Effects of melting ice sheets and orbital forcing on the early Holocene  warming in the extratropical Northern Hemisphere

Zhang, Yurui; Renssen, Hans; Seppä, Heikki

doi:https://doi.org/10.5194/cp-12-1119-2016

Articles | Volume 12, issue 5

https://doi.org/10.5194/cp-12-1119-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/cp-12-1119-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 12, issue 5

Research article

|

04 May 2016

Research article |

| 04 May 2016

Effects of melting ice sheets and orbital forcing on the early Holocene warming in the extratropical Northern Hemisphere

Yurui Zhang, Hans Renssen, and Heikki Seppä

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Final revised paper (published on 04 May 2016)
Supplement to the final revised paper
Preprint (discussion started on 12 Nov 2015)
Supplement to the preprint

Interactive discussion

Status: closed

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

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RC C2407: 'Review of manuscript by Zang et al.', Anonymous Referee #1, 20 Nov 2015
- AC C3099: 'Response to reviewer #1', yurui zhang, 29 Jan 2016
RC C2694: 'Review of ”Effects of melting ice sheets and orbital forcing on the early Holocene warming in extratropical Northern Hemisphere” by Zhang et al.', Anonymous Referee #2, 18 Dec 2015
- AC C3091: 'Response to reviewer #2', yurui zhang, 29 Jan 2016

Peer-review completion

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

ED: Reconsider after major revisions (29 Jan 2016) by Marie-France Loutre

AR by Yurui Zhang on behalf of the Authors (26 Feb 2016) Author's response Manuscript

ED: Referee Nomination & Report Request started (29 Feb 2016) by Marie-France Loutre

RR by Anonymous Referee #1 (15 Mar 2016)

Suggestions for revision or reasons for rejection

Review of manuscript by Zhang et al. entitled “Effects of melting ice sheets and orbital forcing on the early Holocene warming in the extratropical Northern Hemispheres”.

The manuscript by Zhang et al. has greatly improved since the previous version and now presents a study that is both interesting and readable. There are still a number of small questions that remain as well as several technical comments. When those are taken care of I recommend this manuscript for publication in Climate of the Past.

Minor comments:
Throughout the manuscript different the present and past tense are often mixed. Please read the manuscript carefully to be consistent in the usage of the different tenses.

Throughout the manuscript the word ‘the’ is often used when it should not, or missing where it should have been used. For example line 4 on page 9 ‘of FIS’ should be ‘of the FIS’ and use ‘ORBGHG’ or ‘the ORBGHG simulation’.

Throughout the manuscript ‘N’ is used to indicate ‘North’ or ‘Northern’, perhaps a personal preference, but consider writing out the whole word.

Throughout the manuscript be consistent and clear in the use of PI or preindustrial or present or 0ka.

Throughout the manuscript I find the usage of ‘ka’ as ‘ka BP’ a little confusing because then, strictly speaking, you also use for instance °C (ka BP)-1. Consider using ‘ky’ instead of ‘ka’, for instance °C ky-1.

Lines 12-17 page 1: Consider mentioning in the first paragraph what has previously been found in proxy-based studies, as to introduce the importance of your results presented in the remainder of the abstract. For instance something like ‘Proxy-based temperature reconstructions suggest a Northern Hemisphere warming, but also indicate important regional differences. Here we show what forcings and feedbacks can underlie these regional differences…’. If for instance Alaska and Northern Canada are mentioned, then the focus on these two specific regions in the remainder of the abstract doesn’t seem so arbitrary anymore.

Lines 29-31 page 5: So the ice sheet reconstruction that is used is solely based on geological constraints, not on ice-sheet modelling?

Lines 11-12 page 6: How can an equilibrium meltwater forcing match estimates for the early Holocene?

Section 2.3: It is still not clear to me how the two freshwater forcing scenarios are different. Is their initial value the same or different? Is the rate of change the same or different. Please clarify in the text.

The results sections could become a little more clear if you write them all following the same structure. Such a structure could be to first present the summer results, then winter and finally annual mean. Then the reader knows what to expect and where to look for a certain result.

Lines 24 page 12: Shortly introduce the stacks of Shakun et al. (2012) and Marcott et al. (2013).

Line 32 page 12: Is this bias found for specific regions and how does this compare to the 30-90N model-data comparison that is performed here?

Line 34 page 12: CP does not have a page limit, as far as I know, as long as the content is relevant.

Line 12 page 13: And how did they interpret this result and how does it connect to the work presented here? Shortly elaborate.

Line 30 page 13: Explain what causes a southward migration of the tundra under a warming climate.

Lines 31-33 page 13: They counterbalanced, but still led to a substantially cooler climate? Please explain.

Lines 1-3 page 15: Does this part discuss the results of FWF-v1 or FWF-v2? Or both? If the latter, perhaps move to earlier part of the manuscript.

Line 15 page 15: Perhaps shortly repeat the differences between the two freshwater scenario and how they can explain the AMOC differences.

