Can organic matter flux profiles be diagnosed using remineralisation rates derived from observed tracers and modelled ocean transport rates?

Wilson, J. D.; Ridgwell, A.; Barker, S.

doi:https://doi.org/10.5194/bg-12-5547-2015

Articles | Volume 12, issue 18

https://doi.org/10.5194/bg-12-5547-2015

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

https://doi.org/10.5194/bg-12-5547-2015

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

Articles | Volume 12, issue 18

Research article

|

30 Sep 2015

Research article |

| 30 Sep 2015

Can organic matter flux profiles be diagnosed using remineralisation rates derived from observed tracers and modelled ocean transport rates?

J. D. Wilson, A. Ridgwell, and S. Barker

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Final revised paper (published on 30 Sep 2015)
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Preprint (discussion started on 19 Mar 2015)
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Interactive discussion

Status: closed

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

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RC C1424: 'Can organic matter flux profiles be diagnosed using remineralisation rates derived from observed tracers and modelled ocean transport rates? by Wilson et al', Anonymous Referee #1, 18 Apr 2015
RC C1430: 'Review of "Can organic matter flux profiles be diagnosed using remineralisation rates derived from observed tracers and modelled ocean transport rates?"', Anonymous Referee #2, 19 Apr 2015
AC C3479: 'Response to Reviewers' comments on Wilson et al. "Can organic matter flux profiles be diagnosed using remineralisation rates derived from observed tracers and modelled ocean transport rates?"', Jamie Wilson, 10 Jul 2015

Peer-review completion

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

ED: Reconsider after major revisions (28 Jul 2015) by Jack Middelburg

AR by Jamie Wilson on behalf of the Authors (07 Aug 2015) Author's response Manuscript

ED: Referee Nomination & Report Request started (10 Aug 2015) by Jack Middelburg

RR by Anonymous Referee #1 (26 Aug 2015)

Suggestions for revision or reasons for rejection

Overall, I am quite happy with the revised manuscript. I have just a few minor issues (see below), and one slightly more substantial issue, which I think could be addressed or considered in addition to the otherwise very careful analysis of model performance. Some of the (very few) remaining points should have already occurred to me when reading the first version; I therefore do not regard them as mandatory, but would be happy if the authors considered them.

I am a little bit worried about the shallow reference depths z_0 for the MIT-TMM comparison, and also for the later calculation of b values for the Martin curve. I would suggest to expand a little bit more on that and/or briefly mention potential caveats with respect to that calculation. This particularly refers to the following sentences/paragraphs/figures:

p 8, lines 8-9: "However, negative ISSs also exist, indicating a sink of PO4, such as in regions of the subpolar Southern Ocean and Pacific equatorial upwelling." - Couldn't negative ISSs also indicate phosphate loss due to phytoplankton production? (85 m will still be within the euphotic zone, and thus mainly be a local sink of phosphate.)

p 7, line 25, Fig 1, section 4.2: Why choose 25 m as reference depth? This is shallower than in Martin's original approach (z_0=100m), and probably within the depth range of affected by mixing/convection, as well as phytoplankton growth. Note that Lam et al. (2011) note how sensitive the estimate of b is to the value of z_0. Some comments on this (e.g., the effect of a deeper reference depth), would be nice.

Further, the function dF/dz = ... shown in the caption of Fig 1 may a bit confusing when it comes to a regression of b from the log-transformed values of remineralisation. As the function is shown here, b occurs as factor as well as exponent, which at first sight seems to hinder a direct estimate of b from log-transformed values. Martin et al. (1987, their eqn. 7) substitute their factor F_0*b/z_0 by R_0 (remineralisation in depth z0), which - although basically the same as shown here - may be easier for the reader to understand. I'd recommend referring to their derivation/Eqn. 7 (as in that paper everything is already laid out in a quite straightforward way).

Minor comments:

p 3, line 11: "i.e. they display shallower flux curves" - better: "flux curves corresponding to shallower remineralisation"?

p 3, line 14: "analysis"

p 3, line 20: "such as the level of nutrient recycling" - Do you mean "such as the TROPHIC level of nutrient recycling"?

p 4, lines 20-21: "the concentration of Apparent Oxygen Utilisation" sounds somehow strange; skip "the concentration of"?

p 5, line 27: "e.g. Henson et al. (2011)" and elsewhere - wrong style of citation/put brackets around full citation (e.g., in Latex use \citep[e.g.][]{henson2011})

p 6, line 16: "the amount of tracer needed" - better "the amount of tracer SUPPLY needed"? (As this will be a flux or rate, i.e. per unit time).

p 8, line 3: "a regridded annual climatological [PO4] field (...)" - better (for those who are not familiar with WOA): a field of regridded annual climatological PO4 observations"?

p 8, lines 20-21: "The value is however larger than values However, there ..." - ??

p 9, line 13: Point missing.

p 10, line 16: "Michaelis-Menten"

p 10, line 17: time unit of maximum rate?

p 10, line 18-19: "A fixed fraction of the uptake (66 %) is exported from the surface as DOM which can be transported by circulation and remineralised " - Is it really (immediately) exported from the surface? Or do you mean: "A fixed fraction of the uptake (66 %) is immediately released as [or transformed to] DOM, which can be transported by circulation and remineralised "?

p 10, line 25: "sediment interactions" - better: "interactions with a (hypothetical) sediment"?

p 14, line 15 "flux out" - I assume this is simply A, i.e. the pure transport (as indicated by by the color bar units in 5c), correct?

p 14, line 28: "plausible"

p 15, line 17: "large impact of ISSs" - better "on ISSs"?

p 15, line 20: "with the remineralisation flux of PO4 into each grid-box" - better "in each grid box"?

In fig 6 (labels and figure caption): please use consistent notation of either "ISS - Remin" or "Model - ISS".

p 16, lines 2ff and Fig 8: were the SDs of ERR-OBS and ERR-CIRC calculated from the variance over x, y, and among the different experiments, or is this the SD between the different experiments, averaged over x and y?

p 16, line 19 " between observed and modelled circulation rates" - better: "between true and simulated circulation rates"?

p 18, line 3-5: " consistent with the concept that salinity is not significantly increasing or decreasing in the ocean interior." - Do you mean "that there are no local sources or sinks in the ocean interior"?

p 18, line 17: "Redefining"

p 19, line 7: "parameterisation"

p 19, line 21: "is fitted"

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ED: Publish subject to minor revisions (Editor review) (27 Aug 2015) by Jack Middelburg

AR by Jamie Wilson on behalf of the Authors (10 Sep 2015) Author's response Manuscript

ED: Publish subject to technical corrections (15 Sep 2015) by Jack Middelburg

AR by Jamie Wilson on behalf of the Authors (18 Sep 2015) Manuscript

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Short summary

We explore whether ocean model transport rates, in the form of a transport matrix, can be used to estimate remineralisation rates from dissolved nutrient concentrations and infer vertical fluxes of particulate organic carbon. Estimated remineralisation rates are significantly sensitive to uncertainty in the observations and the modelled circulation. The remineralisation of dissolved organic matter is an additional source of uncertainty when inferring vertical fluxes from remineralisation rates.