Dear Dr. Kawagucci and co-authors,

Your manuscript is accepted for publication in Ocean Science. There are only a few technical issues, listed below, that I hope you will account for when submitting your final version of the manuscript.

P1, L27 delete “(147 words)”
P1, L29 Split the sentence: … system. Additionally comparative samplings were done at the northern Mariana Trench using the same methods.

P1, L29-31 “The CTD sensor, calibrated from measurements of seawater samples, demonstrated a well-mixed hydrographic structure below 7,000 m within the Izu-Ogasawara Trench.” Change this to:
A well-mixed hydrographic structure below 7,000 m was observed within the Izu-Ogasawara Trench.
(Simple calibration of CTD probes is common practice and should not appear in the Abstract.)

P2, L8 properties
P9, L11-12 You are certainly correct when mentioning the freezing as a cause. I think you should mention here that the variation of the silicate concentrations is an artefact. It is a well known fact that frozen samples change their silicate concentrations.

P9, L29, 30 Please use format like μmol kg-1 yr-1 Also elsewhere in the manuscript.
P11, L3 properties

P11, L6 “The 13C-moderate CH4” should be changed to something like: “The moderate 13C values in CH4”

P14, data availability: Please provide the website where the public data are shown.
P14, L24 nitrification (typo)

P15, L26 18O: 17O: 16O (use superscript)
Fig 6 On the x-axis add CH4 to concentration

Thank you and with best wishes
Mario Hoppema