Measurements of turbulence in the Denmark Strait overflow

A new tool is developed to provide deep ocean microstructure measurements in combination with standard CTD profiling/water sampling with only a minor increase in deployment time. A microstructure probe is mounted on a standard Rosette system like a sampling bottle. The probe is carried down to a proper depth attached to the Rosette that is performing water sampling and CTD profiling. When the desired depth is reached, the probe is detached from the Rosette using the bottle firing system and begins microstructure measurements in free-falling mode. During its free fall, the probe remains linked with the Rosette by a serviceable thin flexible cord to provide fast recovery. The cord does not disturb the free falling owing to free running from the probe. Turbulent velocity fluctuations are measured by an airfoil sensor. Such regime of microstructure measurements was realized in a cruise of R/V «Maria S. Merian», May-June 2009, performed under the EU 7th Framework Programme Priority Project «Thermohaline Overturning — at Risk?» (THOR). The microstructure measurements were done in the course of CTD surveying of the Danish Strait overflow. Bottom intrusion of cold/dense overflow water propagating downhill from the Danish Strait Sill was found to be characterized by a high level of turbulent velocity fluctuations while in the above lying layers the turbulence was suppressed.