Physical Oceanography is a fundamental discipline for gaining an in-depth understanding of the ocean and its role in the Earth system. It primarily studies the dynamic and physical properties, processes, and mechanisms of the ocean by analyzing movements, distributions, variation of physical and biogeochemical properties of seawater. Over the past century, physical oceanography has evolved from observing, discovering, and understanding regional-scale phenomena into a science that systematically reveals the ocean's variability and its role in the Earth system from a global perspective, relying on observations, theories, and numerical models. Driven by the needs of human social development, continuous innovations in observational technologies, rapid improvements in computing capabilities, and the widespread application of artificial intelligence theories and methods, physical oceanography has become an interdisciplinary science integrating theories, technologies, and engineering, which equally emphasizes ocean exploration and ocean governance and is driven by multiple application scenarios. Ocean plays a unique role in global climate change. In the past century, global climate has been continuously warming under the forcing of greenhouse gas emissions from human activities. During this process, the ocean fundamentally mitigates the rate of global anthropogenic warming, by absorbing more than 90% of the excess heat in the entire climate system and over 30% of the greenhouse gases emitted by human activities. Obviously, a better understanding of the dynamic and physical properties, processes, and mechanisms of the ocean is the core foundation for further clarifying the ocean's role in global change and the impact of human activities on the Earth's climate system. In this context, we systematically reviewed developments and trends of physical oceanography, summarized grand challenges of physical oceanography from three dimensions-research paradigms, spatiotemporal scales, and interface interactions, as follows: (1) Research paradigm: it encompasses observation, numerical simulation, theoretical analysis, and artificial intelligence. Developing new observational technologies, enhancing the construction of ocean observation systems, and acquiring ocean observational data have always been the foundation of the development of physical oceanography. Meanwhile, since no observation system can achieve full and real-time coverage of the global ocean, it is necessary to rely on computer technologies, including computational fluid dynamics and artificial intelligence, to simulate and fully understand the variation processes of the entire ocean. (2) Spatiotemporal scale: global ocean experiences multi-scales temporal and spatial variability, ranging from seconds, minutes to thousands or even tens of thousands of years, and from centimeters, meters to thousands or even tens of thousands of kilometers. Oceanic changes involve energy exchange and interaction between movements across the aforementioned spatiotemporal scales. (3) Interface interaction: it includes not only connections between estuarine and coastal areas and the deep ocean, and between seawater and ice, but also interactions between the ocean and the atmosphere, the ocean and the land (including the seabed), and the ocean and the biosphere. Based on these three dimensions, we refined our understanding into Ten priorities for Physical Oceanography. They are: (1) construction of a cross-scale, real-time global ocean observation system; (2) development of ultra-high-resolution global ocean numerical models and ocean digital twin; (3) meso-and small-scale dynamic processes in the ocean, and their material and energy transport and climatic effects; (4) mechanisms of multi-scale air-sea interaction and extreme climate events; (5) marine energy and material cycles regulated by complex seabed topography; (6) key processes and climatic effects of rapid polar changes; (7) structure, causes, and driving mechanisms of deep ocean circulation; (8) tipping point of thermohaline circulation and its predictability; (9) resilience regulation of estuarine-coastal systems under compound stress; (10) impacts of marine dynamic processes on carbon-nitrogen-oxygen biogeochemical cycles Ten priorities for Physical Oceanography outlines the core development directions of physical oceanography in the coming period and will promote a deeper understanding of the ocean and its role in the Earth system.

Abstract Mesoscale eddy currents influence ocean surface waves, but their imprints on wave height remain poorly described by observations. Here, we examine significant wave height (SWH) variations associated with more than 42,000 mesoscale eddies in the Southern Ocean using along‐track Jason‐3 altimeter measurements. Altimeter composites reveal a pronounced meridional dipole, with reduced SWH where wave propagation aligns with eddy currents and enhanced SWH on the opposing side. Typical eddies (radius ∼45 km, geostrophic velocity anomalies ∼0.15 m s−1) are associated with SWH anomalies of ∼5 cm. Reanalysis data and idealized simulations further suggest that eddy‐related wind anomalies, the relative wind effect and direct current effects all contribute to the observed SWH patterns, with refraction playing a key role. These results highlight the role of mesoscale currents in redistributing wave energy and shaping the spatial distribution of wave height.

