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A
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.

Alley, RB, Marotzke J, Nordhaus WD, Overpeck JT, Peteet DM, Pielke RA, Pierrehumbert RT, Rhines PB, Stocker TF, Talley LD, Wallace JM.  2003.  Abrupt climate change. Science. 299:2005-2010.   10.1126/science.1081056   AbstractWebsite

Large, abrupt, and widespread climate changes with major impacts have occurred repeatedly in the past, when the Earth system was forced across thresholds. Although abrupt climate changes can occur for many reasons, it is conceivable that human forcing of climate change is increasing the probability of large, abrupt events. Were such an event to recur, the economic and ecological impacts could be large and potentially serious. Unpredictability exhibited near climate thresholds in simple models shows that some uncertainty will always be associated with projections. In light of these uncertainties, policy-makers should consider expanding research into abrupt climate change, improving monitoring systems, and taking actions designed to enhance the adaptability and resilience of ecosystems and economies.

B
Billheimer, S, Talley LD.  2013.  Near cessation of Eighteen Degree Water renewal in the western North Atlantic in the warm winter of 2011-2012. Journal of Geophysical Research-Oceans. 118:6838-6853.   10.1002/2013jc009024   AbstractWebsite

The winter of 2011-2012 was a particularly weak season for the renewal of "Eighteen Degree Water" (EDW), the Subtropical Mode Water of the western North Atlantic, as demonstrated by Argo and repeat hydrography. Weak, late winter buoyancy forcing produced shallower than usual winter mixed layers throughout the subtropical gyre, failing to thoroughly ventilate the underlying mode water, and can likely be attributed to the coinciding high, positive phase of the North Atlantic Oscillation (NAO). The only region where EDW was renewed was in the far northeastern Sargasso Sea where it is understood that the Gulf Stream plays a central role in formation; no EDW formed over the large regions of the gyre where deep winter mixed layers driven by surface buoyancy loss normally create EDW. The present investigation evaluates 2011-2012 winter buoyancy content anomalies, surface buoyancy fluxes, and advection of buoyancy via the Gulf Stream and compares them with the previous seven winters that exhibited more vigorous EDW formation. The weak 2011-2012 formation did not result from increased Gulf Stream heat advection, and was also not driven by preconditioning as the buoyancy content of the region prior to the onset of winter forcing was not unusually high. Rather, the weak formation resulted from climatologically weak surface cooling late in winter. The winter of 2007-2008 also experienced particularly weak EDW formation under similar conditions, including a high NAO and weak late winter surface cooling.

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.

Billheimer, S, Talley LD.  2016.  Extraordinarily weak Eighteen Degree Water production concurs with strongly positive North Atlantic Oscillation in late winter 2014/15. State of the Climate in 2015. 97( Blunden J, Arndt DS, Eds.).:Si-S275.   10.1175/2016BAMSStateoftheClimate.1   Abstract

In summary, winter 2014/15 was the weakest EDWformation year on record during the Argo era and wasassociated with an extreme, strongly positive winterNAO. Three of the past four winters have had belowaverage EDW renewal, with the most recent being themost extreme.

Bindoff, NL, Willebrand J, Artale V, Cazenave A, Gregory J, Gulev S, Hanawa K, Le Quere C, Levitus S, Nojiri Y, Shum CK, Talley LD, Unnikrishnan A.  2007.  Observations: Oceanic Climate Change and Sea Level. Climate change 2007 : the physical science basis : contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. ( Solomon S, Qin D, Manning M, Chen Z, Marquis M, Avery KB, Tignor M, Miller H, Eds.).:387-432., Cambridge ; New York: Cambridge University Press Abstract
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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.

Bourassa, MA, Gille ST, Bitz C, Carlson D, Cerovecki I, Clayson CA, Cronin MF, Drennan WM, Fairall CW, Hoffman RN, Magnusdottir G, Pinker RT, Renfrew IA, Serreze M, Speer K, Talley LD, Wick GA.  2013.  High-latitude ocean and sea ice surface fluxes: Challenges for climate research. Bulletin of the American Meteorological Society. 94:403-423.   10.1175/bams-d-11-00244.1   AbstractWebsite

