the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Mesoscale observations of temperature and salinity in the Arctic Transpolar Drift: a high-resolution dataset from the MOSAiC Distributed Network
- 1Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, Bremerhaven, Germany
- 2National Sun Yat-sen University University, 80424 Kaohsiung, Taiwan
- These authors contributed equally to this work.
- 1Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, Bremerhaven, Germany
- 2National Sun Yat-sen University University, 80424 Kaohsiung, Taiwan
- These authors contributed equally to this work.
Abstract. Measurements targeting mesoscale and submesoscale processes in the ice-covered part of the Arctic Ocean are sparse in all seasons. As a result, there are significant knowledge gaps with respect to these processes, in particular related to the role of eddies and fronts in the coupled ocean–atmosphere–sea ice system. Here we present a unique observational dataset of upper ocean temperature and salinity collected by a set of buoys installed on ice floes as part of the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) Distributed Network. The multi-sensor systems, each of them equipped with five temperature and salinity recorders on a 100 m long inductive modem tether, drifted together with the main MOSAiC ice camp through the Arctic Transpolar Drift between October 2019 and August 2020. They transmitted hydrographic in situ data via the iridium satellite network at 10 minute intervals. While three buoys failed early due to ice dynamics, five of them recorded data continuously for 10 months. Four units were successfully recovered in early August 2020, additionally yielding internally stored instrument data at 2 minute intervals. The raw datasets (Hoppmann et al., 2021i) were merged, processed, quality-controlled and validated using independent measurements. Upon acceptance of the manuscript, the finally processed dataset (currently under moratorium) will be made publicly available under Hoppmann et al. (2022i). As an important part of the MOSAiC physical oceanography program, this unique dataset has many synergies with the manifold co-located observational datasets, and is expected to yield significant insights into ocean processes, and to contribute to the validation of high-resolution numerical simulations.
Mario Hoppmann et al.
Status: final response (author comments only)
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RC1: 'Comment on essd-2022-66', Anonymous Referee #1, 09 May 2022
Review of Hoppmann et al., “Mesoscale observations of temperature and salinity in the Arctic Transpolar Drift: a high-resolution dataset from the MOSAiC Distributed Network” submitted for publication in Earth System Science Data.
This is a solid manuscript that I recommend for publication after mildly major revision. The writing and figures are generally very clear. There are some confusing explanations that could use some attention.
My major comment concerns a disconnect that I see between the Introduction, which has a significant discussion of the submesoscale, and the rest of the paper, which lacks analysis on these scales. See my comments near the end. The manuscript’s title has the word “mesoscale” and the eddy analysis supports this. But why is there so much discussion of the submesoscale in the Introduction?
Line 61: Perhaps change “mesoscale scales” -> “mesoscales”
Lines 93 and 101: “upstream in the Transpolar” ie insert “in”
Line 101: “2019/20” -> “2019”, yes?
Line 114: cut the word “already.”
Line 116-117: “the measurements ensued away from the inflow of warm Atlantic Water through the Fram Strait and as close as possible to the Siberian continental slope” I am not sure what you mean by this. Also, I suspect that “ensued” might not be the best choice of verb.
Line 119: “to achieve that aim” What aim?
Line 129: An egg has a pointy end; this buoy hull looks more oval, or perhaps "flattened oval"?
Line 133: Your buoy naming convention is a bit odd, ie the use of the capital letter “O” instead of the number zero “0.” But it is your choice. As noted below, this gets sloppy in the section about the eddy, when both “O” and “0” are used.
Paragraph starting at Line 135: I got a bit confused here. I thought perhaps the CTDs recorded 2-minute data, and then every 10 minutes, all of these data were sent to the satellite. I think instead, the satellite gets only a subsample of the 2-minute data, i.e., 10-minute sampling, is this correct? I wonder if you can make this clearer.
Lines 153-158: This material confused me. The CTDs have pressure accuracy of 0.02 - 0.002 dbar, but the transmission limitation degraded this to 0.1 dbar. So this is a significant reduction in data quality, right? Your text seems to indicate that it’s no big deal.
Further, Table 2 indicates that the pressure accuracy is always 0.1 dbar, even for the CTD data. Why? I thought a direct download could give you 0.02-0.002 dbar. I guess I’m missing something.
Line 191: “an upper threshold of 0.8 m s-1 was applied” Why?
Line 220: what is “sim”? I suspect it is some kind of word processing code.
Line 222: How do you define “suspicious?”
Line 227: How do you define “questionable?”
Line 233: “When CTD data was available…” This caused me some confusion, because the buoy has CTDs. Perhaps you can add a sentence like this to make it clearer: “Buoy data" means all data uploaded to the satellite from the buoys, including from the CTDs, at 10 min sampling, while "CTD data" refers to the directly downloaded CTD data from recovered buoys at 2 min sampling. Is that right?