Climate models robustly project a reduction in the skewness of Indian Ocean Dipole (IOD)-related sea surface temperature anomalies (SSTAs) under future greenhouse warming. However, it remains unclear how strong positive IOD (spIOD) and negative IOD (nIOD) events respectively contribute to the projected skewness changes. Here, using multiple CMIP6 models and large ensemble (LE) simulations that are skillful in simulating nonlinear IOD dynamics, we show that the weakened IOD skewness reflects differential responses of spIOD and nIOD to greenhouse warming induced by mean-state changes. SpIOD events, although occurring more often in the warming 21st century, are projected to weaken in event-average intensity. The opposing changes between the frequency and amplitude of spIODs induce a compensatory effect on the skewness change, with the net contribution depending on model internal variability. In contrast, nIOD events not only occur more frequently but also strengthen in amplitude, both conducive to the weakening of IOD skewness and thus determining the forced skewness response. These differential responses between spIOD and nIOD stem from a pIOD-like mean state change, which induces asymmetric changes in associated air-sea feedbacks under global warming. A drier eastern Indian Ocean (EIO) inhibits atmospheric convection feedback, thereby limiting the nonlinear growth of cold SSTAs, while an elevated EIO thermocline promotes oceanic thermocline feedback favoring the development of warm SSTAs. Collectively, these diverse changes in spIODs and nIODs weaken IOD asymmetry in a warming climate, with nIODs playing an indispensable role.

The rapid development of photovoltaic (PV) energy and its growing penetration in power systems have made accurate and robust PV power forecasting a critical challenge. However, the strong stochasticity, nonlinearity, and heterogeneity of PV output, driven by complex environmental conditions, hinder the performance of conventiona l forecasting methods. To address these issues, this study proposes a novel hybrid framework that integrates TimeGAN-based data augmentation, extended LSTM (xLSTM), and Transformer networks for probabilistic and accurate PV power prediction. First, TimeGAN is employed to synthesize realistic PV time series data, effectively capturing temporal correlations while preserving the irradiance-temperature dependency, thus mitigating the limitations of scarce or imbalanced historical datasets. Second, a hybrid xLSTM-Transformer architecture is developed, where the matrix memory-enhanced xLSTM module focuses on local feature extraction, and the Transformer module models long-range dependencies via self-attention mechanisms. Finally, the proposed model is validated using real-world operation data from the State Grid of China. Experimental results demonstrate that the proposed framework significantly improves prediction accuracy under realistic operating conditions. Compared with conventional LSTM and Transformer baselines, the proposed TimeGAN-xLSTM-Transformer model achieves a reduction of approximately 48.1% in RMSE and 44.1% in MAE, highlighting its superior capability in capturing both short-term fluctuations and long-term temporal dependencies of photovoltaic power generation. This research contributes to advancing intelligent PV forecasting technologies by leveraging data generation, temporal modeling, and attention mechanisms, offering theoretical and practical support for the reliable integration of PV in renewable-dominated power systems.

Atmospheric deposition is a major external nutrient source to the open ocean and, beyond stimulating primary production, may also enhance the emission of climate-active biogenic gases such as isoprene, introducing additional feedbacks to the Earth system. However, its role in regulating oceanic isoprene production and emissions remains poorly understood. Here, we performed shipboard dust-addition experiments during three cruises in the Northwestern Pacific Ocean (NWPO), in which different dust-addition treatments in a microcosm system (0.1-2.0 mg L- 1) were applied to simulate the impact of atmospheric deposition on marine isoprene production. Dust addition significantly stimulated phytoplankton growth and increased isoprene concentrations by 20%-55% relative to the controls. The rise in isoprene was strongly correlated with enhanced Chlorophyll a and was further modulated by phytoplankton functional types and nutrient stoichiometry. The largest isoprene enhancement occurred under conditions where phytoplankton communities have high isoprene production rates and N:P ratios of 10-20. The parameterized model based on these experiments predicts that dust deposition raises annual isoprene emissions by 75 +/- 17 Gg yr- 1 in the NWPO. This enhancement likely contributes to regional organic aerosol formation and underscores the potential climate co-benefits of atmospheric deposition through both a strengthened carbon sink and the emission of biogenic cooling agents.