Polar regions have great sensitivity to climate forcing; however, understanding of the physical processes coupling the atmosphere and ocean in these regions is relatively poor. Improving our knowledge of high-latitute surface fluxes will require close collaboration among meteorologists, oceanographers, ice physicists, and climatologists, and between observationalists and modelers, as well as new combinations of in situ measurements and satellite remote sensing. This article describes the deficiencies in our current state of knowledge about air-sea surface fluxes in high latitutes, the sensitivity of various high-latitude processes to changes in surface fluxes, and the scientific requirements for surface fluxes at high latitutdes. We inventory the reasons, both logistical and physical, why existing flux products do not meet these requirements. Capturing an annual cycle in fluxes requires that instruments function through long periods of cold polar darkness, often far from support services, in situations subject to icing and extreme wave conditions. Furthermore, frequent cloud cover at high latitudes restricts the avilability of surface and atmospheric data from visible and infrared (IR) wavelength satellite sensors. Recommendations are made for improving high-latitude fluxes, including 1) acquiring more in situ observations, 2) developing improved satellite-flux-observing capabilities, 3) making observations and flux products more accessible, and 4) encouraging flux intercomparisons.

Brambilla, E, Talley LD.  2006.  Surface drifter exchange between the North Atlantic subtropical and subpolar gyres. Journal of Geophysical Research-Oceans. 111   10.1029/2005jc003146   AbstractWebsite

[ 1] Surface drifters deployed in the subtropical and subpolar North Atlantic from 1990 to 2002 show almost no connection between the subtropical and subpolar gyres; only one drifter crosses the intergyre boundary even though other data types ( e. g., dynamic topography and tracers) suggest a major connection. Two of several possible causes for the lack of intergyre connectivity in this two-dimensional data set are examined: ( 1) undersampling and short drifter lifetime leading to underestimation of the northward flow, and ( 2) the southward mean Ekman velocity. Advection of a large number of long-lived synthetic drifters through the observed mean velocity results in a 5% increase in cross-gyre flux compared with that for synthetic drifters with realistic lifetimes. By further advecting synthetic drifters through the observed mean velocity field with and without the Ekman component, estimated from the wind field associated with the actual drifters, it is shown that removal of the Ekman component further increases the intergyre flux by up to 6%. With a turbulent component added to the mean velocity field to simulate the eddy field, there is a further increase in connection by 5%. Thus the Ekman and eddy contributions to the drifter trajectories nearly cancel each other. Consideration of three-dimensional processes ( subduction and obduction) is reserved for complete modeling studies.

Brambilla, E, Talley LD.  2008.  Subpolar Mode Water in the northeastern Atlantic: 1. Averaged properties and mean circulation. Journal of Geophysical Research-Oceans. 113   10.1029/2006jc004062   AbstractWebsite

Subpolar Mode Waters (SPMW) in the eastern North Atlantic subpolar gyre are investigated with hydrographic and Lagrangian data (surface drifters and isopycnal floats). Historical hydrographic data show that SPMWs are surface water masses with nearly uniform properties, confined between the ocean surface and the permanent pycnocline. SPMWs represented by densities 27.3(sigma theta), 27.4(sigma theta), and 27.5(sigma theta) are present in the eastern subpolar gyre and are influenced by the topography and the regional circulation. Construction of an absolute surface stream function from surface drifters shows that SPMWs are found along the mean path of each of the several branches of the North Atlantic Current (NAC) and their density increases gradually downstream. The Rockall Trough branch of the NAC carries 27.3(sigma theta), 27.4(sigma theta), and 27.5(sigma theta) SPMW toward the Iceland-Faroe Front. In the Iceland Basin, the Subarctic Front along the western flank of the Rockall Plateau carries a similar sequence of SPMW. The western side of the Central Iceland Basin branch of the NAC, on the other hand, veers westward and joins the East Reykjanes Ridge Current, feeding the 27.5(sigma theta) SPMW on the Reykjanes Ridge. The separation among the various NAC branches most likely explains the different properties that characterize the 27.5(sigma theta) SPMW found on the Reykjanes Ridge and on the Iceland-Faroe Ridge. Since the branches of the NAC have a dominant northeastward direction, the newly observed distribution of SPMW combined with the new stream function calculation modify the original hypothesis of McCartney and Talley (1982) of a smooth cyclonic pathway for SPMW advection and density increase around the subpolar gyre.

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.

