The future direction of Japanese oceanographic research in the next decade is discussed, mainly from a coastal oceanographic perspective. Coastal oceans serve two functions: (1) as a filter-reactor region connecting the open ocean and land, and (2) as a biologically rich and diverse region where environmental changes have a direct impact on society. Therefore, understanding the material cycle within the coastal region is important not only scientifically but also to preserve and maintain the ocean. Process studies are needed, with close collaboration between physical, chemical, and biological science communities. Coastal oceans continue to lack observations to understand and resolve the small spatial and time-scale events that govern the region. However, advances in observational instruments/techniques, satellite measurements, and unmanned aerial vehicles are starting to provide high temporal spatial data than ever before. In addition to long-term monitoring, we discuss the research infrastructure and numerical models needed for future studies.

A review of progress in oceanographic research in the tropics over the past decade is provided. Physical and biogeochemical oceanographic perspectives regarding directions for the next decade are proposed, with a special focus on the El Niño-Southern Oscillation (ENSO) in the tropical Pacific. Although physical understanding of the ENSO has considerably advanced and its dynamical prediction has now become possible, our understanding of mechanisms and ability to predict variations in the material cycles, biological production, and biodiversity associated with the ENSO is still rudimentary. Because effects of internal natural climate variability on the marine system (e.g., ocean warming, acidification, and deoxygenation) have become more serious with global warming, comprehensive understanding and more accurate prediction of the ENSO and its effects on the tropical ocean system are becoming increasingly important. This research will also be key to anticipating changing societal needs as ocean conditions change. In particular, basin-scale studies based on Biogeochemical Argo floats and earth system models, process-oriented studies based on ship/buoy observations and experiment/observation by local research stations, and feedback between the basin-scale studies and the process-oriented studies will be key in the coming decade. The tropical Pacific is an optimal testbed for innovative cross-disciplinary programs that contribute to better understanding and prediction of the ocean system, because its interannual variations associated with the ENSO are highly predictable relative to other oceans.

We reviewed the progress of mid-latitude oceanographic research over the past decade, and identified three new research topics for the western North Pacific and proposed observational and analytical techniques to address them. These topics are as follows: (1) multiscale phenomena in western boundary currents and air–sea interaction, (2) transportation of nutrients and iron between the subarctic and subtropical gyres, and (3) biodiversity and biological hotspots of marine organisms. In the case of observational techniques, we discussed the importance of cutting-edge oceanographic measurements, such as floats equipped with microstructure, biogeochemical, and plankton sensors, sensitive chemical measurements, and metagenomic analysis, for data collection across multispatiotemporal scales. The analyses of large datasets from these observations and high-resolution modeling would increase our ability to reveal the oceanic processes at higher spatial and temporal scales than that in the past decade. These comprehensive and interdisciplinary approaches are necessary to progress the mid-latitude oceanography in the next decade.

Future research challenges in polar oceanography for Japanese oceanographic community are discussed. For both the Arctic and Southern Oceans, the key issues identified are transport of heat and materials from lower latitude ocean regions, the role of sea ice in material transport and biological production, and processes in coastal areas. These topics must be understood quantitatively to better predict future changes in the polar regions. In addition, we propose a novel field campaign to observe ocean-sea ice-air fluxes in early spring, and a comprehensive study of ocean-sea ice-icesheet coupling for the Arctic Ocean and the Southern Ocean, respectively. For the future development of polar oceanography, we also propose new research infrastructures such as submersible research vessels, submarine observation bases, and coastal observation towers, as well as the use of the Sea of Okhotsk and Lake Saroma as a nearby model polar ocean.

Focusing on the deep ocean, in this article, we summarize the existing research topics and discuss the direction and significance of future research. We focused on the ocean biogeochemical cycle in the deep ocean as an interdisciplinary topic that involves physics, chemistry, and biology. In particular, we discussed three issues: (1) transport from the deep to intermediate ocean, (2) transport and changes of organic matter from the surface to deep and intermediate oceans, and (3) temporal changes in the deep ocean. In (1), we discussed the relevance of quantifying the transport from the deep to intermediate layer in the Pacific Ocean to broaden our understanding from a vertical 1D perspective to a 3D one. In (2), we summarized the new concept of recently proposed organic matter pumps and discussed the necessity of approaches from both process and modeling studies. In (3), to understand the future changes in the deep ocean that will progress gradually, we discussed the relevance of various approaches, such as paleoceanographic studies and numerical models, in addition to continuous monitoring by observation.

The ocean significantly influences the Earthʼs climate by exchanging heat, gas, and particles with the atmosphere. The radiation budget of the Earthʼs atmosphere is affected by physical, chemical, and biological processes in the atmospheric boundary layer over the ocean via cloud formation and CO₂ absorption at the sea surface. This in turn influences the ocean through changes in temperature, precipitation, and solar radiation. The air–sea boundary has a direct interaction with human life through the observation and prediction of extreme occurrences, such as typhoons and rogue surface waves, in addition to climate issues. Herein, this paper focuses on “the air–sea boundary,” not limiting as “the air–sea interface.” The air–sea boundary encompasses a large vertical region, extending from the euphotic layer, where primary production occurs, to the troposphere. This paper also focuses on satellite observations relating to air–sea boundary phenomena. Does the deposition of aerosols containing nitrogen, phosphorus, and iron contribute to primary production in terms of nutrient deposition from the atmosphere? What role does the sea surface microlayer play as an air–sea interface, and what factors influence its physical properties? What information is required to calculate the amount of greenhouse gas and marine biogenic gas exchange? What types of marine aerosols influence cloud formation and the radiation budget? What approaches are required to comprehend the spatiotemporal distributions that affect the amount of matter and energy exchanged during wave processes? To answer these questions and help humans live in harmony with the natural environment, this paper presents a 10-year vision for necessary research and collaboration between the Oceanographic Society of Japan and neighboring societies.

Although several new technologies have promoted the development of modern oceanography, human activities have caused many environmental problems, such as ocean pollution. In this paper, we focus on three topics of environmental DNA, BGC Argo, and bio-logging as the new methods contributing to the future development in oceanography. Accidentally released radionuclides have been a severe concern since the accident of the Fukushima Dai-ichi nuclear power plant in 2011. In addition, plastic debris has recently attracted considerable attention as an international issue. We thus focus on these two topics as a problem in the current ocean environments.