the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Sea ice loss translates into major shifts in the carbonate environmental conditions in Arctic Shelf Sea
Brita Irving
Sam Dupont
Remi Pages
Donna Hauser
Seth Danielson
Abstract. Healthy Arctic marine ecosystems are essential to the food security and sovereignty, culture and wellbeing of Indigenous Peoples in the Arctic. At the same time, Arctic marine ecosystems are highly susceptible to impacts of climate change and ocean acidification. While increasing ocean and air temperatures and melting sea ice act as direct stressors on the ecosystem, they also indirectly enhance ocean acidification, accelerating the associated changes in the inorganic carbon system. Yet, much is to be learned about the current state and variability of the inorganic carbon system in remote places. Here, we present pH and pCO2 time-series (2016–2020) from the Chukchi Ecosystem Observatory. The subsurface observatory is located in the midst of a biological hotspot with high primary productivity and a rich benthic food web that support coastal Iñupiat, whales, ice seals, walrus (Odobenus rosmarus), and Arctic cod (Boreogadus saida). Our observations suggest that near-bottom waters (33 m depth, 13 m above the seafloor) are a high carbon dioxide and low pH and aragonite saturation state environment in summer and fall, when organic material from the highly productive summer remineralizes. During this time, the aragonite saturation state can be as low as 0.4, triggering free CaCO3 dissolution. During the sea ice covered winter period, pH was < 8 and aragonite remained undersaturated under the sea ice. There are only two short seasonal periods with relatively higher pH and Ωarag, which we term ocean acidification relaxation events. In spring, high primary production from sea ice algae and phytoplankton blooms and ikaite dissolution lead to spikes in pH (pH > 8) and aragonite oversaturation. In late fall, strong wind driven mixing events that bring CO2 depleted surface water to the shelf also lead to events with elevated pH and Ωarag. Given the recent observations of high rates of ocean acidification, and sudden and dramatic shift of the physical, biogeochemical, and ecosystem conditions in the Chukchi Sea, it is possible that the observed extreme conditions at the Chukchi Ecosystem Observatory are significantly deviating from the carbonate conditions to which many species are adapted and may have negative impacts on the ecosystem.
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Claudine Hauri et al.
Status: open (until 27 Sep 2023)
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CC1: 'Comment on egusphere-2023-1386', Lauren Barrett, 12 Jul 2023
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Hi! Great paper; I was really excited to see more information about this topic. Here are some notes.
L69-71,80-83,87-88,629: fix sub- and super-scripts
L99: italicize species name
L116: delete "and variability"
L111,123: can you cite primary literature instead of IPCC?
L156: delete parentheses around reference since you're directly talking about it
L290: silicate can be quite high in this region, affecting your TA calculation. Also, the assumption of zero nutrient concentrations might work for surface water, but not near-bottom, especially as you observed the results of respiration in your pCO2 and pH, that should translate to increased nutrients as well.
L293: I agree. Can you be more specific about the uncertainty that the pH-pCO2 pair can lead to? Especially because you're using pCO2 and pH calculated from it, so really just pCO2. What range or at least order of magnitude of error do you expect this to lead to in your reported TA, DIC, and sat arag? Additionally include error propagation from CO2SYS calculations (should be available in most new versions). To that end I think you need error envelopes around your data lines in Figure 2.
L374: correct to "drivers"
L385: here and all the times after, use Greek letter μ instead of u
L395: In this whole discussion I think it's important to include your uncertainties in observations of DIC or TA increase (I suspect could be quite high), as that will inform how disparate the Redfield ratio calculations actually are from your measurements.
L409: change "we're attributing" to "we attribute"
L421: delete "to" leaving "temperature increase"
L437: Can you discuss this in the context of nutrient data as well? Is it possible that some amount of pCO2 decrease is also attributable to mixing stimulating phytoplankton blooms?
L466: Again I think error discussion is important here (as in write 85.5 +/- X umol/kg), the error could easily be on the order of these discrepancies
L554: Correct 'maybe' to 'may'
L612: I find this paragraph too speculative (off the back of the paragraph discussing the uncertainty about the carbonate chemistry impacts on organisms here) for the serious claims it brings up
L625: change 'was' to were' (subject is 'events')
L630: italicize species name
L650-653: again a bold claim for how speculative it is. Also see Mordy et al. 2020 Deep Sea Res II, they have nitrate data from a very similar region (looks like you referenced them but not for your discussion here)
L663: overestimates pH "by" ...
