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In the past two decades, the Argo Program has collected, processed, and distributed over two million vertical profiles of temperature and salinity from the upper two kilometers of the global ocean. A similar number of subsurface velocity observations near 1,000 dbar have also been collected. This paper recounts the history of the global Argo Program, from its aspiration arising out of the World Ocean Circulation Experiment, to the development and implementation of its instrumentation and telecommunication systems, and the various technical problems encountered. We describe the Argo data system and its quality control procedures, and the gradual changes in the vertical resolution and spatial coverage of Argo data from 1999 to 2019. The accuracies of the float data have been assessed by comparison with high-quality shipboard measurements, and are concluded to be 0.002 degrees C for temperature, 2.4 dbar for pressure, and 0.01 PSS-78 for salinity, after delayed-mode adjustments. Finally, the challenges faced by the vision of an expanding Argo Program beyond 2020 are discussed.

An update on the Eastern South Pacific Intermediate Water (ESPIW) distribution has been possible based on ARGO (Array for Real-Time Geostrophic Oceanography) data. This study comprised over 46,000 profiles obtained during 2007-2012 from an area between the western coast of South America and 150°W, and 5° and 40°S. This information was complemented with data from the World Ocean Circulation Experiment (WOCE) P06 transects conducted in 1992 and 2010 at 32°30’S in the South Pacific Ocean. Based on a comparison of this update and data from 1990-2001, it was established that the ESPIW volume has increased by approximately 53%. Moreover, the area occupied by ESPIW in the 2010 WOCE P06 transect was 48% higher than in 1992. Ekman pumping velocity, calculated from the wind for the time and region of ESPIW formation, showed a significant increase in Ekman pumping between 2000 and 2012. The increase in Ekman pumping from 2000 onward could explain the observed changes in ESPIW distribution (the water mass had extended zonally) and properties (salinity showed a decrease of 0.1). These changes could be explained as the consequence of atmospheric climate variability over the interior ocean.

The distribution and quantification of the source waters of the North Atlantic Deep Water (NADW) and the Antarctic Bottom Water (AABW) in the Atlantic Ocean were investigated using 40 years of climatology data (1973–2014) constructed from the dataset available in the 2013 World Ocean Database. The quasi-interdecadal variability of NADW and AABW source waters spanned the late 1980s until early 2010 in the analysis of three World Ocean Circulation Experiment sections (WOCE A05, A10 and A16). The study was performed by applying optimum multiparameter analysis to quantify the mixture of six NADW and AABW source waters (four for NADW and two for AABW). The NADW source waters decrease their contributions from north to south, except for the region between 30°S and 45°S where the Labrador Sea Water (LSW) contribution suggests an upper NADW deepening. In addition, Iceland-Scotland Overflow Water (ISOW) and LSW contribute to the southernmost boundary of NADW in the Southern Ocean. The AABW source waters were observed as far as 45°N with a 15% contribution, with significant recirculation in equatorial regions and higher contributions in Argentine and Brazil basins. The Denmark Strait Overflow Water (DSOW) and ISOW showed the highest temporal variability (±20%) not only near their formation region but also in the South Atlantic. The AABW source waters did not present high temporal variability, although temporal changes were found near their formation region. Based on their spatial distribution, the Argentine and Brazil basins were noted as the main locations to use for investigating this issue. The results provide new insights into the mixing inside the deep Atlantic Ocean and the global circulation cell; the results also specify the source water masses that present higher temporal variability and the suitable locations to observe these changes.

In 1999, the consortium on Estimating the Circulation and Climate of the Ocean (ECCO) set out to synthesize the hydrographic data collected by the World Ocean Circulation Experiment (WOCE) and the satellite sea surface height measurements into a complete and coherent description of the ocean, afforded by an ocean general circulation model. Twenty years later, the versatility of ECCO's estimation framework enables the production of global and regional ocean and sea-ice state estimates, that incorporate not only the initial suite of data and its successors, but nearly all data streams available today. New observations include measurements from Argo floats, marine mammal-based hydrography, satellite retrievals of ocean bottom pressure and sea surface salinity, as well as ice-tethered profiled data in polar regions. The framework also produces improved estimates of uncertain inputs, including initial conditions, surface atmospheric state variables, and mixing parameters. The freely available state estimates and related efforts are property-conserving, allowing closed budget calculations that are a requisite to detect, quantify, and understand the evolution of climate-relevant signals, as mandated by the Coupled Model Intercomparison Project Phase 6 (CMIP6) protocol. The solutions can be reproduced by users through provision of the underlying modeling and assimilation machinery. Regional efforts have spun off that offer increased spatial resolution to better resolve relevant processes. Emerging foci of ECCO are on a global sea level changes, in particular contributions from polar ice sheets, and the increased use of biogeochemical and ecosystem data to constrain global cycles of carbon, nitrogen and oxygen. Challenges in the coming decade include provision of uncertainties, informing observing system design, globally increased resolution, and moving toward a coupled Earth system estimation with consistent momentum, heat and freshwater fluxes between the ocean, atmosphere, cryosphere and land.

Decadal changes of radiocarbon (14C) of seawater in the eastern tropical Indian Ocean are evaluated by the reoccupation of three stations previously measured by the Geochemical Ocean Sections Study (GEOSECS) and the World Ocean Circulation Experiment (WOCE) expedition in the spring of 2014. The bomb-14C inventory in the whole water column increased by ~56% to a level of 7.7 × 109 atoms /cm2 from 1978 to 2014, and the bomb-14C mean penetration depth reached ~550 m, which is more than triple of the depth in 1978. This is accompanied by a significant decrease of Δ14C in the upper layer, with an average decline rate of 2.5‰ per year for the surface water. The Δ14C in the range of ~100 m – ~750 m depth is found to increase with time, revealing an active downward transfer of bomb-14C signature from the upper water to the intermediate layer. The enhanced bomb-14C inventory through the water column in the region is attributed to the incursion of Pacific water into the Indian Ocean through the Indonesian Throughflow and the advection of 14C-enriched waters from the southern subtropical gyre. In addition, the Southwest Monsoon Current is inferred to have contributed to the observed small increase of 14C at the site within the Bay of Bengal. This study therefore highlights the dynamic redistribution of anthropogenic bomb-14C through shallow-to-deep vertical mixing processes, as well as through the inter- and intra- basin circulations between the eastern tropical Indian Ocean and its adjacent areas.

The application of T-junction has already been extended from the petroleum engineering to the emerging advanced thermodynamic cycles. How a T-junction, as a separator in an emerging thermodynamic cycle, affects the cycle efficiency is discussed in this paper. Firstly, based on the Eulerian method, parametric studies on the local pressure drop coefficients are conducted and two new local pressure drop (LPD) coefficients are predicted in this paper. Then, the effects of pressure drop on a composition adjustable organic Rankine cycle efficiency is analyzed. In the process, a composition adjustable organic Rankine cycle with zeotropic mixtures R245fa/R123 is chosen to calculate the effects of pressure drop on thermodynamic cycle efficiency. The quality of the outlet of the evaporator is assumed as 0.7, and the composition ratio as 0.6/0.4. The results show that the pressure variation of T-junction affects the adjustable organic Rankine cycle efficiency, and reasonable phase separation ratio can improve the thermodynamic cycle efficiency. The pressure drop could cause composition diffusion. In addition, two new local pressure drop coefficients are obtained. And the results demonstrate that K12J declines slowly with the increases of density ratio (ρ2/ρ1) and decreases with the increases of mass fraction of taken off (F). K13J shows an obvious trend with diameter ratio (d3/d1) and F. This work could push the research of T-junction as a separator in the adjustable organic Rankine cycle, Sí

A box inverse model of the Southern Ocean during the World Ocean Circulation Experiment is constructed to investigate the three-dimensional structure of the regional overturning circulation in that era. The model has many features in common with various preceding inverse studies, but also contains several novel elements that make it well suited for addressing many of the significant uncertainties that surround the circulation at present. The net overturning circulation of the Southern Ocean is found to consist of two well-defined cells of similar strength. The upper cell consists of a northward transport of 18.8 ± 5.5 Sv of surface, mode and intermediate waters lighter than the 27.5 kg m−3 isoneutral, and an equivalent southward flow in the approximate 27.5–27.9 kg m−3 neutral density range, encompassing the bulk of the Upper Circumpolar Deep Water. The lower cell involves the northward export of 18.6 ± 0.9 Sv of Antarctic Bottom Water and Lower Circumpolar Deep Water denser than 28.08 kg m−3, and an opposing transport in the lighter classes of that water mass. Substantial structural differences between the overturning circulations of the Atlantic, Indian and Pacific basins are indicated by the model’s solution. Overall, the diagnosed Southern Ocean circulation shares many qualitative and some quantitative features with previous inverse estimates, particularly as regards the large-scale, depth-integrated lateral circulation and associated energy fluxes in the subtropics and in the Antarctic Circumpolar Current, and the strength of the upper overturning cell. However, it also suggests several significant adjustments to current views of the regional circulation. Most notable amongst these are: the subpolar circulation of the Southern Ocean is more vigorous and zonally interconnected than generally thought; the associated lower overturning cell is more intense than indicated by most preceding estimates; contrary to common perception, sub-surface mixing processes play a role of comparable importance to air–sea–ice exchanges of buoyancy in underpinning the dianeutral closure of the Southern Ocean overturning, even at shallow (mode and intermediate water) levels; and the connection between North Atlantic deep water formation and Southern Ocean upwelling is fundamentally three-dimensional, such that deep waters from the North Atlantic must upwell dianeutrally before being returned to the permanent pycnocline of the northern oceans.