Briggs, EM, Martz TR, Talley LD, Mazloff MR, Johnson KS.  2018.  Physical and biological drivers of biogeochemical tracers within the seasonal sea ice zone of the Southern Ocean from profiling floats. Journal of Geophysical Research-Oceans. 123:746-758.   10.1002/2017jc012846   AbstractWebsite

Here we present initial findings from nine profiling floats equipped with pH, O-2, , and other biogeochemical sensors that were deployed in the seasonal ice zone (SIZ) of the Southern Ocean in 2014 and 2015 through the Southern Ocean Carbon and Climate Observations and Modelling (SOCCOM) project. A large springtime phytoplankton bloom was observed that coincided with sea ice melt for all nine floats. We argue this bloom results from a shoaling of the mixed layer depth, increased vertical stability, and enhanced nutrient and light availability as the sea ice melts. This interpretation is supported by the absence of a springtime bloom when one of the floats left the SIZ in the second year of observations. During the sea ice covered period, net heterotrophic conditions were observed. The rate of uptake of O-2 and release of dissolved inorganic carbon (derived from pH and estimated total alkalinity) and is reminiscent of biological respiration and is nearly Redfieldian for the nine floats. A simple model of mixed layer physics was developed to separate the physical and biological components of the signal in pH and O-2 over one annual cycle for a float in the Ross Sea SIZ. The resulting annual net community production suggests that seasonal respiration during the ice covered period of the year nearly balances the production in the euphotic layer of up to 5 molCm(-2) during the ice free period leading to a net of near zero carbon exported to depth for this one float.

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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.

Carter, BR, Talley LD, Dickson AG.  2014.  Mixing and remineralization in waters detrained from the surface into Subantarctic Mode Water and Antarctic Intermediate Water in the southeastern Pacific. Journal of Geophysical Research-Oceans. 119:4001-4028.   10.1002/2013jc009355   AbstractWebsite

A hydrographic data set collected in the region and season of Subantarctic Mode Water and Antarctic Intermediate Water (SAMW and AAIW) formation in the southeastern Pacific allows us to estimate the preformed properties of surface water detrained into these water masses from deep mixed layers north of the Subantarctic Front and Antarctic Surface Water south of the front. Using 10 measured seawater properties, we estimate: the fractions of SAMW/AAIW that originate as surface source waters, as well as fractions that mix into these water masses from subtropical thermocline water above and Upper Circumpolar Deep Water below the subducted SAMW/AAIW; ages associated with the detrained surface water; and remineralization and dissolution rates and ratios. The mixing patterns imply that cabbeling can account for similar to 0.005-0.03 kg m(-3) of additional density in AAIW, and similar to 0-0.02 kg m(-3) in SAMW. We estimate a shallow depth (similar to 300-700 m, above the aragonite saturation horizon) calcium carbonate dissolution rate of 0.4 +/- 0.2 mmol CaCO3 kg(-1) yr(-1), a phosphate remineralization rate of 0.031 +/- 0.009 mu mol P kg(-1) yr(-1), and remineralization ratios of P:N:-O-2:C-org of 1:(15.5 +/- 0.6):(143 +/- 10):(104 +/- 22) for SAMW/AAIW. Our shallow depth calcium carbonate dissolution rate is comparable to previous estimates for our region. Our -O-2:P ratio is smaller than many global averages. Our model suggests neglecting diapycnal mixing of preformed phosphate has likely biased previous estimates of -O-2:P and C-org:P high, but that the C-org:P ratio bias may have been counteracted by a second bias in previous studies from neglecting anthropogenic carbon gradients.

Carter, BR, Feely RA, Wanninkhof R, Kouketsu S, Sonnerup RE, Pardo PC, Sabine CL, Johnson GC, Sloyan BM, Murata A, Mecking S, Tilbrook B, Speer K, Talley LD, Millero FJ, Wijffels SE, Macdonald AM, Gruber N, Bullister JL.  2019.  Pacific anthropogenic carbon between 1991 and 2017. Global Biogeochemical Cycles. 33:597-617.   10.1029/2018gb006154   AbstractWebsite

