Vertically stable in density, stratified-water conditions ‘SW’ exist in the deep Mediterranean Sea that are characterized by temperature differences of 0.0002–0.01 °C over 125 m above a flat seafloor. These result in mean buoyancy frequency N = (1.5–2)f, where f denotes the inertial frequency. Although N are one order of magnitude smaller than found in the ocean, they govern a dynamical deep sea as demonstrated using observations from a 3D mooring-array equipped with nearly 3000 high-resolution temperature sensors. SW-conditions can last up to a fortnight, before waters become near-homogeneous, and occur about 40
We analyzed 53 years (1973–2025) of water quality observations collected through the Fisheries Monitoring Program in the Seto Inland Sea (SIS), one of the longest-standing coastal monitoring efforts in Japan. Using climatological anomalies and non-parametric statistical tests, we quantified long-term trends and significant change points in water temperature, salinity, transparency, dissolved oxygen (DO), and dissolved inorganic nitrogen and phosphorus (DIN and DIP) across the SIS. Water temperature exhibited significant long-term increases in both surface and bottom layers (+ 1.25 °C 50-yr⁻1 and +1.03 °C 50-yr⁻1, respectively), with widespread shifts occurring in the mid-1990s, indicating basin-wide warming linked to atmospheric and offshore ocean conditions. Surface salinity showed basin-wide downward shifts around 2010, particularly in the central SIS. Transparency increased markedly over the study period, especially in the eastern SIS, consistent with long-term declines in nutrient concentrations. Trends in bottom-layer DO varied regionally: long-term increases were detected in Beppu Bay and Osaka Bay, whereas declining or non-significant trends characterized other regions. DIN concentrations decreased substantially after the late 1990s, particularly in the eastern SIS, while DIP showed large reductions from the 1970s to the 1980s followed by stabilization or increases in western regions. Although long-term and basin-wide impacts of anthropogenic activities remain substantial, the rates of nutrient declines were not proportional to reductions in land-based loading, reflecting the influence of biogeochemical processes and multiple nutrient sources. Our study reveals substantial climatic and anthropogenic impacts on the SIS and provides essential baseline information for fisheries resource assessment and adaptive coastal management.
Accurate skin sea surface temperature (SSTskin) estimation is essential for air-sea flux computation, satellite SST validation, and ocean-atmosphere modeling. This study presents a new multi-stage parameterization scheme for converting bulk SST (SSTbulk) to SSTskin, developed using high-resolution ship-based observations from the Arabian Sea. The scheme sequentially accounts for the effects of wind speed, diurnal stratification, longwave radiative cooling, and precipitation-induced surface cooling, each empirically derived from observed relationships. Unlike existing models, the proposed method explicitly incorporates rainfall effects, enhancing its accuracy during precipitation events. Evaluation against direct SSTskin measurements from the Arabian Sea shows that the new model achieves the lowest mean bias ( − 0.02 °C) and rmse ( 0.2 °C) compared to other established schemes. Independent validation using ship-borne data from the subtropical Pacific, and satellite SST validation at a Bay of Bengal mooring location, demonstrated similarly strong performance, a bias of 0.04 °C and rmse of < 0.6 °C. These results demonstrate that the scheme performs well in the Arabian Sea and remains competitive when applied to independent datasets in the subtropical Pacific and Bay of Bengal. Including a precipitation correction improves the representation of SSTskin variability during rain-affected conditions encountered in the observational datasets used in this study. The proposed scheme hence provides a practical, observation-based approach for estimating SSTskin from SSTbulk and may support improved air-sea interaction studies in monsoon-influenced regions.
This article reviews recent achievements in the study of mid-latitude atmosphere-ocean-marine ecosystem interactions from two Japanese research programs: the Climatic Hotspot2 project (FY2019–2023) and the first two years of the Habitable Japan project (FY2024–2028). Understanding of the mid-latitude ocean-atmosphere interactions, particularly the ocean’s influence on the atmosphere established in the Climatic Hotspot1 project (FY2010–2014), has advanced through the two projects addressing changing climate and oceanic/atmospheric extreme events, such as the longest observed Kuroshio large meander from 2017 to 2025, northward meandering of the upstream Kuroshio Extension in 2023–2024, marine/atmospheric heatwaves, heavy rainfall and snowfall, and tropical cyclones. Relations between weather and its extremes over East Asia and global climate variations have also been clarified. Both projects have conducted and are conducting in-situ observation campaigns to clarify various processes in the ocean, atmosphere, and their interactions and improve numerical models. By incorporating atmospheric/marine chemistry, marine ecosystems, and fisheries as new research domains and putting more emphasis on prediction, the Habitable Japan project aims to answer the main question: Will mild climate and abundant water/fisheries resources persist as a basis of survival for those of us living in Japan in the future?
Two Argo profiling floats equipped with biogeochemical sensors for pH and oxygen were deployed in winter 2021 in the northwestern region of the North Pacific subtropical gyre near Japan. They were used to observe the seasonal evolution of total dissolved inorganic carbon and dissolved oxygen, and to diagnostically assess their budgets in its upper layers. For the period from April to September 2021, net community production in the upper 100 dbar, as evaluated by converting pH to total dissolved inorganic carbon, was 3.3 ± 0.3 mol C m− 2 at 24° N−26° N and 3.5 ± 0.3 mol C m− 2 at 31°N−36° N, and the net sea-to-air oxygen flux was 5.1 ± 0.5 and 6.3 ± 0.5 mol O2 m− 2, respectively, in these regions when integrated over the period. The large O2 release during these months is attributed to the decrease in oxygen solubility due to rising water temperature and is reinforced by biological oxygen production associated with net community production that occurs despite inorganic nutrient limitation in the euphotic layer. In the Shallow Oxygen Maximum, which is broadly observed below the surface density cap during the warmer months in the western North Pacific subtropical gyre, oxygen release to the atmosphere was in close balance with biological oxygen production. The larger net oxygen release into the atmosphere above and net oxygen consumption by community respiration below are responsible for the emergence of the Shallow Oxygen Maximum.