The Kuroshio–Oyashio Transition Zone (KOTZ) serves as a vital dynamic interface between the warm Kuroshio Extension and the cold Oyashio Current. However, severe sea conditions with strong ocean currents, winds and waves pose challenges for sustained in situ observations of both oceanic and atmospheric variables. This paper introduces the China Kuroshio Extension Observatory (CKEO), a moored observatory program designed for long-term observations in the KOTZ. We provide a dataset of meteorological and oceanographic properties, including sea surface wind, air temperature, atmospheric pressure, relative humidity, sea surface temperature, sea surface salinity, ocean currents in the upper 100 m, and temperature profile in the upper 500 m. The CKEO, which began operations in 2019, provides a continuous air–sea observational dataset of the KOTZ to the scientific community and advances the understanding of multiscale physical processes in this region.

Mesoscale oceanic fronts and eddies form coherent structures that regulate transport, retention, and mixing in the upper ocean, yet how their internal physical and biogeochemical structure shapes the distribution of mobile predators remains poorly understood. Here we adopt an active Lagrangian perspective to investigate the distribution of neon flying squid (Ommastrephes bartramii) using a decade-long fisheries dataset from the Northwest Pacific, combined with mesoscale diagnostics and Biogeochemical Argo observations.Across multiple frontal systems, squid catches exhibit a robust cross-frontal asymmetry: catches are on average 1.6-fold higher on the warm side, with an optimal fishing offset of ~10 km toward warmer waters. This pattern arises from behaviorally mediated effective transport across a sloping frontal interface. Squid undergo diel vertical migration, occupying colder subsurface layers during daytime and ascending toward frontal zones at night. Because frontal surfaces tilt downward toward the warm side, subsurface squid habitats are systematically displaced relative to surface frontal indicators and fishing locations, producing a persistent warm-side bias without invoking passive advection.In mesoscale eddies, squid distributions display a contrasting but complementary structure. Squid preferentially aggregate near the cores of warm-core eddies, whereas in cold-core eddies they are predominantly distributed along the outer periphery. Biogeochemical Argo float observations reveal that these patterns are closely linked to differences in the vertical structure of temperature and dissolved oxygen, which modulate habitat depth and suitability. Warm-core eddies provide vertically expanded, oxygen-rich habitats conducive to retention near the eddy center, while cold-core eddies constrain suitable habitat to peripheral regions.Together, these results demonstrate how mesoscale coherent structures—fronts acting as transport barriers and eddies acting as retentive or exclusionary features—interact with active predator behavior to shape asymmetric spatial distributions. This study highlights how effective transport and mixing of mobile marine organisms can be interpreted within a Lagrangian framework integrating physical structure, biogeochemical environment, and behavioral dynamics.

Abstract The Northern Recirculation Gyre (NRG) of the Kuroshio Extension (KE) has traditionally been viewed as subsurface‐intensified and difficult to identify at the sea surface. We combine a 2016–2025 subsurface mooring record, satellite altimetry, Argo trajectory‐based velocities, and historical near‐bottom velocities to reassess the sea‐surface expression of the NRG‐related westward flow and its relation to subsurface variability. At and near the mooring site, velocities show low‐frequency covariability across sampled depths and a westward time‐mean structure. In the altimetry‐defined surface‐expression region, westward surface flow becomes clearer and more frequent in the later record, while retaining strong interannual modulation. The clearer sea‐surface expression is accompanied by local eddy–mean adjustment in the adjacent KE–NRG shear band, as indicated by barotropic‐conversion and Reynolds‐stress diagnostics.

