Primary production sensitivity to phytoplankton light attenuation parameter increases with transient forcing

Kvale, Karin F.; Meissner, Katrin J.

doi:https://doi.org/10.5194/bg-14-4767-2017

Articles | Volume 14, issue 20

https://doi.org/10.5194/bg-14-4767-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/bg-14-4767-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 14, issue 20

Research article

|

25 Oct 2017

Research article |

| 25 Oct 2017

Primary production sensitivity to phytoplankton light attenuation parameter increases with transient forcing

Karin F. Kvale and Katrin J. Meissner

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Final revised paper (published on 25 Oct 2017)
Preprint (discussion started on 13 Apr 2017)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Referee Comment', Anonymous Referee #1, 09 May 2017
- AC1: 'Author response to Reviewer 1', Karin Kvale, 15 Jun 2017
RC2: 'Review of "Primary production sensitivity to phytoplankton attenuation parameter increases with transient forcing" by Kvale and Meissner', Anonymous Referee #2, 18 May 2017
- AC2: 'Author response to Reviewer 2', Karin Kvale, 15 Jun 2017

Peer-review completion

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

ED: Reconsider after major revisions (16 Jun 2017) by Victor Brovkin

AR by Karin Kvale on behalf of the Authors (16 Jun 2017) Author's response

ED: Referee Nomination & Report Request started (14 Jul 2017) by Victor Brovkin

RR by Anonymous Referee #1 (21 Jul 2017)

Suggestions for revision or reasons for rejection

The revised manuscript has been improved substantially and most concerns have been addressed. Yet, I still recommend to address the points below.

p3, l14: The scientific question that the study wants to address could still be articulated more explicitly. The fact that this sensitivity assessment of a collection of output variables to this one input parameter using one EMIC has not been published previously seems insufficient to me.

p4, l1: Which values exactly are taken from Table 4 of Dutkiewicz et al. (2015)? Is it the maximum Chl : C ratio? For which phytoplankton group?
This conversion of rates, and possibly other parts of the last paragraph of the introduction, seem to fit better into the methods section.

In the results section: Is the modelled NPP in agreement with observational data (for the historical period / present) and other model data (for pre-industrial, historical, and future), for regional patterns of vertically integrated or surface values, for zonal means, and for profiles? And why is the model data from the pre-industrial (and not the historical) simulation compared to present-day observational data for the biogeochemical tracers?
p6, l23: The sentence about the observations should be moved to the methods section and could be more specific: which tracer data are taken from which dataset?

The authors have thoroughly addressed some potential limitations of their study in the discussion section. Yet, I think the authors go a bit too far with their conclusions and could make them more specific.
In this context, (p12, l2) please specify in what way the UVic ESCM is “typical” and what “these limitations” are. Is the UVic a typical Earth system model or a typical Earth system model of intermediate complexity (EMIC)? Or does mainly the ocean physical and biogeochemical model part matter?
p12, l5-9: Strictly speaking, the present study does not really support these claims, but can only support them for the case of (this version of) the UVic ESCM.

More technical comments:

The second and the last sentence in the abstract could be split into two parts each to improve clarity.

The first sentence in the discussion could be made more explicit: What is “pre-industrial equilibrium sensitivity”? Maybe rewrite as “The pre-industrial equilibrium simulations demonstrate a sensitivity…”.

p12, l1: There is no “runaway” feedback here. I suggest to remove the word or replace it by “positive”.

In the figures, are annual means of single years shown or are those multi-year means?

For Figure 1, please add that in the left plot zonal means(?) are shown and correct the unit (should be m^-2, not m^-3). For the description of the right plot replace “spatially” by “globally” or “horizontally”.

For Figure 2 left and Figure 6, please correct the unit (m^-2, not m^-3).

For Figure 4 and 7, please add whether these are annual means / climatologies.

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RR by Anonymous Referee #2 (30 Jul 2017)

Suggestions for revision or reasons for rejection

Overall I am happy with the revised manuscript, the authors appear to have put a lot of effort into addressing both sets of reviewer comments in detail. The Discussion section is much improved. The manuscript overall is now much more coherent and concise as a whole. I recommend publication with a few very minor suggestions for changes to the text.

Page 3, line 20+: This paragraph needs better integration into the Introduction. In particular, the Methods requires some description of the parameter range used in the experiments and the Introduction ideally would finish the aims of the study (I appreciate I suggested moving this from the methods and my apologies for not being clearer the first time around!). My issue with this paragraph is that it contains details that are specific to the use of the model in the study (e.g., see Page 4, lines 1 to 9) and better suited to the Methods but also details that are general to the use of eqn 1 in modeling (e.g., see Page 3, lines 26 to 35) and more relevant to the discussion of eqn 1 in the Introduction.

Page 6, lines 26 – 28: The reason for the choice of two different ranges of K values is not particularly clear here but becomes apparent in the following paragraphs. If I understand correctly, K3 – K8 represent the parameter ranges that better represent the pre-industrial tracer observations and K1 – K8 is the full range tested. I suggest rewording this sentence to something along the lines of comparing the differences between the full sensitivity range tested (K1 – K8) and a subset of the range excluding those two runs that cannot reproduce the preindustrial tracers (K3 – K8).

Page 10, lines 10 – 12: The comment on deep ocean inventories also needs to be included within the Results section when discussing the carbon and nutrient distributions (i.e., pages 5 & 6) as this is a component of the net change in NPP in the pre-industrial steady-state runs alongside the initial changes in NPP driven by the choice of attenuation-parameter. I note this is perhaps less a component for the transient run as the timescales of nutrient re-distribution are generally longer.

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ED: Publish subject to minor revisions (Editor review) (01 Sep 2017) by Victor Brovkin

AR by Karin Kvale on behalf of the Authors (03 Sep 2017) Manuscript

ED: Publish as is (21 Sep 2017) by Victor Brovkin

AR by Karin Kvale on behalf of the Authors (23 Sep 2017)

Short summary

Climate models containing ocean biogeochemistry contain a lot of poorly constrained parameters, which makes model tuning difficult. For more than 20 years modellers have generally assumed phytoplankton light attenuation parameter value choice has an insignificant affect on model ocean primary production; thus, it is often overlooked for tuning. We show that an empirical range of light attenuation parameter values can affect primary production, with increasing sensitivity under climate change.