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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.

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Billheimer, S, Talley LD.  2016.  Annual cycle and destruction of Eighteen Degree Water. Journal of Geophysical Research-Oceans. 121:6604-6617.   10.1002/2016jc011799   AbstractWebsite

Eighteen Degree Water (EDW), the subtropical mode water of the western North Atlantic, is a voluminous, weakly stratified upper ocean water mass that acts as a subsurface reservoir of heat, nutrients, and CO2. This thick layer persists throughout the year, but nearly half of its volume is dispersed or mixed away, diffusing its properties into the thermocline, from the time it outcrops in winter until it is renewed the following year. CTD observations from Argo profiling floats and acoustically tracked, isothermally bound profiling floats are used to quantify EDW destruction rates and investigate the relevant processes responsible for the large annual cycle of EDW. EDW destruction occurs primarily at the top of the EDW layer, with the highest EDW destruction rates occurring during early summer. Slower, steadier EDW destruction is observed in early winter. EDW destruction is dominated by 1-D vertical diffusion, while mesoscale, along-isopycnal stirring is also significant, explaining approximately 1/3 of the total annual EDW destruction. Destruction via along-isopycnal processes is more prevalent near the Gulf Stream than in the southern Sargasso Sea, due to higher potential vorticity gradients and enhanced mesoscale activity.

Bingham, FM, Talley LD.  1991.  Estimates of Kuroshio Transport Using an Inverse Technique. Deep-Sea Research Part a-Oceanographic Research Papers. 38:S21-S43.   10.1016/S0198-0149(12)80003-3   AbstractWebsite

Two CTD/hydrographic sections across the Kuroshio were combined using an inverse technique to estimate the absolute transport. The hydrographic data were obtained as part of a transpacific section across 24-degrees-N in 1985. The inverse technique treats the two sections as ends of a channel and conserves mass flowing into and out of the channel as a whole and within certain discrete layers. The strong topographic constraints imposed by the region of the East China Sea resulted in transport estimates independent of the initial reference level for the geostrophic calculation. The calculated transports were 26.6 Sv northwest of Okinawa and 21.9 Sv across the Tokara Straits. The accuracy of the estimate was approximately 3.3 Sv for the Okinawa section and 5.1 Sv for the Tokara Straits section. The principal errors in the calculation came from lack of knowledge of the flow in the shallow areas of both sections, inadequate sampling of the rapidly varying topography, an estimate of 5 Sv transport in the Tsushima Current and Osumi branch of the Kuroshio and uncertainty over the relative weighting given in the inverse solutions to the different sections. A set of acoustic Doppler current profiler (ADCP) data taken simultaneously was combined with the inverse model. Because initial mass imbalances were smaller, the combined model gave a better estimate of transport than that of the model using the CTD data alone. Two different methods of using the ADCP data in the inverse model were compared. It was found to be preferable to use the ADCP data as an initial reference for the geostrophic velocities, rather than as a set of separate constraints.

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.

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Carter, BR, Feely RA, Mecking S, Cross JN, Macdonald AM, Siedlecki SA, Talley LD, Sabine CL, Millero FJ, Swift JH, Dickson AG, Rodgers KB.  2017.  Two decades of Pacific anthropogenic carbon storage and ocean acidification along Global Ocean Ship-lebased Hydrographic Investigations Program sections P16 and P02. Global Biogeochemical Cycles. 31:306-327.   10.1002/2016gb005485   AbstractWebsite