Internal tides are internal gravity waves with tidal frequencies, generated by the interaction of barotropic tides with rough seafloor topography. The breaking of internal tides constitutes one of the fundamental mechanisms for sustaining mixing within the deep ocean. However, past lack of large-scale deep-ocean observations caused uncertainties in characterizing their properties and spatial distribution patterns. The Southwestern Atlantic, with complex and diverse seafloor topography, provides an ideal site for studying deep-ocean internal tides while Deep Argo floats with full-water-depth observation capabilities enable this research. Based on data collected by Deep Argo floats during parking phase, the characteristics and spatial distribution of internal tides at 3000-4000 m in the deep Southwestern Atlantic Ocean are investigated. The analysis quantifies significant amplitudes of internal tides in the deep ocean, revealing spatial patterns distinct from the upper ocean. While upper-ocean internal tides are primarily modulated by large-scale topography, deep-ocean internal tides are subject to small-scale seafloor topography. Consequently, deep-ocean internal tides are spatially locked to local topography features rather than following far-field propagation paths, with semidiurnal internal tides exhibiting higher amplitudes in the Mid-Atlantic Ridge region, whereas diurnal internal tides are intensified near 28°S. These findings provide essential observational support for unraveling complex dynamics driven by small-scale seafloor topography.

Abstract The Pacific saury (Cololabis saira), a key pelagic fish in the Northwest Pacific, exhibits autumn migration modulated by Kuroshio–Oyashio Extension mesoscale features, yet daily fishing ground variability remains unexplained. Traditional reliance on remote sensing data has limited understanding of the three‐dimensional mechanisms governing the fishing patterns. Through integration of continuous mooring observations with satellite data, we reveal how multi‐scale oceanic processes drove an anomalous southward shift of Pacific saury in November 2016. Key findings demonstrate that: (1) Anticyclonic eddies enhanced the Oyashio intrusion, shaping the corridor for the southern fishing grounds; (2) Synoptic winds better explained the daily fishing vessel distributions than chlorophyll‐a; (3) Westerly winds enhanced Pacific saury's feeding conditions by intensifying cold tongue–eddy interaction through Ekman transport. This study underscores the importance of synoptic‐scale winds and continuous subsurface observations in understanding the three‐dimensional evolution mechanisms of fishing ground, advocating for expanded mooring establishment for sustainable management.

Dissolved organic matter (DOM) represents the largest reservoir of reduced carbon in the oceans; however, the characteristic changes in DOM during oceanic dynamic mixing remain inadequately understood. This study examined the concentrations of dissolved organic carbon (DOC), the optical properties of chromophoric and fluorescent dissolved organic matter (CDOM and FDOM), and the composition of microbial communities in water samples collected in June 2022 from the Kuroshio-Oyashio confluence region of the northwest Pacific Ocean. A three end-member mixing model based on the conservative components of CDOM and neutral density was established to quantitatively differentiate the contributions of SubTropical Mode Water (STMW), Oyashio Water (OW), and North Pacific Deep Water (NPDW) to North Pacific Intermediate Water (NPIW). Building on this model, the variations in the sources and composition of DOM and the mechanisms governing these changes during water mass mixing in this region were investigated. The primary objective of this study was to examine whether the mixing processes of water masses can promote the formation of refractory DOM (RDOM) and to assess the contribution of NPDW to the formation of NPIW and the transformation of DOM properties within it. The results indicated that, depending on the degree of water mass influence, NPIW can be further categorized into three sub-components: upper, middle, and lower NPIW. In the upper NPIW (NPIWu), both humic-like and protein-like substances are consumed, with microorganisms such as Ca. Nitrosopumilus and SUP05 likely playing significant roles. In the middle NPIW (NPIWm), in addition to the aforementioned processes, there is also an influence from deep-water microorganisms like Nitrosopumilaceae and Marine group B, leading to the accumulation of high molecular weight, more humified, and recalcitrant DOM (RDOM). In the lower NPIW (NPIWl), Ca. Nitrosopumilus and other microorganisms gradually decline, leaving predominantly the influence of deep-water microorganisms, resulting in a continued accumulation of RDOM. The potential priming effects of microbial activity may play a crucial role in the transformation of DOM properties. This study enhances our understanding of the controls on the transport and transformation processes of DOM during water mass mixing, thereby contributing to our knowledge of the mechanisms underlying the production and persistence of RDOM in oceanic environments.

