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Schaffer, Janin; Kanzow, Torsten; Jochumsen, Kerstin; Lackschewitz, Klas Sven; Tippenhauer, Sandra; Zhurbas, Victor M; Quadfasel, Detlef (2016): Physical oceanography, current meter data, and microstructure measurements 180 km downstream of Denmark Strait sill during Maria S. Merian cruise MSM21/1b. PANGAEA,, Supplement to: Schaffer, J et al. (2016): Enhanced turbulence driven by mesoscale motions and flow-topography interaction in the Denmark Strait Overflow plume. Journal of Geophysical Research: Oceans, 121(10), 7650-7672,

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The Denmark Strait Overflow (DSO) contributes roughly half to the total volume transport of the Nordic overflows. The overflow increases its volume by entraining ambient water as it descends into the subpolar North Atlantic, feeding into the deep branch of the Atlantic Meridional Overturning Circulation. In June 2012, a multiplatform experiment was carried out in the DSO plume on the continental slope off Greenland (180 km downstream of the sill in Denmark Strait), to observe the variability associated with the entrainment of ambient waters into the DSO plume. In this study, we report on two high-dissipation events captured by an autonomous underwater vehicle (AUV) by horizontal profiling in the interfacial layer between the DSO plume and the ambient water. Strong dissipation of turbulent kinetic energy of O(10**-6) W/kg was associated with enhanced small-scale temperature variance at wavelengths between 0.05 and 500 m as deduced from a fast-response thermistor. Isotherm displacement slope spectra reveal a wave number-dependence characteristic of turbulence in the inertial-convective subrange ( math formula) at wavelengths between 0.14 and 100 m. The first event captured by the AUV was transient, and occurred near the edge of a bottom-intensified energetic eddy. Our observations imply that both horizontal advection of warm water and vertical mixing of it into the plume are eddy-driven and go hand in hand in entraining ambient water into the DSO plume. The second event was found to be a stationary feature on the upstream side of a topographic elevation located in the plume pathway. Flow-topography interaction is suggested to drive the intense mixing at this site.
Median Latitude: 65.196526 * Median Longitude: -28.933681 * South-bound Latitude: 64.219670 * West-bound Longitude: -31.444500 * North-bound Latitude: 66.399330 * East-bound Longitude: -22.412000
Date/Time Start: 2012-06-09T13:00:00 * Date/Time End: 2012-06-21T10:37:00
The main objectives of the cruise MSM21/1b were to characterize the spatio-temporal variability of the Denmark Strait overflow and to identify processes responsible for the exchange of the overflow plume with ambient water downstream of Denmark Strait. A multi-platform approach was taken to achieve the goals, based on moorings, an autonomous underwater vehicle (AUV), as well as lowered and vessel-mounted observations. From these platforms, measurements of temperature, salinity, dissolved oxygen, current velocity, dissipation of turbulent kinetic energy, and bottom pressure were obtained.
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