3-7 September 2018
Audimax | Kiel University
Europe/Berlin timezone

Recent deoxygenation in the Japan Sea Proper Water in the northeastern Japan Basin

Not scheduled
Audimax | Kiel University

Audimax | Kiel University

Christian-Albrechts-Platz 2 | 24118 Kiel | GERMANY
Poster 01 Prediction and Monitoring


Dr Toshiya NAKANO (Japan Meteorological Agency)


The Japan Sea is a semi-closed deep sea located in the northwestern margin of the North Pacific. Its deep layers below about 300 m is filled with a quite homogeneous water called Japan Sea Proper Water (JSPW). Here, a gradual decrease of dissolved oxygen (O2) and an increase of potential temperature (θ) have been observed by hydrographic measurements since 1950s. The O2 decrease and the warming have been considered to be associated with the weakened cooling and ventilation in winter due to climate change in the northwestern region of the Japan Sea where the JSPW is formed. In this work, we investigated the temporal variability in the properties of the JSPW in the northeastern Japan Basin of the Japan Sea where the water depth exceeds 3500 m, using high-quality data of ship-based measurements being conducted each year since 2010 by the Japan Meteorological Agency. From the vertical profiles of θ and O2 and their temporal variabilities, the JSPW is classified into three distinctive layers such as the Upper JSPW, the Deep Water and the Bottom Water. The largest O2 decreases (11 to 18 µmol/kg for 2010-2017) was observed in the Upper JSPW between 500 m and 1000 m where the vertical gradients of θ and O2 are both much larger than in the Deep Water below. Consequently, an O2 minimum layer emerged at around 1000 m in 2013 and is being developed to date. The decrease of O2 in the Upper JSPW accompanied the increase of nitrate, thereby they are attributed to the increased remineralization in this water. The decrease of O2 and warming (4 µmol/kg and 0.01°C, respectively, for the same period) were also observed on σθ=27.349 kg/m3 in the deeper Bottom Water below 2500 m where the water is vertically uniform. The results of this study are helpful in understanding the difference of circulation structure in the Japan Basin, the formation of JSPW, and mixing and biological process. Further examination is also necessary to reveal the variability and its mechanism of warming and deoxygenation in the JSPW by analysis of a comparable high-quality hydrographic observation data in the Japan Sea.

Affiliation Japan Meteorological Agency
Email Address nakano_t@met.kishou.go.jp
Position Senior Scientist
Are you a SFB 754 / Future Ocean member? No

Primary authors

Dr Toshiya NAKANO (Japan Meteorological Agency) Dr Daisuke SASANO (Japanmeteorological Agency) Mr Takahiro KITAGAWA (Japan Meteorological Agency) Mr Naoki NAGAI (Japan Meteorological Agency) Dr Yoshiteru KITAMURA (Japan Meteorological Agency) Dr Michio AOYAMA (Japan Agency for Marine-Earth Science and Technology/Institute of Environmental Radioactivity, Fukushima University) Dr Masao ISHII (Meteorological Research Institute)

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