Detection and attribution of hydrographic and biogeochemical changes in the deep ocean are challenging due to the small magnitude of their signals and to limitations in the accuracy of available data. However, there are indications that anthropogenic and climate change signals are starting to manifest at depth. The deep ocean below 2000 m comprises about 50% of the total ocean volume, and changes in the deep ocean should be followed over time to accurately assess the partitioning of anthropogenic carbon dioxide (CO 2 ) between the ocean, terrestrial biosphere, and atmosphere. Here we determine the changes in the interior deep-water inorganic carbon content by a novel means that uses the partial pressure of CO 2 measured at 20 °C, p CO 2 (20), along three meridional transects in the Atlantic and Pacific oceans. These changes are measured on decadal time scales using observations from the World Ocean Circulation Experiment (WOCE)/World Hydrographic Program (WHP) of the 1980s and 1990s and the CLIVAR/CO 2 Repeat Hydrography Program of the past decade. The p CO 2 (20) values show a consistent increase in deep water over the time period. Changes in total dissolved inorganic carbon (DIC) content in the deep interior are not significant or consistent, as most of the signal is below the level of analytical uncertainty. Using an approximate relationship between p CO 2 (20) and DIC change, we infer DIC changes that are at the margin of detectability. However, when integrated on the basin scale, the increases range from 8–40% of the total specific water column changes over the past several decades. Patterns in chlorofluorocarbons (CFCs), along with output from an ocean model, suggest that the changes in p CO 2 (20) and DIC are of anthropogenic origin.

Evidence from physical and geochemical tracers measured during the World Ocean Circulation Experiment (WOCE) shows that there are four sub-types of Antarctic Intermediate Water (AAIW) in the South Pacific. The main formation region of AAIW is the southeast Pacific, where fresh, cold, high oxygen, low nutrient, intermediate waters are created. This AAIW is transported north and mixes with Equatorial Pacific Intermediate Waters (EqPIW), themselves a combination of AAIW and nutrient rich, old North Pacific deep waters. ‘Tasman’ AAIW found in the Coral and Tasman Seas is more saline and warmer than the main subtropical gyre, and appears to have formed from mixing of AAIW with thermocline waters in the Tasman Gyre. Tasman AAIW leaks out of the Tasman basin to the north of New Zealand and along Chatham Rise, and also in the South Tasman Sea via the Tasman Leakage. Another source of relatively fresh, high oxygen, low nutrient, young AAIW comes directly from the Southern Ocean, flowing into the southwest and central South Pacific Basin, west of the East Pacific Rise. This ‘Southern Ocean’ (SO) AAIW is most likely a mixture of AAIW formed locally at the Subantarctic Front (SAF), and AAIW formed along the SAF in the southeast Pacific or Indian oceans and transported by the Antarctic Circumpolar Current (ACC). Interpreting physical and geochemical tracers, combined with velocity estimates from Argo floats, and previous research, has allowed us to refine the detailed circulation pattern of AAIW in the South Pacific, especially in the topographically complex southwest Pacific.

Fronts, baroclinic transport, and mesoscale variability of the Antarctic Circumpolar Current (ACC) along 115°E are examined on the basis of CTD data from two hydrographic cruises occupied in 1995 as a part of the World Ocean Circulation Experiment (WOCE cruise I9S) and in 2004 as a part of CLIVAR/CO2 repeat hydrography program. The integrated baroclinic transport across I9S section is (97.2×106±2.2×106) m3/s relative to the deepest common level (DCL). The net transport at the north end of I9S, determined by the south Australian circulation system, is about 16.5×106 m3/s westward. Relying on a consistent set of water mass criteria and transport maxima, the ACC baroclinic transport, (117×106±6.7×106) m3/s to the east, is carried along three fronts: the Subantarctic Front (SAF) at a mean latitude of 44°–49°S carries (50.6×106±13.4×106) m3/s; the Polar Front (PF), with the northern branch (PF-N) at 50.5°S and the southern branch (PFS) at 58°S, carries (51.3×106±8.7×106) m3/s; finally, the southern ACC front (SACCF) and the southern boundary of the ACC (SB) consist of three cores between 59°S and 65°S that combined carry (15.2×106±1.8×106) m3/s. Mesoscale eddy features are identifiable in the CTD sections and tracked in concurrent maps of altimetric sea level anomalies (SLA) between 44°–48°S and 53°–57°S. Because of the remarkable mesoscale eddy features within the SAF observed in both the tracks of the cruises, the eastward transport of the SAF occurs at two latitude bands separating by 1°. Both the CTD and the altimetric data suggest that the mesoscale variability is concentrated around the Antarctic Polar Frontal Zone (APFZ) and causes the ACC fronts to merge, diverge, and to fluctuate in intensity and position along their paths.

Evidence from geochemical tracers (salinity, oxygen, silicate, nutrients, alkalinity, dissolved inorganic carbon (DIC), carbon isotopes (δ13CDIC) and radiocarbon (Δ14C)) collected during the Pacific Ocean World Ocean Circulation Experiment (WOCE) voyages (P10, P15, P17 and P19) indicate there are three main water types at intermediate depths in the Pacific Ocean; North Pacific Intermediate Water (NPIW), Antarctic Intermediate Water (AAIW) and Equatorial Pacific Intermediate Waters (EqPIW). We support previous suggestions of EqPIW as a separate equatorial intermediate depth water as it displays a distinct geochemical signature characterised by low salinity, low oxygen, high nutrients and low Δ14C (older radiocarbon). Using the geochemical properties of the different intermediate depth waters, we have mapped out their distribution in the main Pacific Basin. From the calculated pre-formed δ13Cair–sea conservative tracer, it is evident that EqPIW is a combination of AAIW parental waters, while quasi-conservative geochemical tracers, such as radiocarbon, also indicate mixing with old upwelling Pacific Deep Waters (PDW). The EqPIW also displays a latitudinal asymmetry in non-conservative geochemical tracers and can be further split into North (NEqPIW) and South (SEqPIW) separated at ∼2°N. The reason for this asymmetry is caused by higher surface diatom production in the north driven by higher silicate concentrations. The δ13C signature measured in benthic foraminifera, Cibicidoides spp. (δ13CCib), from four core tops bathed in AAIW, SEqPIW and NPIW, reflects that of the overlying intermediate depth waters. The δ13CCib from these cores show similarities and variations down-core that highlight changes in mixing over the last 30,000 yr BP. The reduced offset between the δ13CCib of AAIW and SEqPIW during the last glacial indicates that AAIW might have had an increased influence in the eastern equatorial Pacific (EEP) region at this time. Additional intermediate depth cores and other paleo-geochemical proxies such as Cd/Ca and radiocarbon are required from the broader Pacific Ocean to further understand changes in intermediate depth water formation, circulation and mixing over glacial/interglacial cycles.

We conducted full-depth hydrographic observations between 8°50′ and 44°30′N at 165°W in 2003 and analyzed the data together with those from the World Ocean Circulation Experiment and the World Ocean Database, clarifying the water characteristics and deep circulation in the Central and Northeast Pacific Basins. The deep-water characteristics at depths greater than approximately 2000 dbar at 165°W differ among three regions demarcated by the Hawaiian Ridge at around 24°N and the Mendocino Fracture Zone at 37°N: the southern region (10–24°N), central region (24–37°N), and northern region (north of 37°N). Deep water at temperatures below 1.15 °C and depths greater than 4000 dbar is highly stratified in the southern region, weakly stratified in the central region, and largely uniform in the northern region. Among the three regions, near-bottom water immediately east of Clarion Passage in the southern region is coldest ( θ S >34.70), highest in dissolved oxygen (O 2 >4.2 ml l −1 ), and lowest in silica (Si −1 ). These characteristics of the deep water reflect transport of Lower Circumpolar Deep Water (LCDW) due to a branch current south of the Wake–Necker Ridge that is separated from the eastern branch current of the deep circulation immediately north of 10°N in the Central Pacific Basin. The branch current south of the Wake–Necker Ridge carries LCDW of θ 6 m 3 s −1 ) into the Northeast Pacific Basin through Horizon and Clarion Passages, mainly through the latter (∼3.1 Sv). A small amount of the LCDW flows northward at the western boundary of the Northeast Pacific Basin, joins the branch of deep circulation from the Main Gap of the Emperor Seamounts Chain, and forms an eastward current along the Mendocino Fracture Zone with volume transport of nearly 1 Sv. If this volume transport is typical, a major portion of the LCDW (∼3 Sv) carried by the branch current south of the Wake–Necker and Hawaiian Ridges may spread in the southern part of the Northeast Pacific Basin. In the northern region at 165°W, silica maxima are found near the bottom and at 2200 dbar; the minimum between the double maxima occurs at a depth of approximately 4000 dbar ( θ ∼1.15 °C). The geostrophic current north of 39°N in the upper deep layer between 1.15 and 2.2 °C, with reference to the 1.15 °C isotherm, has a westward volume transport of 1.6 Sv at 39–44°30′N, carrying silica-rich North Pacific Deep Water from the northeastern region of the Northeast Pacific Basin to the Northwest Pacific Basin.

