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2002 ; Badin and Williams 2010 ; Downes et al. 2011 ; Cerovečki et al. 2013 ). Here, we directly diagnose not only formation by surface buoyancy fluxes, but also formation by diapycnal ocean mixing. This is facilitated by the fact that the SOSE potential temperature θ and salinity S budgets are exactly closed and that all the terms in these budgets have been archived. Following Iudicone et al. (2008b) , we combined the SOSE θ and S budgets to obtain a potential density budget that can
2002 ; Badin and Williams 2010 ; Downes et al. 2011 ; Cerovečki et al. 2013 ). Here, we directly diagnose not only formation by surface buoyancy fluxes, but also formation by diapycnal ocean mixing. This is facilitated by the fact that the SOSE potential temperature θ and salinity S budgets are exactly closed and that all the terms in these budgets have been archived. Following Iudicone et al. (2008b) , we combined the SOSE θ and S budgets to obtain a potential density budget that can
Deep Water (CDW) along poleward-shoaling isoneutrals, and isoneutral-following, northward downwelling of denser Antarctic Bottom Water (AABW) and of lighter Subantarctic Mode Water (SAMW) and Antarctic Intermediate Water (AAIW). Water mass transformations [defined here as transfers of water between adjacent potential temperature–salinity ( θ – S ) classes] are commonly assumed to be confined to the surface mixed layer. This assumption, however, appears at odds with the observation of widespread
Deep Water (CDW) along poleward-shoaling isoneutrals, and isoneutral-following, northward downwelling of denser Antarctic Bottom Water (AABW) and of lighter Subantarctic Mode Water (SAMW) and Antarctic Intermediate Water (AAIW). Water mass transformations [defined here as transfers of water between adjacent potential temperature–salinity ( θ – S ) classes] are commonly assumed to be confined to the surface mixed layer. This assumption, however, appears at odds with the observation of widespread
instruments. The locations of these stations are shown as red stars in Fig. 1 . In optimal conditions, we would compare the microstructure κ estimates against separate finescale κ estimates derived from HRP2/DMP, CTD, and XCTD density profiles. However, the HRP2 microstructure profiler suffered from salinity spiking issues, for which a correction has not yet been determined (L. C. St. Laurent 2012, personal communication). We considered using temperature profiles below the subsurface temperature
instruments. The locations of these stations are shown as red stars in Fig. 1 . In optimal conditions, we would compare the microstructure κ estimates against separate finescale κ estimates derived from HRP2/DMP, CTD, and XCTD density profiles. However, the HRP2 microstructure profiler suffered from salinity spiking issues, for which a correction has not yet been determined (L. C. St. Laurent 2012, personal communication). We considered using temperature profiles below the subsurface temperature
. The role of double-diffusive instability in driving mixing in the Southern Ocean has not been addressed using microstructure measurements. Studies focusing on the intrusive water mass characteristics in this region suggested that double-diffusive instability could be important to the dynamics ( Joyce et al. 1978 ; Toole and Georgi 1981 ; You 2002 ), but a comprehensive effort to study this using direct fine- and microstructure temperature T and salinity S has been missing. This work seeks to
. The role of double-diffusive instability in driving mixing in the Southern Ocean has not been addressed using microstructure measurements. Studies focusing on the intrusive water mass characteristics in this region suggested that double-diffusive instability could be important to the dynamics ( Joyce et al. 1978 ; Toole and Georgi 1981 ; You 2002 ), but a comprehensive effort to study this using direct fine- and microstructure temperature T and salinity S has been missing. This work seeks to
1. Introduction In the middle of the twentieth century, the prevailing view of the ocean circulation below the main pycnocline was that deep and bottom waters were subject to a wide-scale upwelling of order 10 −7 m s −1 ( Stommel and Arons 1960 ; Wyrtki 1961 ; and others). The implication of a diapycnal diffusivity of 10 −4 m 2 s −1 then followed from the idea that observed vertical profiles of temperature, salinity, radioisotopes, and oxygen between 1000- and 4000-m depth were maintained
1. Introduction In the middle of the twentieth century, the prevailing view of the ocean circulation below the main pycnocline was that deep and bottom waters were subject to a wide-scale upwelling of order 10 −7 m s −1 ( Stommel and Arons 1960 ; Wyrtki 1961 ; and others). The implication of a diapycnal diffusivity of 10 −4 m 2 s −1 then followed from the idea that observed vertical profiles of temperature, salinity, radioisotopes, and oxygen between 1000- and 4000-m depth were maintained
