Seasonal variability of the Atlantic Meridional Overturning Circulation at 11°&thinsp;S inferred from bottom pressure measurements

Herrford, Josefine; Brandt, Peter; Kanzow, Torsten; Hummels, Rebecca; Araujo, Moacyr; Durgadoo, Jonathan V.

doi:https://doi.org/10.5194/os-17-265-2021

Articles | Volume 17, issue 1

Ocean Sci., 17, 265–284, 2021

https://doi.org/10.5194/os-17-265-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Ocean Sci., 17, 265–284, 2021

https://doi.org/10.5194/os-17-265-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 17, issue 1

Research article 10 Feb 2021

Research article | 10 Feb 2021

Seasonal variability of the Atlantic Meridional Overturning Circulation at 11° S inferred from bottom pressure measurements

Josefine Herrford et al.

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Final revised paper (published on 10 Feb 2021)
Preprint (discussion started on 26 Jun 2020)

Interactive discussion

Status: closed

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

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RC1: 'Formal review for authors', Anonymous Referee #1, 28 Jul 2020
- AC1: 'Answers to Referee#1', Josefine Herrford, 19 Oct 2020
RC2: 'Seasonal variability of the AMOC at 11S inferred from bottom pressure measurements', Anonymous Referee #2, 17 Aug 2020
- AC2: 'Answers to Referee#2', Josefine Herrford, 19 Oct 2020

Peer-review completion

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

AR by Josefine Herrford on behalf of the Authors (02 Nov 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (10 Nov 2020) by Erik van Sebille

RR by Anonymous Referee #1 (20 Nov 2020)

RR by Anonymous Referee #2 (05 Dec 2020)

Suggestions for revision or reasons for rejection

The paper analyzes the seasonal cycle of the meridional overturning circulation in the tropical South Atlantic along 11S using bottom pressure measurements (BPRs and PIES) on the boundary, satellite winds, sea level from altimetry, as well as information provided from a model (INALT01). The authors did a great job of responding to all of my comments. Thank you! I think that this paper is improved and the analysis is cleark. The paper is suitable for publication, and I only have a few minor comments (apologies, as I made a lot of comments the last time around).

Minor comments:
- Abstract, line 25: Not clear what is meant by “particularly relevant”. Do you mean that the wind forcing uncertainties “dominate the AMOC uncertainties”?
- Line 90, unnecessary comma before dash “, -“
- Line 96, two periods “. .”
- Table 1, The weblink in Table 1 isn’t working yet.
- Line 106, suggest “Note, that the two PIES at 500m” instead of “Note, that the two PIES”
- Line 147, point to Section 5.4 rather than pointing ahead to Fig. 13a.
- Line 165-167, construction of the sentence isn’t symmetric, suggest: “In the WBC region, Hummels et al. (2015) …. and Zhang et al. (2011) found decadal … “
- Line 207, “Section 4b” instead of “Chapter 4b”
- Line 229-231, Here it sounds like you are saying the annual and semi-annual dominate variations at both the eastern and western boundary… which seems weird on the western boundary when only 18-24% of the variance is captured. You could reword the western boundary part of the statement to reflect that while the annual and semi-annual signals are the most dominant, they only capture 18-24% of the variance.
- Line 249, “Eq. (3) and Eq. (5), respectively.”
- Figure 4 caption, line 719, should it be “c, d, f” instead of “c,f”
- Line 296: Suggest rewording to “We found similar results for 2-year subsets of the western boundary BP time series.”
- Line 316-319. I think what tripped me up in the previous version, is that you are talking about the phasing of the western boundary contribution to Ekman transport, which is not in phase with the basin-integral Ekman transport. Suggest "January to March - resulting a locally weaker southward Ekman transport near the boundary" and "southward Ekman transport is locally strongest" in the first sentence. Suggest “For both wind products, the Ekman transport across the entire basin along 11S, is strongest in the boreal winter because it is governed by the seasonal cycle of the southeasterly trade winds…” to possibly remedy this. I leave that up to the authors whether they agree or not with this suggestion.
- Line 330, I think the purple and magenta lines are mislabeled in the caption relative to what the legend says in Figure 8a. On my computer though one line looks pink and the other looks purple.
- Line 338, Suggest: “ASCAT and INALT01 (Fig. 9c,d).”
- Line 345, Suggest “December (Fig. 9a,b)”
- Line 346-348, I think the cyan and blue lines in Figure 9 are mislabeled. Looks like cyan line (Tg, eofs) has bigger amplitude than (Tg, points). Text in manuscript says the opposite is true.
- Line 349: Period missing at the end of the sentence.
- Line 358: In abstract and conclusions you give peak-to-peak amplitude of Tamoc, but don’t actually give the amplitude in the main text. This seems like a good place in the main body of the text to give the amplitude of Tamoc.

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ED: Publish subject to technical corrections (07 Dec 2020) by Erik van Sebille

Short summary

The Atlantic Meridional Overturning Circulation (AMOC) is an important component of the climate system. Understanding its structure and variability is a key priority for many scientists. Here, we present the first estimate of AMOC variations for the tropical South Atlantic from the TRACOS array at 11° S. Over the observed period, the AMOC was dominated by seasonal variability. We investigate the respective mechanisms with an ocean model and find that different wind-forced waves play a big role.