Table 2: Is the surface temperature thermistor really accurate to 0.01 degC? I think these are usually not so good, e.g., 0.1 or 0.05 at best.
Line 395: The MLD is not evident to me from this figure. How was it computed?
Line 397: Perhaps change “a corresponding decrease in temperature” -> “a corresponding decrease in temperature along the freezing line”
Lines 399-400: Perhaps change this text to: "...partly explained by a combination of upward mixing of deep salty water from below and salt rejection during ice formation from above, both forced by two February storms (with wind speeds up to 16 ms-1 and air temperatures of XX degC)."
Lines 400-401: why is “vertical mixing properties” in quotation marks?
Line 403: I can’t see MLD in Figure 4.
Line 404: What is “air-line distance?”
Line 413: “The position of the eddy remains approximately the same” The same as what?
Lines 417 & 419: check your velocity units. m-1 is wrong, yes?
Line 417: “estimated diameter of the eddy” estimated how?
Line 421: Here you are using zero “0” instead of capital “O.” There are several other examples in this eddy section.
Line 426: “by a factor of” i.e., add “a”
Line 428: “radii” -> “radius”
Lines 431-432: Great point!
Line 439: “measured the the upper ocean quasi-synoptically over submesoscales” Two comments: (1) cut one “the” (2) Your introduction has a lot of material about submesoscales, but the paper itself has no corresponding analysis. I suggest you either cut / trim down the introduction material on this subject, or do more work to follow up on it. For example, you could create a histogram for one or all the buoys with a horizontal axis of del-x = the distance travelled by a buoy over 2 or 10 minutes. If you have a lot of sampling between 100 m – 10 km (or maybe shorter? Your introduction implies that Arctic submesoscales are shorter) then yes, you can justify this statement on Line 439 and the extensive discussion of this subject in the Introduction.
But I would also ask this question: Did you really need to sample at 2 or even 10 minutes? What if you sampled hourly, or even daily? What would this histogram look like? I suppose I am suggesting that you do some analysis to find the right time interval for buoy data recording to adequately sample the submesoscale, as you claim without proof that you are doing now.
Line 473: code is available “upon request.” Is this sufficient for this journal? Should it instead be available on github or equivalent?
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RC2: 'Comment on essd-2022-66', Anonymous Referee #2, 17 May 2022
This is a solid contribution to the field, it does have some issue with grammar and word choice throughout the text, however, it did not hinder my ability to read or understand the content, maybe the authors could run it through a grammar checking program (I use Grammarly). From the title of the manuscript I expected the focus to be primarily on analysis of the data, however the focus of the paper is really on describing the buoy system and the handling of the data. I think that this does fit within the scope of the journal, but the authors may want to change the title to better fit with the focus of the paper. I have no issues with the substance of the paper, just a few comments to improve clarity.
The description of the data handling and QC is well thought out and helpful for others who are starting out with automated buoy systems.
Line 135. I was a bit confused by the statement “polled for an additional measurement by the buoy itself” I think that you mean that the CTDs recorded data every 2 mins and then they were also collected a measurement every 10 mins that was sent via iridium. This paragraph is not very clear.
Line 404: ‘air-line distance’ do you mean the the straight line distance rather than the distance along the drift track.
Line 404: Is there a better way to visualize the MLD in Figure 7?
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RC3: 'Comment on essd-2022-66', Anonymous Referee #3, 18 May 2022
The authors present a dataset of upper ocean temperature and salinity from drifting buoys that were deployed as part of the MOSAiC Distributed Network. The dataset represents valuable observations from the central Arctic Ocean over a 10-month period, including the scarcely observed Arctic winter. Observational methods, data processing steps and the resulting dataset(s) are described in detail, and some preliminary analyses of the data to investigate the signature of an eddy in the distributed network are shown.
The manuscript is in general well written with mostly clear and useful figures. Some revisions could help to improve readability and avoid confusion in an otherwise highly relevant publication.
Main concerns:
- There is a bit of repetition between the Methods and the Results section, esp. with 4.1. This is maybe not surprising given the nature of a data paper, but could still be avoided, and the manuscript could be more streamlined.
- The introduction is quite lengthy about mesoscale and submesoscale features, but then there is nothing more these throughout the methods and the results section. First in the discussion, you pick up the topic again by describing the passage of an eddy. To show that the dataset is useful to investigate (sub)mesoscale features, which you explicitly present as an aim of the design of the DN and this manuscript, a bit more analysis in this direction would be useful. For example, more detail on the drift trajectories of the buoys relative to each other beyond just the map in Figure 3 (and the short sentence on Lines 267-269) could easily provided, such as a timeseries of the relative distance of the buoys to each other or of the maximum diameter of the area covered by the buoys. That would link nicely to the discussion around the size of the eddy and could indeed demonstrate that this buoy network can capture (sub)mesoscale features.