collected in December 2010 are contoured. The TerrainBase dataset was created by the National Geophysical Data Center and World Data Center-A for Solid Earth Geophysics in Boulder, Colorado. The moorings comprised a series of paired current meters and Seabird MicroCAT instruments (measuring temperature, pressure, and salinity) at different depths, with the most heavily instrumented C mooring having 12 such pairs ( Table 1 ). Unfortunately, owing to a large mooring knockdown event in late January 2010
collected in December 2010 are contoured. The TerrainBase dataset was created by the National Geophysical Data Center and World Data Center-A for Solid Earth Geophysics in Boulder, Colorado. The moorings comprised a series of paired current meters and Seabird MicroCAT instruments (measuring temperature, pressure, and salinity) at different depths, with the most heavily instrumented C mooring having 12 such pairs ( Table 1 ). Unfortunately, owing to a large mooring knockdown event in late January 2010
assumption we do not wish to make here, as one of the goals of this work is to examine the relative contributions of geostrophic and ageostrophic terms to vertical flow. We thus chose to linearly interpolate measurements of potential temperature θ , salinity S , u , and υ onto surfaces of constant pressure at 100-dbar intervals and confined our analysis to the part of the water column that had measurements at all times (i.e., depths greater than 1300 m). However, we did test the sensitivity of our
assumption we do not wish to make here, as one of the goals of this work is to examine the relative contributions of geostrophic and ageostrophic terms to vertical flow. We thus chose to linearly interpolate measurements of potential temperature θ , salinity S , u , and υ onto surfaces of constant pressure at 100-dbar intervals and confined our analysis to the part of the water column that had measurements at all times (i.e., depths greater than 1300 m). However, we did test the sensitivity of our
produced by the motion of seawater through Earth’s magnetic field ( Sanford et al. 2005 ). The floats are autonomous and typically collect about 300 vertical profiles before exhausting battery power. The data are relayed back for processing through the Iridium satellite network. In addition to velocity measurements, the floats are equipped with a Sea-Bird Electronics SBE 41 CTD. The floats record horizontal velocity, conductivity, salinity, and pressure every 25 s, corresponding to a depth resolution
produced by the motion of seawater through Earth’s magnetic field ( Sanford et al. 2005 ). The floats are autonomous and typically collect about 300 vertical profiles before exhausting battery power. The data are relayed back for processing through the Iridium satellite network. In addition to velocity measurements, the floats are equipped with a Sea-Bird Electronics SBE 41 CTD. The floats record horizontal velocity, conductivity, salinity, and pressure every 25 s, corresponding to a depth resolution
. (a) AVISO geostrophic eddy current speeds (EKE 1/2 ) and (b) modeled eddy current speeds. The EKE is defined as the temporal fluctuation about the averages shown in Fig. 3 . a. Comparison of the model with observations We begin by comparing the Drake Passage transports, eddy kinetic energy (EKE), and temperature–salinity hydrography with the Drake Patch simulation. The model vertically integrated zonal transport across the Drake Passage has a mean of 152 Sverdrups (Sv; 1 Sv ≡ 10 6 m 3 s −1
. (a) AVISO geostrophic eddy current speeds (EKE 1/2 ) and (b) modeled eddy current speeds. The EKE is defined as the temporal fluctuation about the averages shown in Fig. 3 . a. Comparison of the model with observations We begin by comparing the Drake Passage transports, eddy kinetic energy (EKE), and temperature–salinity hydrography with the Drake Patch simulation. The model vertically integrated zonal transport across the Drake Passage has a mean of 152 Sverdrups (Sv; 1 Sv ≡ 10 6 m 3 s −1
depth-independent velocity that is added back to the relative velocity. This method also provides an estimate for subsurface float position ( x , y ), in meters, in the zonal and meridional direction from the point of descent. In situ and potential density as well as buoyancy frequency were calculated from CTD temperature, salinity, and pressure measurements using the International Thermodynamic Equation Of Seawater—2010 (TEOS-10; IOC et al. 2010 ). Smooth reference potential density profiles
depth-independent velocity that is added back to the relative velocity. This method also provides an estimate for subsurface float position ( x , y ), in meters, in the zonal and meridional direction from the point of descent. In situ and potential density as well as buoyancy frequency were calculated from CTD temperature, salinity, and pressure measurements using the International Thermodynamic Equation Of Seawater—2010 (TEOS-10; IOC et al. 2010 ). Smooth reference potential density profiles