L666: air-sea gas...
L679: I think this is an important discussion and highlights the necessity for time-series monitoring like this, especially since most of the long-term changes in pH and sat arag are assumed from some discrete datasets that are biased to fall, which you identify as the high-pCO2 time periodOverall, I find this paper interesting and high temporal resolution measurements are super important due to the historical paucity of data, as we try to parse future changes due to climate change. The main thing to change here is the lack of transparency regarding uncertainty in carbonate chemistry parameters, especially since most of them are calculated and not directly measured. I really think that could alter some of your discussion and implications. I also wonder if the discussion couldn't focus more on physical processes than on biological impacts, since by your own admission those are relatively unclear for organisms in the Chukchi Sea?
Thanks very much for an interesting read!
Citation: https://doi.org/10.5194/egusphere-2023-1386-CC1 -
RC1: 'Comment on egusphere-2023-1386', Anonymous Referee #1, 17 Aug 2023
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The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-1386/egusphere-2023-1386-RC1-supplement.pdf
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RC2: 'Comment on egusphere-2023-1386', Anonymous Referee #2, 12 Sep 2023
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Review comments for manuscript: “Sea ice loss translates into major shifts in the carbonate environmental conditions in Arctic Shelf Sea” submitted to Biogeosciences by Hauri et al.
General comments
Time-series observations of marine biogeochemical properties in coastal regions are important for assessing environmental changes that are directly linked to peoples’ livelihoods. In addition, there are few time-series stations, especially high-latitude oceans, where comprehensive biogeochemical observations have been made. Therefore, it is invaluable to present new data in the Arctic coastal area, although there is a large amount of missing data. At this point, I believe that this manuscript can contribute to scientific progress within the scope of Biogeosciences.
However, caution should be exercised when interpreting the observed results. This is because coastal areas usually show high spatial and temporal variations in biogeochemical properties, and data from vertical one-dimensional observations cannot remove the influences of lateral advection and diffusion. The latter is particularly important in coastal areas. To interpret the observed results, it does not seem that the discussion is conducted appropriately. Overall, there was a sense of over-discussion. For these reasons, I have to judge whether the scientific quality is inadequate.
For the presentation, the resolutions of the figures are poor for the discussion of monthly variations. I recommend focusing on the relevant time series in addition to the entire time series, as shown in Fig. 2. In the introduction, I could not find the purpose of this work. It just refers presenting data. For the discussion, I had the impression that the authors made a forced interpretation of the results. One of the reasons is probably that the authors do not have a clear purpose. Based on these points, the presentation of the manuscript as a research paper is inappropriate. And, about one-third of the manuscript is used for the description of materials and methods. I recommend submission to a journal with a purpose of data presentation.
As a whole, with the current version of the manuscript, I cannot recommend publication in Biogeosciences. Judging from a lot of missing references, I think the manuscript is not completed.
Specific comments
(1) The CEO is located at the Chukchi Sea site, where water masses from the Pacific flow to the Arctic basin. Therefore, it is expected that the physical and biogeochemical properties are influenced by lateral advection and mixing. However, there were almost no words related to these influences. The authors discussed variations and changes in biogeochemical properties, mostly from the viewpoint of vertical mixing. Therefore, it is necessary to confirm that the lateral advection and mixing are negligible at the site.
(2) DIC, TA and Ωarag are calculated from pCO2 and pH. As pointed out by the authors, this combination leads to large error, although the error of Ωarag is not so large. Therefore, it is necessary to show ranges of uncertainty as a result of calculation (propagation of errors), if authors are purposed to discuss carbon budget-like calculation. Or, it seems to be a good way to compare the calculated and observed values. But this is made only for DIC but not for TA. The authors conduct carbon budget-like discussion in some sections of the manuscript. For this, uncertainty of DIC and TA should be clarified.
