Andreas M. Thurnherr, Kelvin J Richards, Christopher R. German, Gregory F. Lane‐Serff, K. G. Speer
Издательство: American Meteorological Society
Источник: Journal of Physical Oceanography
Ключевые слова: Oceanographic and Atmospheric Processes, Geology and Paleoclimatology Research, Geological formations and processes
Открытый доступ: bronze
Том: 32
Выпуск: 6
Страницы: 1763–1778