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Llanillo, PJ, Pelegri JL, Talley LD, Pena-Izquierdo J, Cordero RR.  2018.  Oxygen pathways and budget for the Eastern South Pacific Oxygen Minimum Zone. Journal of Geophysical Research-Oceans. 123:1722-1744.   10.1002/2017jc013509   AbstractWebsite

Ventilation of the eastern South Pacific Oxygen Minimum Zone (ESP-OMZ) is quantified using climatological Argo and dissolved oxygen data, combined with reanalysis wind stress data. We (1) estimate all oxygen fluxes (advection and turbulent diffusion) ventilating this OMZ, (2) quantify for the first time the oxygen contribution from the subtropical versus the traditionally studied tropical-equatorial pathway, and (3) derive a refined annual-mean oxygen budget for the ESP-OMZ. In the upper OMZ layer, net oxygen supply is dominated by tropical-equatorial advection, with more than one-third of this supply upwelling into the Ekman layer through previously unevaluated vertical advection, within the overturning component of the regional Subtropical Cell (STC). Below the STC, at the OMZ's core, advection is weak and turbulent diffusion (isoneutral and dianeutral) accounts for 89% of the net oxygen supply, most of it coming from the oxygen-rich subtropical gyre. In the deep OMZ layer, net oxygen supply occurs only through turbulent diffusion and is dominated by the tropical-equatorial pathway. Considering the entire OMZ, net oxygen supply (3.8 +/- 0.42 mu mol kg(-1) yr(-1)) is dominated by isoneutral turbulent diffusion (56.5%, split into 32.3% of tropical-equatorial origin and 24.2% of subtropical origin), followed by isoneutral advection (32.0%, split into 27.6% of tropical-equatorial origin and 4.4% of subtropical origin) and dianeutral diffusion (11.5%). One-quarter (25.8%) of the net oxygen input escapes through dianeutral advection (most of it upwelling) and, assuming steady state, biological consumption is responsible for most of the oxygen loss (74.2%).

Abernathey, RP, Cerovecki I, Holland PR, Newsom E, Mazlo M, Talley LD.  2016.  Water-mass transformation by sea ice in the upper branch of the Southern Ocean overturning. Nature Geoscience. 9:596-+.   10.1038/ngeo2749   AbstractWebsite

Ocean overturning circulation requires a continuous thermodynamic transformation of the buoyancy of seawater. The steeply sloping isopycnals of the Southern Ocean provide a pathway for Circumpolar Deep Water to upwell from mid depth without strong diapycnal mixing(1-3), where it is transformed directly by surface fluxes of heat and freshwater and splits into an upper and lower branch(4-6). While brine rejection from sea ice is thought to contribute to the lower branch(7), the role of sea ice in the upper branch is less well understood, partly due to a paucity of observations of sea-ice thickness and transport(8,9). Here we quantify the sea-ice freshwater flux using the Southern Ocean State Estimate, a state-of-the-art data assimilation that incorporates millions of ocean and ice observations. We then use the water-mass transformation framework(10) to compare the relative roles of atmospheric, sea-ice, and glacial freshwater fluxes, heat fluxes, and upper-ocean mixing in transforming buoyancy within the upper branch. We find that sea ice is a dominant term, with differential brine rejection and ice melt transforming upwelled Circumpolar Deep Water at a rate of similar to 22 x 10(6) m(3) s(-1). These results imply a prominent role for Antarctic sea ice in the upper branch and suggest that residual overturning and wind-driven sea-ice transport are tightly coupled.