Submesoscale symmetric instability (SI) is considered to effectively transfer oceanic geostrophic kinetic energy into small-scale dissipation and enhance the vertical exchange of tracers. While SI is widely reported to be active within the ocean boundary layer, only a few studies have claimed the occurrence of SI in the ocean subsurface layer, and the processes that enable subsurface SI development away from the boundary layer still remain poorly understood. Here, based on high-resolution in situ observations in the Kuroshio Extension, the anticyclonic potential vorticity (PV) that favors SI is observed in the subsurface layer (the core is at similar to 180 m depth in contrast to the surface mixed layer depth similar to 40 m) of an intense submesoscale front with a drastic sea surface temperature change of 12 degrees C across 5 km. The analysis results show that the anticyclonic PV preconditioning subsurface SI is generated at the surface layer due to atmospheric-forced surface buoyancy loss. Subsequently, the diagnosed downward vertical velocity reaches similar to 175 m/day, primarily driven by strain-induced frontogenesis and overturning instabilities. These along-isopycnal submesoscale processes facilitate the subduction of surface-origin anticyclonic PV into the subsurface layer. The Lagrangian particle tracking experiments based on model simulation further identify this mechanism. These findings reveal a dynamic pathway linking surface forcing, submesoscale frontogenesis, and the development of subsurface SI, with important implications for the vertical transport of heat, salt, and biogeochemical tracers in frontal regions.

The upper-layer circulation in the South China Sea (SCS) exhibits significant intraseasonal oscillation (ISO), influencing the regional ocean environment and climate. However, the evolution of this ISO under global warming and its underlying mechanisms remain poorly understood. Using a high-resolution Community Earth System Model, this study identifies a strengthening trend of 7.8% in the ISO intensity of the western boundary current (WBC) speed during 1901–2100. Further analysis reveals a 24% intensification of oceanic stratification, while basin-scale wind stress and its ISO show weakening trends of 10% and 18%, respectively. Quasi-geostrophic model experiments demonstrate that the ISO enhancement is primarily driven by intensified upper-ocean stratification, with the weakening wind field exerting a dampening effect. This amplified upper-layer circulation ISO is closely linked to increased sea surface temperature (SST) variability, suggesting higher intensity and frequency of marine heatwaves in the SCS. Furthermore, enhanced SST variability may amplify intraseasonal ocean heat release, potentially altering regional climate. This study elucidates the intensification mechanism of upper-ocean ISO in the SCS under global warming and its climatic impacts, providing new insights into the response of tropical marginal sea climate variability to a warming climate.

Oceanic mesoscale eddies play a crucial but underexplored role in regulating carbon fluxes and climate change. While they redistribute heat, salt, nutrients, and other tracers, their effects on CO 2 uptake remain uncertain. Using observation-based machine learning to estimate CO 2 fluxes throughout the lifetimes of thousands of eddies, we show that anticyclonic eddies substantially enhance CO 2 uptake on average, while cyclonic eddies marginally diminish it. This asymmetry yields an overall net increase in CO 2 absorption by 9.98 ± 2.28 and 13.82 ± 9.94% in the Kuroshio Extension and Gulf Stream, respectively, major carbon sequestration regions. The primary driver of this enhanced uptake is the downward pumping of dissolved inorganic carbon within anticyclonic eddies. Asymmetric biological responses between anticyclonic and cyclonic eddies contribute to the overall eddy-induced CO 2 flux imbalance. The finding suggests a potential underestimation of the ocean’s capacity for carbon sequestration because of insufficient incorporation of eddies in current observations, emphasizing the need for expanded monitoring in eddy-rich, undersampled regions.

