FN Archimer Export Format
PT J
TI Mixing and Transformation in a Deep Western Boundary Current: A Case Study
BT 
AF Spingys, Carl P.
   Naveira Garabato, Alberto C.
   Legg, Sonya
   Polzin, Kurt L.
   Abrahamsen, E. Povl
   Buckingham, Christian
   Forryan, Alexander
   Frajka-Williams, Eleanor E.
AS 1:1;2:1;3:2;4:3;5:4;6:5;7:1;8:6;
FF 1:;2:;3:;4:;5:;6:;7:;8:;
C1 Ocean and Earth Science, National Oceanography Centre, University of Southampton, Southampton, UK
   National Oceanic and Atmospheric Administration Geophysical Fluid Dynamics Laboratory and Atmospheric and Oceanic Sciences Program, Princeton University, Princeton, USA
   Department of Physical Oceanography, Woods Hole Oceanographic Institution, Woods Hole, USA
   Polar Oceans, British Antarctic Survey, Cambridge, UK
   Laboratoire d’Oceanographie Physique et Spatiale, CNRS, IRD, Ifremer, UBO, Plouzané, FR
   National Oceanography Centre, Southampton, UK
C2 NOC, UK
   NOAA, USA
   WHOI, USA
   BRITISH ANTARCTIC SURVEY, UK
   UBO, FRANCE
   NOC, UK
UM LOPS
IN WOS Cotutelle UMR
   copubli-europe
   copubli-int-hors-europe
IF 3.806
TC 13
UR https://archimer.ifremer.fr/doc/00677/78887/81183.pdf
LA English
DT Article
DE ;Bottom currents;Diapycnal mixing;Turbulence;Southern Ocean;Abyssal circulation
AB Water-mass transformation by turbulent mixing is a key part of the deep-ocean overturning, as it drives the upwelling of dense waters formed at high latitudes. Here, we quantify this transformation and its underpinning processes in a small Southern Ocean basin: the Orkney Deep. Observations reveal a focussing of the transport in density space as a deep western boundary current (DWBC) flows through the region, associated with lightening and densification of the current’s denser and lighter layers, respectively. These transformations are driven by vigorous turbulent mixing. Comparing this transformation with measurements of the rate of turbulent kinetic energy dissipation indicates that, within the DWBC, turbulence operates with a high mixing efficiency, characterized by a dissipation ratio of 0.6 to 1 that exceeds the common value of 0.2. This result is corroborated by estimates of the dissipation ratio from microstructure observations. The causes of the transformation are unravelled through a decomposition into contributions dependent on the gradients in density space of the: dianeutral mixing rate, isoneutral area, and stratification. The transformation is found to be primarily driven by strong turbulence acting on an abrupt transition from the weakly-stratified bottom boundary layer to well-stratified off-boundary waters. The reduced boundary-layer stratification is generated by a downslope Ekman flow associated with the DWBC’s flow along sloping topography, and is further regulated by submesoscale instabilities acting to re-stratify near-boundary waters. Our results provide observational evidence endorsing the importance of near-boundary mixing processes to deep-ocean overturning, and highlight the role of DWBCs as hot spots of dianeutral upwelling. 
PY 2021
PD APR
SO Journal Of Physical Oceanography
SN 0022-3670
PU American Meteorological Society
VL 51
IS 4
UT 000644279200014
BP 1205
EP 1222
DI 10.1175/JPO-D-20-0132.1
ID 78887
ER

EF