Long-term response of oceanic carbon uptake to global warming via physical and biological pumps

Yamamoto, Akitomo; Abe-Ouchi, Ayako; Yamanaka, Yasuhiro

doi:https://doi.org/10.5194/bg-15-4163-2018

Articles | Volume 15, issue 13

https://doi.org/10.5194/bg-15-4163-2018

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

https://doi.org/10.5194/bg-15-4163-2018

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

Articles | Volume 15, issue 13

Research article

|

10 Jul 2018

Research article |

| 10 Jul 2018

Long-term response of oceanic carbon uptake to global warming via physical and biological pumps

Akitomo Yamamoto, Ayako Abe-Ouchi, and Yasuhiro Yamanaka

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Final revised paper (published on 10 Jul 2018)
Supplement to the final revised paper
Preprint (discussion started on 10 Nov 2017)
Supplement to the preprint

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Review comments on: "Long-term response of oceanic carbon uptake to global warming via physical and biological pumps"', Neil Swart, 18 Dec 2017
- AC1: 'Reply: RC1: 'Review comments on: "Long-term response of oceanic carbon uptake to global warming via physical and biological pumps"', Neil Swart, 18 Dec 2017', Akitomo Yamamoto, 26 Jan 2018
RC2: 'Review for Long-term response of oceanic carbon uptake to global warming via physical and biological pumps by Yamamoto et al.', Anonymous Referee #2, 22 Dec 2017
- AC2: 'Reply: RC2: 'Review for Long-term response of oceanic carbon uptake to global warming via physical and biological pumps by Yamamoto et al.', Anonymous Referee #2, 22 Dec 2017', Akitomo Yamamoto, 26 Jan 2018
RC3: 'Review of "Long-term response of oceanic carbon uptake to global warming via physical and biological pumps" by Yamamoto et al.', Anonymous Referee #3, 23 Dec 2017
- AC3: 'Reply: RC3: 'Review of "Long-term response of oceanic carbon uptake to global warming via physical and biological pumps" by Yamamoto et al.', Anonymous Referee #3, 23 Dec 2017', Akitomo Yamamoto, 26 Jan 2018

Peer-review completion

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

ED: Reconsider after major revisions (14 Feb 2018) by Laurent Bopp

AR by Akitomo Yamamoto on behalf of the Authors (20 Mar 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (29 Mar 2018) by Laurent Bopp

RR by Anonymous Referee #3 (08 May 2018)

Suggestions for revision or reasons for rejection

I have previously reviewed a first version of this manuscript. I think the authors have done a fairly good
job in revising their manuscript. I have, however, two important points and several minor/technical issues
that should be addressed.

Main points:

1) In Section 2.4.1, which describes the abiotic experiments, we read "The biological effect is calculated as the
residual ("Total" - "SST" - "Circulation", as described in Table 2)." Then, in Section 4.1 (Abiotic experiments):
"Biological changes enhance CO2 uptake at high latitudes and reduce it at low latitudes; the resulting global CO2
uptake increase by 46 PgC due to biological changes." Later, on page 14 (lines 29 to 30): "In the abiotic experiments,
the biological contribution is calculated as the residual. The enhanced CO2 uptake owing to the reduced upward
transport of natural CO2 is included in the biological effect." Also, in Figure 5 panel a, which displays the
results from the abiotic experiments there are grey bars indicating an "organic matter contribution".

What kind of abiotic experiment did the authors perform here? This needs clarification.

2) On page 9 lines 6-11, and later scattered throughout the text: It is rather surprising that the efficiency of the
biological pump (calculated in terms of AOU) is going down. This is the opposite of what is seen in CMIP5 models for
the 1% simulation (Schwinger et al. 2014). In all of these models (no exception) the lower export production is
overcompensated by the slower circulation such that AOU increases. So in all of these models the efficiency of the
biological pump is actually going UP not DOWN. Could the authors try to explain why this is different for their
model (or at least mention that this is different to CMIP5 models)? Since the reduced efficiency is used as an
explanation for changes in section 4.2.3, I think this is important.

Minor points and technical corrections:

page 4, lines 17-18: "...a physiological trade-off between the efficiency of nutrient encounters at the cell surface and
the maximum assimilation rate...". Should this read "encountered"?

page 4, lines 29-31: Using "although" does not make sense here, please check logic of this scentence.

page 5, line 2: "climate variability" is not the correct term here. This should read "short-term variability" or
"forcing variability" or something similar.

page 6, line 11: "...assuming that the individual contributions to total change are linear." I do not understand this
addition. The nonlinearity is quantified in Table 2, and briefly discussed for the biological pump contribution in
Sec. 4.2.3. So I don't see where an assumption is made.

page 7, line 15-16: Consider replacing "effects" with "sensitivity experiments" or "experiments" or similar.

page 11, line 10: "the previous" -> "previous"

page 11, line 14, and Table 2: The total for the abiotic experiments should be calculated as (4)-(3) I assume,
not (2)-(1) as done here. It would be very surprising if the total uptake for the abiotic experiments is the
same as in the biotic.

page 12, lines 8-9: I think it is better to write "... a significant nonlinearity ... is found for the organic
matter cycle."

page 12, line 9: It would help the reader to add a sentence "The large differences relative to the abiotic
simulation are discussed below (Sec. 4.3)." or something similar.

page 12, line 18: "...secondary importance of circulation changes". I would suggest to replace the "secondary
importance" as in other places of the revised manuscript, since this is misleading with respect to the role of
circulation changes via biology.

page 15, lines 14-15: "...with the previous studies" -> "...with those previous studies"

page 15, line 19: "...under the pre-industrial condition" -> "...under pre-industrial conditions"

Figure 1: The caption says this is salinity-normalised DIC. But in the Figure title it reads "Delta sDIC", while
the the range (-100 to 300 mmol/m^3) indicates that this must be some change or deviation. It is however not
clear from what. Please clarify.

References:

Schwinger, J., J. F. Tjiputra, C. Heinze, L. Bopp, J. R. Christian, M. Gehlen, T. Ilyina, C. D. Jones, D. Salas-Mélia,
J. Segschneider, R. Séférian, and I. Totterdell (2014), Nonlinearity of ocean carbon cycle feedbacks in CMIP5 earth
system models, J. Clim., 27, doi:10.1175/JCLI-D-13-00452.1.

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ED: Publish subject to minor revisions (review by editor) (09 May 2018) by Laurent Bopp

AR by Akitomo Yamamoto on behalf of the Authors (30 May 2018) Author's response Manuscript

ED: Publish as is (02 Jul 2018) by Laurent Bopp

AR by Akitomo Yamamoto on behalf of the Authors (02 Jul 2018) Author's response Manuscript

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Short summary

Millennial-scale changes in oceanic CO₂ uptake due to global warming are simulated by a GCM and offline biogeochemical model. Sensitivity studies show that decreases in oceanic CO₂ uptake are mainly caused by a weaker biological pump and seawater warming. Enhanced CO₂ uptake due to weaker equatorial upwelling cancels out reduced CO₂ uptake due to weaker AMOC and AABW formation. Thus, circulation change plays only a small direct role in reduction of CO₂ uptake due to global warming.