PrefaceBiogeochemical and physical processes in the Sea of Okhotsk and the linkage to the Pacific Ocean
Introduction
To understand Earth systems, it is important to understand how the land and ocean are linked, and marginal seas are key sites where such linkage occurs. The South China Sea, the East China Sea, the Japan Sea, the Sea of Okhotsk, and the Bering Sea, i.e., marginal seas along the northwest rim of the Pacific Ocean, are all strongly influenced by the land via river discharges, which also reflect human influences. Compared with other oceanic regions, marginal seas have high productivity and biogeochemical cycling activity, which are controlled by separate local processes, such as freshwater discharge, interior current systems, tidal mixing, local upwelling, interactions with the continental shelf, sea ice production and melting, and flow through straits. Further, some marginal seas have been shown to have a strong influence on physical and biogeochemical processes in the open Pacific Ocean. Therefore, it is important to investigate the role that marginal seas play in linking the land with oceanic regions to clarify the whole Pacific Ocean system.
The Sea of Okhotsk is located in the sub-polar region at the northwest rim of the Pacific Ocean (Fig. 1). It has a total area of 1,528,100 km2 and is bounded by Siberia, Sakhalin Island, Hokkaido Island, the Kuril Island chain, and the Kamchatka Peninsula. A broad continental shelf extends along the Kamchatka and Siberian coasts, and a deep basin (Kuril Basin) occupies its southern part. The Sea of Okhotsk is connected to the Japan Sea via the Tatar Strait (sill depth, ∼10 m) and the Soya Strait (∼50 m), and to the Pacific via the Kuril Straits, the two deepest of which are the Bussol’ Strait (sill depth, ∼2300 m) and the Kruzenstern Strait (∼1800 m). The Sea of Okhotsk receives a large amount of freshwater discharge from the Amur River, which at 4444 km long is one of the 10 longest rivers in the world (Simonov and Dahmer, 2008). The Amur River basin covers 2,129,700 km2 (Simonov and Dahmer, 2008). The water discharge of the Amur River, whose mean transport is 11,000 m3/s (Ogi et al., 2001), is the major source of freshwater to the Sea of Okhotsk. Every winter, the cold winter winds that blow from East Siberia cause large amounts of sea ice to form along the Siberian coast on the northwestern continental shelf of the Sea of Okhotsk, which is recognized as the lowest latitude seasonal sea-ice area in the world (Alfultis and Martin, 1987, Kimura and Wakatsuchi, 2000). The formation of sea ice produces a large volume of cold brine, which subsequently causes vigorous mixing to the bottom of the shelf and forms Dense Shelf Water (DSW: 26.8–27.0σθ) (Kitani, 1973, Martin et al., 1998, Gladyshev et al., 2000). Previous studies have suggested that the Sea of Okhotsk is important as a source of North Pacific Intermediate Water (NPIW) (Talley, 1991, Warner et al., 1996, Watanabe and Wakatsuchi, 1998, Wong et al., 1998, Yasuda, 1997, Nakamura and Awaji, 2004).
The first comprehensive observations were carried out in the Sea of Okhotsk from 1998 to 2001 (hereafter, the “first era”) by a joint Japanese-Russian-U.S. study. The main findings of their studies were summarized in a special issue of the Journal of Geophysical Research by Ohshima and Martin (2004), which mainly concerned processes related to sea-ice formation and ventilation in the Sea of Okhotsk. In their studies, the generation of DSW by brine rejection was directly observed on the northwestern Okhotsk shelf (Shcherbina et al., 2003, Shcherbina et al., 2004a, Shcherbina et al., 2004b); and the East Sakhalin Current (ESC), which is the western Okhotsk boundary current (Ohshima et al., 2002, Mizuta et al., 2003) as well as the DSW pathway to the southern Okhotsk (Okhotsk Sea Intermediate Water, OSIW; Itoh et al., 2003, Fukamachi et al., 2004, Ohshima et al., 2004), was discovered. In addition, it was clearly shown that the Bussol’ Strait is the main gateway through which water is exchanged between the Sea of Okhotsk and the Pacific (Katsumata et al., 2004, Katsumata and Yasuda, 2010, Ohshima et al., 2010), and that strong tidal currents in and around the Kuril Straits are associated with diapycnal mixing (Ono et al., 2007, Ono et al., 2013). They also produced several biogeochemical studies. Nakatsuka et al., 2002, Nakatsuka et al., 2004 reported that sedimentary materials are transported in DSW and OSIW from the northwestern continental shelf to the open sea. These findings are compatible with the findings of other studies conducted in the Pacific Ocean that reported high concentrations of Dissolved Organic Carbon (DOC) in NPIW, and they suggest that the increased DOC in NPIW may be due to injections of organic matter from the Sea of Okhotsk (Hansell et al., 2002, Hernes and Benner, 2002, Yamashita and Tanoue, 2008). Observations of chlorofluorocarbons and dissolved inorganic carbon in the DSW production area have also revealed that DSW actively exchanges gases with the atmosphere during its formation, and these gases are subsequently transported to NPIW (Wong et al., 1998, Yamamoto-Kawai et al., 2004, Wakita et al., 2003).