(3) The pH algorithm (eq.1) is evaluated with ship-based data. But I wonder the evaluation can be related to the evaluation of pH and pCO2 data obtained by sensors attached to the mooring. I think that the evaluation by ship-based data is independent to the mooring data.
(4) It is pointed (lines 681-684) out that a large gradient of pCO2 exists. This implies that a slight tilt of mooring system causes an artificial variation of properties. With this condition, is it possible to detect fine carbon budget calculation? In this point also, uncertainty of the data should be clarified.
(5) At line 632, it is described that CaCO3 mineral dissolution was observed. But it is very hard to find the evidence of CaCO3 mineral dissolution through the manuscript. Discussion at lines 632-642 is too speculative. TA increases under the supersaturation of aragonite and calcite can be accounted for by e.g., water mixing.
(6) From the title of manuscript, I expected examination of climate change, which leads to “shift” of carbonate system from one condition (sea ice existence) to another (sea ice loss). However, the content of manuscript does not show shift of climatological time scale. It is however possible to see a shift of seasonal time scale. Even in this case, differences of carbonate system between conditions in the sea ice existence and those in sea ice loss should be clarified.
(7) Salinity influence is examined in the manuscript (section 2.8) but from the viewpoint of river water alone. Influence of sea-ice melting water should be also examined.
(8) In marine CO2 community, it is required to indicate that pH is measured at which water temperature. Please describe that the pH is at in situ temperature.
As a whole, discussion on processes based on water mixing are acceptable, although examination of horizontal mixing should be added. But discussion on processes based on biogeochemical changes are too speculative.
Technical corrections:
In this manuscript, the observed results and the interpretation/speculation based on the result are written together in the section of results (section 3). This may lead readers and authors themselves to misunderstanding. For example, bloom and CaCO3 dissolution are described in the abstract. But these are not observations but speculation. I think that there are no problems to describe them in the main text, but description in the abstract makes readers misunderstand as if they were observed. I recommend the authors rewriting section 3, separating observed results and speculation.
Through the manuscript, “CO2-deplete” or “CO2 depleted” is repeatedly used. It is very rare that CO2 is depleted, being different from nutrients. “CO2 reduced” is better.
Lines 56-57: If “National Snow and Ice Data Center” is a reference, add published year. Not found in the reference.
Line 69: “CaCO3”, “CaCO3”
Line 70: Bednarsek et al. 2021 is cited here. But it is difficult to find the reference because of incomplete information of the reference at lines 762-764.
“CO32-“, “CO32-”
Line 79: Bates, 2015; Bates et al., 2009; Pipko et al., 2002; Mathis and Questel, 2013 are not found in the reference.
Line 80: “CO2”, “CO2”
Line 81: Bates, 2015; Bates et al., 2009 are not found in the reference.
Line 83: Bates et al., 2009 is not found in the reference. “pCO2”, “pCO2”
Lines 85-86: Mathis and Questel, 2013; Pipko et al., 2002; Bates, 2015 are not found the reference.
Line 87: “pCO2”, “pCO2”
Line 88: “pCO2”, “pCO2”
Lines 88-89: Hauri et al., 2013 is not found in the reference.
Line 89: Yamamoto-Kawai et al. (2016) is not found in the reference.
Line 95: “CEO”, “The Chukchi Ecosystem Observatory (CEO)”
Line 96: Grebmeier et al., 2015; Moore et al., 2000 are not found in the reference.
Line 98: Grebmeier et al., 2015; Blanchard et al., 2013 are not found in the reference.
Line 101: Moore et al. 2022 is not found the reference.
Line 111: IPCC 2022 is not found in the reference.
Line 123: IPCC 2022 is not found in the reference.
Line 141: “The Chukchi Ecosystem Observatory (CEO)”, “The CEO”
Line 172: “quadrature”, “quadruple”?
Lines 196 and 199: “pHext”, “pHSeaFET”, define terms at the first appearance.
Line 204: “quadrature”, “quadruple”?
Line 219: “2.5 CTD and Oxygen”, it is better to remove the description written at lines 190-193 and summarize it here.
Line 220: What is the CEO-2? Different from CEO?
“morning”, “mooring”
Line 235: What do you mean “relative oxygen values from the pumped SBE63”? In the figures, absolute values seem to be used.
