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July 13, 2018

First Full-Depth Observations in the Izu–Ogasawara Trench
- Chemical Characteristics of Hadal Waters Identified -


A group of scientists led by Dr. Shinsuke Kawagucci at the Japan Agency for Marine-Earth Science and Technology (JAMSTEC: Asahiko Taira, President) have recorded the first full-depth profiles of hydrographic and geochemical properties in the Izu–Ogasawara Trench south of Japan. Using a conductivity-temperature-depth profiler with carousel multiple sampling system (CTD-CMS) installed on the research vessel Kaimei (Figure 1), the researchers observed a well-mixed hydrographic structure below 7,000 m depth, in the so-called hadal zone (the deepest region of the ocean). In addition, seawater samples collected from this layer exhibited constant concentrations of nitrate, phosphate, silicate, and nitrous oxide as well as constant nitrogen and oxygen isotopic compositions of nitrate and nitrous oxide. These results agree with previous observations of hadal waters in, and deep-sea water surrounding, the Izu–Ogasawara Trench.

In addition, methane concentrations and isotopic compositions indicated spatial heterogeneity within the well-mixed hadal water mass. This strongly suggests a local methane source within the trench in addition to the background methane originating from the general deep-sea bottom water. Releases of sedimentary compounds associated with sediment re-suspension are a likely mechanism for generating this significant methane anomaly.

The above study was published in Ocean Science on July 13, 2018 (JST).

Title: Hadal water biogeochemistry over the Izu-Ogasawara Trench observed with a full-depth CTD-CMS
Authors: Shinsuke Kawagucci1,2,3,#,*, Akiko Makabe2,3,# Taketoshi Kodama4, Yohei Matsui2,3, Chisato Yoshikawa2,5, Etsuro Ono6, MasahideWakita7, Takuro Nunoura3,8, Hiroshi Uchida6, and Taichi Yokokawa3,8.*

Department of Subsurface Geobiological Analysis and Research (D-SUGAR), JAMSTEC
Research and Development Center for Submarine Resources (SRRP), JAMSTEC
Project Team for Development of New-Generation Research Protocol for submarine resources, JAMSTEC
Japan Sea National Fisheries Research Institute, Japan Fisheries Research and Education Agency
Department of Biogeochemistry, JAMSTEC
Research and Development Center for Global Change (RCGC), JAMSTEC
Mutsu Institute for Oceanography, JAMSTEC
Research and Development Center for Marine Biosciences, JAMSTEC
Present address: Japan Meteorological Agency
These authors contributed equally to this work
Corresponding authors

Figure 1. (a) Research Vessel Kaimei
(http://www.jamstec.go.jp/e/about/equipment/ships/kaimei.html) and (b) CTD-CMS profiler.


Figure 2. Seafloor topography of (a) the western North Pacific and (b–g) cross sections of the inner trench. Horizontal red lines in (a) represent the sections shown in (b–g). Vertical dashed lines in (b–g) represent CTD-CMS profile locations.


Figure 3. Vertical profiles of measured parameters. Symbol shapes and colors are classified by location relative to the axis and latitude, respectively. Horizontal dashed lines indicate the abyssal–hadal zone boundary. Bold horizontal lines at panel bottoms represent 1σanalytical errors (not shown when errors are smaller than symbol size).


(For this study)
Shinsuke Kawagucci, Scientist, Department of Subsurface Geobiological Analysis and Research (D-SUGAR)
(For press release)
Tsuyoshi Noguchi, Manager, Press Division, Public Relations
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