A modified version of the extended multiple linear regression (eMLR) method is used to estimate anthropogenic carbon concentration (C-anth) changes along the Pacific P02 and P16 hydrographic sections over the past two decades. P02 is a zonal section crossing the North Pacific at 30 degrees N, and P16 is a meridional section crossing the North and South Pacific at similar to 150 degrees W. The eMLR modifications allow the uncertainties associated with choices of regression parameters to be both resolved and reduced. Canth is found to have increased throughout the water column from the surface to similar to 1000 m depth along both lines in both decades. Mean column Canth inventory increased consistently during the earlier (1990s-2000s) and recent (2000s-2010s) decades along P02, at rates of 0.53 +/- 0.11 and 0.46 +/- 0.11 mol Cm-2 a(-1), respectively. By contrast, Canth storage accelerated from 0.29 +/- 0.10 to 0.45 +/- 0.11 mol Cm-2 a(-1) along P16. Shifts in water mass distributions are ruled out as a potential cause of this increase, which is instead attributed to recent increases in the ventilation of the South Pacific Subtropical Cell. Decadal changes along P16 are extrapolated across the gyre to estimate a Pacific Basin average storage between 60 degrees S and 60 degrees N of 6.1 +/- 1.5 PgC decade(-1) in the earlier decade and 8.8 +/- 2.2 PgC decade(-1) in the recent decade. This storage estimate is large despite the shallow Pacific Canth penetration due to the large volume of the Pacific Ocean. By 2014, Canth storage had changed Pacific surface seawater pH by -0.08 to -0.14 and aragonite saturation state by -0.57 to -0.82.

Cerovecki, I, Talley LD, Mazloff MR.  2011.  A Comparison of Southern Ocean Air-Sea Buoyancy Flux from an Ocean State Estimate with Five Other Products. Journal of Climate. 24:6283-6306.   10.1175/2011jcli3858.1   AbstractWebsite

The authors have intercompared the following six surface buoyancy flux estimates, averaged over the years 2005-07: two reanalyses [the recent ECMWF reanalysis (ERA-Interim; hereafter ERA), and the National Centers for Environmental Prediction (NCEP)-NCAR reanalysis 1 (hereafter NCEP1)], two recent flux products developed as an improvement of NCEP1 [the flux product by Large and Yeager and the Southern Ocean State Estimate (SOSE)], and two ad hoc air sea flux estimates that are obtained by combining the NCEP1 or ERA net radiative fluxes with turbulent flux estimates using the Coupled Ocean Atmosphere Response Experiment (COARE) 3.0 bulk formulas with NCEP1 or ERA input variables. The accuracy of SOSE adjustments of NCEP1 atmospheric fields (which SOSE uses as an initial guess and a constraint) was assessed by verification that SOSE reduces the biases in the NCEP1 fluxes as diagnosed by the Working Group on Air-Sea Fluxes (Taylor), suggesting that oceanic observations may be a valuable constraint to improve atmospheric variables. Compared with NCEP1, both SOSE and Large and Yeager increase the net ocean heat loss in high latitudes, decrease ocean heat loss in the subtropical Indian Ocean, decrease net evaporation in the subtropics, and decrease net precipitation in polar latitudes. The large-scale pattern of SOSE and Large and Yeager turbulent heat flux adjustment is similar, but the magnitude of SOSE adjustments is significantly larger. Their radiative heat flux adjustments patterns differ. Turbulent heat fluxes determined by combining COARE bulk formulas with NCEP1 or ERA should not be combined with unmodified NCEP1 or ERA radiative fluxes as the net ocean heat gain poleward of 25 degrees S becomes unrealistically large. The other surface flux products (i.e., NCEP1, ERA, Large and Yeager, and SOSE) balance more closely. Overall, the statistical estimates of the differences between the various air-sea heat flux products tend lobe largest in regions with strong ocean mesoscale activity such as the Antarctic Circumpolar Current and the western boundary currents.

Chereskin, TK, Talley LD, Sloyan BM.  2010.  Nonlinear vorticity balance of the Subantarctic Front in the southeast Pacific. Journal of Geophysical Research-Oceans. 115   10.1029/2009jc005611   AbstractWebsite

Direct velocity observations from shipboard and lowered acoustic Doppler current profilers are used to examine the velocity and vorticity structure of the Subantarctic Front (SAF) between the East Pacific Rise and Drake Passage from surveys made in 2005 and 2006. The SAF is characterized by meanders of horizontal wavelength approximately 250-300 km in this region of relatively smooth topography. The depth-averaged SAF jet is observed to be closely aligned with the flow at 150 m, as in an equivalent barotropic flow. The barotropic or depth-averaged vorticity exhibits a balance between advection of planetary vorticity and relative vorticity, as would be seen in a Doppler-shifted short barotropic Rossby wave in a mean flow. The implied wave speed is consistent with the observed range of current speeds. An exponential fit to the vertical structure of the current consistent with the vorticity balance suggests a vertical decay scale of about 1900 m. The vorticity balance at 150 m implies a surface divergence which must be balanced at depth by a divergence of the opposite sign. The calculation confirms the tentative conclusions of Hughes (2005) for this region, which were based on a surface climatology but indicates a larger vertical decay scale and wave speed.