We estimate anthropogenic carbon (C-anth) accumulation rates in the Pacific Ocean between 1991 and 2017 from 14 hydrographic sections that have been occupied two to four times over the past few decades, with most sections having been recently measured as part of the Global Ocean Ship-based Hydrographic Investigations Program. The rate of change of C-anth is estimated using a new method that combines the extended multiple linear regression method with improvements to address the challenges of analyzing multiple occupations of sections spaced irregularly in time. The C-anth accumulation rate over the top 1,500 m of the Pacific increased from 8.8 (+/- 1.1, 1 sigma) Pg of carbon per decade between 1995 and 2005 to 11.7 (+/- 1.1) PgC per decade between 2005 and 2015. For the entire Pacific, about half of this decadal increase in the accumulation rate is attributable to the increase in atmospheric CO2, while in the South Pacific subtropical gyre this fraction is closer to one fifth. This suggests a substantial enhancement of the accumulation of C-anth in the South Pacific by circulation variability and implies that a meaningful portion of the reinvigoration of the global CO2 sink that occurred between similar to 2000 and similar to 2010 could be driven by enhanced ocean C-anth uptake and advection into this gyre. Our assessment suggests that the accuracy of C-anth accumulation rate reconstructions along survey lines is limited by the accuracy of the full suite of hydrographic data and that a continuation of repeated surveys is a critical component of future carbon cycle monitoring.

Centurioni, LR, Hormann V, Talley LD, Arzeno I, Beal L, Caruso M, Conry P, Echols R, Fernando HJS, Giddings SN, Gordon A, Graber H, Harcourt RR, Jayne SR, Jensen TG, Lee CM, Lermusiaux PFJ, L'Hegaret P, Lucas AJ, Mahadevan A, McClean JL, Pawlak G, Rainville L, Riser SC, Seo H, Shcherbina AY, Skyllingstad E, Sprintall J, Subrahmanyam B, Terrill E, Todd RE, Trott C, Ulloa HN, Wang H.  2017.  Northern Arabian Sea Circulation Autonomous Research (NASCar): A research initiative based on autonomous sensors. Oceanography. 30:74-87.   10.5670/oceanog.2017.224   AbstractWebsite

The Arabian Sea circulation is forced by strong monsoonal winds and is characterized by vigorous seasonally reversing currents, extreme differences in sea surface salinity, localized substantial upwelling, and widespread submesoscale thermohaline structures. Its complicated sea surface temperature patterns are important for the onset and evolution of the Asian monsoon. This article describes a program that aims to elucidate the role of upper-ocean processes and atmospheric feedbacks in setting the sea surface temperature properties of the region. The wide range of spatial and temporal scales and the difficulty of accessing much of the region with ships due to piracy motivated a novel approach based on state-of-the-art autonomous ocean sensors and platforms. The extensive data set that is being collected, combined with numerical models and remote sensing data, confirms the role of planetary waves in the reversal of the Somali Current system. These data also document the fast response of the upper equatorial ocean to monsoon winds through changes in temperature and salinity and the connectivity of the surface currents across the northern Indian Ocean. New observations of thermohaline interleaving structures and mixing in setting the surface temperature properties of the northern Arabian Sea are also discussed.

Cerovečki, I, Talley LD, Mazloff MR, Maze G.  2013.  Subantarctic Mode Water Formation, Destruction, and Export in the Eddy-Permitting Southern Ocean State Estimate. Journal of Physical Oceanography. 43:1485-1511.: American Meteorological Society   10.1175/JPO-D-12-0121.1   AbstractWebsite

Subantarctic Mode Water (SAMW) is examined using the data-assimilating, eddy-permitting Southern Ocean State Estimate, for 2005 and 2006. Surface formation due to air–sea buoyancy flux is estimated using Walin analysis, and diapycnal mixing is diagnosed as the difference between surface formation and transport across 30°S, accounting for volume change with time. Water in the density range 26.5 <σθ < 27.1 kg m−3 that includes SAMW is exported northward in all three ocean sectors, with a net transport of (18.2, 17.1) Sv (1 Sv ≡ 106 m3 s−1; for years 2005, 2006); air–sea buoyancy fluxes form (13.2, 6.8) Sv, diapycnal mixing removes (−14.5, −12.6) Sv, and there is a volume loss of (−19.3, −22.9) Sv mostly occurring in the strongest SAMW formation locations. The most vigorous SAMW formation is in the Indian Ocean by air–sea buoyancy flux (9.4, 10.9) Sv, where it is partially destroyed by diapycnal mixing (−6.6, −3.1) Sv. There is strong export to the Pacific, where SAMW is destroyed both by air–sea buoyancy flux (−1.1, −4.6) Sv and diapycnal mixing (−5.6, −8.4) Sv. In the South Atlantic, SAMW is formed by air–sea buoyancy flux (5.0, 0.5) Sv and is destroyed by diapycnal mixing (−2.3, −1.1) Sv. Peaks in air–sea flux formation occur at the Southeast Indian and Southeast Pacific SAMWs (SEISAMWs, SEPSAMWs) densities. Formation over the broad SAMW circumpolar outcrop windows is largely from denser water, driven by differential freshwater gain, augmented or decreased by heating or cooling. In the SEISAMW and SEPSAMW source regions, however, formation is from lighter water, driven by differential heat loss.

