Reply to comments by Mastalerz, V. on “Shallow gasoff the Rhône prodelta, Gulf of Lions” Marine Geology 234 (215–231)

doi:10.1016/j.margeo.2007.05.009

Marine Geology

Volume 248, Issues 1–2, 8 February 2008, Pages 118-121

https://doi.org/10.1016/j.margeo.2007.05.009 Get rights and content

Abstract

We really appreciate the interest and comments regarding our manuscript. We hope we address all the lingering issues in this reply. This also gives us the opportunity of publishing an update on our dataset that will complete the original manuscript (see Table 1). We have followed the author pattern in our answers: 1-Gas sampling procedure, 2-Reported gas concentrations results, 3-General remarks, 4-Conclusions.

Section snippets

Gas sampling procedure

The gas data are reported in ppm by volume (raw data) and in microliters gas/liter wet sediment. The later units normalize the gas concentration to sediment sample volume. The gas data is reported with 3 significant figures for both units (ppm and μl/l)-see updated table. Phase partitioning of methane was not corrected for in the gas concentration. If it were done, the concentration of the methane would be about 1.25 times higher than reported. It should be emphasized that gas collected from

Reported gas concentrations results

As the author points out, Table 1 is in the units of microLiters/Liter uL/L wet sediment NOT mL/L milliLiters/Liter. Unfortunately this typo was published in the original version. We have attached a new corrected Table 1. We have taken this opportunity to add the results for isotopes we obtained recently and requested by the reply to our paper.

The following are the particulars about the GC analysis:

General remarks

We have included all the final isotopic information in the table. The results show that the methane collected from the Rhone delta sediments is from microbial sources. Methane oxidation is likely in several samples (g31, h30, e56, j63, e48b, BF05, BF06, BF09). It is unknown if this reflects methane oxidation in the environment or the aerobic oxidation of methane to carbon dioxide in the sample container.

Conclusions

We hope the manuscript is now more complete and all the issues are addressed with the updated table and the explanations regarding the methodology and sampling. From our point of view the paper presents a complete new dataset for shallow gas off the prodelta and we hope it is useful to further studies in the area.

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DiscussionReply to comments by Mastalerz, V. on “Shallow gasoff the Rhône prodelta, Gulf of Lions” Marine Geology 234 (215–231)