Maureen A. Kennelly

Mediterranean outflow mixing and dynamics

The Mediterranean Sea produces a salty, dense outflow that is strongly modified by entrainment as it first begins to descend the continental slope in the eastern Gulf of Cadiz. The current accelerates to 1.3 meters per second, which raises the internal Froude number above 1, and is intensely turbulent through its full thickness. The outflow loses about half of its density anomaly and roughly doubles its volume transport as it entrains less saline North Atlantic Central water. Within 100 kilometers downstream, the current is turned by the Coriolis force until it flows nearly parallel to topography in a damped geostrophic balance. The mixed Mediterranean outflow continues westward, slowly descending the continental slope until it becomes neutrally buoyant in the thermocline where it becomes an important water mass.

The Depth Dependence of Shear Finestructure off Point Arena and near Pioneer Seamount

Abstract High-resolution velocity profiles to depths of 1600 m were collected off Point Arena and near Pioneer Seamount, California. They reveal shear increasing with depth relative to the GM76 model spectrum. Using an empirical parameterization found to collapse microstructure data the “dissipation rate” and “eddy diffusivity” are estimated from these shears. Away from the seamount, dissipation rates are depth invariant at 3–6(×10−10 W kg−1). As a result, the eddy diffusivity increases with depth, approaching 0.2–0.3(×10−4 m2 s−1) below 1200-m depth. This may be a result of the proximity of the continental rise and sloping topography, but there is evidence that it is a general result for the abyssal ocean. Immediately above the seamount, there is a 300–400-m thick layer of elevated shear, corresponding to an eddy diffusivity of ∼ 10−4 m2 s−1. If this localized enhancement is typical of seamounts, topographically induced mixing is insufficient to significantly modify global average mixing.