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Dong, S, Sprintall J, Gille ST, Talley L.  2008.  Southern Ocean mixed-layer depth from Argo float profiles. Journal of Geophysical Research-Oceans. 113   10.1029/2006jc004051   AbstractWebsite

Argo float profiles of temperature, salinity, and pressure are used to derive the mixed-layer depth (MLD) in the Southern Ocean. MLD is determined from individual profiles using both potential density and potential temperature criteria, and a monthly climatology is derived from individual MLDs using an objective mapping method. Quantitative data are available in the auxiliary material. The spatial structures of MLDs are similar in each month, with deep mixed layers within and just north of the Antarctic Circumpolar Current (ACC) in the Pacific and Indian oceans. The deepest mixed layers are found from June to October and are located just north of the ACC where Antarctic Intermediate Water (AAIW) and Subantarctic Mode Water ( SAMW) are formed. Examination of individual MLDs indicates that deep mixed layers ( MLD >= 400 m) from both the density and temperature criteria are concentrated in a narrow surface density band which is within the density range of SAMW. The surface salinity for these deep mixed layers associated with the SAMW formation are slightly fresher compared to historical estimates. Differences in air-sea heat exchanges, wind stress, and wind stress curl in the Pacific and Indian oceans suggest that the mode water formation in each ocean basin may be preconditioned by different processes. Wind mixing and Ekman transport of cold water from the south may assist the SAMW formation in the Indian Ocean. In the eastern Pacific, the formation of mode water is potentially preconditioned by the relative strong cooling and weak stratification from upwelling.

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Fiedler, PC, Talley LD.  2006.  Hydrography of the eastern tropical Pacific: A review. Progress in Oceanography. 69:143-180.   10.1016/j.pocean.2006.03.008   AbstractWebsite

Eastern tropical Pacific Ocean waters lie at the eastern end of a basin-wide equatorial current system, between two large subtropical gyres and at the terminus of two eastern boundary currents. Descriptions and interpretations of surface, pycnocline, intermediate and deep waters in the region are reviewed. Spatial and temporal patterns are discussed using (1) maps of surface temperature, salinity, and nutrients (phosphate, silicate, nitrate and nitrite), and thermocline and mixed layer parameters, and (2) meridional and zonal sections of temperature, salinity, potential density, oxygen, and nutrients. These patterns were derived from World Ocean Database observations by an ocean interpolation algorithm: loess-weighted observations were projected onto quadratic functions of spatial coordinates while simultaneously fitting annual and semiannual harmonics and the Southern Oscillation Index to account for interannual variability. Contrasts between the equatorial cold tongue and the eastern Pacific warm pool are evident in all the hydrographic parameters. Annual cycles and ENSO (El Nino-Southern Oscillation) variability are of similar amplitude in the eastern tropical Pacific, however, there are important regional differences in relative variability at these time scales. Unique characteristics of the eastern tropical Pacific are discussed: the strong and shallow pycnocline, the pronounced oxygen minimum layer, and the Costa Rica Dome. This paper is part of a comprehensive review of the oceanography of the eastern tropical Pacific. (c) 2006 Elsevier Ltd. All rights reserved.

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Gordon, AL, Ma SB, Olson DB, Hacker P, Ffield A, Talley LD, Wilson D, Baringer M.  1997.  Advection and diffusion of Indonesian throughflow water within the Indian Ocean South Equatorial Current. Geophysical Research Letters. 24:2573-2576.   10.1029/97gl01061   AbstractWebsite