Brambilla, E, Talley LD, Robbins PE.  2008.  Subpolar Mode Water in the northeastern Atlantic: 2. Origin and transformation. Journal of Geophysical Research-Oceans. 113   10.1029/2006jc004063   AbstractWebsite

The processes that lead to the transformation and origin of the eastern North Atlantic Subpolar Mode Waters (SPMW) are investigated from observational data using an extended Walin framework. Air-sea flux data from the National Oceanography Center, Southampton (NOCS), and hydrographic data from the A24 cruise collected during the World Ocean Circulation Experiment (WOCE) are used to estimate the contribution of diapycnal and isopycnal fluxes to the density classes that include SPMW. Surface diapycnal volume flux is the dominant source of waters in the SPMW density. In the North Atlantic subpolar gyre the diapycnal volume flux occurs along the main branches of the North Atlantic Current (NAC) and it has an average transport of 14 +/- 6.5 Sv, with a maximum of 21.5 Sv across the 27.35(sigma theta) isopycnal. The regional distribution of the diapycnal flux on isopycnal surfaces is computed to identify the areas with the largest diapycnal flux. These regions coincide with the location of SPMW based on potential vorticity. The surface diapycnal flux is associated with obduction and subduction through the permanent pycnocline. Therefore, the water involved in the transformation of SPMWs is continuously exchanged with the ocean interior. In addition, we suggest that subduction is not associated with smooth advection from the mixed layer to the ocean interior, but is water mass loss entrainment into the deep overflows of the subpolar gyre. The isopycnal component of the SPMW throughput is estimated from the geostrophic transport across the A24 section from Greenland to Scotland and is 10% to 40% of the diapycnal flux.

Yun, JY, Talley LD.  2003.  Cabbeling and the density of the North Pacific Intermediate Water quantified by an inverse method. Journal of Geophysical Research-Oceans. 108   10.1029/2002jc001482   AbstractWebsite

North Pacific Intermediate Water (NPIW), defined as the main salinity minimum in the subtropical North Pacific, at a density of 26.7-26.8sigma(theta), is denser than the winter surface water in the Oyashio which is the source of the salinity minimum. We showed previously that cabbeling and double diffusion during mixing between the Oyashio water and more saline Kuroshio water can account for the density increase from the surface source water to the salinity minimum. An inverse method is employed herein to quantify the effect of cabbeling, using CTD data from the western North Pacific. The difference between proportional mixing between parcels of Oyashio and Kuroshio waters and mixing along isopycnals is exploited to compute the convergence of water into density layers. The diapycnal transport convergence associated with cabbeling into the NPIW density layer is estimated to be 0.56 Sv for an assumed turnover time of 1 year in the region between 142degreesE and 152degreesE. Diapycnal transport convergences in the regions 152degreesE-165degreesE, 165degreesE-175degreesW, and 175degreesW-136degreesW are similarly estimated by assuming longer turnover times. We estimate that the total diapycnal transport convergence into the NPIW density layer may be up to 2.3 Sv in the entire NPIW region.

Talley, LD.  1993.  Distribution and Formation of North Pacific Intermediate Water. Journal of Physical Oceanography. 23:517-537.   10.1175/1520-0485(1993)023<0517:dafonp>;2   AbstractWebsite

The North Pacific Intermediate Water (NPIW), defined as the main salinity minimum in the subtropical North Pacific, is examined with respect to its overall property distributions. These suggest that NPIW is formed only in the northwestern subtropical gyre; that is, in the mixed water region between the Kuroshio Extension and Oyashio front. Subsequent modification along its advective path increases its salinity and reduces its oxygen. The mixed water region is studied using all bottle data available from the National Oceanographic Data Center, with particular emphasis on several winters. Waters from the Oyashio, Kuroshio, and the Tsugaru Warm Current influence the mixed water region, with a well-defined local surface water mass formed as a mixture of the surface waters from these three sources. Significant salinity minima in the mixed water region are grouped into those that are directly related to the winter surface density and are found at the base of the oxygen-saturated surface layer, and those that form deeper, around warm core rings. Both could be a source of the more uniform NPIW to the east, the former through preferential erosion of the minima from the top and the latter through simple advection. Both sources could exist all year with a narrowly defined density range that depends on winter mixed-layer density in the Oyashio region.