the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 16 Aug 2023
Regional variations in mineralogy of dust in ice cores obtained from northeastern and northwestern Greenland over the past 100 years
Abstract. To investigate regional and temporal variations in the sources and atmospheric transport processes for mineral dust deposited on the Greenland Ice Sheet, we analysed the morphology and mineral composition of dust in an ice core from northeastern Greenland (East Greenland Ice-Core Project, EGRIP), representing the period from 1910 to 2013, using scanning electron microscopy and energy-dispersive X-ray spectroscopy, and compared the results with those previously obtained for an ice core from northwestern Greenland (SIGMA-D). The composition of the SIGMA-D ice-core dust, comprising mostly silicate minerals, varied on a multi-decadal timescale due to an increased contribution of minerals originating from local ice-free areas during recent warming periods. In contrast, for the EGRIP ice-core dust, also consisting mostly of silicate minerals, there was relatively low compositional variation among the samples, suggesting that the mineral sources have not changed dramatically over the past 100 years. The subtle variation in the EGRIP ice-core mineral composition is likely due to a minor contribution of local dust. The type of silicate minerals differed significantly between the two ice cores; micas and chlorite, which form in cold dry regions, were abundant in the EGRIP ice core, whereas kaolinite, which forms in warm humid regions, was abundant in the SIGMA-D ice core. This indicates that the EGRIP ice-core dust likely originated from different geological sources than those for the SIGMA-D dust. A back-trajectory analysis indicated that the ice-core dust was transported from Northern Eurasia and North America to the EGRIP site, and that the contribution from each source was likely smaller and larger, respectively, than those for the SIGMA-D ice core. Furthermore, the higher illite content in the EGRIP ice core suggests dust transportation from Asian deserts. Although the back-trajectory analysis suggests that most of the air mass that arrived at the EGRIP site came from the Greenland coast, the mineral grain size and composition results showed that the local dust contribution was likely small.
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RC1: 'Comment on egusphere-2023-1666', Anonymous Referee #1, 14 Sep 2023
In this manuscript Nagatsuka and colleagues analyze the mineral content of dust particles in a shallow ice core from central Greenland, and estimate the potential source contribution through backtrack trajectory modeling. They compare their results with a similar core drilled further west and published previously.
The main contribution of this manuscript are the detailed mineralogical analyses of this new shallow core since 1910. Although the results are new, they are rather incremental and it is not clear how these new data are improving our knowledge of Central Greenland dust advection or source contribution. That dust in central Greenland mostly originates from distant sources (mostly in East Asia) and not local ones was already known from other cores. This study mostly repeats this result at higher resolution. In addition, the authors imply links between their results with recent warming in Greenland, which is poorly supported since any kind of analyses including Atlantic and Pacific oscillations are missing. Finally, the discussion of volcanic particles is mostly a literature review without any contribution from this manuscript.
For these reasons I suggest to reject this manuscript as it does not include sufficient scientific advances for Climate of the Past. Instead, I suggest to publish these results in a more specialized journal.
Major Comments:
The authors mostly compare their results with an ice core from northeast Greenland (sigma-d) for which similar data are available. However, the comparison to central Greenland, east Greenland (Renland) and southeast Greenland (Dye-3) should be included in the discussion. In particular, the comparison with NGRIP should be made, as the claim that EGRIP represents Eastern Greenland and NGRIP central Greenland is a bit shaky, considering both sites are at similar altitudes and quite close to each other.
The authors group Europe and NorthEast Asia, as well as Africa and SouthEast Asia into single potential source areas in their analysis. Considering the long debate about Asian, European and African dust sources for Greenland, these should probably be split into four, unless the authors can justify their choice.
The authors talk about trends in the data in various sections of the manuscript, in particular comparing the last 20 years with the mid-section of the core. In particular, the authors imply that the recent warming has been responsible for various changes in dust mineralogy and concentrations. But looking at the complete record, these look more like multidecadal oscillations to me and should not be described as trends. Although recent warming in Greenland may have been responsible for some of the observed changes, such a hypothesis has to be put in context with the complete oscillations shown in the records. The authors briefly mention NAO at some point, but the link between their record and various Atlantic and Pacific oscillations should be discussed in much more details.
Minor Comments:
Line 18: Abstract could benefit from a more general introductory phrase at the beginning.