Warm, low salinity Pacific water weaves through the Indonesian Seas into the eastern boundary of the Indian Ocean. The Indonesian Throughflow Water (ITW) adds freshwater into the Indian Ocean as it spreads by the advection and diffusion within the Indian Ocean's South Equatorial Current (SEC). The low salinity throughflow trace, centered along 12 degrees S, stretches across the Indian Ocean, separating the monsoon dominated regime of the northern Indian Ocean from the more typical subtropical stratification to the south. ITW is well represented within the SEC thermocline, extending with concentrations above 80% of initial characteristics from the sea surface to 300-m within the eastern half of the Indian Ocean, with 60% concentration reaching well into the western Indian Ocean. The ITW transport within the SEC varies from 4 to 12 x 10(6) m(3)sec(-1), partly in response to variations of the injection rate at the eastern boundary and to the likelihood of a zonally elongated recirculation cell between the Equatorial Counter Current and the SEC within the Indian Ocean. Lateral mixing disperses the ITW plume meridionally with an effective isopycnal mixing coefficient of 1.1 to 1.6 x 10(4) m(2)sec(-1).

Gordon, AL, Giulivi CF, Lee CM, Furey HH, Bower A, Talley L.  2002.  Japan/East Sea intrathermocline eddies. Journal of Physical Oceanography. 32:1960-1974.   10.1175/1520-0485(2002)032<1960:jesie>2.0.co;2   AbstractWebsite

Intrathermocline eddies (ITE) with diameters of 100 km and of thickness greater than 100 m are observed within each of the three quasi-stationary meanders of the Tsushima Current of the Japan/East Sea. Within the ITE homogenous, anticyclonic flowing core, the temperature is near 10degreesC with a salinity of 34.12 psu. Because of compensatory baroclinicity of the upper and lower boundaries of the ITE core, the ITE has minor sea level expression. The ITE core displays positive oxygen and negative salinity anomalies in comparison to the surrounding thermocline water, indicative of formation from winter mixed layer water along the southern side of the Japan/East Sea subpolar front. The winter mixing layer is then overridden, or slips below, the regional upper thermocline stratification with its characteristic salinity maximum layer. The winter mixed layer off the coast of Korea closely matches the ITE core characteristics, and is considered as a potential source region. Other sources may be present along the southern boundary of the subpolar front, including a frequently observed warm eddy over the western side of Yamato Rise.

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Holte, J, Talley LD, Gilson J, Roemmich D.  2017.  An Argo mixed layer climatology and database. Geophysical Research Letters. 44:5618-5626.   10.1002/2017gl073426   AbstractWebsite

A global climatology and database of mixed layer properties are computed from nearly 1,250,000 Argo profiles. The climatology is calculated with both a hybrid algorithm for detecting the mixed layer depth (MLD) and a standard threshold method. The climatology provides accurate information about the depth, properties, extent, and seasonal patterns of global mixed layers. The individual profile results in the database can be used to construct time series of mixed layer properties in specific regions of interest. The climatology and database are available online at . The MLDs calculated by the hybrid algorithm are shallower and generally more accurate than those of the threshold method, particularly in regions of deep winter mixed layers; the new climatology differs the most from existing mixed layer climatologies in these regions. Examples are presented from the Labrador and Irminger Seas, the Southern Ocean, and the North Atlantic Ocean near the Gulf Stream. In these regions the threshold method tends to overestimate winter MLDs by approximately 10% compared to the algorithm.

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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%).

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McCarthy, MC, Talley LD, Roemmich D.  2000.  Seasonal to interannual variability from expendable bathythermograph and TOPEX/Poseidon altimeter data in the South Pacific subtropical gyre. Journal of Geophysical Research-Oceans. 105:19535-19550.   10.1029/2000jc900056   AbstractWebsite

Estimates of dynamic height anomalies from expendable bathythermograph (XBT) and TOPEX/Poseidon (T/P) sea surface height (SSH) measurements were compared along a, transect at similar to 30 degrees S in the South Pacific. T/P SSH anomalies were calculated relative to a 5 year time mean. XBT dynamic height was calculated relative to 750 m using measured temperature and an objectively mapped climatological temperature-salinity relationship. The anomaly was obtained by subtracting out an objectively-mapped climatological dynamic height relative to 750 m. XBT temperature sections show evidence of a double-gyre structure, related to changes in shallow isopycnals near the gyre's center. XBT dynamic height and T/P SSH anomalies compare well with an RMS difference of 3.8 cm and a coherence above 0.7 for scales larger than 300 km. The differences between the two measures of dynamic height yield systematic patterns. Time-varying spatial averages of the differences are found to be related to changes in Sverdrup transport, zonal surface slope differences, and the 6 degrees C isotherm depth. Higher zonally averaged altimetry SSH than zonally averaged XBT height and larger northward transport from altimetry SSH than from XBT height correspond to gyre spinup determined from Sverdrup transport changes. This implies mass storage during gyre spinup due to the phase lag between the Ekman pumping and the full baroclinic Sverdrup response. Increases in the spatially averaged differences and zonal slope differences, associated with gyre spinup, correspond to shoaling in the 6 degrees C isotherm depth, requiring deep baroclinic changes out of phase with the 6 degrees C isotherm depth changes.

