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The World Ocean Database 2023 (WOD23) is the world’s most complete and representative digital collection to date of near real time and delayed mode oceanographic in situ profile measurements collected from ocean observing systems over the 1772 to 2022 instrumental record. It is a collection of irreplaceable data records containing ~18.6 million water column profiles with ~3.6 billion measurements of 27 commonly measured physical and chemical variables, including 17 essential ocean and 11 climate variables, ~22.7 million meteorological and sea state observations, and more than 245 thousand plankton tows. WOD23 serves as a foundational and reliable data resource by and for global marine communities by making globally scattered and heterogeneous data FAIR, uniformly formatted, quality controlled, and searchable by means of extensive granular metadata. The data were sourced from long-term archived primary data, thus preserving its provenance, traceability, and authoritativeness. New and updated data are made available as quarterly updates to WOD23. The data are used in research applications, including earth system models, climate data reanalysis, and diagnostic studies. WOD23 is an activity of the International Oceanographic Data and Information Exchange, World Data System, and Center for Marine Meteorology and Ocean Climate Data.

We quantify the interannual-to-decadal variability of the heat content (mean temperature) of the world ocean from the surface through 3000-meter depth for the period 1948 to 1998. The heat content of the world ocean increased by ∼ 2× 1023joules between the mid-1950s and mid-1990s, representing a volume mean warming of 0.06°C. This corresponds to a warming rate of 0.3 watt per meter squared (per unit area of Earth's surface). Substantial changes in heat content occurred in the 300- to 1000-meter layers of each ocean and in depths greater than 1000 meters of the North Atlantic. The global volume mean temperature increase for the 0- to 300-meter layer was 0.31°C, corresponding to an increase in heat content for this layer of ∼ 1023joules between the mid-1950s and mid-1990s. The Atlantic and Pacific Oceans have undergone a net warming since the 1950s and the Indian Ocean has warmed since the mid-1960s, although the warming is not monotonic.

We compared the temporal variability of the heat content of the world ocean, of the global atmosphere, and of components of Earth's cryosphere during the latter half of the 20th century. Each component has increased its heat content (the atmosphere and the ocean) or exhibited melting (the cryosphere). The estimated increase of observed global ocean heat content (over the depth range from 0 to 3000 meters) between the 1950s and 1990s is at least one order of magnitude larger than the increase in heat content of any other component. Simulation results using an atmosphere-ocean general circulation model that includes estimates of the radiative effects of observed temporal variations in greenhouse gases, sulfate aerosols, solar irradiance, and volcanic aerosols over the past century agree with our observation-based estimate of the increase in ocean heat content. The results we present suggest that the observed increase in ocean heat content may largely be due to the increase of anthropogenic gases in Earth's atmosphere.

Yearly upper-ocean in situ temperature anomaly data for the period 1961–90 are analyzed to reveal spatial structure and evolution of decadal variability in the North Pacific Ocean. An EOF analysis has been performed on individual temperature anomaly fields at upper-ocean standard levels, as well as simultaneously on the entire upper-ocean data to depict the combined three-dimensional structure in a coherent manner. Time evolution of anomaly fields is depicted by using a regression analysis. The analyses detect the principal basin-scale structure of decadal warm period (DWP) and decadal cold period (DCP). There is a well-defined subsurface thermal anomaly pattern, characterized by a prominent seesaw structure with opposite anomaly polarity between the midlatitude North Pacific and the subtropical regions. During a DWP, a positive temperature anomaly is found in the central midlatitude upper ocean, with the maximum at about 100-m depth. This is accompanied by a corresponding negative anomaly in the American coastal region and in the subtropics. A reverse pattern of these anomalies is observed during the DCP. Evolution between the DWP and the DCP involves significant zonal and meridional propagation of anomaly phase around the North Pacific, showing consistent and coherent variations from subsurface to sea surface, from central midlatitudes to the American coastal regions, and to the subtropical Pacific Ocean. This phase propagation is much more well-organized at subsurface depths than that at the sea surface, suggesting an anomaly decadal-scale cycle circulating clockwise around the subtropical gyre, which supports earlier findings by Latif and Barnett. There is a systematic and coherent westward transpacific phase propagation in the subtropical region. These analyses present evidence of the manner in which upper-ocean temperature anomalies evolved in the North Pacific, thus providing an observational basis for evaluating theoretical studies and model simulations. The dynamical implication for physical understanding and prediction of decadal climate variability are discussed.

