Possible source regions of the North Pacific Intermediate Water (NPIW) were investigated with synoptic conductivity‐temperature‐depth surveys. In the Okhotsk Sea Kuril Basin a pycnostad (referred to as the Okhotsk Sea Mode Water (OSMW)) was found in the density range of 26.6–27 σθ. The pycnostad is not seen in the Western Subarctic Gyre (WSAG); thus it is an indicative water peculiar to the Okhotsk Sea. The maximum thickness is at 26.7–26.9 σθ (centered at 26.8 σθ) which coincides with the NPIW density range in the North Pacific Subtropical Gyre. In the Oyashio area east of the southern Kuril Islands and Hokkaido, waters that have intermediate temperature, salinity, and potential vorticity between the OSMW and the WSAG water were distributed, suggesting a following transport route of the NPIW source water. The thick (thus low‐Q; Q is potential vorticity) and low‐salinity water mass outflowing from the Okhotsk Sea mixes with the relatively warm, saline, and high‐Q WSAG water to form the Oyashio water. A coastal part of the Oyashio water flows southwestward along the east coast of the southern Kuril Islands and Hokkaido, retaining the pycnostad (Q minimum). A large part of the low‐Q Oyashio water flows further southward and merges with the Kuroshio Extension and then flows eastward, forming new NPIW. In this process a salinity minimum develops and the Q minimum disappears because of the mixing with a saline Kuroshio water (old NPIW) without a pycnostad in the NPIW density range. These results suggest that the origin of NPIW is the water mass in the Okhotsk Sea (OSMW) and the density of the water mass primarily determines the NPIW density centered at around 26.8 σθ.

The Argo Program has been implemented and sustained for almost two decades, as a global array of about 4000 profiling floats. Argo provides continuous observations of ocean temperature and salinity versus pressure, from the sea surface to 2000 dbar. The successful installation of the Argo array and its innovative data management system arose opportunistically from the combination of great scientific need and technological innovation. Through the data system, Argo provides fundamental physical observations with broad societally-valuable applications, built on the cost-efficient and robust technologies of autonomous profiling floats. Following recent advances in platform and sensor technologies, even greater opportunity exists now than 20 years ago to (i) improve Argo's global coverage and value beyond the original design, (ii) extend Argo to span the full ocean depth, (iii) add biogeochemical sensors for improved understanding of oceanic cycles of carbon, nutrients, and ecosystems, and (iv) consider experimental sensors that might be included in the future, for example to document the spatial and temporal patterns of ocean mixing. For Core Argo and each of these enhancements, the past, present, and future progression along a path from experimental deployments to regional pilot arrays to global implementation is described. The objective is to create a fully global, top-to-bottom, dynamically complete, and multidisciplinary Argo Program that will integrate seamlessly with satellite and with other in situ elements of the Global Ocean Observing System (Legler et al., 2015). The integrated system will deliver operational reanalysis and forecasting capability, and assessment of the state and variability of the climate system with respect to physical, biogeochemical, and ecosystems parameters. It will enable basic research of unprecedented breadth and magnitude, and a wealth of ocean-education and outreach opportunities.

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This study investigates the distribution of the sea surface height anomaly (SSHA) with the aim of quantifying the characteristics of mesoscale eddies in the Kuroshio–Oyashio extension region (KOER), where intense mesoscale eddies are commonly observed during hydrographic surveys. Dense distributions of both anticyclonic eddies (AEs) and cyclonic eddies (CEs) are detected for the first time in KOER with sufficient temporal and spatial coverage, using the Okubo–Weiss parameter without smoothing. Their contribution to the total SSHA variance is estimated to be about 50%. The zones of highest amplitudes are located north and south of the axis of the Kuroshio Extension (KE) for AEs and CEs, which represent warm-core and cold-core rings, respectively; the areas extend poleward along the Japan and Kuril–Kamchatka Trenches, especially for AEs. Eddies of both polarities and with moderate amplitudes are also recognized along the Subarctic Front (SAF). Eddies in areas north and south of the KE generally propagate westward, at a mean rate of 1–5 cm s−1; those along the trenches south of 46°N and along the SAF propagate poleward at mean rates of 1–2 and 0.5–1 cm s−1, respectively. Because of the asymmetric distribution of the AEs and CEs in the areas north and south of the KE, and the asymmetric amplitude of them along the Japan and Kuril–Kamchatka Trenches, there exist significant eddy fluxes of vorticity, heat, and salinity in these areas.

Abstract. Recently obtained World Ocean Circulation Experiment (WOCE) sections and pre-WOCE hydrography are used to study the water -mass structure and formation and transformation of North Pacific Intermediate Water (NPIW). Five neutral density surfaces are selected and mapped, encompassing NPIW from 400 to 900 m in the subtropical latitudes with a distance of-100 m between a pair of surfaces. NPIW is defined as a subtropical gyre salinity minimum which is well followed by a neutral density surface ON=26.9.