Diapycnal mixing

While some of the nutrient stream nitrate originates in the southern hemisphere with SAMW, a fraction has recirculated within the subtropical gyre (Fig. 13.9B). Jenkins and Doney (2003) hypothesize a nutrient spiral in which enhanced diapycnal mixing associated with the eddy-rich, western boundary current also leads to a significant vertical transfer of nutrients (and other properties including helium) into the mixed-layer of the subtropical gyre. 

Diapycnal mixing occurs in a number of ways within the ocean. The mechanisms include (in no particular order) ... 

The penetration of tritium into the thermocline has been used to estimate vertical and diapycnal mixing rates. The first quantitative attempt was by Rooth and Ostlund (1972), who utilized an empirical relationship between bomb-tritium and temperature in the main thermocline to... 

Diapycnal mixing in the turbulent regime below the surface layer was estimated by a relation according to Osborne (1980), which is based on the balance between the shear turbulent production and the work on buoyancy forces and the dissipation rate assuming a constant Richardsson flux number. 

FIGURE 2.9 Averaged diapycnal mixing coefficients according to Equations 2.40 and 2.41. Vertical exchange coefficients estimated by the bulk method in the Baltic Sea (Matthaus, 1990b) at 75 m depth and Axell (1998) at 150 m depth and by dye tracer dispersion at about 300 m depth in the ocean thermocline by Ledwell et al. (1998). 

This suggests that a large fraction of the vertical salt flow through the halocline is maintained by turbulent diapycnal mixing and some additional vertical transport by entrainment by vertical convection and upwelling at the rim of the basin is likely. 

Gregg, M. C., 1987. Diapycnal mixing in the thennocline a review. Journal of Geophysical Research, 92(C5), 5249-5286. 

The trace metal flux caused by vertical diapycnal mixing accounted <0.5% for Pb, 6.4% for Cd, 8.5% for Zn, and —36% for Cu in relation to the external atmospheric input. The diapycnal flux played a subordinated role in the whole balance. The main sink for trace... 

Dependency of Diapycnal Mixing and Buoyancy Frequency from Tracer Release Experiments... 

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