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The density-compensated salinity anomalies (spiciness anomalies) in the upper North Pacific were investigated using Argo float profiles during 2004–2018. The freshening of the subtropical thermocline was found within the Central Mode Water (CMW) and the North Pacific Intermediate Water (salinity minimum). Meanwhile, the increase of salinity was found in the lighter layer within the North Pacific Tropical Water (salinity maximum). The interannual and longer spiciness anomalies were interpreted with three-dimensional evolutions and were linked to the fate of three mode waters (i.e., Subtropical Mode Water (STMW), Eastern Subtropical Mode Water (ESTMW), and CMW) for the first time. In the STMW, the salinity was dominated by a quasi-decadal variability, which was consistent with the KE variability with a 1-year lag, and did not show rapid freshening. In the CMW, the salinity decreased with a quasi-decadal variability, which was weaker and out of the phase compared with the STMW. In the ESTMW, the salinity was dominated by year-to-year variability. The spiciness anomalies originated mainly in the outcrop region of the isopycnals, where they were accompanied by the formation and the subduction of the mode waters. They also propagated and decayed downstream the geostrophic currents. However, a few of the interannual anomalies found in the northern part of the CMW were almost dampened before their spread further south. In addition, some anomalies in the ESTMW appeared and intensified without a connection to the mixed layer. These anomalies occurred far from the outcrop line, suggesting these were caused likely by salt fingering associated with the modification of the mode waters. Furthermore, the propagation of the spiciness anomalies in the western to the central subtropics was significantly faster than the geostrophic current and inclined to the inner side of streamlines. These indicated the transport by eddies in addition to the mean geostrophic currents.

We deployed two profiling floats in the region south of the Kuroshio Extension in March 2000. Temperature and salinity profiles from a depth of 1500 × 104 Pa to the surface are reported every two and four weeks, respectively. The floats performed very well for first four months after deployment. Later they failed in surfacing for a few months when the sea surface temperature in the region was high. The salinity sensors seemed to suffer from some damage during their failure-in-surfacing period. Despite this trouble, the results clearly demonstrate that the profiling float is a very useful and cost-effective tool for physical oceanographic observation in the open sea.

ISSN: 1042-8275; International audience; In only 10 years, the Argo Program has grown from an idea into a functioning global observing system for the subsurface ocean. More than 3000 Argo floats now cover the world ocean. With these instruments operating on 10-day cycles, the array provides 9000 temperature/salinity/depth profiles every month that are quickly available via the Global Telecommunications System and the Internet. Argo is recognized as a major advance for oceanography, and a success for Argo's parent programs, the Global Ocean Data Assimilation Experiment and Climate Variability and Predictability, and for the Global Earth Observation System of Systems. The value of Argo data in ocean data assimilation (ODA) and other applications is being demonstrated, and will grow as the data set is extended in time and as experience in using the data set leads to new applications. The spatial coverage and quality of the Argo data set are improving, with consideration being given to sampling under seasonal ice at higher latitudes, in additional marginal seas, and to greater depths. Argo data products of value in ODA modeling are under development, and Argo data are being tested to confirm their consistency with related satellite and in situ data. Maintenance of the Argo Program for the next decade and longer is needed for a broad range of climate and oceanographic research and for many operational applications in ocean state estimation and prediction.