Reciprocal bias compensation and ensuing uncertainties in model-based climate projections: pelagic biogeochemistry versus ocean mixing

Löptien, Ulrike; Dietze, Heiner

doi:https://doi.org/10.5194/bg-16-1865-2019

Articles | Volume 16, issue 9

https://doi.org/10.5194/bg-16-1865-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/bg-16-1865-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 16, issue 9

Research article

| Highlight paper

|

06 May 2019

Research article | Highlight paper |

| 06 May 2019

Reciprocal bias compensation and ensuing uncertainties in model-based climate projections: pelagic biogeochemistry versus ocean mixing

Ulrike Löptien and Heiner Dietze

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Final revised paper (published on 06 May 2019)
Preprint (discussion started on 18 Dec 2018)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Review of "Reciprocal bias compensation and ensuing uncertainties in model-based climate projections: pelagic biogeochemistry versus ocean mixing" by Ulrike Löptien and Heiner Dietze', Anne Willem Omta, 07 Jan 2019
- AC1: 'Answer to Reviewer #1', Ulrike Loeptien, 31 Jan 2019
RC2: 'review of "Reciprocal bias compensation and ensuing uncertainties in model-based climate projections: pelagic biogeochemistry versus ocean mixing"', Anonymous Referee #2, 10 Jan 2019
- AC2: 'Answer to Reviewer #2', Ulrike Loeptien, 31 Jan 2019

Peer-review completion

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

ED: Reconsider after major revisions (05 Feb 2019) by Katja Fennel

AR by Ulrike Loeptien on behalf of the Authors (06 Mar 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (13 Mar 2019) by Katja Fennel

RR by Anonymous Referee #2 (26 Mar 2019)

Suggestions for revision or reasons for rejection

The structure of the manuscript has improved considerably in this first revision (especially its second half) and I have just 2 major comments that I would like the authors to address.

general comments:

While the structure of the manuscript has indeed improved and some statements are no longer repeated again and again, there are still a lot mistakes in the use of the English language which makes the manuscript difficult to follow in places. I have outlined some mistakes in my specific comments below but there are too many smaller mistakes to list them all. I would recommend that the authors allow a native English speaker to carefully go through the manuscript before resubmitting it.

In my first review I was curious how the parameter values for the TUNE experiment were chosen. In the revised version of the manuscript, I still cannot find the information I was looking for (it is not on page 6, line 29ff as the response to first review suggests). Furthermore, I am now wondering how the two experiments with decreased sinking fit into the picture. How were the parameter values determined, were they randomly chosen? Why are there exactly 2 simulations with decreased sinking and what are the values for the remaining parameters for those two simulations? Just a few sentences might be all that is required, at the moment the reader is not given enough information to recreate the experiment and obtain a similar reduction in model-data misfit.

specific comments:

p1 l4: "Respective model applications" -> "Applications for these models"

p1 l17: "global warming": I prefer the term "climate change" but leave this decision to the authors.

p1 l17: "trigger ... geo-engineering options": I'd suggest "have triggered ... geo-engineering options to combat its effects on our planet."

p2 l3: "that govern the dynamics of the set of underlying partial differential equations" -> "that are included in the model's partial differential equations which govern its dynamics"

p2 l5: remove "and/"

p2 l6: remove "generic" ("typical" is enough)

p2 l12: "In this study..." This sentence is not very precise, try to tie in biological models and model-data misfit reduction. Something like "In this study we illustrate how a model-data misfit arising from biases and deficiencies in the physical model can impact the estimation of biological parameters."

p2 l16: "to" -> "and"

p2 l19: "balancing ... away from". Do you mean "counteracting the effects of", please rephrase.

p2 l27: "where actual mixing compounds explicitly prescribed mixing rates with spurious mixing ...": I had to re-read this sentence several times, please simplify and rephrase.

p2 l33: "we do not know the values for diapycnal diffusivity that are to be set explicitly in Earth System Models" -> "we do not have exact values for diapycnal diffusivity for use in Earth System Models"

p2 l33: "Changes" -> "Yet, changes"

p3 l5: "Earth System Models contains several components and module after module is coupled together" -> "Earth System Models are made up of several modules which are coupled together"

p3 l6: "Thus, pelagic biogeochemistry modules are developed within a rather "fixed" physical model environment." I'd suggest "Thus, pelagic biogeochemistry modules are often developed presuming a fixed physical model component."

p3 l17: "biogeochemical mixing" This sound like a physical process, I think you mean "biogeochemical cycling".

p3 l18: "sometimes without even the modellers knowing" Are you suggesting most modellers know about their model having two flawed model components.

p4 l2: "UVic" is introduced here for the second time.

p4 l17: "in the reference version": Is that the Genuine Truth, if so mention that.

p4 l27: "such as differences between growth and death" -> "growth and mortality"

p4 l32: There is a "(3)" missing here. But why not introduce these in the same order they are later presented in the equations?