- Be more precise with the variable names – I have to assume that you talk about in situ temperature and practical salinity but cannot know for sure, so please make this clear at the start of the manuscript.
- Many of the figures are not colour-blind (or greyscale friendly) – consider modifying them.
Other comments:
Line 21: “much greater than” – can you be more precise? E.g. give order of magnitude or similar?
Line 21&22: “the vertical velocity” and “the horizontal velocity” – sounds odd (like there is only one fixed vertical velocity and one horizontal velocity); suggest to change to “vertical velocities are … weaker than horizontal velocities”.
Line 41: “submesoscale processes are responsible for … restratification” – suggest to change to “contribute to”. Du Plessis et al. (2019) still state that the main driver for springtime restratification is surface heating.
Line 66: Is “synopticity” really a word? (Or rather, a word in this context?) Suggest to rephrase.
Line 84: Which feedback? Sounds like there is only one…
Line 93: Do you mean upstream IN or OF the Transpolar Drift?
Line 101: Same issue: upstream in or of the TPD?
Line 109-110: “the ice relative drift across the liquid ocean” – weird formulation. Rephrase?
Line 117: “ensued” – is this the right word? Or should it rather be something like “took place” or “were done”? I assume there was a degree of planning involved in the location of the DN.
Line 135-138: This part is confusing. So the CTDs are measuring every 2 minutes regardless of what the buoy is doing. Then there’s an extra measurement when the buoy is polling – so “its measurement interval” means the buoy’s measurement interval? And the data the buoy sends back via iridium – that’s only those extra measurements or all of them?
Following on from that, on line 142 you write “All data” – is that now the data from the measurements polled by the buoy or indeed “all” data??
Please rework this part to clarify.
Line 145 and throughout: when you write “temperature”, is that in situ temperature? Please clarify in the text.
Line 147: “the other variables” – I assume that’s conductivity, (in situ?) temperature and pressure?
Line 147 (and throughout the manuscript) provide version numbers of software and toolboxes used.
Line 169: Protection from what? Towels don’t strike me as the best protector from freezing in -15deg C.
Line 171: What do you mean by “hydrohole”?
Line 179: The CTD data from recovered instruments then also provide higher accuracy pressure data?
Line 186: Replace “using” with “indicated by” or something similar (you didn’t “use” the flag to modify the data).
Line 190: How did you fill the gaps in the GPS record after removing outliers?
Line 191: What was the consequence of applying the threshold? A different flag? Or removing data points?
Line 192: How did you determine “plausibility”?
Line 220: What do you mean by “sim”?
Line 223: How big was the drop in conductivity?
Line 229: Capital O in the buoy name.
Line 240: Add “practical” to salinity.
Line 243: Is the closing bracket in the right place? Bit confusing at the moment.
Line 253-254: It would be useful to include this information in one of the tables, e.g. Table 1. If you explicitly state here all buoy numbers of the ones you can provide a merged product from, then also provide the numbers of the ones with buoy data only.
Line 255: I guess the measured temperature is in situ temperature? And the derived salinity practical salinity (and not absolute salinity)?
Figure 2: Nice schematic! You could mark which of the steps were not included in the processing for buoy-only datasets.
Table 2: In situ temperature?
Figure 5d: axis labels in the salinity panel are missing. If they are not included because of the icing issues, why show the data at all?
Presentation of the timeseries starting Line 274: Refer to the respective figures/panels.
Line 276: delete “a”
Line 276-277: Isn’t 2.5 weeks a pretty long time for ice in the conductivity cell to disappear? Was the water at freezing point at 50 m depth throughout this period?
Line 286: So all but the 50 m sensor?
Line 318-319: Is a drop in pressure not equivalent to instruments rising? “… causing the surface buoy to drop” => shouldn’t that then lead to an increase in pressure? I can’t follow your argument here.
Line 323-324: How long did this issue last? The entire record?
Line 329: Replace “in” by “the”.
Line 338: Where below? Provide section/section number.
Line 374: What is the stated accuracy?
Figure 7: I’m confused by the shading in panels c and d – please provide a clearer description in the caption.
Line 472: Publish the code together with the dataset or place it on e.g. github or similar sites.
Figure A1 is not referred to in the text.
Mario Hoppmann et al.
Data sets
Raw data of CTD buoys 2019O1 to 2019O8 as part of the MOSAiC Distributed Network Hoppmann, Mario; Kuznetsov, Ivan; Fang, Ying-Chih; Rabe, Benjamin https://www.pangaea.de/tok/88bfe8f850838ba2de6da30302f9079a35723e63
Processed data of CTD buoys 2019O1 to 2019O8 as part of the MOSAiC Distributed Network Hoppmann, Mario; Kuznetsov, Ivan; Fang, Ying-Chih; Rabe, Benjamin https://www.pangaea.de/tok/147f801ef2a96849e4c64c1fd3eedf31aa802c21
Mario Hoppmann et al.
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