Double Diffusive Intrusions, Mixing and Deep Sea Convection Processes in the Black Sea

Abstract

Hydrographic measurements obtained during Leg 4 oceanographic expedition of the RV Knorr in the Black Sea point to important processes deserving scientific attention. The destabilizing effects of the cooling near the surface and the influx of geothermal heat at the bottom combined with the stable salinity gradients provide an environment suitable for double-diffusion in the water column. The hydrographic data do not provide any evidence for the replenishment of the bottom water by the inflowing Mediterranean waters. On the other hand, there is clear evidence that the renewal of intermediate waters takes place at or below the pycnocline level by the transformed intrusion waters. Temperature-salinity anomalies at the shelf break demonstrate that the Mediterranean water mixes with the ambient cold intermediate waters and then sinks in the form of a plume with high aspect ratio. Later, horizontal transport of water in the form of multiple layers with anomalous properties is often evident and is also traced by the transport of suspended matter from the continental slope towards the interior region of the Black Sea. The geothermal heating gives rise to the convective turnover of the deep waters in a bottom mixing layer. The extent and features of this convective layer are quite unique. On the other hand, models derived from laboratory experiments and the available theory appear to be insufficient to describe its evolutionary aspects. The identification of such unique physical processes in the Black Sea make it an ideal environment for scientific studies of these processes, as well as providing new insights into some of its chemical, and sedimentological puzzles.