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Oka, E, Talley LD, Suga T.  2007.  Temporal variability of winter mixed layer in the mid- to high-latitude North Pacific. Journal of Oceanography. 63:293-307.   10.1007/s10872-007-0029-2   AbstractWebsite

Temperature and salinity data from 2001 through 2005 from Argo profiling floats have been analyzed to examine the time evolution of the mixed layer depth (MLD) and density in the late fall to early spring in mid to high latitudes of the North Pacific. To examine MLD variations on various time scales from several days to seasonal, relatively small criteria (0.03 kg m(-3) in density and 0.2 degrees C in temperature) are used to determine MLD. Our analysis emphasizes that maximum MLD in some regions occurs much earlier than expected. We also observe systematic differences in timing between maximum mixed layer depth and density. Specifically, in the formation regions of the Subtropical and Central Mode Waters and in the Bering Sea, where the winter mixed layer is deep, MLD reaches its maximum in late winter (February and March), as expected. In the eastern subarctic North Pacific, however, the shallow, strong, permanent halocline prevents the mixed layer from deepening after early January, resulting in a range of timings of maximum MLD between January and April. In the southern subtropics; from 20 degrees to 30 degrees N, where the winter mixed layer is relatively shallow, MLD reaches a maximum even earlier in December-January. In each region, MLD fluctuates on short time scales as it increases from late fall through early winter. Corresponding to this short-term variation, maximum MLD almost always occurs 0 to 100 days earlier than maximum mixed layer density in all regions.

Oka, E, Uehara K, Nakano T, Suga T, Yanagimoto D, Kouketsu S, Itoh S, Katsura S, Talley LD.  2014.  Synoptic observation of Central Mode Water in its formation region in spring 2003. Journal of Oceanography. 70:521-534.   10.1007/s10872-014-0248-2   AbstractWebsite

Hydrographic data east of Japan from five research cruises and Argo profiling floats in spring 2003 have been analyzed to examine the relationship of the formation of Central Mode Water (CMW) and Transition Region Mode Water (TRMW) in late winter 2003 to thermohaline fronts and mesoscale eddies. TRMW and the denser variety of CMW (D-CMW) were formed continuously just south of the subarctic frontal zone between 155 degrees E and 165 degrees W with little relation to eddies, suggesting that the absence of the permanent thermocline and halocline in this area is essential for the formation. The lighter variety of CMW (L-CMW) was formed south of the Kuroshio bifurcation front and east of 165 degrees E, partly in an anticyclonic eddy associated with the Kuroshio Extension. Some portion of D-CMW and L-CMW likely had been subducted to the permanent pycnocline by crossing southward the Kuroshio bifurcation front and the Kuroshio Extension front, respectively. In contrast, the formation of these waters in the western regions was inactive and was significantly different from that described previously using multiyear Argo float data. West of 155 degrees E, TRMW and D-CMW were formed only in two anticyclonic eddies that had been detached from the Kuroshio Extension 1-2 years ago. L-CMW was hardly formed west of 165 degrees E, which might be related to the upstream Kuroshio Extension being in its stable state characterized by low regional eddy activity.