To address questions concerning the intensity and spatial structure of the three-dimensional circulation within the Pacific Ocean and the associated advective and diffusive property flux divergences, data from approximately 3000 high-quality hydrographic stations collected on 40 zonal and meridional cruises have been merged into a physically consistent model. The majority of the stations were occupied as part of the World Ocean Circulation Experiment (WOCE), which took place in the 1990s. These data are supplemented by a few pre-WOCE surveys of similar quality, and time-averaged direct-velocity and historical hydrographic measurements about the equator. An inverse box model formalism is employed to estimate the absolute along-isopycnal velocity field, the magnitude and spatial distribution of the associated diapycnal flow and the corresponding diapycnal advective and diffusive property flux divergences. The resulting large-scale WOCE Pacific circulation can be described as two shallow overturning cells at mid- to low latitudes, one in each hemisphere, and a single deep cell which brings abyssal waters from the Southern Ocean into the Pacific where they upwell across isopycnals and are returned south as deep waters. Upwelling is seen to occur throughout most of the basin with generally larger dianeutral transport and greater mixing occurring at depth. The derived pattern of ocean heat transport divergence is compared to published results based on air–sea flux estimates. The synthesis suggests a strongly east/west oriented pattern of air–sea heat flux with heat loss to the atmosphere throughout most of the western basins, and a gain of heat throughout the tropics extending poleward through the eastern basins. The calculated meridional heat transport agrees well with previous hydrographic estimates. Consistent with many of the climatologies at a variety of latitudes as well, our meridional heat transport estimates tend toward lower values in both hemispheres.

Data collected from hydrographic stations occupied within the Venezuelan and Columbian basins of the Caribbean Sea from 1922 through 2003 are analyzed to study the decadal variability of deep temperature in the region. The analysis focuses on waters below the 1815-m sill depth of the Anegada–Jungfern Passage. Relatively dense waters (compared to those in the deep Caribbean) from the North Atlantic spill over this sill to ventilate the deep Caribbean Sea. Deep warming at a rate of over 0.01 °C decade –1 below this sill depth appears to have commenced in the 1970s after a period of relatively constant deep Caribbean Sea temperatures extending at least as far back as the 1920s. Conductivity–temperature–depth station data from World Ocean Circulation Experiment Section A22 along 66°W taken in 1997 and again in 2003 provide an especially precise, albeit geographically limited, estimate of this warming over that 6-year period. They also suggest a small (0.001 PSS-78, about the size of expected measurement biases) deep freshening. The warming is about 10 times larger than the size of geothermal heating in the region, and is of the same magnitude as the average global upper-ocean heat uptake over a recent 50-year period. Together with the freshening, the warming contributes about 0.012 m decade –1 of sea level rise in portions of the Caribbean Sea with bottom depths around 5000 m.

The inter-ocean exchange of water masses at the Agulhas Current termination comes about through the shedding of rings, and this process plays an important role in the global thermohaline circulation. Using several hydrographic sections collected during the ARC (Agulhas Retroflection Cruise), MARE (Mixing of Agulhas Rings Experiment) and WOCE (World Ocean Circulation Experiment), this investigation aims to establish the degree to which Red Sea Intermediate Water (RSIW) is involved in this exchange and at what level of purity. To this end a wide range of hydrographic parameters were used. Upstream from the Agulhas Current retroflection water with clear RSIW origin is shown to move downstream on both the landward and seaward sides of the Agulhas Current with the highest water sample purity or water-mass content exceeding 15%. The least mixed water was found close to the continental shelf. At the retroflection the RSIW purity shows considerable variability that ranges between 5% and 20%. This suggests that RSIW moves down the current in patches of considerably varying degrees of previous mixing. This pattern was also observed in a ring sampled during the ARC experiment. The MARE sections in turn indicate that at times RSIW may be entirely absent in the Agulhas Current. RSIW is therefore shown to travel down the current as discontinuous filaments, and this intermittency is reflected in its presence in Agulhas Rings. From the sections investigated it is therefore clear that any calculation of RSIW fluxes involved in inter-ocean exchange can only be done on the basis of event scales. RSIW not trapped in Agulhas Rings flows east with the Agulhas Return Current.

Heat transports estimated CTD data collected during the World Ocean Circulation Experiment (WOCE) along the January 1993 30°S hydrographic transect (A10) and the output from a numerical model show a mean heat transport of 0.40 and 0.55±0.24 PW (standard deviation), respectively. The model shows a large annual cycle in heat transport (more than 30% of the variance) with a maximum (minimum) heat transport in July (February) of 0.68 (0.41) PW. Using these data, a method is proposed and evaluated to calculate the heat transport from temperature data obtained from a trans-basin section of expendable bathythermographs (XBTs) profiles. In this method, salinity is estimated from Argo profiles and CTD casts for each XBT temperature observation using statistical relationships between temperature, latitude, longitude and salinity computed along constant-depth surfaces. Full-depth temperature/salinity profiles are obtained by extending the profiles to the bottom of the ocean using deep climatological data. The meridional transport is then determined by using the standard geostrophic method, applying NCEP-derived Ekman transports, and requiring that the salt flux through the Bering Straits be conserved. The results indicate that the methods described here can provide heat transport estimates with a maximum uncertainty of ±0.18 PW (1 PW=1015 W). Most of this uncertainty is due to the climatology used to estimate the deep structure and issues related to not knowing the absolute velocity field and most especially characterizing barotropic motions. Nevertheless, when the methodology is applied to temperatures collected along 30°S (A10) and direct model integrations, the results are very promising. Results from the numerical model suggest that ageostrophic non-Ekman motions can contribute less than 0.05 PW to heat transport estimates in the South Atlantic.

The three-end-member mixing model of Li and Peng [Latitudinal change of remineralization ratios in the oceans and its implication for nutrient cycles. Global Biogeochemical Cycles 16, 1130–1145] was applied to the World Ocean Circulation Experiment (WOCE) data from Indian Ocean to obtain additional estimates on the remineralization ratios ( P ⧹ N ⧹ C org ⧹ ‐ O 2 ) of organic matter in the oxygenated regions. The results show systematic changes of the remineralization ratios with latitude and depth in the Indian Ocean. The average remineralization ratios for Indian warm water masses (potential temperature θ > ∼ 10 ∘ C ) are P ⧹ N ⧹ C org ⧹ ‐ O 2 = 1 ⧹ ( 15.6 ± 0.7 ) ⧹ ( 110 ± 9 ) ⧹ ( 159 ± 8 ) . These are comparable to the traditional Redfield ratios ( P ⧹ N ⧹ C org ⧹ ‐ O 2 = 1 ⧹ 16 ⧹ 106 ⧹ 138 ) , and are in good agreement with Anderson's [On the hydrogen and oxygen content of marine phytoplankton. Deep-Sea Research I 42, 1675–1680.] values of P ⧹ N ⧹ C org ⧹ ‐ O 2 = 1 ⧹ 16 ⧹ 106 ⧹ 150 within the given uncertainties. Separation of nitrate deficits resulting from aerobic partial nitrification (dN) and anaerobic denitrification (dN″) processes using empirical equations is shown to be useful and consistent with other observations. The dN maximum coincides with the phosphate and nitrate maximums, lies within the oxycline below the oxygen minimum zone, and is in contact with the continental slope sediments. The dN″ maximum lies within the oxygen minimum zone with O2

The focus of this review article is on the anthropogenic CO 2 taken up by the ocean. There are several methods of identifying the anthropogenic CO 2 signal and quantifying its inventory in the ocean. The ?C* method is most frequently used to estimate the global distribution of anthropogenic CO 2 in the ocean. Results based on analysis of the dataset obtained from the comprehensive surveys of inorganic carbon distribution in the world oceans in the 1990s are given. These surveys were jointly conducted during the World Ocean Circulation Experiment (WOCE) and the Joint Global Ocean Flux Study (JGOFS). This data set consists of 9618 hydrographic stations from a total of 95 cruises, which represents the most accurate and comprehensive view of the distribution of inorganic carbon in the global ocean available today. The increase of anthropogenic CO2 in the ocean during the past few decades is also evaluated using direct comparison of results from repeat surveys and using statistical method of Multi-parameter Linear Regression (MLR). The impact of increasing oceanic anthropogenic CO 2 on the calcium carbonate system in the ocean is reviewed briefly as well. Extensive studies of CaCO 3 dissolution as a result of increasing anthropogenic CO 2 in the ocean have revealed several distinct oceanic regions where the CaCO 3 undersaturation zone has expanded.

