Ten priorities for Physical Oceanography

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 cyclesTen 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.