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Purkey, SG, Johnson GC, Talley LD, Sloyan BM, Wijffels SE, Smethie W, Mecking S, Katsumata K.  2019.  Unabated bottom water warming and freshening in the South Pacific Ocean. Journal of Geophysical Research-Oceans. 124:1778-1794.   10.1029/2018jc014775   AbstractWebsite

Abyssal ocean warming contributed substantially to anthropogenic ocean heat uptake and global sea level rise between 1990 and 2010. In the 2010s, several hydrographic sections crossing the South Pacific Ocean were occupied for a third or fourth time since the 1990s, allowing for an assessment of the decadal variability in the local abyssal ocean properties among the 1990s, 2000s, and 2010s. These observations from three decades reveal steady to accelerated bottom water warming since the 1990s. Strong abyssal (z>4,000m) warming of 3.5 (1.4) m degrees C/year (m degrees C=10(-3)degrees C) is observed in the Ross Sea, directly downstream from bottom water formation sites, with warming rates of 2.5 (0.4) m degrees C/year to the east in the Amundsen-Bellingshausen Basin and 1.3 (0.2) m degrees C/year to the north in the Southwest Pacific Basin, all associated with a bottom-intensified descent of the deepest isotherms. Warming is consistently found across all sections and their occupations within each basin, demonstrating that the abyssal warming is monotonic, basin-wide, and multidecadal. In addition, bottom water freshening was strongest in the Ross Sea, with smaller amplitude in the Amundsen-Bellingshausen Basin in the 2000s, but is discernible in portions of the Southwest Pacific Basin by the 2010s. These results indicate that bottom water freshening, stemming from strong freshening of Ross Shelf Waters, is being advected along deep isopycnals and mixed into deep basins, albeit on longer timescales than the dynamically driven, wave-propagated warming signal. We quantify the contribution of the warming to local sea level and heat budgets. Plain Language Summary Over 90% of the excess energy gained by Earth's climate system has been absorbed by the oceans, with about 10% found deeper than 2,000m. The rates and patterns of deep and abyssal (deeper than 4,000m) ocean warming, while vital for understanding how this heat sink might behave in the future, are poorly known owing to limited data. Here we use highly accurate data collected by ships along oceanic transects with decadal revisits to quantify how much heat and freshwater has entered the South Pacific Ocean between the 1990s and 2010s. We find widespread warming throughout the deep basins there and evidence that the warming rate has accelerated in the 2010s relative to the 1990s. The warming is strongest near Antarctica where the abyssal ocean is ventilated by surface waters that sink to the sea floor and hence become bottom water, but abyssal warming is observed everywhere. In addition, we observe an infusion of freshwater propagating along the pathway of the bottom water as it moves northward from Antarctica. We quantify the deep ocean warming contributions to heat uptake as well as sea level rise through thermal expansion.

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Shcherbina, AY, Talley LD, Rudnick DL.  2003.  Direct observations of North Pacific ventilation: Brine rejection in the Okhotsk Sea. Science. 302:1952-1955.   10.1126/science.1088692   AbstractWebsite

Brine rejection that accompanies ice formation in coastal polynyas is responsible for ventilating several globally important water masses in the Arctic and Antarctic. However, most previous studies of this process have been indirect, based on heat budget analyses or on warm-season water column inventories. Here, we present direct measurements of brine rejection and formation of North Pacific Intermediate Water in the Okhotsk Sea from moored winter observations. A steady, nearly linear salinity increase unambiguously caused by local ice formation was observed for more than a month.

Sloyan, BM, Talley LD, Chereskin TK, Fine R, Holte J.  2010.  Antarctic Intermediate Water and Subantarctic Mode Water Formation in the Southeast Pacific: The Role of Turbulent Mixing. Journal of Physical Oceanography. 40:1558-1574.   10.1175/2010jpo4114.1   AbstractWebsite

During the 2005 austral winter (late August-early October) and 2006 austral summer (February-mid-March) two intensive hydrographic surveys of the southeast Pacific sector of the Southern Ocean were completed. In this study the turbulent kinetic energy dissipation rate epsilon, diapycnal diffusivity kappa, and buoyancy flux J(b) are estimated from the CTD/O(2) and XCTD profiles for each survey. Enhanced kappa of O(10(-3) to 10(-4) m(2) s(-1)) is found near the Subantarctic Front (SAF) during both surveys. During the winter survey, enhanced kappa was also observed north of the "subduction front,'' the northern boundary of the winter deep mixed layer north of the SAF. In contrast, the summer survey found enhanced kappa across the entire region north of the SAF below the shallow seasonal mixed layer. The enhanced kappa below the mixed layer decays rapidly with depth. A number of ocean processes are considered that may provide the energy flux necessary to support the observed diffusivity. The observed buoyancy flux (4.0 x 10(-8) m(2) s(-3)) surrounding the SAF during the summer survey is comparable to the mean buoyancy flux (0.57 x 10(-8) m(2) s(-3)) associated with the change in the interior stratification between austral summer and autumn, determined from Argo profiles. The authors suggest that reduced ocean stratification during austral summer and autumn, by interior mixing, preconditions the water column for the rapid development of deep mixed layers and efficient Antarctic Intermediate Water and Subantarctic Mode Water formation during austral winter and early spring.