This study quantifies uncertainties in closing the seasonal cycle of diabatic heat storage (DHS) over the Pacific Ocean from 20°S to 60°N through the synthesis of World Ocean Circulation Experiment (WOCE) reanalysis products from 1993 to 1999. These products are DHS from Scripps Institution of Oceanography (SIO); near-surface geostrophic and Ekman currents from Earth and Space Research (ESR); and air–sea heat fluxes from Comprehensive Ocean-Atmosphere Data Set (COADS), National Centers for Environmental Prediction (NCEP), and European Center for Mid-Range Weather Forecasts (ECMWF). With these products, we compute residual heat budget components by differencing long-term monthly means from the long-term annual mean. This allows the seasonal cycle of the DHS tendency to be modeled. Everywhere latent heat flux residuals dominate sensible heat flux residuals, shortwave heat flux residuals dominate longwave heat flux residuals, and residual Ekman heat advection dominates residual geostrophic heat advection, with residual dissipation significant only in the Kuroshio–Oyashio current extension. The root-mean-square (RMS) of the differences between observed and model residual DHS tendencies (averaged over 10° latitude-by-20° longitude boxes) is −2 in the interior ocean and −2 in the Kuroshio–Oyashio current extension. This reveals that the residual DHS tendency is driven everywhere by some mix of residual latent heat flux, shortwave heat flux, and Ekman heat advection. Suppressing bias errors in residual air–sea turbulent heat fluxes and Ekman heat advection through minimization of the RMS differences reduces the latter to −2 over the interior ocean and −2 in the Kuroshio–Oyashio current extension. This reveals air–sea temperature and specific humidity differences from in situ surface marine weather observations to be a principal source of bias error, overestimated over most of ocean but underestimated near the Intertropical Convergence Zone.

The circulation of deep water in the south-western Indian Ocean has been studied from hydrographic observations and current measurements, obtained during the Dutch–South African Agulhas Current Sources Experiment programme, and from similar public data from the World Ocean Circulation Experiment. The three major water masses involved are the saline North Atlantic deep water (NADW), its derivative in the Antarctic circumpolar current, lower circumpolar deep water (LCDW), and the aged variety of deep water, North Indian deep water (NIDW). Although bound by the shallow topography near Madagascar, about 2×10 6 m 3 /s from the upper half of the NADW core appears to flow across the sill in the Mozambique Channel into the Somali Basin, while the remaining NADW flows east at about 45°S and is transformed to LCDW by lateral and diapycnal mixing. East of Madagascar the deep circulation is dominated by the southward flow of NIDW. Northward inflow of LCDW into the Indian Ocean therefore can take place only in the eastern half of the Indian Ocean, along the Southeast Indian Ridge and the Ninetyeast Ridge.

We present 3He data froma repeat section across Drake Passage, fromthree sections off the South American continent in the Pacific, at 28?S, 35?S, and 43?S, and fromthree sections in the Atlantic, eastward of the Malvinas, close to 35?W, and near the Greenwich Meridian. In Drake Passage, a distinct high-3He signal is observed that is centered just above the boundary of the Lower and the Upper Circumpolar Deep Water (LCDW, UCDW), and is concentrated towards the northern continental slope. 3He concentrations in the Antarctic Circumpolar Current (ACC) upstream of Drake Passage (World Ocean Circulation Experiment section P19 at 88?W) are markedly lower than those found in Drake Passage, and a regional source of primordial helium in the path of the ACC that might cause the high-3He feature can be ruled out. We explain the feature by addition of high-3He waters present at the 43?S Pacific section. This supports a previous, similar interpretation of a low-salinity anomaly in Drake Passage (Naveira Garabato et al., Deep- Sea Research I 49 (2002) 681), that is strongly related to the high-3He feature. Employing multiparameter water mass analysis (including 3He as a parameter), we find that deep waters as met at the 43?S Pacific section, flowing south along the South American continental slope, contribute substantially to the ACC waters in Drake Passage (fractions exceed 50% locally). Lesser, but laterally more extended contributions are found east of the Malvinas, and still smaller ones are present at 35?W and at the Greenwich Meridian. Using velocity measurements from one of the two Drake Passage sections, we estimate the volume transport of these waters to be 7.071.2 Sv, but the average transport may be somewhat lower as the other realization had a less pronounced signal. The enhanced 3He signature in Drake Passage is essentially confined north of the Polar Front. Further downstreamthe signature crosses this front, to the extent that at 35?W the contributions south and north of it are of similar magnitude. At the same time, the 3He levels north of the front are reduced due to a substantial admixture of low-3He North Atlantic Deep Water, such that 3He becomes highest south of the front. The flow of Southeast Pacific deep slope waters entering the ACC constitutes the predominant exit pathway of the primordial helium released in the deep Pacific, and represents a considerable fraction of the deep water return flow fromthe Pacific into the ACC. Therefore and also because the density range of the added deep slope waters is intermediate between those of UCDW and LCDW, they must be considered a distinct water mass. r 2003 Elsevier Ltd. All rights reserved.

We present and assess the distribution of neon in South Atlantic and South Pacific waters, on the basis of more than 3000 mostly new neon data which were obtained primarily under the hydrographic program of the World Ocean Circulation Experiment (predominantly southern summer to fall cruises). Data precision is better than±0.5%, and the set is internally consistent within±0.3% and partly better, and compatible with reported high-quality neon values. Using suitably averaged data (precision 0.1–0.3%), we find that the total range of neon anomalies relative to a solubility equilibrium with atmospheric neon at the observed potential temperature and salinity (using the solubilities of Weiss, J. Chem. Eng. Data 16 (1971) 235) is approximately 0–4%, and below 2000 m depth, 3–4% only. We consistently observe two types of neon depth profiles, one for the temperate-latitudes ocean, which is characterized by a near-surface maximum and a minimum in Antarctic Intermediate Water, and one for the Southern Ocean that essentially displays a steady increase with depth. The neon distribution reflects the influence of air injected by submerged air bubbles, the areal distribution of atmospheric pressure, seasonal temperature changes in the mixed layer and solar heating below it, and interaction with sea ice and glacial ice, largely in keeping with previous work. However, it appears that interaction with sea ice reduces neon anomalies distinctly less than the literature suggests. The temperate-ocean shallow maxima point to widespread subsurface heating in the course of the summer season by roughly 1 K. Among the major source water masses of the deep waters, the neon anomalies are lowest in Antarctic Intermediate Water (∼1.5%), intermediate in North Atlantic Deep Water (∼3%, confirming previous work) and similarly in Circumpolar Deep Water, and highest in Antarctic Bottom Water (∼3.8%). The anomalies in Southeast Pacific deep waters (>2500 m) are comparatively less (only∼3.3%), as a result of the contribution of Antarctic Intermediate Water. The present study is the first attempt to deal with the oceanic distribution of neon in a systematic fashion. The results can serve to assist assessments of the oceanic distributions of other dissolved gases.

Water mass formation rates were calculated for subtropical underwater (STUW) in the North and South Pacific by two partially independent methods. One is based on the World Ocean Circulation Experiment (WOCE)/TOGA drifter array over two periods: 1988–1992, and 1992–1996. Drifter velocities were used to calculate two components of the subduction rate, lateral induction and vertical pumping. The second method used CFC-12 data (1987–1994) from WOCE and Pacific Marine Environmental Laboratory to calculate ages on σ θ surfaces. Subduction rates were estimated from the inverse age gradient. The two subduction rate methods are independent, but they share a common identification of STUW formation area based on satellite-derived surface temperature maps. Using both methods, one can put bounds on the formation rates: 4–5 Sv in the North and 6–7 Sv in the South Pacific. The drifter calculated STUW subduction rates for 1988–1992 and 1992–1996 are 21 and 13 m/yr in the North Pacific and 25 and 40 m/yr in the South. The CFC-12 calculated STUW subduction rate in the North Pacific is 26 m/yr, and 32 m/yr in the South. The South Pacific rates exceed those in the North Pacific. Consistent differences between the two methods support earlier studies, they conclude that mixing contributes to STUW formation in addition to the larger-scale circulation effects. The drifter and tracer rates agree well quantitatively, within 22%, except for the second period in the North Pacific and there are some differences in spatial patterns. Tracer rates integrate over time, and drifters allow analysis of interannual variability. The decrease in subduction rate between periods in the North Pacific is due to negative lateral induction entraining STUW into the mixed layer. The increase in the South Pacific rate is due to an increase in the vertical pumping. Although Ekman pumping is in phase in the North and South, the subduction rate is out of phase. These results confirm that subduction depends on the large-scale circulation and a combination of the outcrop pattern and air–sea fluxes. Temporal differences in rates and partitioning between the hemispheres are consistent with interannual changes in gyre intensity and current positions.

