Dear Dr. Bell and co-authors,
Thank you for your series of answers and discussions and also making revision in response to reviewers comments. Most of revisions are satisfied for us except for one point.

As Reviewer 1 made a comment,

P26 lines 585-587: If the siboglinid worms harbored thioautotrophic endosymbiont, sulfur isotopic ratios of the worm reflect the ratio of hydrogen sulfide. Therefore, the difference of 6 ‰ is meaningless.

You have answered as follows.

The 6‰ highlights that the Bransfield Strait are lower than siboglinid worms found in other locations and puts the Bransfield Strait worms in a wider ecological context. The sulphur isotopic ratios of mineralized sulphide in the Bransfield Strait (Petersen et al. 2004) vary widely and their signatures do overlap with those of the siboglinids presented here. However, the reviewer’s comment does not consider the role of trophic fractionation, which can easily account for large differences in isotopic signature in sulphur metabolism.

Trophic fractionation of salfer isotope is small as similar to carbon isotopes. this is well known phenomena as that has already described in Fry, 1983; 1988 and Peterson and Howarth, 1988. If you do not agree on their opinion, you should refer following papers.

Fry B. (1983) Fishery Bulletin 81: 789-801
Fry B. (1988) Limnology and Oceanography 33: 1182-1190
Peterson B.J. and Howarth R.W. (1987) Limnology and Oceanography 32: 1195-1213

Then, you are requested to change following sentence to suggested one.

(your revision)
Sulphur isotopic signatures in Siboglinum spp. from Atlantic mud volcanoes ranged between -16.8 ‰ to 6.5 ‰ (Rodrigues et al. 2013) with the lowest value still being 6 ‰ greater than that of Bransfield strait specimens.

(recommended correction)
Sulphur isotopic signatures in Siboglinum spp. from Atlantic mud volcanoes ranged between -16.8 ‰ to 6.5 ‰ (Rodrigues et al. 2013), whereas the lowest value of this study was still 6 ‰ lower. It reflects the relative lower sulphur isotopic ratios of hydrogen sulphide yielding in the study sites(, that is also suggesting that bacterial sulphide is main source of hydrogen sulfide).

Please consider this point.

Best wishes,

Hiroshi Kitazato

Dear Dr. Bell and co-authors,

I am pleased to inform you that your manuscript is reached at mature stage and is worth to publish on BG.

Congratulations,

Hiroshi Kitazato