Line 27 page 15: Perhaps shortly mention future plans: comparison with previously performed transient deglacial/early Holocene experiments etc.

Technical comments:
Line 2 page 2: illustrate

Line 1-3 page 2: This is a little hard to read, consider rewording. Moreover, it would be good to say that this kind of work has the potential to constrain the uncertainties in ice sheet reconstructions.

Line 2 page 2: configuration instead of deglaciation?

Line 14 page 2: Consider “a couple degrees of warming (Vinther et al., 2009).

Line 21 page 2: ‘in planktonic’.

Line 24 page 2: ‘drivers of climate’.

Line 28 page 2: consider removing ‘critical’.

Lines 2-6 page 3: Difficult to read, please rewrite.

Line 20 page 3: Consider removing ‘particular’.

Line 20 page 3: “influence of the decay of the LIS..”.

Line 26 page 3: ‘renamed to’.

Lines 28-29: Consider removing this sentence since it is very obvious.

Line 34 page 3: Not sure if ‘in preparation’ is allowed in CP, I’ll leave it to the editor.

Line 5 page 4: Consider removing “in the present study”.

Line 22 page 4: ‘the ice sheet evolution and GHGs where prescribed’

Line 2 page 5: Younger Dryas strictly speaking not an example of a Holocene study.

Line 7 page 5: It is preferable to use ‘that’ instead of ‘which’.

Line 26 page 5: PMIP3 protocol up to 11.5ka?

Line 1 page 6: The average thickness?

Line 27 page 6: Was instead of were.

Line 28 page 6: Why mention experiments that are not presented in the manuscript?

Line 12 page 7: cold instead of cooler.

Line 18 page 7: PI simulations, with a maximum

Lines 18-19 page 7: in the central parts of the Northern Hemisphere continents

Lines 19-20 page 7: than that over the continents.

Lines 26-28 page 7: Please rephrase.

Line 30 page 7: ‘southern regions’, where is that?

Line 8 page 8: Additionally, SSTs where also

Lines 7-10 page 8: Please rephrase.

Line 29 page 8: overall cooling of about

Lines 29-30 page 8: Too obvious, consider removing.

Line 32 page 8: of ORBGHG ……of the Holocene

Lines 2-3 page 9: It was …..further. Consider removing whole sentence.

Line 4 page 9: the FIS

Line 8 page 9: insolation anomalies.

Line 9 page 9: by the demise in the orbital forcing.

Line 11 page 9: indicates

Line 14 page 9: Please rephrase.

Line 22 page 9: The ORBGHG simulation

Lines 27-29 page 9: Isn’t this part of the equilibrium response?

Line 31 page 9: temperature rise

Line 15 page 10: remove ‘up’.

Line 26 page 10: remove ‘climate’.

Line 32 page 10: higher instead of warmer.

Line 6 page 11: Alaskan temperature trend.

Lines 8, 9 and 14 page 11: temperatures

Line 32 page 11: and slightly lower SSTs

Line 5 page 12: The only

Lines 6-7 page 12: suggest similar early Holocene summer temperature anomalies compared to the present

Line 9 page 12: palaeotemperature proxy?

Line 18 page 12: which indicates warmer

Line 19 page 12: temperatures

Line 20 page 12: challenged instead of changed?

Line 22 page 12: is instead of was?

Line 4 page 13: variations are

Line 8 page 13: Geopotential with a capital letter?

Line 16 page 13: and overwhelms the warming

Line 17 page 13: partly be……..by enhanced albedo

Line 23 page 13: which caused locally cooler conditions.

Line 23 page 14: use either ‘net’ or ‘overall’.

Line 23 page 14: the climate

Section 4.3: Perhaps the description of AMOC changes in section 3.2 could be moved to section 4.3?

Line 27 page 14: around 10 degrees?

Line 32 page 14: Perhaps ‘with a further AMOC weakening’.

Line 32 page 14: 1-2Sv compared to?

Line 2 page 16: The temperature anomalies at 11.5ka relative to PI were….

Line 3 page 16: higher? Do you mean positive?

Line 15 page 16: in promoting these cold conditions.

Lines 17-18 page 16: heat transport and sea-ice feedbacks.

Line 21 page 16: at 11.5 ka over central Siberia can be….

Line 24 page 16: The dominant factors driving the climate in the eastern Arctic Ocean were

Line 2 page 7: This sounds a little double.

Lines 10-11 page 17: can potentially be constrained by applying different deglacial scenarios and compare them with networks of proxy-records.

Line 14 page 17: Perhaps mention that this also helps in understanding the differences between proxy-records.

Table 2: What is FWF? FWF_v1 or FWF_v2 or are those also the same for 11.5ka?

Caption figure 3: Define ones (in the main manuscript or in a figure caption) what is meant with summer and winter (JJA and DJF?).

Figures in general: When figures include a clear legend than the meaning of the different colours does not need to be repeated in the caption.

Figure 2: present? PI, 0ka?

Figure 4: why is the shaded bar only shown for the top panel?

Figure 4: On basis of which scenario are these slopes calculated?