Batch to batch differences of IAPSO standard seawater (SSW) batches P103 to P129 were examined. Several comparison experiments, in which 2–23 batches of SSW were compared with each other, were carried out during the period from 1991 to 1997. Batch to batch differences for the KCl-labeled batches, P91 through P129 except for P113, P115, P117, P125 and P126, ranged from −2.2×10−3 to 1.2×10−3 in salinity with an average of −0.1×10−3 in salinity. Within-batch differences were observed to be

Seasonal surface water nitrate and phosphate depletions were calculated for the Subantarctic Zone (SAZ) and Polar Frontal Zone (PFZ) of the Southern Ocean along the World Ocean Circulation Experiment SR3 repeat section south of Tasmania, Australia, and three other transects slightly to the west. The depletions were calculated between a single winter (July) section and eight other sections from October to March in the years 1991-1998 and corrected for frontal movements and changes in water masses between the cruises using observed quasi-linear nutrient-salinity relationships. Arranged in a seasonal progression, depletion began in approximately October and continued through March, in good agreement with satellite biomass-based estimates of production. Nitrate depletion in the SAZ (510 mmol N m−2) was approximately twice that of the PFZ (250 mmol N m−2), but phosphate depletions were similar (29 and 24 mmol P m−2 for the SAZ and PFZ, respectively). The SAZ exhibited a Redfield N/P depletion ratio (15.1±2.3), but the PFZ ratio was much lower (8.3±5.4). While the SAZ exhibits greater seasonal nutrient depletion, the relative magnitudes of export in the two zones remain uncertain because supply of nutrients from south of the Polar Front may lower the observed nutrient depletions in the PFZ. However, comparisons with sediment trap and production measurements for the region south of Australia suggest the SAZ and PFZ differences derive from differences in production. Assuming a Redfield C/N ratio (6.6), carbon export for the longest period examined (July-March) averaged 3400±430 mmol C m−2 in the SAZ, with a range between 2700 and 3900 mmol C m−2 depending on latitude. In the PFZ, carbon export averaged 1600±350 mmol C m−2, with a range of 1100 to 2000 mmol C m−2. These averages represent minimum annual export production estimates because neither resupply nor export outside the July-March observational period is included.

The seasonal formation of a large anticyclonic circulation pattern, Southern Arabian Sea High (SAH), appears in the southern Arabian Sea during the northeast monsoon. SAH is studied on the basis of the recent observations that include the World Ocean Circulation Experiment (WOCE)/Tropical Ocean-Global Atmosphere (TOGA) experiment drifting buoys along with TOPEX/ERS-2 satellite altimeter data in conjunction with the climatological hydrography observations. The SAH forms west of the Laccadive High (LH), first appears in January, and grows rapidly in situ to form a well-developed anticyclonic eddy, extending across the southern Arabian Sea by March. The center of the eddy is ∼65°E, 5°N. The SAH is bounded by a strong eastward current to the north and a weak southward flow between 65° and 70°E, which separates SAH from the LH. The westward flowing North Equatorial Current (NEC) is on the southern flank. A strong northward flow along 55°E during January and February marks the western boundary. SAH propagates westward as a Rossby wave between March and April. The arrival of SAH in the western boundary in April is accompanied by intensification of current along the coast of Somalia. In May, part of the SAH has subsequently moved northward to form an anticyclonic eddy with an apparent center 13°N, 53°E in the vicinity of the Gulf of Aden (Gulf of Aden Eddy (GAE)). The GAE extends horizontally nearly 600 km (along 13°) and is vertically extended down through the upper main thermocline to ∼250 m. Comparisons of hydrography, buoy, and altimetry reveal a good agreement in eddy size, location, and time of appearance of the GAE.

A subsurface chlorophyll maximum (SCM), composed principally of large diatoms, has been consistently observed in summer and autumn between 53° and 58°S along 140°E on Australian World Ocean Circulation Experiment and Joint Global Ocean Flux Study cruises from 1994 to 1998. This region lies in a zone of weak northward flow, between two branches of the Polar Front (hence the Interpolar Frontal Zone (IPFZ)). In the IPFZ, mixed layer nitrate concentrations are high (>24 μM) year-round, while mixed layer silicic acid is intermediate (about 15 μM) in winter but is depleted to 2 μM or less in late summer. Dissolved Fe concentrations, only available for summer, are low (

A World Ocean Circulation experiment Hydrographic Program section along 66°W in the North Atlantic was made in 1997. In addition to the usual variables (hydrographic and tracer) measured in WOCE onetime sections, we made lowered acoustic doppler current profiler (LADCP) measurements at nearly all of the stations. The section closed off a portion of the western North Atlantic to the west of the line, making a closed volume for constraining the circulation. In addition, the deep portions of the Caribbean do not communicate with the rest of the basin. By combining mass, silica, and LADCP information as constraints an inverse calculation obtained reveals a strong eastward transport in the Gulf Stream bounded by westward flowing water on either side. Within these energetic flows we see evidence for recently ventilated Classical Labrador Sea Water, which has not reached the Deep Western Boundary Current north of Puerto Rico in any significant amounts. Within the Caribbean our major new finding is a deep cyclonic circulation below sill depth in excess of 100 times the inflow of deep Atlantic water through the major deep sill: the Anegada-Jungfern Passage. The signature of the deep Atlantic source water is most prominent in CFCs and both a bottom and mid-depth maximum are present in the Caribbean to the south of Puerto Rico. Off the coast of Venezuela, however, only the deeper CFC maximum is found. For the entire section the net overturning circulation, heat flux, and freshwater fluxes are all consistent with expectations based on water mass formation and air-sea exchanges to the west of our section, but the annual mean air-sea fluxes of heat and freshwater from Comprehensive Ocean-Atmosphere Data Sets appear somewhat too small in comparison with our single-section result.

A warm and saline water transport to the North Pacific subarctic region which could feed the mesothermal (intermediate temperature maximum) water is investigated through the analysis of World Ocean Circulation Experiment and Subarctic Gyre Experiment hydrographic data. The analysis of individual cruise data supports the hypothesis that warm and saline water is transported from the area east of Japan to the Gulf of Alaska and also indicates that the isopycnal mixing is active in the area east of 165°E. The transport route obtained from individual cruise data mostly agrees with that based on climatological data. As a whole, isopycnal potential temperature and potential vorticity are conserved along the transport route using both the climatological and individual data excepting that the potential vorticity at 26.8σθ rapidly increases along streamlines in the Gulf of Alaska when the climatological data are used. This discrepancy might be attributed to the existence of the strong potential vorticity front in the Gulf of Alaska and excessive smoothing in the climatological data.

A new compilation of Lagrangian velocity observations describes the state of the North Atlantic surface circulation during the 1990s. Gridded fields of velocity and eddy kinetic energy (EKE) are constructed from trajectories of more than 1500 15-m drogued satellite-tracked surface drifters in service between January 1990 and December 1999. This time period overlaps a coordinated field study of circulation and variability in the North Atlantic completed between 1996–2000 as part of the World Ocean Circulation Experiment. We describe the construction of a self-consistent drifter climatology, present decadal-mean quasi-Eulerian velocity and EKE fields computed on a 1° grid, and compare these results with contemporary satellite measurements. Detailed discussion of the inferred surface circulation is focused on three regions: (1) The Gulf Stream and North Atlantic Current, (2) the Labrador Sea and subpolar gyre, and (3) the Caribbean Sea. The swiftest drifter motions were found in the equatorial region and along the tropical, subtropical, and subpolar western boundaries. The maximum instantaneous speed determined from a single (quality-controlled and filtered) drifter observation was 273 cm s−1 in the Gulf Stream southeast of Cape Cod. The highest EKE value in the North Atlantic (2790 cm2 s−2) was found in the Gulf Stream just downstream of the New England Seamounts. Over most of the Atlantic basin, drifter-derived EKE values were found to be O(100 cm2 s−2) higher than corresponding values derived from satellite altimetry. In the Labrador Sea a region of sharply elevated EKE appears to be geographically related to the localized ejection of drifters (and by extension, mass and kinetic energy) from the energetic West Greenland Current between 60° and 62°N. When compared to drifter measurements made in the late 1970s our results suggest (but do not statistically confirm) an enhancement and slight northward shift of the zonal Gulf Stream extension. Such a shift is consistent in sign with expectations based on observed interdecadal variations in wind stress and subtropical gyre potential energy associated with the North Atlantic Oscillation.

Hydrographic data about latitudes 30°–32°S in the Pacific Ocean are presented and used together with direct velocity observations from floats and moorings to investigate the spatial distribution of meridional flow and its associated transports. An initial velocity scheme is developed with reference to the water property distributions that is subsequently adjusted to meet constraints on net mass and dissolved silica transports. The resulting circulation is found to be sensitive to a priori scaling assumptions and differs in detail from past estimates of the flow in this region. Additionally constraining the flow with directly measured time averaged estimates of the velocity from floats and a current meter array significantly reduces the uncertainty in the derived flow field and improves consistency between the velocity and the property distributions. The derived circulation includes a nearly closed bottom-to-deep-water overturning circulation of 16–20 Sv, below a subtropical gyre flow of thermocline and surface waters consisting of nearly distinct Tasman Sea (∼30 Sv) and basin interior (∼10 Sv) circulations and (a prescribed) ∼10±5 Sv of net northward flow to supply the Indonesian and Bering Strait throughflows. On the basis of this circulation scheme, the heat flux divergence for the Pacific north of the P6 line is estimated to be 0.75±0.56 pW (ocean gaining heat from the atmosphere) and the net freshwater divergence is estimated to be 0.1±0.1 Sv (ocean gains fresh water via air-sea exchange and runoff). The former is highly dependent on the strength of the Indonesian throughflow; the latter also depends on the intensity of the lateral subtropical gyre circulation, which is constrained by the float data. Combined with estimates from the Indian and Atlantic Oceans, we find the subtropical Southern Hemisphere oceans transport 0.46±0.38 PW poleward, less than half the poleward heat transport achieved by the subtropical oceans in the Northern Hemisphere.

