Observed bottom warming in the East Siberian  Sea driven by the intensified vertical mixing

Wang, Xiaoyu; Mu, Longjiang; Chen, Xianyao

doi:https://doi.org/10.5194/os-21-577-2025

Articles | Volume 21, issue 2

https://doi.org/10.5194/os-21-577-2025

© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/os-21-577-2025

© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 21, issue 2

Research article

|

13 Mar 2025

Research article |

| 13 Mar 2025

Observed bottom warming in the East Siberian Sea driven by the intensified vertical mixing

Xiaoyu Wang, Longjiang Mu, and Xianyao Chen

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Final revised paper (published on 13 Mar 2025)
Preprint (discussion started on 29 Jul 2024)

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2024-2271', Anonymous Referee #1, 12 Aug 2024

This ms tackles and important topic - the warming of deep water in the shelf seas around the Arctic Ocean and by implication the potential impact on the melting of methane hydrates. The paper essentially proposes that increased open water leads to more momentum transfer to TKE and so mixing via larger storm generated surface waves. Whilst there is good published evidence to support the more open water, more mixing due to storms hypothesis (eg. Polyakov et al, 2020, https://doi.org/10.1029/2020GL089469; Rippeth and Fines, 2022, https://doi.org/10.5670/oceanog.2022.103) different mechanisms are invoked. The authors do not consider these alternatives and so the final step in their argument, ie. more mixing via a more vigorous wave field is not proven as the paper stands.
These mechanisms include wind triggered inertial oscillations, eg in the Laptev Sea under under both open water and sea ice conditions (Lenn et al., 2011, https://doi.org/10.1175/2010JPO4425.1). Note as shown in this paper the mixing is intermittent with short term events dominating the downward heat flux (how do these heat fluxes compare to those in line 155). The same wind shear alignment mechanism can also drive the deepening of the surface mixed layer (Lincoln et al., https://doi.org/10.1002/2015JC011382).
Also, the development of continental shelf waves trigger by remote storms which drive periods of intense mixing. See (Schulz et al., 2021, http://10.1029/2021GL092988).
A few minor points:
line 26: do you mean "increasing down" mixing of heat? 27-28: a citation is required. Is the 'dramatic and abrupt' warming due to complete mixing of the water column (more likely than diapcynal mixing)?
32: citation required.
41-42: I assume that the: "during this period" are your original observations - this needs to be made clearer. Figure 1e - there is no label on the x-axis to say what the numbers refer to?
126: "previous studies" needs a citation to direct to the pervious studies?
155: Heat flux - how does this compare to others on the Arctic continental shelf?
Figure 3: I am not clear on what the geostrophic currents are showing?

Citation: https://doi.org/10.5194/egusphere-2024-2271-RC1
- AC1: 'Reply on RC1', Xianyao Chen, 28 Oct 2024
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-2271/egusphere-2024-2271-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2024-2271-AC1
RC2:
'Comment on egusphere-2024-2271', Anonymous Referee #2, 03 Sep 2024

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-2271/egusphere-2024-2271-RC2-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2024-2271-RC2
- AC2: 'Reply on RC2', Xianyao Chen, 28 Oct 2024
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-2271/egusphere-2024-2271-AC2-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2024-2271-AC2

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

AR by Xianyao Chen on behalf of the Authors (28 Oct 2024) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (30 Oct 2024) by Anne Marie Treguier

RR by Anonymous Referee #2 (15 Nov 2024)

RR by Anonymous Referee #1 (28 Nov 2024)

Suggestions for revision or reasons for rejection

The paper presents observation of temperature structure across the East Siberian Sea with one particularly interesting profile showing the water column to be well mixed thus exposing the seabed to warmer water mixed down from the surface.
My main criticism of the paper as it stands is that the evidence used to support the claim that the water column is completely mixed is weak – ie the wavelength matches the water depth at the location of the completely mixed water column.
I would suggest to make this work more publishable additional evidence should be sort. For example, an using an energy argument, such as the calculation of the different components of potential energy anomaly (see for example the analysis in Rippeth et al, 2001, Journal of Physical Oceanography, 31(8)). In the way the relative contributions of tidal, direct wind, waves etc can be calculated to support the idea that the vertical mixing is due to waves.
Other points:
Line 9: Surely downward not upward?
11: seabed – are we talking about the water temperature at the bottom of the water column, or the temperature of the seabed? Quite an important distinction.
13: Uniform stirring, normally referred to as a well mixed water column
14: Increased space to develop. Do you mean a longer wave fetch?
22: Does the 50% refer to a methane flux or is it the amount of methane stored in the sea bed?
25: Barrier? You mean the cold water isolates the sea bed from the warmer surface layer.
27: Downward heat transport. Do you mean mixing down of heat? Try and be consistent.
54: I don’t understand why the tides only become dominant under ice free conditions? You need to explain this.
63: “long term” is generally taken to mean over a number of years, you are only considering a season?
63: “Intensification” do you mean the mixing is stronger?
240: calculation showing the SST doesn’t drop enough and so advection must be moving heat? Is this change consistent with the lateral gradients you have measured in the CTD survey?
284: Discussion – I would start by summarising the results before discussing the conseuqneces?
292: “Straightly” – do you mean mixed down? Please be consistent with language.
296: Is the 14,000 km2 the area of the sea bed? It is not clear what you mean.
299: Is it increasing solar radiation, or increasing exposure to solar heating due to sea ice retreat?
301: You need a reference to support your statement that there are more storms in the summer.

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ED: Reconsider after major revisions (30 Nov 2024) by Anne Marie Treguier

AR by Xianyao Chen on behalf of the Authors (23 Dec 2024) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (03 Jan 2025) by Anne Marie Treguier

RR by Anonymous Referee #1 (06 Jan 2025)

ED: Publish as is (06 Jan 2025) by Anne Marie Treguier

AR by Xianyao Chen on behalf of the Authors (09 Jan 2025) Manuscript

Short summary

The East Siberian Sea has nearly 80 % of the subsea permafrost worldwide. The cold layer with a temperature around −1.5 ºC above the seafloor prevents heat transporting from above to melt permafrost and release methane from sediments. However, we observed a warming trend at the seafloor caused by wave-induced vertical mixing in the shelf. The intensified mixing can transport enormous heat downward, leading to warming of more than 3 °C at the bottom, putting the subsea permafrost at high risk.