The Agulhas leakage is expected to increase as the Southern Hemisphere westerly winds change under climate warming. An increased Agulhas leakage could potentially strengthen the Atlantic Meridional Overturning Circulation (AMOC). To date, however, it remains elusive how much this process could affect the AMOC, which is projected to weaken in the future. Here we carry out a suite of ocean-only simulations, which represent the present climate, and show that an arbitrary 10 Sv increase in the Agulhas leakage strengthens the AMOC by less than 1.3 Sv, which will unlikely substantially offset the projected AMOC weakening. The weak AMOC intensification arises due to compensation between subsurface warming and salinification. However, the AMOC responses to Agulhas leakage increases may depend on the climate background state. Initialized from a collapsed AMOC, which likely occurred during the glacial period, an increased Agulhas leakage can vigorously strengthen the AMOC due to a more unstable AMOC.

AbstractThe extreme positive Indian Ocean Dipole (EXpIOD) peaking in 2023 boreal fall exhibited the strongest variations in sea level and subsurface temperature in the eastern Indian Ocean (IO), and the most equatorially westward extension of cooling observed during the satellite era to date. Its pattern resembled the 1997 EXpIOD, contrasting with other coastally‐concentrated EXpIODs. Here we show that the distinctive air‐sea responses of equatorial EXpIODs stem from the energetic central IO zonal winds fueled by concurrent strong El Niños, which were absent in other cases. The exceptionally strong easterly anomaly generates prominent nonlinear vertical advection cooling the central IO, with nonlinear zonal advection and the Ekman feedback playing supportive roles. Current coupled models can capture this Pacific shaping effect, despite with divergent strengths. Under strong El Niño's inter‐basin forcing, the westward extension of cooling has profound implications for regional hydrology and coral ecology, and warrants closer attention in future predictions.

Ocean wave-current interactions are important physical processes at the sea surface, which can potentially cause extreme sea states under certain conditions. Usually, such interactions are more notable in regions with strong waves and background currents. In this study, focusing on the Kuroshio Extension, we used buoy-measured and altimeter-derived wave data to determine variations in wave properties with the background currents. Statistically, the wave height can be underestimated (overestimated) by approximately 4

The intensifying hot extreme events under anthropogenic warming severely affect human health and the natural environment, yet the factors driving their heterogeneous geographical distribution remain unclear. Here we utilize an eddy-resolving high-resolution climate model alongside multiple simulations from Coupled Model Intercomparison Project Phase 6, we find baseline temperature variability as a key factor shaping the global distribution of projected hot extremes, with over 80% of the global increase in hot extremes anticorrelated with baseline temperature variability, a relationship interpretable within the signal-to-noise ratio framework. We further demonstrate that the baseline temperature variability is anchored by persistent land-atmosphere coupling, which endures over century timescales and sustains the spatial heterogeneity of future hot extremes. Our findings suggest that baseline temperature variability could serve as a potential indicator for future hot extreme distribution, offering valuable insights for developing targeted adaptation strategies and improving regional resilience.

The eastward flow of the Kuroshio Extension (KE) is accompanied by intense eddy activities at both the mesoscale and submesoscale levels, exerting a substantial effect on biogeochemical processes in the upper ocean. The present study focused on how the KE jet and pinch-off cyclonic eddy influenced mesozooplankton community structure and functional traits in the northwestern Pacific. The zooplankton communities in the investigated regions formed a four-segment pattern from north to south, with significant differences in the species and functional trait compositions of each group. The KE stream acted as a barrier that prevented water exchange between the Kuroshio-Oyashio mixed water (KOMW) and North Pacific Subtropical Gyre (NPSG) regions. A comparatively higher proportion of current–feeding omnivore–herbivore zooplankton was recorded in the NPSG region when compared to the KOMW and KE regions, which can be attributed to the influence of the pinch-off cyclonic eddy. Red Noctiluca scintillans was carried from the coast of Japan to open water by the KE’s eastward advection, and it bloomed (1.2 × 104 ind·m−3) in the KOMW under favorable hydrological and nutritional environments, changing the community structure of zooplankton. The pinch-off cyclonic eddy could increase zooplankton abundance but had no significant impact on species composition and functional traits. In addition, the divergence effect of the eddy resulted in greater zooplankton abundance at its edges than in the center. This study enhanced our knowledge of the impacts of the KE on zooplankton communities and has significant implications for understanding pelagic plankton and nutrient responses to pinch-off mesoscale eddies.