We have analyzed deep helium isotope data from World Ocean Circulation Experiment section P17 along 135°W in the Pacific Ocean. Combining these data with neon data, we have derived the isotopic ratio (Rt) of the nonatmospheric part of helium (terrigenic helium). The calculated Rt values are significantly lower than helium isotope ratios from mid-ocean ridge (MOR) sources (RMOR ≈ 8Ra; Ra: = (3He/4He)air), which are generally presumed to dominate the isotope characteristics of helium of nonatmospheric origin. For the depths most influenced by the southern East Pacific Rise (EPR) helium plume the isotopic ratio of terrigenic helium is ∼7.4 Ra. However, both the northern EPR plume and the Juan de Fuca Ridge (JdFR) plume show significantly lower Rt values of ∼6.8 Ra. We find minimum Rt values of ∼5.6 Ra at about 20°N to 30°N from 2000 m depth to the ocean floor. We conclude that in addition to the EPR and JdFR helium sources (having MOR isotope characteristics) there is a flux of radiogenic 4He out of deep-sea sediments and the oceanic crust which causes a significant deviation of Rt toward values lower than RMOR. Using our calculated terrigenic 4He concentrations and isotope ratios Rt and the helium isotope ratios of the two end-members (MOR helium and crustal helium), we derive concentrations and ocean bottom fluxes of crustal 4He (4Hecrust). Maximum concentrations of 4Hecrust (up to ∼30 pmol kg−1) are found at about 20°N to 30°N between 2000 m and 4000 m along the P17 section. The mean crustal 4He flux is obtained as 1.0 (±0.4) 109 atoms m−2Earth s−1.

A dynamically consistent steady state circulation pattern of the North Pacific (NP) ocean is presented. The fields describing oceanic state and atmospheric forcing are obtained by fitting a steady state large-scale circulation model to the 1.0 release of World Ocean Circulation Experiment hydrology, da Silva atmospheric climatologies, TOPEX-Poseidon altimetry, and Marine Environmental Data Service drifter data. Heat, salt, and mass transports of the major circulation features of the NP are presented. All the estimates are supplied with error bars obtained via the approximate inversion of the Hessian matrix. The optimized pattern shows, in particular, that NP is heated at an average rate of 11±7 W m−2 and loses 26±18 cm of fresh water from its surface per year. Zonal mean transport north of 20°N is characterized by an upwelling of 7±2 Sv (1 Sv = 106 m3 s−1) in the intermediate layers (500–3000 m) within the latitudes 30°–50°N. A weaker overturning cell characterized by the downwelling of 3±1 Sv at 55°–60°N contributes to the meridional circulation pattern north of 51°N. The net meridional advective heat transport in the midlatitudes is statistically undistinguishable from zero and amounts to −0.1±0.4 PW (1 PW = 1015 W). At 35°N, fresh water is transported southward at the rate equivalent to the average rainfall to the north of 35°N of 18±14 cm yr−1. Analysis of the water mass transformation rates reveals the major NP intermediate water formation site to be east of Hokkaido and South Kuril Islands. A much weaker source is detected in the Alaskan Gyre. The net production rate of the NPIW source water east of Kuril Islands is estimated as 2.5 Sv.

A continuous 4 year record of in situ bottom temperature measurements at 3690 m within Drake Passage (59°43.7S, 55°29.5W) from November 1992 to November 1996 is presented. The record shows fluctuations of order 0.02°C over monthly periods throughout the 4 years, but the annual mean temperature is the subject under discussion in this work. Between June 1994 and May 1995 the water sampled was of the order of 0.1°C cooler than the water sampled on either side of this time period. This temporal temperature anomaly has only become apparent because of the availability of a continuous data set. Hydrographic data sampled from the same location as part of the World Ocean Circulation Experiment SR1 repeat section provide potential temperature and salinity values that enable the bottom temperature record to be linked to variability in Weddell Sea Deep Water (WSDW). Oxygen isotope measurements demonstrate that the year-long period of cooler WSDW measured in Drake Passage is a signature of Ice Shelf Water in the formation process of deep and bottom waters within the Weddell Sea.

The spreading and mixing of deep and bottom waters from the Weddell Sea (originating with potential temperature

Between September 1991 and March 1994 the oceanic region off the east coast of Australia at 30°S was the subject of an intense observational program Part of the World Ocean Circulation Experiment, the objective was to improve our understanding of the dynamics of the East Australian Current (EAC) and to measure its volume and energy flux. The two main components were the Pacific Current Meter Array 3 (PCM3) with six moorings spanning a total distance of 120 km, and repeat, high-resolution hydrographic surveys. The long-term average fromPCM3 shows the EAC as a narrow, swift, and highly variable current centered at 40 km from the coast with strong shear in the upper 1000 m and mean southward velocities of 0.6 m s−1 in the core. The measurements also revealed a thick countercurrent underneath the poleward flow. The mean volume transport for the entire section covered by the array (between the coast and 154.4°E) was 22.1±4.6 Sv toward the south with an rms variability of 30 Sv. Combining the data from the PCM3 array with the hydrographic sections generated nine detailed snapshots of the absolute geostrophic current field. The snapshots were used to evaluate the reliability of the PCM3 data for determining volume transports. The rms difference between transports derived from direct current observations and from hydrographie data was 3.8 Sv, indicating that the PCM3 array can be used to describe the current variability despite the sparse spatial distribution of velocity measurements. Transport variability was dominated by periods between 90 and 140 days, which are attributed to eddy shedding in the region. Occasional intense northward flow events were observed where total transports reached up to 50 Sv northward. On those occasions the southward boundary current changed from being surface intensified and mainly baroclinic to northward and more barotropic, related to the northward migration past the array of the EAC coastal separation point.

A new method is presented for combining historical hydrography with the acoustic travel time measurements from an inverted echo sounder (IES) to obtain time series of full water column profiles of temperature T and specific volume anomaly. Hydrography is used to demonstrate that profiles constructed from the IES measurement account for more than 90% of the T and δ variance through the main thermocline range. Horizontal gradients between neighboring pairs of instruments, when combined with measurements from bottom pressure sensors and deep current meters, provide accurate estimates of absolute geostrophic velocity profiles. A section of IESs and current meters across the North Atlantic Current (NAC) along World Ocean Circulation Experiment line ACM6 near 42.5°N is analyzed using these methods, and the Eulerian mean temperature and absolute velocity sections are calculated. The mean transport for the combined NAC and northward flow within the inshore portion of the Mann Eddy is 146±13 (× 106 m3 s−1). The temporal standard deviation of the northward transport is 41×106 m3 s−1, arising not only from changes in the transport of the NAC but also from lateral shifts of the currents and eddies captured by the fixed span of moorings. Assumption of a level of no motion at the bottom and at 2000 dbar underestimates the true absolute transport by 33 or 60%, respectively. Historical measurements indicate that 50–60×106 m3 s−1 circulates within the Mann Eddy adjacent to the North Atlantic Current, thus 86–96×106 m3 s−1 appears to be throughput at the ACM6 line. Because the throughput observed on the ACM6 line considerably exceeds the combined historical estimates of northward and eastward outflow from the Newfoundland Basin of ≈ 30×106 m3 s−1, these measurements suggest a substantial (≈ 50 × 106 m3 s−1) recirculation or southward flow within the Newfoundland Basin in addition to the historical recirculation within the Mann Eddy.

As a result of its remarkably high salinity and despite its small volume input, remnants of Red Sea Water (RSW) have been identified in the Agulhas Current, over 6000 km distant of their source. This provided the motivation to investigate the long-term mean spreading of RSW throughout the Indian Ocean, using a comprehensive set of observations, taken from the National Oceanographic Data Center archives and from the World Ocean Circulation Experiment Hydrographic Program for the Indian Ocean. After emerging from the Gulf of Aden into the Arabian Sea, RSW spreads predominantly southwestward along the African continental slope, as indicated by strongly inclined isohalines across the Arabian Sea. There is some monsoon variability, so that during the winter monsoon there is more RSW present in the Gulf of Aden and an intensification of southward spreading along the western boundary, between 12° and 5°N. Elsewhere the intermediate depth salinity field of the Indian Ocean appears relatively stationary. Between 5° and 10°S, in the region of the South Equatorial Current, isohalines of the RSW layer become quasi-zonal across the width of the Indian Ocean, only dipping southward toward the western boundary west of 50°E. South of here, there is a strong tongue of RSW spreading southward through the Mozambique Channel and into the Agulhas Current. These conclusions concur with previous localized investigations of intermediate water properties. Using a simple mixing model, the percentage of RSW throughout the Indian Ocean was quantified. It was found that the flux of salt into the Gulf of Aden from the Red Sea is similar to that estimated to cross 32°S in the Agulhas Current. This result implies that all the RSW which is mixed into the interior of the Indian Ocean may eventually be exported at the western boundary. Furthermore, it implies that RSW is the dominant component of the salt budget for the intermediate layer and that input from the Indonesian Seas and via diapycnic processes are small.