Line 257: In the caption of Fig. 3, explanation of dots is not found. Indicate which displays pHSeaFET.
Line 258: No explanation of black dots is found in the caption of Fig. 3. Instead, black circles are explained.
Line 261: Define “pHSeaFET” clearly.
Line 283: “quadrature”, “quadruple”?
Line 290: “to be zero”, “to be negligible” is better because there observed ~10-20 umol/kg NO3 is observed.
Line 302: Show which temperature is used for pH, at in-situ temperature or a constant temperature (e.g., 25°C).
Line 306: “(Sulpis et al., 2020)”, ”Sulpis et al. (2020)”
Lines 306-307: “(Lueker et al., 2000), “Lueker et al. (2000)”
Line 308: “(Lueker et al., 2000), “Lueker et al. (2000)”
Line 311: “DIC(pHest, pCO2)”, “DIC calculated from pHest and pCO2”
Lines 336-338: The comparison does not deny influences of freshwater. It just shows that the large changes cannot be accounted for by freshwater alone.
Line 338: “(S3)”, “(Figure S3)”?
Line 345: “(S4)”, “(Figure S4)”? Figure S4 does not display the average temperature.
Line 354: DiGirolamo et al. (2022) is not found in the reference. 2013?
Line 361: Sivers et al. 2018 and Horowitz et al. (2018) are not found in the reference.
Line 362: Boucher et al. (2020) and Seferian (2019) are not found in the reference.
Lines 381-383: If sea-ice melting are associated with the TA and DIC variations, both should be decreased. As NO3 also seems to be reduced, partially effects of biological activity?
Line 384: Increased from what?
Line 387: Again, decreased from what?
Line 391: From Fig. 2, Ωarag shows > 1.0 in the corresponding period. Can we expect dissolution of CaCO3? It may be possible that it occurred as a result of dissolution. But for the explanation, time-lag is necessary between the phenomena.
Lines 415-418: This part seems to insist that less dense water goes down to the deeper layer. I recommend discussion from the viewpoint of horizontal water transport.
Line 448: “Bottom waters”, Not waters at 33m?
Lines 457-459: Is TA value of 4 umol kg-1 significant?
Lines 481-484. Figure 8 displays changes of TA/DIC ratio. What does it mean and how can we realize relationship with organic matter remineralization?
Lines 510-528: The discussion made here is related to long-term changes of acidification. It is not appropriate to short-term changes of carbonate properties obtained in the present study.
Line 611: Boyd et al. (2018) is not found in the reference.
Lines 628-629: Stabeno et al. (2020) and Koch et al. (2020) are not found in the reference.
Line 629: “pCO2”, “pCO2”
Line 632: CaCO3 mineral dissolution is not observed. That is just a speculation from TA changes.
Lines 632-633: Are there any evidences that show or suggest ikaite crystal dissolution? At least, citation of previous studies is necessary.
Lines 645-646: In section 3.3, no evidence is presented, only possibility.
Lines 646-647: Increase in density does not always leads to resuspension. Data from e.g., turbidity meter are necessary.
Line 662: The weather quality goal of is not +/-0.003 but 0.02.
Line 663: From Figs. 3 and 4c, it is hard to see overestimation of 0.0008. It is too good.
Line 682: Hauri et al. (2013) is not found in the reference.
Lines 762-764: There are no pieces of information of journal.
Lines 893-895: There are no pieces of information of journal.
Line 852: Insert one line before this line.
Line 1065: “pCO2”, “pCO2”
Lines 1085-1087: There are no pieces of information of journal.
Line 1272: DiGirolamo et al., 2022 is not found in the reference.
Line 1273: It is very hard to distinguish between black and gray on the figure.
Lines 1334-1336: The top figure is a figure for O2, but no explanation is given. What dashed lines indicate?
Table 1: Table 1 needs to be reworked. It is an unfriendly table for readers. Parameters such as NO3, pCO2, CTD, are placed in rows of the first column.
Table 2: This table also needs to be reworked.
Citation: https://doi.org/10.5194/egusphere-2023-1386-RC2
Claudine Hauri et al.
Claudine Hauri et al.
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