Speer, KG, Siedler G, Talley L.  1995.  The Namib Col Current. Deep-Sea Research Part I-Oceanographic Research Papers. 42:1933-1950.   10.1016/0967-0637(95)00088-7   AbstractWebsite

Recent measurements indicate the transatlantic extent of the Namib Col Current at depths of 1300-3000 m near Lat. 22 degrees S in the South Atlantic Ocean. This current forms a continuous circulation structure from the Namib Col on the Walvis Ridge to the western trough, though its characteristic change as deepwater with varying properties enters and leaves the current owing to a meridional flow component. Transport estimates from hydrographic sections on the Walvis Ridge and at 15 degrees W near the crest of the Mid-Atlantic Ridge indicate a strength of about 3 x 10(6) m(3) s(-1) The current is part of a larger-scale eastward Row at Lon. 25 degrees W; transport estimates across the salinity maximum core there show a similar strength. Associated with this high-salinity high-oxygen current is a basin-wide front in these properties of varying intensity (weaker in the east) marking the transition to deep water whose North Atlantic characteristics have been partly erased by mixing with Circumpolar Deep Water in the southwest South Atlantic. The water which finally crosses the Walvis Ridge is supplied both by the eastward flow of this (diluted) North Atlantic Deep Water and by a general southeastward interior flow from the northern Angola Basin. Evidence suggests that this deep water continues south in the eastern Cape Basin, leaving the South Atlantic near the African continent.

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Talley, LD.  2003.  Shallow, intermediate, and deep overturning components of the global heat budget. Journal of Physical Oceanography. 33:530-560.   10.1175/1520-0485(2003)033<0530:siadoc>2.0.co;2   AbstractWebsite

The ocean's overturning circulation and associated heat transport are divided into contributions based on water mass ventilation from 1) shallow overturning within the wind-driven subtropical gyres to the base of the thermocline, 2) overturning into the intermediate depth layer (500-2000 m) in the North Atlantic and North Pacific, and 3) overturning into the deep layers in the North Atlantic (Nordic Seas overflows) and around Antarctica. The contribution to South Pacific and Indian heat transport from the Indonesian Throughflow is separated from that of the subtropical gyres and is small. A shallow overturning heat transport of 0.6 PW dominates the 0.8-PW total heat transport at 24degreesN in the North Pacific but carries only 0.1-0.4 PW of the 1.3-PW total in the North Atlantic at 24degreesN. Shallow overturning heat transports in the Southern Hemisphere are also poleward: -0.2 to -0.3 PW southward across 30degreesS in each of the Pacific and Indian Oceans but only -0.1 PW in the South Atlantic. Intermediate water formation of 2 and 7 Sv (1 Sv = 10(6) m(3) s(-1)) carries 0.1 and 0.4 PW in the North Pacific and Atlantic, respectively, while North Atlantic Deep Water formation of 19 Sv carries 0.6 PW. Because of the small temperature differences between Northern Hemisphere deep waters that feed the colder Antarctic Bottom Water (Lower Circumpolar Deep Water), the formation of 22 Sv of dense Antarctic waters is associated with a heat transport of only -0.14 PW across 30degreesS (all oceans combined). Upwelling of Circumpolar Deep Water north of 30degreesS in the Indian (14 Sv) and South Pacific (14 Sv) carries -0.2 PW in each ocean.