We use data of satellite-tracked, mixed-layer drifters collected for the World Ocean Circulation Experiment/Tropical Ocean-Global Atmosphere (WOCE/TOGA) Surface Velocity Program in the East Sea (Sea of Japan) and the northwest Pacific Ocean during 1991-1997 to obtain reliable estimates of geographically varying horizontal diffusivity, integral timescale and space scale. For the diffusivity we suggest calculation of both the minor principal component of the diffusivity tensor in a definition by Davis [1991] and the half growth rate of the minor principal component of the displacement variance tensor. Numerical simulation of particle motion is used to prove that the minor principal component estimates of diffusivity, in contrast to regular estimates, are insensitive to ensemble averaging over particles taken from a finite area in a shear mean flow. In the East Sea, typical values of the diffusivity, timescale, and space scale are (1.7-5.2) × 10 7 cm -2 s -1 , 0.7-1.7 days, and 10-25 km, respectively. In the northwest Pacific Ocean, typical estimates of the diffusivity, timescale, and space scale in mean are a factor 2-3 larger, namely, (2.3-15.1) X 10 7 cm -2 s -1 , 1.7-3.7 days, and 18-62 km, respectively. It was found that the space scale L and the first mode internal Rosshy radius Ri are related as L Ri, which suggests a parameterization of lateral diffusivity k∞ of the form k∞ = u Ri, where u is the rms current velocity fluctuation.

Observations of the hydrography and water movements in the East China Sea in areas where the bottom topography interferes with the Kuroshio indicate a vigorous exchange between the Kuroshio and a continental shelf water mass that is relatively cool and fresh. South of about 28°N, the Kuroshio runs into the continental shelf and is uplifted. The resulting onshore intrusion of the Kuroshio is compensated by an offshore flow in the surface layer of continental shelf water which is a part of the horizontal circulation created in part by the intrusion itself. North of about 28°N, the blocking of the Kyushu coastal topography forces a turn of the Kuroshio to the east and a separation of part of the Kuroshio flow on the left-hand side. The separation gives rise to the Tsushima Current and appears confirmed by recently obtained trajectories of World Ocean Circulation Experiment (WOCE) surface drifters. Thus, the surface layer flow along the East China Sea continental margin along which the Kuroshio flows is marked by a convergence in the southern stretches and a divergence in the north. Further confirmation of this surface flow characteristics is found in a high-resolution numerical model of the Kuroshio flow-through. Based upon the model output, the exchange due to these cross-margin flows amounts to a 7% loss in heat and salt to the Kuroshio and a gain of freshwater by the Kuroshio at the rate of about 1.0 Sv.

Ocean heat transport in the South Atlantic of a coupled climate model has been diagnosed and compared with observational estimates. The coupled model overestimates the northward heat transport in the South Atlantic. This corresponds to an underestimate of the northward flux of bottom water across World Ocean Circulation Experiment (WOCE) section A11 (the model transports less than 1 Sv compared with climatological estimates of 6 Sv). The magnitude of the southward outflow of North Atlantic deep water agrees well with observational estimates while the northward flux of surface and intermediate waters is larger than observational estimates. We show that with the correct water mass properties a realistic northward flux of bottom water across 30°S is only possible, in the climate model, if the depths of the channels linking the Argentine and Brazil basins are properly represented. We find that an increase in the northward flow of bottom water corresponds to an increase in the southward flow of deep water, rather than a reduction in the northward flux of surface and intermediate waters. This indicates that the upper and lower limb of the overturning are decoupled in the model. As a consequence, increasing the northward transport of bottom water leads to a small reduction of the northward heat transport across 30°S. The magnitude of the heat transport from the Indian to the Atlantic ocean in the model (the warm water path) is surprisingly large for a noneddy resolving model. We find that the magnitude of the Indonesian Throughflow is important in climate resolution models for determining the strength of the warm water path. However, the relative strengths of the warm and cold water paths do not significantly change the heat transported across 30°S.

In March–April 1995, as part of the World Ocean Circulation Experiment section A23, we completed 49 hydrographic stations across the Weddell Gyre and southern Antarctic Circumpolar Current, from the Antarctic continental shelf (72.5°S, 16.5°W) to South Georgia (55°S, 34.5°W). Chlorofluorocarbon (CFC-11, CFC-12, and CFC-113) data collected at these stations reveal that distinct sources renew the Antarctic Bottom Water (defined as waters with potential temperatures less than 0°C) of the Weddell Gyre. Weddell Sea Bottom Water (defined as waters with potential temperatures less than −0.7°C) formed in the western Weddell Sea has CFC concentrations about 5 to 6 times higher in the eastward flowing northern Weddell Gyre than in the westward flowing southern limb. Our CFC measurements suggest that distinct sources of Weddell Sea Bottom Water exist in the western Weddell Sea, in agreement with previous descriptions based on potential temperature and salinity signals. In the northern Weddell Gyre, high CFC concentrations in Weddell Sea Deep Water, potential temperatures between 0°C and −0.7°C, confirm the long-recognized sources for this water mass in the western and southwestern Weddell Sea. In the southern Weddell Gyre at about 20°W and along the Antarctic continental slope, Weddell Sea Deep Water with potential temperatures around −0.45°C shows a deep CFC maximum about 1000 m above the seafloor. CFC concentrations in this deep southern core are about 80% of those of new Weddell Sea Deep Water in the northern Weddell Gyre near 30°W. The A23 CFC and hydrographic data are not consistent with the hypothesis that Weddell Sea Deep Waters are derived from a single source in the western Weddell Sea. Instead, these tracers suggest that an important portion of the Weddell Sea Deep Water in the southern Weddell Gyre originates outside the western Weddell Sea, probably near the Amery Basin and environs, around 75°E. These features of the circulation and renewal of the deep Weddell Gyre should be carefully considered in simulations dealing with fluxes, pathways, and formation rates of Antarctic Bottom Water.

High-quality hydrographic sections occupied during the World Ocean Circulation Experiment (WOCE) have allowed the first estimates to be made of property changes in the deep ocean on a decadal time-scale. The magnitude of the property variability on deep isothermal surfaces (below about 2–3°C) was found to be comparable with the magnitude of possible systematic errors in the data (except for a few regions where formation of deep and bottom waters occurs). However, the problem of systematic errors in hydrographic data was only marginally addressed in the literature. We conducted an analysis of property offsets between the cruises of an expansive global hydrographic dataset, including 1314 cruises. Because of significant differences in quality, a distinction is made between the high-quality modern data (1970–1998) and less accurate historical data (since 1920s). Inter-cruise offsets are determined on isothermal surfaces for salinity, oxygen, silicate, nitrate and phosphate within crossover areas. Offsets are decomposed into a systematic part (the difference of respective systematic errors (biases)) and a non-systematic part (a combined effect of temporal and spatial variability). For the reference subset of N=384 high-quality cruises with M=2201 crossover areas (for salinity) a system of M algebraic equations in N unknown cruise biases is obtained and solved by least squares. Accounting for biases allows a drastic reduction of inter-cruise offsets (a factor of 2–4 depending on property and dataset considered), bringing data from different cruises to agreement within WOCE quality requirements. For a composite WOCE/non-WOCE high-quality dataset calculated root-mean-square inter-cruise offsets before and after adjustment (in parentheses) are 3.2*10−3 (1.34*10−3) for salinity, 2.498 (0.782) μmol/kg for oxygen, 2.4 (0.95) μmol/kg for silicate, 0.55 (0.26) μmol/kg for nitrate and 0.045 (0.018) μmol/kg for phosphate. Our results demonstrate, that quality requirements for the WOCE Hydrographic Programme have been obviously fulfilled. Biases for historical cruises are calculated relative to the corrected reference data and are found to be on average a factor of 3–6 larger than the modern cruise biases. Calculated property offsets and biases for both high-quality and historical data are found to be in a good agreement with independent offset estimates. Though small differences of IAPSO Standard Seawater salinity from label salinity are reported in the literature, they can not explain observed inter-cruise offsets, and operator/salinometer related errors seem to be the main cause for inter-cruise differences. Systematic biases can provide an explanation for apparent changes in deep water temperature–parameter relationships as an alternative to natural variability. For instance, we argue that apparent variability of the deep water salinity in the Argentine Basin during 1980s as reported by Coles, McCartney, and Olson (J. Geophys. Res. 101, 1996, 8957–8970) is mostly the result of systematic errors in the data used for their analysis. Removing inconsistencies in a composite data set is also important for producing consistent climatological property fields even in the data abundant regions.

International audience; We investigate the variability of upper ocean temperature and surface salinity between Iceland and Newfoundland along World Ocean Circulation Experiment line AX2 in 1993-1998. North of 54°N, as well as close to Newfoundland, deviations from the seasonal cycle indicate upper ocean warming from 1994 to 1998, with largest anomalous warming during late 1995/early 1996 and during the winter 1997/1998. North of 54°N, surface salinity increases after mid-1996. The winter of 1995/1996 is the first winter of weak westerlies after more than 20 years of strong westerly conditions in the subarctic gyre, and the ocean loses less heat during that winter than during a normal year. The magnitude of upper ocean heat content change is at least twice as large as what results from the change in air-sea fluxes, which indicates a complementary contribution to heat content change by advection. Altimetric sea level data indicate also an increase of sea level of the order of 6.5 cm during that year, out of which more than 4 cm is contributed by the steric change associated with the temperature increase. A principal component analysis of the sea level data suggests that the increase sensed along line AX2 west of the Reykjanes ridge is found in most of the subpolar gyre, although to a lesser extent in most other areas.