Over the last 50 years, the Intergovernmental Oceanographic Commission (IOC) has had a profound influence upon the willingness of United Nations Member States to share and provide access to their international and interdisciplinary oceanographic data. (For an early history and review of IOC achievements, see Roll, 1979.) Ocean science over the last half century has been transformed from a predominately modular, single-disciplinary, and individualistic science into a national and multinational interdisciplinary enterprise (Briscoe, 2008; Powell, 2008). The transformation began slowly, but as computing power increased, the pace accelerated, and along with these alterations came shifts in cultural practices regarding the sharing of data. The transformation of ocean science to a multidisciplinary national and international enterprise was abetted by the new availability of a multiplicity of data sources, thanks, in no small part, to IOC. Observations from ships, moorings, satellites, and manned submersibles are now complemented by remotely operated vehicles and autonomous underwater vehicles, floats, and gliders (D’Asaro et al., 2008). Both at sea and in shore-based laboratories, biogeochemical and genetic tools and techniques have changed the nature of the experimental side of the science. High-resolution coupled physical, biogeochemical, and biological models are now used to hindcast with existing data sets and are setting the stage for the forecasting needed to assist in anticipating climate change and the future management of our planet (Rothstein, 2006).

In a previous paper (Oguma and Nagata, 2002), it was shown that frequency distributions of temperature and salinity in the sea off Sanriku Coast, Japan are skewed, and sometimes observed values exceed m + 5 sigma (m = mean, sigma = standard deviation). This means that, if we apply a 3 sigma criterion for a range check, many real data would be lost. We have expanded our analysis to the subarctic North Pacific, the subarctic North Atlantic and their surrounding areas, by computing the distributions of skewness and kurtosis. It is found that the region of high positive skewness extends in an eastnorth-east direction in the Mixed Water Region from off Sanriku, and reaches to about 155 degree E. A high negative skewness zone is recognized along the southern margin of the Kuroshio Extension. These are thought to be generated by the breaking of the meander of the Kuroshio Extension and subsequent ejection of warm and cold eddies to the north and south, respectively. Other high positive skewness areas are found to the south of Kuril Islands and in the Japan Sea. These are generated due to very sharp vertical gradients of temperature and salinity. The situation in the North Atlantic is very similar to the North Pacific, though the detailed nature is changed due to differences of oceanographic condition. The effect of grid size on the skewed nature of the distribution is also discussed.

Upper-ocean temperature and surface marine meteorological observations are used to examine interannual variability of the coupled tropical Pacific climate system. The basinwide structure and evolution of meteorological and oceanographic fields associated with ENSO events are described using composites, empirical orthogonal functions, and a lagged correlation analysis. The analyses reveal well-defined spatial structures and coherent phase relations among various anomaly fields. There are prominent seesaw patterns and orderly movement of subsurface ocean thermal anomalies. During an El Niño year, positive temperature anomalies occur in the eastern and central tropical Pacific upper ocean. Westerly wind anomalies, displaced well to the west of SST anomalies, occur over the western and central equatorial region. These patterns are accompanied by subsurface negative temperature anomalies in the west, with maxima located at thermocline depths off the equator. A reverse pattern is observed during La Niña. The ENSO evolution is characterized by a very slow propagation of subsurface thermal anomalies around the tropical Pacific basin, showing consistent and coherent oceanic variations in the west and in the east, at subsurface depths and at the sea surface, and on the equator and off the equator of the tropical North Pacific. A common feature associated with the onset of El Niño is an appearance of subsurface thermal anomalies in the western Pacific Ocean, which propagate systematically eastward along the equator. Their arrival to the east results in a reversal of SST anomaly polarity, which then correspondingly produces surface wind anomalies in the west, which in turn produce and intensify the subsurface anomalies off the equator, thus terminating one phase of the Southern Oscillation. At the same time, the continual anomaly movement at depth from east to west off the equator provides a phase transition mechanism back to the west. In due course, opposite anomalies are located in the subsurface equatorial western Pacific, introducing an opposite SO phase and beginning a new cycle. Therefore, the phase transitions at the sea surface in the east and at depth in the west are both caused by these preferential, slowly propagating subsurface temperature anomalies, which are essential to the ENSO evolution. Their cycling time around the tropical Pacific basin may determine the period of the El Niño occurrence. The authors’ data analyses show an important role of the thermocline displacement in producing and phasing SST anomalies in the eastern and central equatorial Pacific. The coherent subsurface anomaly movement and its phase relation with SST and surface winds determine the nature of interannual variability and provide an oscillation mechanism for the tropical Pacific climate system. It appears that interannual variability represents a slowly evolving air–sea coupled mode, rather than individual free oceanic Rossby and Kelvin wave modes. These results provide an observational basis for verifying theoretical studies and model simulations.

Analyses of historical ocean temperature data at a depth of 125 meters in the North Atlantic Ocean indicate that from 1950 to 1990 the subtropical and subarctic gyres exhibited linear trends that were opposite in phase. In addition, multivariate analyses of yearly mean temperature anomaly fields between 20°N and 70°N in the North Atlantic show a characteristic space-time temperature oscillation from 1947 to 1990. A quasidecadal oscillation, first identified at Ocean Weather Station C, is part of a basin-wide feature. Gyre and basin-scale variations such as these provide the observational basis for climate diagnostic and modeling studies.

\"Ocean Circulation and Climate: Observing and Modeling the Global Ocean\" edited by G. Siedler, J. Church, and J. Gould is reviewed.