Figure 8: mention the start and end of this shorter period for completeness.

Figure 9: Perhaps the proxy data for the modern period can be removed since no human induced warming is included in the simulations.

Figure 10: Wind vectors could perhaps give a clearer picture of the changes in atmospheric circulation.

Figure 12: Consider giving the maximum AMOC strength for the different panels for illustration.

Figure 14: Some units have an asterisks in them, like 10E+12*, perhaps a latex issue?

Figure S2: include colour scale.

Figure S4: why 10ka?

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RR by Anonymous Referee #2 (21 Mar 2016)

Suggestions for revision or reasons for rejection

Review of “Effects of melting ice sheets and orbital forcing on the early Holocene warming in the extratropical Northern Hemisphere” by Zhang et al

The authors have improved the manuscript and I am reasonably happy with it. Particularly the science and the structure have improved making the paper a more solid and straightforward read. There are, however, still some concerns in terms of the presentation. For instance, the language is still clumsy or even outright wrong in many places and figure numberings are sometimes off.

## Claimed edits ##
Old numbering 5353.11: The authors claim in their rebuttal to have added a description and reference (Ramaswamy) for how they calculate the GHG radiative forcing. I cannot find this.
Old numbering 5353.22-23: The authors say they rephrased a sentence to […]. But it appears to have been deleted entirely.
Old numbering 5365.17: You say you have swapped the order of figures 10 and 11, but I cannot see that you have.

## Figure numbering ##
Please do not trust me to have found all of them; go over them all carefully.
8.10 Fig 4e->3e
8.14 3f
9.18: Fig 4x, right?
9.24 Fig 5
10.10 Fig 6

## Minor points ##
6.1: What do you mean by relative thickness?
6.28: Why do you mention that you did more simulations than you present?
7.3+4: Why do you refer to Fig 2b and Fig 2c for the two FWF’s, respectively? Both figures show both FWF’s, don’t they?
7.6 Default what?
7.10: “Surface temperatures” or “near-surface air temperatures”? Is it actually the surface temperature?
7.12-13: What does this sentence about the 0.5 C cooler bias mean? I don’t really understand it.
9.10: It is interesting that the annual mean warming is about twice that of both summer and winter. This indicates that something drastic is taking place in the two other seasons. What? And why isn’t this shown/discussed?
13.23-24 Again, I don’t understand this sentence about the cooling bias.

## Language ##
This is not necessarily a comprehensive list and I urge the authors, in addition to making the edits below, to have a native English speaker go over the manuscript.
4.9: enables
5.5-6: “simulates a reasonably well meridional overturning” -> “simulates the… reasonably well” or “simulates reasonably well the meridional overturning”
5.9: it -> its
5.10: “lower end of estimation in of” -> “lower end of coupled… model estimates”
5.20: gradually
7.17-18 (about 7 edits in the following): “In the experiment OG11.5, summer temperatures were…over most of the extratropical continents than in the PI simulation, with a maximum… part of the continents.”
7.27-28: “slightly stronger warm climate in winter” –> “slightly larger warming in winter”
8.7 “the Alaska region”
8.8 “than in the PI”
8.9 “expanded more in”
8.10 “fell below” Do you mean “well below”?
8.13: “in OGIS11.5”
8.32 “the Holocene”
9.15. 500 yr period (2 edits)
11.10 “over the course of”
12.5 The only available
12.7: to that of the present
12.9 serves
12.10: signal
12.23 features indicated in
12.28 “as representative”
13.4 one of “the”/”the most” important
13.8 geopotential
13.22 the ice-sheet
13.31”minor warmer” -> “slightly warmer” or “minor warming in the”
14.27-28: “with a stronger temperature reduction of around 10 ka”. Do you mean “with a stronger temperature reduction around 10 ka”? Or do you mean “with a stronger temperature reduction of around XX deg C”? Either way, the sentence sounds strange.
15.5 applying -> application/addition
15.13 dependent
17.10 implies
Fig 2a: Title: Ice sheet area…
Fig 2c: What do the symbols show? They aren’t mentioned in the caption and aren’t shown in the legend
Fig 5a: Does the linear slope really make any sense to show in this case where things are behaving so obviously non-linearly?
Fig 9, caption: Please add reference for the reconstruction.

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ED: Publish subject to minor revisions (review by Editor) (24 Mar 2016) by Marie-France Loutre

AR by Yurui Zhang on behalf of the Authors (01 Apr 2016) Author's response Manuscript

ED: Publish subject to technical corrections (04 Apr 2016) by Marie-France Loutre

AR by Yurui Zhang on behalf of the Authors (05 Apr 2016) Author's response Manuscript

Short summary

We explore how forcings contributed to climate change during the early Holocene that marked the final transition to the warm and stable stage. Our results indicate that 1) temperature at the Holocene onset was lower than in the preindustrial over the northern extratropics with the exception in Alaska, and the magnitude of this cooling varies regionally as a response to varying climate forcings and diverse mechanisms, and 2) the rate of the early Holocene warming was also spatially heterogeneous.