Hydrographic observations of pressure, temperature, salinity, dissolved oxygen, and shipboard acoustic Doppler current profiler measurements are used to study the upper circulation in the Western equatorial Atlantic Ocean, limited to the region bounded by the 10°S and 14°N latitudes between the longitudes 30°W and 52°W. Data were obtained during four World Ocean Circulation Experiment cruises, carried out in January-March 1993, January-March 1994, September-October 1995 and April-May 1996. In the upper layer, the continuity of the northwestward flowing North Brazil Current along the American continent toward the Caribbean Sea is confirmed in boreal spring. Furthermore, part of the North Brazil Current also continues northwestward in the subthermocline layer during short periods in boreal spring, contrary to previous estimates. The North Equatorial Countercurrent (NECC) is present in boreal spring west of 40°W fed, with water of Northern Hemisphere origin only. The southeastward flowing current observed at 3°N-44°W is fed by the North Brazil Current retroflection and by a cyclonic recirculation of the southern edge of the North Equatorial Current. The upper layer of this current at 3°N-44°W, feeds the Equatorial Undercurrent (EUC) and the NECC, when its subthermocline layer feeds the EUC and the North Equatorial Undercurrent. Near-surface eastward flow is present above the EUC during all cruises, yielding to a strong increase of the eastward warm water transport. (Résumé d'auteur)

Measurements of the ratio of stable isotopes of oxygen (18O and 16O) from samples collected on World Ocean Circulation Experiment sections SR1b (eastern Drake Passage) and A11 (Punta Arenas to Cape Town) are used, together with hydrographic data, to deduce information about the formation and variability of South Atlantic and Southern Ocean water masses. The Drake Passage surface waters south of the Polar Front (PF) are isotopically light (δ18O around −0.4‰) owing to the influence of meteoric waters. The salinity and δ18O of the A11 surface waters yield an apparent freshwater end-member which is much isotopically lighter than the local precipitation, thus advection of these waters from farther south dominates over local effects in determining the surface water properties. The Drake Passage section shows unusual proximity of the two main fronts of the Antarctic Circumpolar Current (the PF and Subantarctic Front (SAF)), and we observe cold, fresh, and isotopically light water derived from the temperature-minimum Winter Water at the SAF. This water is of the correct density to freshen the intermediate water north of the SAF and thus play a role in the formation of the comparatively fresh Antarctic Intermediate Water (AAIW) of the South Atlantic. This confirms the role of Antarctic water in forming the South Atlantic variety of AAIW. Across the A11 section the oxygen isotope and salinity data at the AAIW core show very similar traces, with waters in the Malvinas Current loop showing lowest values of both. At the eastern boundary of the South Atlantic, the input of Red Sea Water from east of South Africa is observed via the presence of anomalously isotopically heavy AAIW. We deduce potentially significant temporal variability in the isotopic composition of Weddell Sea Deep Water (WSDW) by comparing the Drake Passage data to earlier data covering the outflow of the Weddell Sea. The A11 data show WSDW consistent with such variability, indicating that its effects could persist in the waters as they flow north into the western South Atlantic. We speculate that such variability could be due to small changes in the amount of glacial ice melt in WSDW.

In January 1993, two Agulhas rings were sampled in the eastern South Atlantic during the World Ocean Circulation Experiment one-time hydrographic section A11. The first of these, Ring 1, was sampled at 36°S, 4°E in the Subtropical Frontal Zone and was smaller and less energetic than other, more typical Agulhas rings, owing partly to its interactions with the North Subtropical Front. The other, Ring 2, was sampled at 33°S, 10°E in the subtropics. This ring was average in size and reasonably representative of the rings observed in the southeast Atlantic during the early 1990s. The path of the rings is found to be dominated by advection in the mean flow rather than self-induced velocities of eddies under the β effect. We observe significant differences in reduced gravity and available heat and salt anomalies in the rings; from these we infer temporal variability in the stratification of rings upon their formation at the Agulhas Retroflection. This temporal variability in the structure of rings will affect the fluxes associated with them. Data collected within Ring 2 show that neglecting consideration of the water beneath the 10°C isotherm underestimates the volume flux by half and the potential temperature and salinity flux by in excess of one third and one half, respectively. Using a base of the 3.5°C isotherm and including the high-salinity intermediate water from the Indian Ocean is found to be more appropriate. With these conditions, six Agulhas rings per year entering the subtropical South Atlantic would equate to a volume flux of 9 Sv and an absolute potential temperature and salinity flux of 84 Sv°C and 322 Sv psu (1 Sv psu ≈ 106 kg s−1). The significant flux of intermediate water from the Indian Ocean may be as important in the return path of the thermohaline circulation as the intermediate water that enters the South Atlantic through Drake Passage. Further, the water associated with Agulhas rings and cooler than 10°C potentially contributes a larger volume flux to the warm water return path than the corresponding surface and upper thermocline water.

A hydrographic section between Tasmania and Antarctica was occupied in late winter 1991 as part of the World Ocean Circulation Experiment (WOCE). The primary purpose of the WOCE repeat section SR3 is to measure the exchange between the Indian and Pacific Oceans south of Australia. This paper describes the fronts, water masses and transport observed on the first occupation of the repeat section. The Subantarctic Front (SAF) is located between 50°S and 51°S and is the most striking feature of the vertical sections. Two additional fronts at 53°S and 59°S are associated with the Polar Front (PF), part of which turns northward to flow along the section before turning back to the east near 53°S. Very deep (>500 m) mixed layers are found north of the SAF, confirming that Subantarctic Mode Water (SAMW) is formed in this region by deep convection in winter. Chlorofluorocarbons (CFCs) are significantly undersaturated (≈90–92% of equilibrium values) in these deep mixed layers, indicating that gas exchange rates are not rapid enough to bring these deep mixed layers to equilibrium by the end of the winter period of deep convective mixing. Northward Ekman drift of cold, fresh water across the SAF is likely to be responsible for the cooler, fresher mixed layers observed immediately north of the SAF. The Antarctic Intermediate Water (AAIW) on the SR3 section is relatively low in oxygen and CFCs (≈60–70% and 10–20% of saturation values, respectively), high in potential vorticity, and high in nutrients. These characteristics suggest that the AAIW on this section is not renewed by direct and rapid ventilation near this location. Water mass properties suggest that water from the Tasman Sea spreads south and west across the northern portion of the SR3 section between 800 and 3000 m depth. A cold, fresh, CFC-rich variety of Antarctic Bottom Water is formed along the Wilkes-Adelie coast of Antarctica. The net transport across the section relative to the deepest common depth is 160 Sv. The band of eastward flow between 50°S and 53°S including the SAF carries 137 Sv to the east and dominates the net transport. Weaker flow south of 58°S contributes an additional 70 Sv. The eastward flow is compensated in part by 37 Sv of westward flow between Tasmania and 48.5°S and 8 Sv of flow to the west over the southern flank of the mid-ocean ridge. The trajectories of six ALACE floats deployed at about 950 m confirm the sense of flow inferred from the choice of a deep reference level.

The three-dimensional isoneutral potential vorticity structure of the Indian Ocean is examined using World Ocean Circulation Experiment and National Oceanic and Atmospheric Administration conductivity-temperature-depth data and historical bottle data. The distribution of the potential vorticity is set by the Indian Ocean's source waters and their circulation inside the basin. The lower thermocline has a high potential vorticity signal extending westward from northwest of Australia and a low signal from the Subantarctic Mode Water in the south. The Antarctic Intermediate Water inflow creates patches of high potential vorticity at intermediate depths in the southern Indian Ocean, below which the field becomes dominated by planetary vorticity, indicating a weaker meridional circulation and weaker potential vorticity sources. Wind-driven gyre depths have lower potential vorticity gradients primarily due to same-source waters. Homogenization and western shadow zones are not observed. The β-effect dominates the effect of the Somali Current and the Red Sea Water on the potential vorticity distribution. Isopleths tilt strongly away from latitude lines in the deep and abyssal waters as the Circumpolar Deep Water fills the basins in deep western boundary currents, indicating a strong meridional circulation north of the Antarctic Circumpolar Current. The lower-gradient intermediate layer surrounded vertically by layers with higher meridional potential vorticity gradients in the subtropical Indian Ocean suggests that Rossby waves will travel ∼1.3 times faster than standard theory predicts. To the south, several pools of homogenized potential vorticity appear in the upper 2000 m of the Southern Ocean where gyres previously have been identified. South of Australia the abyssal potential vorticity structure is set by a combination of the Antarctic Circumpolar Current and the bathymetry.

The suitability of basin-scale, satellite-based scatterometer winds for forcing of numerical ocean models is examined using a reduced gravity, primitive equation model of the tropical Pacific Ocean. Three surface forcing fields are validated in a comparison of upper layer thickness (ULT) from the ocean model with observed sea level data. The forcing fields are the Florida State University observed winds, winds derived from the NASA Scatterometer (NSCAT), and stresses derived directly from NSCAT. The sea level data sets are the World Ocean Circulation Experiment “fast” sea level data set from island measurements and sea level anomalies from TOPEX/POSEIDON. Results of this comparison demonstrate that while the three model results are qualitatively similar, the results are quantitatively better when forcing with the NSCAT derived stresses. This is particularly true in the eastern tropical Pacific and in convergent zones where forcing with the NSCAT stresses can lead to large differences in ULT (>40 m) compared with results from the other two wind products.