p5 l7: "(T) up to 20C" the "up to 20C" is confusing here, I'd suggest to just use "(T in units of C)".

p5 l14: "In one of our configurations": Name the configuration! The configurations have been introduced in the previous section and TUNE should be mentioned explicitly in this section.

p6 l9: These 3 parameters were all just mentioned on the previous page.

p6 l11: "these": the changes were not yet specified, use "the" or "our" instead.

p6 l13: "changes to biogeochemical model parameters in TUNE are chosen such that the bias between the Genuine Truth and MIX+ (that is effected by the choice of a higher background diffusivity) is compensated" Be specific here, bias in what variables? If you had observations of diffusivity, changes in the parameters could not compensate for that. However the bias in select "observed" biogeochemical variables can be reduced this way.

p6 l18: "ranges regularly" What exactly does this mean, how were the parameter values chosen?

p6 l19: The two extra runs with decreased sinking feel a bit like an afterthought. How were the rest of the parameters chosen?

p7 l27: "increases up to 1 PSU" -> "increases by up to 1 PSU"

p8 l16: "has opposing effects" -> "has two opposing effects"

p9 l5: ". The latter" -> ", which"

p9 l9: Here you use "RMSE", before "RMSD" is used.

p9 l20: "doubled below 1500 m depth" What exactly is doubled, the temperature difference?

p9 l26: "are" -> "can be"

p10 l18: Fig. 10 shows phosphate, not phytoplankton.

p11 l21: Here you are comparing a relative number (0.5%) to an absolute one (200GT), which makes it difficult to assess the significance of the change. Add, for example, information about the relative change to the absolute number "200Gt C (x%)". Also, change "T" to "t".

p12 l20: Here, the mixing parameter settings are described as "extreme cases", later it is argued that literature values were chosen. What is it, are the literature values extreme or are reasonable values chosen here? A bit more explanation is needed or maybe the use of "extreme" is a bit too extreme here?

p12 l29 (on p13, the line numbers keep sliding): It would be good to point out here that changes to the vertical diffusivity are the only changes to the physical model component but that there are also changes to the biogeochemical model. If the Keller 2012 configuration only includes the physical model component, this should be pointed out in the first paragraph of Section 4.1.

p13 l11: "To summarize: the uncertainty is substantial." I'd suggest: "To summarize: the uncertainty in the value of the vertical diffusion parameter of our physical model component is substantial and it can currently not be well constrained by either observations or experiments. Hence, ..."

p13 l14: "which saves considerable computational cost": This sounds a bit like the change in advection scheme makes the model run faster, I don't think this information is needed here.

p13 l18: Why start a new paragraph in the middle of the explanation of the effects of modifying the vertical diffusion parameter? Start new paragraph at the beginning of said explanation "<new paragraph> Using ad-hoc measures, ..."

p13 l27: It would be good to mention that the parameter values were chosen to reduce the misfit between model and data (generated by Genuine Truth).

p14 l2: "pretty" -> "quite" (or just "effective")

p14 l4: "the Genuine Truth configuration is considered state-of-the-art" I do not disagree with this assessment, however previously it is stated that "The model is relatively simple
[...] and rather coarsely resolved (≈ 200km), compared to the cutting-edge generation of IPPC-type Atmosphere-Ocean General Circulation Models (AOGCMs)." You should make the argument for why this model is considered state-of-the-art in Section 4.1. Otherwise it comes as a surprise to the reader that in Section 4.3 the previously "simple" model is now considered "state-of-the-art".

p14 l8: "As outlined above, it is hard to argue based on a-priori knowledge as concerns the differences among their underlying model parameters, which model configuration, the Genuine Truth or TUNE, is more realistic.": I repeat my argument: If one of the model configurations has "extreme" parameter values (as stated previously), then it would be reasonable to presume based on a-priori knowledge that it is less realistic.

p15 l9: To someone just reading the conclusions, you should point out that the values of the biogeochemical model parameters were chosen to counteract the effects of modifying the diffusivity.

p16 l9: "constricted" -> "constrained"

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ED: Publish subject to minor revisions (review by editor) (28 Mar 2019) by Katja Fennel

AR by Ulrike Loeptien on behalf of the Authors (09 Apr 2019) Author's response Manuscript

ED: Publish subject to technical corrections (17 Apr 2019) by Katja Fennel

AR by Ulrike Loeptien on behalf of the Authors (18 Apr 2019) Author's response Manuscript

Short summary

Anthropogenic greenhouse gas emissions trigger complex climate feedbacks. Output form Earth system models provides a basis for related political decision-making. One challenge is to arrive at reliable model parameter estimates for the ocean biogeochemistry module. We illustrate pitfalls through which flaws in the ocean module are masked by wrongly tuning the biogeochemistry and discuss ensuing uncertainties in climate projections.