No abstract

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 • 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.

The Copernicus Marine Environment Monitoring Service (CMEMS) Ocean State Report (OSR) provides an annual report of the state of the global ocean and European regional seas for policy and decision-makers with the additional aim of increasing general public awareness about the status of, and changes in, the marine environment. The CMEMS OSR draws on expert analysis and provides a 3-D view (through reanalysis systems), a view from above (through remote-sensing data) and a direct view of the interior (through in situ measurements) of the global ocean and the European regional seas. The report is based on the unique CMEMS monitoring capabilities of the blue (hydrography, currents), white (sea ice) and green (e.g. Chlorophyll) marine environment. This first issue of the CMEMS OSR provides guidance on Essential Variables, large-scale changes and specific events related to the physical ocean state over the period 1993–2015. Principal findings of this first CMEMS OSR show a significant increase in global and regional sea levels, thermosteric expansion, ocean heat content, sea surface temperature and Antarctic sea ice extent and conversely a decrease in Arctic sea ice extent during the 1993–2015 period. During the year 2015 exceptionally strong large-scale changes were monitored such as, for example, a strong El Niño Southern Oscillation, a high frequency of extreme storms and sea level events in specific regions in addition to areas of high sea level and harmful algae blooms. At the same time, some areas in the Arctic Ocean experienced exceptionally low sea ice extent and temperatures below average were observed in the North Atlantic Ocean

No abstract

The depth of the upper ocean mixed layer provides fundamental information on the amount of seawater that directly interacts with the atmosphere. Its space‐time variability modulates water mass formation and carbon sequestration processes related to both the physical and biological pumps. These processes are particularly relevant in the Southern Ocean, where surface mixed‐layer depth estimates are generally obtained either as climatological fields derived from in situ observations or through numerical simulations. Here we demonstrate that weekly observation‐based reconstructions can be used to describe the variations of the mixed‐layer depth in the upper ocean over a range of space and time scales. We compare and validate four different products obtained by combining satellite measurements of the sea surface temperature, salinity, and dynamic topography and in situ Argo profiles. We also compute an ensemble mean and use the corresponding spread to estimate mixed‐layer depth uncertainties and to identify the more reliable products. The analysis points out the advantage of synergistic approaches that include in input the sea surface salinity observations obtained through a multivariate optimal interpolation. Corresponding data allow to assess mixed‐layer depth seasonal and interannual variability. Specifically, the maximum correlations between mixed‐layer anomalies and the Southern Annular Mode are found at different time lags, related to distinct summer/winter responses in the Antarctic Intermediate Water and Sub‐Antarctic Mode Waters main formation areas.