Although there were comprehensive studies in the Sea of Okhotsk from the first era, data were still limited in the Sea of Okhotsk, and many biogeochemical features of this marginal sea, especially regarding its linkage to the Pacific Ocean, remained unknown.
Section snippets
International joint study: the second era
Although many features of the Sea of Okhotsk were clarified by the joint Japanese–Russian–U.S. study of the first era, to understand the whole the Sea of Okhotsk–Pacific Ocean system (hereafter, the Okhotsk–Pacific system), more detailed information about the Sea of Okhotsk, especially biogeochemical information, was needed. Therefore, a second joint international collaborative study was carried out from 2005 to 2013 (hereafter, the “second era”). The second era collaborators included more than
Concluding remarks
In this special issue, we present key findings regarding physical and biogeochemical processes in the Okhotsk–Pacific system and the mechanisms that determine them (Fig. 2). Our studies clearly reveal that the Amur River discharge influences the distributions of materials (Fe and organic matter in our studies) and that transport of these materials in the surface layer by the ESC influences the biological systems in the Sea of Okhotsk. The Amur River discharge also strongly influences a wide
Acknowledgements
The Guest Editors express our sincere gratitude to the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) of Japan, the Canon Foundation, and participating institutes and universities in Japan, Russia, and Hong Kong for the financial support they provided for this international studies. We also would like to thank all of the authors for their patience during the preparation of manuscripts and the scientific reviewers who anonymously donated their time and expertise to
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A review of the oceanographic structure and biological productivity in the southern Okhotsk Sea
2024, Progress in OceanographyDistribution and stoichiometry of Al, Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb in the Seas of Japan and Okhotsk
2022, Marine ChemistryCitation Excerpt :Although they proposed that coal burning generates a significant fraction of Al in aerosols, the median of enrichment factors in aerosols was higher than 50 for Zn, Pb, and Cd. Nishioka et al. (2007, 2014a, 2014b) proposed that the formation of Fe rich DSW and its subsequent transport by the OSIW is an important source of Fe to the NPIW. Here we discuss the effect of this mechanism on the other trace metals.
Biogeochemical and physical linkages between the Arctic Ocean and Sub-Arctic Pacific through marginal seas
2022, Progress in OceanographyA neural network-based method for satellite-based mapping of sediment-laden sea ice in the Arctic
2022, Remote Sensing of EnvironmentPrecession and atmospheric CO<inf>2</inf> modulated variability of sea ice in the central Okhotsk Sea since 130,000 years ago
2018, Earth and Planetary Science LettersCitation Excerpt :Sea ice easily forms on the shallow continental shelves in the north-west Okhotsk Sea and is also influenced by the large fresh water input by the Amur River. As a result, the Okhotsk Sea is the southernmost region of subarctic sea ice distribution in the world (Kimura and Wakatsuchi, 2004; Nishioka et al., 2014). Marine sediment core MD01-2414 (53°11.77′N, 149°34.80′E, water depth 1123 m, total sediment length 52.76 m, Chou et al., 2011, Supplementary Fig. 1) was drilled from the Deryugin Basin during the circum-Pacific initiative cruise in 2001 as part of the IMAGES project (Fig. 1).
Deglacial variability in Okhotsk Sea Intermediate Water ventilation and biogeochemistry: Implications for North Pacific nutrient supply and productivity
2017, Quaternary Science ReviewsCitation Excerpt :Concurrent Fe maxima observed in all sediment records along the pathway of the southward-flowing ESC indicate that in addition the amount of lithogenic material increased within the OSIW, thus creating an “optimal nutrient mix” by adding iron to the sediment suspension. Even if the enhanced amount of terrigenous Fe provision to the suspension load of OSIW waters may have not become fully bio-available, a number of recent studies provided evidence that a close coupling exists on instrumental time scales between fluvial Amur Fe discharge and bio-available Fe in the pelagic subarctic Pacific and its marginal seas (Kanna et al., 2014; Lam and Bishop, 2008; Nishioka et al., 2014a, 2014b). Such higher (than modern) concentrations of suspended macronutrients together with Fe were further reinforced through the observed low primary production of biogenic silica within the Okhotsk Sea, especially during the B-A (Fig. 11e) likely caused by local stratification processes, e.g. due to high freshwater runoff (Okazaki et al., 2014; Riethdorf, 2013).