Towards an assessment of riverine dissolved organic carbon  in surface waters of the western Arctic Ocean based on  remote sensing and biogeochemical modeling

Le Fouest, Vincent; Matsuoka, Atsushi; Manizza, Manfredi; Shernetsky, Mona; Tremblay, Bruno; Babin, Marcel

doi:https://doi.org/10.5194/bg-15-1335-2018

Articles | Volume 15, issue 5

https://doi.org/10.5194/bg-15-1335-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/bg-15-1335-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 15, issue 5

Research article

|

05 Mar 2018

Research article |

| 05 Mar 2018

Towards an assessment of riverine dissolved organic carbon in surface waters of the western Arctic Ocean based on remote sensing and biogeochemical modeling

Vincent Le Fouest, Atsushi Matsuoka, Manfredi Manizza, Mona Shernetsky, Bruno Tremblay, and Marcel Babin

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Final revised paper (published on 05 Mar 2018)
Supplement to the final revised paper
Preprint (discussion started on 11 Jul 2017)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Reviewer comments on Towards an assessment of riverine dissolved organic carbon in surface waters of the Western Arctic Ocean based upon remote sensing and biogeochemical modeling', Anonymous Referee #1, 11 Aug 2017
- AC1: 'Answers to referee #1', Vincent Le Fouest, 04 Oct 2017
RC2: 'Review of Towards an assessment of riverine dissolved organic carbon in surface waters of the Western Arctic Ocean based on remote sensing and biogeochemical modeling', Anonymous Referee #2, 29 Aug 2017
- AC2: 'Answers to referee #2', Vincent Le Fouest, 04 Oct 2017

Peer-review completion

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

ED: Reconsider after major revisions (10 Oct 2017) by Carol Robinson

AR by Vincent Le Fouest on behalf of the Authors (08 Nov 2017) Author's response Manuscript

ED: Referee Nomination & Report Request started (26 Nov 2017) by Carol Robinson

RR by Anonymous Referee #3 (06 Dec 2017)

Suggestions for revision or reasons for rejection

The authors use a constant value of 15% bioavailable tDOC for DOC delivered to the Canadian Arctic Ocean by rivers based on Wickland et al 2012 Table 5. (Wickland et al 2012 is missing from Reference list). That value is based on an extrapolation from Yukon river experiments applied to the six largest Arctic rivers. The 15% value is at the low end of what other studies have found, e.g. Holmes et al. 2008 estimated 15-33%, Alling et al 2010 found 30-50% tDOC removal over inner ESAS, Letscher et al 2011; 2013 found 40-60% removal of tDOC and tDON over the ESAS. This underestimate of the bioavailable fraction of tDOC upon delivery to the Arctic Ocean could be the major reason why their simulated values of tDOC are consistently overestimated when compared to satellite estimated tDOC for the outer shelf and offshore locations (Fig 1, Table 1). An underestimation of the tDOC remineralization rate could also drive a similar pattern.

The authors should state what tDOC remineralization rate they are using in their model since a few observational based estimates exist in the literature for their study region.

However, for the computed lateral transport fluxes of tDOC (Fig 3) it is shown that the model overestimates of tDOC concentration don’t have a large effect on the computed lateral tDOC transport fluxes (<20%). Thus I don't see a major detriment to the utility of this study and its conclusions related to this consistent model tDOC bias. The authors do point out the likely reasons for this model discrepancy and how targeted field and laboratory studies could help inform model parameterization of tDOC removal in the Arctic Ocean.

Major comment:
Line 251-254. How are the rates of primary production and bacterioplankton production due to tDOC decomposition to ammonium computed? How is the source of ammonium (tDOC breakdown vs internal marine recycling) differentiated in the model? Is there a model sensitivity test performed with a simulation with tDOC cycling turned on and one simulation with no tDOC cycling and the primary/bacterial production rates compared?

The authors need to provide more detail on how these estimates are computed from their model outputs.

Lastly, the Perspectives section provides an accurate telling of the state of the field with regards to being able to model the fate of tDOC and its current limitations. Numerous suggestions are made for where focused observational and laboratory studies can help inform improved tDOC parameterizations in Arctic coupled physical-biogeochemical models.

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RR by Anonymous Referee #1 (10 Dec 2017)

Suggestions for revision or reasons for rejection

I think the authors have made a significant and sufficient effort to address the suggestions that I made in my initial review. There are some minor editing issues that would improve communication of the results if they can be addressed prior to final acceptance.

Line 40. Add a comma prior to "of which"

Line 44. Replace "into" with "in"

Line 58. Add "be" prior to 33-37.7 TgC

Line 60. Delete "as" before new carbon

Line 61. Start the sentence with "In" rather than "To"

Line 62. Delete "the" prior to AO primary productivity.

Line 70. Change in East Siberian shelves to on East Siberian shelves

Line 71. Delete "the" prior to sea surface

Line 84. Add "in order" prior to "to assess"

Line 99. Add "the" prior to Aqua satellite

Line 101. Add "the" at the end of this line and prior to atmospheric correction.

Line 114. Not clear to me what a scene image is

Line 220. "range" would be better here than "span"

Line 223. Add "with respect to" prior to "the direction" and remove "on" prior to "the direction"

Line 234. "June and August were very close months" is awkward phrasing.

Line 298-302. This is a very lengthy and complex sentence that should be broken up, for example after tDOC on line 299. Start a new sentence here that states that it is difficult to estimate biogeochemical processing of tDOC due to limited field data or something equivalent.

Line 306. Add a comma and "which is" at the end of the line after bioavailability.

Line 312. replace "evidenced" with "present"

Line 313-316. Break this lengthy and complex sentence up into smaller parts.

Line 318. "precludes" is better here than "prevented"

Line 350-354. These two sentences are very awkwardly phrased and the second sentence is a run-on construction.

Line 355. Rather that state that "we suggest", just start the sentence by stating that "Bacterioplankton dynamics also must be better represented in biogeochemical models."

Line 356. Add "such" prior to as dissolved organic carbon

Line 359-360. change "would help" to "would be helpful"

Figure 1. It is hard to the Mackenzie Bay label on the figure with the color scheme being used. The sub-figures could also be larger and a larger scale map of the Mackenze delta and locating it within a regional map of the Arctic would be helpful.

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ED: Publish subject to minor revisions (review by editor) (14 Dec 2017) by Carol Robinson

AR by Vincent Le Fouest on behalf of the Authors (21 Dec 2017)

ED: Publish as is (25 Jan 2018) by Carol Robinson

AR by Vincent Le Fouest on behalf of the Authors (26 Jan 2018) Author's response Manuscript

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Short summary

Climate warming could enhance the load of terrigenous dissolved organic carbon (tDOC) of Arctic rivers. We show that tDOC concentrations simulated by an ocean–biogeochemical model in the Canadian Beaufort Sea compare favorably with their satellite counterparts. Over spring–summer, riverine tDOC contributes to 35 % of primary production and an equivalent of ~ 10 % of tDOC is exported westwards with the potential for fueling the biological production of the eastern Alaskan nearshore waters.