Radiocarbon isotopic evidence for assimilation of atmospheric CO<sub>2</sub> by the seagrass <i>Zostera marina</i>

Watanabe, K.; Kuwae, T.

doi:https://doi.org/10.5194/bg-12-6251-2015

Articles | Volume 12, issue 20

https://doi.org/10.5194/bg-12-6251-2015

© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/bg-12-6251-2015

© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 12, issue 20

Research article

|

30 Oct 2015

Research article |

| 30 Oct 2015

Radiocarbon isotopic evidence for assimilation of atmospheric CO₂ by the seagrass Zostera marina

K. Watanabe and T. Kuwae

Download

Final revised paper (published on 30 Oct 2015)
Preprint (discussion started on 21 May 2015)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

- Printer-friendly version

- Supplement

RC C2731: 'Review on “Radiocarbon isotopic evidence for assimilation of atmospheric CO2 by the seagrass Zostera marina” by K. Watanabe and T. Kuwae', Anonymous Referee #1, 11 Jun 2015
RC C2955: 'Review of bg-2015-135', Anonymous Referee #2, 19 Jun 2015
RC C3241: 'Lacks an oceanographic context and application may be location-specific', Anonymous Referee #3, 01 Jul 2015
AC C4535: 'Replies to the comments on "Radiocarbon isotopic evidence for assimilation of atmospheric CO2 by the seagrass Zostera marina"', Kenta Watanabe, 21 Aug 2015

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

ED: Reconsider after major revisions (25 Aug 2015) by Christoph Heinze

AR by Kenta Watanabe on behalf of the Authors (26 Aug 2015) Author's response Manuscript

ED: Referee Nomination & Report Request started (26 Aug 2015) by Christoph Heinze

RR by Anonymous Referee #3 (11 Sep 2015)

Suggestions for revision or reasons for rejection

The study has been improved but there is still insufficient quantification of variation in end-members, especially the oceanic DIC source, and the fact that the seagrass leaves reflect a one-three month growing period prior to sampling. Together these issues mean that the approach cannot support the conclusion regarding atmospheric carbon uptake for half the sampling events (no Δ14C gradient), and may be confounded for the other two sampling events when a gradient in Δ14C was evident. It is difficult to have confidence in the approach and conclusions without adequate quantification and assessment of end-member variability.

Responses to previous major comments

1. I am still not convinced the oceanographic variation in Δ14C has been adequately quantified and excluded as an explanation for the Δ14C of the seagrass leaves in addition to atmospheric carbon uptake. I think better quantification of the oceanic end-member is needed, e.g. a time series of Δ14C of offshore water entering the lagoon; this may already have been measured but the seasonal variability in end members should be explicitly presented in a figure. The authors state that the endmembers were sufficiently distinct during point sampling in May and July, but what about other times? The same processes that meant the approach was invalid based on end-member estimates in September and November could apply at any time, e.g. due to sporadic upwelling. This issue is especially important given the highly seasonal impact on the validity of the approach and capacity to draw conclusions about atmospheric carbon uptake.
2. The short growing season in this location seems like it should constrain the issue of turnover times somewhat, but as above, the Δ14C of the seagrass leaves likely reflects an integration of the variation in in end-members over the one to three month prior to sampling the leaves – this variation has not been adequately quantified.
3. The location map has been vastly improved, but how about showing the Δ14C of the end members here (and their seasonal range, e.g. with the currents).

Hide

RR by Anonymous Referee #2 (11 Sep 2015)

ED: Reconsider after major revisions (18 Sep 2015) by Christoph Heinze

AR by Kenta Watanabe on behalf of the Authors (16 Oct 2015) Author's response Manuscript

ED: Publish as is (20 Oct 2015) by Christoph Heinze

AR by Kenta Watanabe on behalf of the Authors (21 Oct 2015) Manuscript

Short summary

Our empirical study demonstrates the quantitative evidence of assimilating atmospheric modern CO2 by the seagrass Zostera marina, by analyzing the radiocarbon isotope concentrations (Δ14C) of both the seagrass and two carbon sources in a brackish lagoon. CO2 exchange between the air and water would occur at the very thin film of water over the air-exposed seagrass leaves. Our finding offers better understanding of the role of seagrass meadows in global coastal carbon dynamics.

Radiocarbon isotopic evidence for assimilation of atmospheric CO2 by the seagrass Zostera marina

Download

Interactive discussion

Peer-review completion

Radiocarbon isotopic evidence for assimilation of atmospheric CO₂ by the seagrass Zostera marina