Diapycnal Mixing in the Bransfield Strait

During the austral midsummer near the South Shetland Islands, an interdisciplinary cruise (COUPLING) was carried out in January 2010 (Sangrà et al, 2014). For this study we selected one transect of 12 stations across the Central Bransfield Strait with vertical profiles of Conductivity, Temperature and Depth (CTD) and Acoustic Doppler Current Profiler (ADCP). Vertical profiles of microstructure turbulence were measured at stations of the transect located in specific dynamic features (two fronts: Bransfield Front and Peninsula Front; and an anticyclonic eddy) from a free-fall turbulence profiler. Using CTD and ADCP data, we computed the Thorpe scales, gradient Richardson numbers and density ratios that were compared with microstructure data.

We found that the most active turbulent layer was observed within the upper mixed layer (UML) of the anticyclonic eddy between stations 3 and 6 of the transect. However, intense inversions below the UML were found at the axis of the Peninsula Front (station 9). In the region of the Bransfield Front, it is noteworthy that there were obtained relative high values of kinetic energy dissipation rate (ε) with mixing processes due to vertical shear instabilities and double diffusion.  With this work, we have a deeper understanding of the mixing processes in the Bransfield Strait, which will allow a better estimation of the vertical fluxes of heat, salt and nutrients for this region.

Key words:

Bransfield Strait, Diapycnal Mixing, Microstructure Turbulence.

References:

Sangrà, P., C. García-Muñoz, C.M. García, A. Marrero-Díaz, C. Sobrino, B. Mouriño-Carballido, B. Aguiar-González, C. Henríquez-Pastene, A. Rodríguez-Santana, L. M. Lubián, M. Hernández-Arencibia, S. Hernández-León, E. Vázquez, S.N. Estrada-Allis (2014). Coupling between upper ocean layer variability and size-fractionated phytoplankton in a non-nutrient-limited environment. Marine Ecology Progress Series, 499, 35-46.