Talley, LD, Joyce TM.  1992.  The Double Silica Maximum in the North Pacific. Journal of Geophysical Research-Oceans. 97:5465-5480.   10.1029/92jc00037   AbstractWebsite

The North Pacific has two vertical silica maxima. The well-known intermediate maximum occurs between 2000 and 2500 m with a potential density relative to 2000 dbar of 36.90 in the northeastern Pacific. The deep maximum, which has not been observed extensively before, is found at or near the ocean bottom in the northern North Pacific in a narrow latitude range. Maps of silica on isopycnals which intersect the intermediate and bottom maxima show that the lowest silica is found in the western tropical North Pacific, suggesting a route for the spread of South Pacific water into the deep North Pacific. Low-silica water is found along the western boundary of the North Pacific, with a separate broad tongue south of Hawaii. The highest silica on both isopycnals is in the northeast Pacific. A bottom maximum in the Cascadia Basin in the northeastern Pacific can be differentiated from both open-ocean maxima. Four sources for the vertical maxima are considered: in situ dissolution of sinking panicles, bottom sediment dissolution, hydrothermal venting, and upslope advection in the northeastern Pacific. Because not enough is known about any of these sources, only rough estimates of their contributions can be made. The bottom maximum is most likely to result from bottom sediment dissolution but requires a flux larger than some current direct estimates. The Cascadia Basin bottom maximum may result from both bottom sediment dissolution and hydrothermal venting. The intermediate maximum is likely to result primarily from dissolution of sinking particles. There is no quantitative estimate of the effect of possible upslope advection or enhancement of bottom fluxes due to the Columbia River outflow.

Talley, LD.  1997.  North Pacific intermediate water transports in the mixed water region. Journal of Physical Oceanography. 27:1795-1803.   10.1175/1520-0485(1997)027<1795:npiwti>2.0.co;2   AbstractWebsite

Initial mixing between the subtropical and subpolar waters of Kuroshio and Oyashio origin occurs in the mixed water region (interfrontal zone) between the Kuroshio and Oyashio. The relatively fresh water that enters the Kuroshio Extension from the Mixed Water Region is this already mixed subtropical transition water. Subtropical transition water in the density range 26.64-27.4 sigma(theta) can be considered to be the newest North Pacific Intermediate Water (NPIW) in the subtropical gyre; this density range is approximately that which is ventilated in the subpolar gyre with significant influence from the Okhotsk Sea. Freshening of the Kuroshio Extension core occurs between 140 degrees and 165 degrees E in the upper part of the NPIW (26.64-27.0 sigma(theta)), with the greatest freshening associated with the eastern side of the first and second Kuroshio meanders. Kuroshio Extension freshening in the lower part of the NPIW (27.0-27.4 sigma(theta)) occurs more gradually and farther to the east. There is nearly no distinction in water properties north and south of the Kuroshio Extension by 175 degrees W. The upper part of the NPIW in the Mixed Water Region progresses from very intrusive and including much freshwater in the west, to much smoother and more saline water in the east. The lower part of the NPIW in the mixed water region progresses from very intrusive and fresh in the far west, to noisy and more saline at 152 degrees E, to smooth and fresher in the east. These suggest a difference between the two layers in both advection direction and possibly transport across the Subarctic Front. Assuming that all waters in the region are an isopycnal mixture of subtropical and subpolar water, the zonal transport of subpolar water in the subtropical gyre at 152 degrees E is estimated at about 3 Sv (Sv = 10(6) m(3) s(-1)). This could be approximately one-quarter of the Oyashio transport in this density range.

Talley, LD, Lobanov V, Ponomarev V, Salyuk A, Tishchenko P, Zhabin I, Riser S.  2003.  Deep convection and brine rejection in the Japan Sea. Geophysical Research Letters. 30   10.1029/2002gl016451   AbstractWebsite

Direct water mass renewal through convection deeper than 1000 m and the independent process of dense water production through brine rejection during sea ice formation occur at only a limited number of sites globally. Our late winter observations in 2000 and 2001 show that the Japan (East) Sea is a part of both exclusive groups. Japan Sea deep convection apparently occurs every winter, but massive renewal of bottom waters through brine rejection had not occurred for many decades prior to the extremely cold winter of 2001. The sites for both renewal mechanisms are south of Vladivostok, in the path of cold continental air outbreaks.

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>2.0.co;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.