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.

Chamberlain, P, Talley LD, Mazloff M, Riser S, Speer K, Gray AR, Schwartzman A.  2018.  Observing the ice-covered Weddell Gyre with profiling floats: position uncertainties and correlation statistics. Journal of Geophysical Research: Oceans.   10.1029/2017JC012990   Abstract

Argo-type profiling floats do not receive satellite positioning while under sea ice. Common practice is to approximate unknown positions by linearly interpolating latitude-longitude between known positions before and after ice cover, although it has been suggested that some improvement may be obtained by interpolating along contours of planetary-geostrophic potential vorticity. Profiles with linearly interpolated positions represent 16% of the Southern Ocean Argo dataset; consequences arising from this approximation have not been quantified. Using three distinct datasets from the Weddell Gyre - 10 day satellite-tracked Argo floats, daily-tracked RAFOS-enabled floats, and a particle release simulation in the Southern Ocean State Estimate (SOSE) - we perform a data withholding experiment to assess position uncertainty in latitude-longitude and potential vorticity coordinates as a function of time since last fix. A spatial correlation analysis using the float data provides temperature and salinity uncertainty estimates as a function of distance error. Combining the spatial correlation scales and the position uncertainty, we estimate uncertainty in temperature and salinity as a function of duration of position loss. Maximum position uncertainty for interpolation during 8 months without position data is 116 ± 148 km for latitude-longitude and 92 ± 121 km for potential vorticity coordinates. The estimated maximum uncertainty in local temperature and salinity over the entire 2,000 m profiles during 8 months without position data is 0.66 ° C and 0.15 psu in the upper 300 m and 0.16 ° C and 0.01 psu below 300 m.

on Change, NRCCAC(US).  2002.  Abrupt climate change : inevitable surprises. :xii,230p.., Washington, D.C.: National Academy Press Abstract
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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.

Cronin, MF, Bond N, Booth J, Ichikawa H, Joyce TM, Kelly K, Kubota M, Qiu B, Reason C, Rouault M, Sabine C, Saino T, Small J, Suga T, Talley LD, Thompson LA, Weller RA.  2010.  Monitoring Ocean - Atmosphere Interactions in Western Boundary Current Extensions. Proceedings of OceanObs’09: Sustained Ocean Observations and Information for Society. 2( Hall J, Harrison DE, Stammer D, Eds.).   doi:10.5270/OceanObs09.cwp.20   Abstract
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Delman, AS, McClean JL, Sprintall J, Talley LD, Yulaeva E, Jayne SR.  2015.  Effects of eddy vorticity forcing on the mean state of the Kuroshio Extension. Journal of Physical Oceanography. 45:1356-1375.   10.1175/jpo-d-13-0259.1   AbstractWebsite

Eddy-mean flow interactions along the Kuroshio Extension (KE) jet are investigated using a vorticity budget of a high-resolution ocean model simulation, averaged over a 13-yr period. The simulation explicitly resolves mesoscale eddies in the KE and is forced with air-sea fluxes representing the years 1995-2007. A mean-eddy decomposition in a jet-following coordinate system removes the variability of the jet path from the eddy components of velocity; thus, eddy kinetic energy in the jet reference frame is substantially lower than in geographic coordinates and exhibits a cross-jet asymmetry that is consistent with the baroclinic instability criterion of the long-term mean field. The vorticity budget is computed in both geographic (i. e., Eulerian) and jet reference frames; the jet frame budget reveals several patterns of eddy forcing that are largely attributed to varicose modes of variability. Eddies tend to diffuse the relative vorticity minima/maxima that flank the jet, removing momentum from the fast-moving jet core and reinforcing the quasi-permanent meridional meanders in the mean jet. A pattern associated with the vertical stretching of relative vorticity in eddies indicates a deceleration (acceleration) of the jet coincident with northward (southward) quasi-permanent meanders. Eddy relative vorticity advection outside of the eastward jet core is balanced mostly by vertical stretching of the mean flow, which through baroclinic adjustment helps to drive the flanking recirculation gyres. The jet frame vorticity budget presents a well-defined picture of eddy activity, illustrating along-jet variations in eddy-mean flow interaction that may have implications for the jet's dynamics and cross-frontal tracer fluxes.

