Spatial and Temporal Patterns of Small-Scale Mixing in Drake Passage

• Published in: Journal of Physical Oceanography
• Main Authors: Thompson, Andrew F., Gille, Sarah T., MacKinnon, J. A., Sprintall, Janet
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: American Meteorological Society 2007
• Subjects: Mixing; Eddy diffusivity; Turbulence; Strain; Thermohaline intrusions; Drake Passage
• Online Access: https://doi.org/10.1175/JPO3021.1

Temperature and salinity profiles obtained with expendable CTD probes throughout Drake Passage between February 2002 and July 2005 are analyzed to estimate turbulent diapycnal eddy diffusivities to a depth of 1000 m. Diffusivity values are inferred from density/temperature inversions and internal wave vertical strain. Both methods reveal the same pattern of spatial variability across Drake Passage; diffusivity estimates from inversions exceed those from vertical strain by a factor of 3 over most of Drake Passage. The Polar Front (PF) separates two dynamically different regions. Strong thermohaline intrusions characterize profiles obtained north of the PF. South of the PF, stratification is determined largely by salinity, and temperature is typically unstably stratified between 100- and 600-m depth. In the upper 400 m, turbulent diapycnal diffusivities are O(10^(−3) m2 s^(−1)) north of the PF but decrease to O(10^(−4) m2 s^(−1)) or smaller south of the PF. Below 400 m diffusivities typically exceed 10^(−4) m^2 s^(−1). Diffusivities decay weakly with depth north of the PF, whereas diffusivities increase with depth and peak near the local temperature maximum south of the PF. The meridional pattern in near-surface mixing corresponds to local maxima and minima of both wind stress and wind stress variance. Near-surface diffusivities are also found to be larger during winter months north of the PF. Wind-driven near-inertial waves, strong mesoscale eddy activity, and double-diffusive convection are suggested as possible factors contributing to observed mixing patterns © 2007 American Meteorological Society. Manuscript received 9 November 2005, in final form 26 June 2006. XBT and XCTD sampling in Drake Passage is performed with the assistance of NSFsupported Raytheon Polar Services personnel and other cruise participants. Their support is appreciated and essential to the continued success of the sampling program. We thank Alberto Naveira Garabato both for conversations that led us to pursue this study and ...