Delman, AS, McClean JL, Sprintall J, Talley LD, Bryan FO.  2018.  Process-specific contributions to anomalous Java mixed layer cooling during positive IOD events. Journal of Geophysical Research-Oceans. 123:4153-4176.   10.1029/2017jc013749   AbstractWebsite

Negative sea surface temperature (SST) anomalies associated with positive Indian Ocean Dipole (pIOD) events first appear in the seasonal upwelling zone along the southern coast of Java during May-July. The evolution of anomalous SSTs in this coastal region is analyzed by computing a temperature budget using output from a strongly eddy-active ocean general circulation model. The seasonal cooling south of Java in May-July is driven by a reduction in incoming shortwave radiation and by vertical mixing, consistent with earlier studies in the region; however, the model budget also shows an advective contribution that drives anomalous cooling at the onset of pIOD events. To identify which process(es) are responsible for the anomalous advective cooling during pIOD events, a novel process index regression method is used to estimate the contributions of wind stress, equatorial Kelvin waves, mesoscale eddies, and Lombok Strait flow to anomalous cooling south of Java. Using this method, wind stress forcing along the west coast of Sumatra is found to make the most substantial contribution to anomalous cooling south of Java, with lesser contributions from equatorially sourced Kelvin waves and local wind stress. Mesoscale eddies redistribute heat from the Lombok Strait outflow, and have an anomalous warming effect on the eastern side of the upwelling region. The process-specific temperature budget south of Java highlights the importance of wind stress forcing west of Sumatra relative to equatorial and local forcing, and explains most of the mixed layer temperature anomaly evolution associated with advection during pIOD events. Plain Language Summary Climate variations from year to year in much of the Indian Ocean region are controlled by a phenomenon called the Indian Ocean Dipole, which is similar to El Nino but centered on the Indian Ocean basin. The positive phase of the Indian Ocean Dipole, or pIOD, typically brings drought conditions to Indonesia and unusually heavy rainfall to east Africa. These pIOD events are caused in part by unusually strong cooling in sea surface temperatures south of the Indonesian island of Java, but the series of events that causes this strong cooling has not been well understood previously. This paper uses the results obtained from a high-resolution ocean model, together with a new method for analyzing these results, to study exactly how much sea surface cooling (or warming) is caused by specific processes in the Java region. The study finds that changes in wind patterns adjacent to the Indonesian island of Sumatra can explain nearly all of the unusual cooling that develops south of Java in years when these pIOD events happen. The analysis method introduced in this paper may be adapted to study how processes in the ocean or atmosphere cause changes in the Earth's climate system.

Delman, AS, Sprintall J, McClean JL, Talley LD.  2016.  Anomalous Java cooling at the initiation of positive Indian Ocean Dipole events. Journal of Geophysical Research: Oceans.   10.1002/2016JC011635   AbstractWebsite

Anomalous sea surface temperature (SST) cooling south of Java, initiated during May–July, is an important precursor to positive Indian Ocean Dipole (pIOD) events. As shown previously, the Java SST anomalies are spatially and temporally coincident with seasonal upwelling induced locally by southeasterly trade winds. However, we confirm earlier findings that interannual variability of the Java cooling is primarily driven by remote wind forcing from coastal Sumatra and the equatorial Indian Ocean (EqIO); we also find an influence from winds along the Indonesian Throughflow. The wind forcing in the EqIO and along coastal Sumatra does not initiate SST cooling locally due to a deep thermocline and thick barrier layer, but can force upwelling Kelvin waves that induce substantial surface cooling once they reach the seasonally shallower thermocline near the coast of Java. Satellite altimetry is used to obtain a Kelvin wave coefficient that approximates Kelvin wave amplitude variations along the equator. All pIOD years in the satellite record have anomalous levels of upwelling Kelvin wave activity along the equator during April–June, suggesting that upwelling waves during this season are necessary for pIOD event development. However, a change to wind-forced downwelling Kelvin waves during July–August can abruptly terminate cool Java SST anomalies and weaken the pIOD event. Upwelling Kelvin wave activity along the equator and wind stress anomalies west of Sumatra are both robust predictors of the IOD index later in the calendar year, while values of the Kelvin wave coefficient are the most reliable predictor of pIOD events specifically.