Line 33-34: Since Greenland is an island, all air masses must come from a coast. Be more precise.
Line 38: 100,000 years seems a bit short for the geological timescale, although I am not a geologist and may be wrong. Maybe Milankovitch timescale?
Line 42: “ice-core dust shows…”. Also this is only shown for Central Greenland, not the whole of Greenland.
Line 44-45: This is not at all the message of Svensson et al., 2000. Generally, I very much doubt that the seasonal variability in dust advection to Greenland is due to climate change…
Line 46: Not “predict”. “estimate” maybe.
Line 47: “partly responsible”. Grain size and partial melt is very important as well for albedo.
Line 53-58: The message of these phrases is unclear. Are you suggesting to collect dust from outcropped ice in the ablation zone to measure old dust? Or just dust in fresh snow on the surface? Then why talk about the movement of ice and dust through the ice sheet?
Line 60: Ujvari et al. used Hf not Pb.
Line 75: Can you give some references to support that hypothesis?
Line 117: Is the Beckman CC located in a normal laboratory or a clean room or a laminar flow bench? What kind of aperture tube was used?
Line 145, Table 1: Why is South America included as a possible source for Type A particles? I’m not saying it’s wrong (although I do doubt it), but I wonder why it was included in the list.
Lines 171-174: Snow cover fractions vary substantially from one model to another. Please provide and uncertainty estimate due to the choice of the model.
Lines 209-216: What do the numerical ranges indicate? 1-sigma range? If so how were the mean and standard deviations calculated?
Citation: https://doi.org/10.5194/egusphere-2023-1666-RC1 - AC1: 'Reply on RC1', Naoko Nagatsuka, 23 Sep 2023
- AC3: 'Reply on RC1', Naoko Nagatsuka, 19 Dec 2023
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RC2: 'Comment on egusphere-2023-1666', Anonymous Referee #2, 18 Oct 2023
This paper documents analyses of dust particles in the EGRIP Greenland ice core. The analyses consist of size information, and a set of SEM observations that have allowed mineralogical classification to be made. The work covers only the last century in 10 decade-long bins. The data are certainly worthwhile to make available, and a significant amount of work has gone into the SEM study. However it must be said that the new insights gained from this study are quite minor. I appreciate the authors’ point that isotopic analyses would be demanding in terms of sample size (though not with modern instruments quite as demanding as implied); however the coarse mineralogical separation here is simply not capable of defining source areas. It might (as in the previous work from SIGMA-D) be capable of defining the appearance of local sources but in this work no evidence of any local material is presented. Additionally the time series all appear flat (within statistical variation) meaning that there is no story about changing sources here. The back trajectory work is used in a way I think is inappropriate to try to define source areas (I will elaborate later). The work about volcanic material presents nothing new – we would not expect to see tephra from most eruptions, and indeed we don’t. In summary, there are data here that are worthwhile to make available, but there is no scientific story, and the data are not capable of defining source areas. It is therefore for the editor to decide: the authors could be encouraged to strip the paper down and correct/remove unsupported statements so that a correct but unexciting paper appears in CP: this would be a major revision as there are some issues that are conceptually wrong (especially regarding back trajectories) at present. Or they could recommend submission of a stripped down version to a journal such as ESSD that takes datasets without expecting too much in the way of interpretation.
Detailed comments
Abstract. There are a couple of sentences I don’t think are supported by the data and text. On lines 26-27 (local dust), I don’t think the case is made at all for a local dust source. On lines 31-33, the back trajectories really don’t make this case as presented. And the last sentence is contradictory as written.
Section 2.3: please be more precise with this explanation. As written, my reading is that you collected a total of 11 filters, and analysed 200 particles on each. However was each sample an average of all the vials from the 10 year interval or is it a spot measurement from one or more vials within the section? This is crucial to whether the samples are representative. And if you only analysed 200 particles per filter, then how are you later giving mineralogies to 0.1% accuracy (Table 3)? If this is really what was done (I hope not) then most of the differences between time periods would be completely statistically insignificant, so it’s really important to understand this.
Back trajectories: Starting with lines 153-5. I don’t understand what you are telling us about wet deposition here? Standard HYSPILT trajectories are simply that – trajectories of air masses, which take no account of the contents of the air and therefore take no account of what is lost en route or how it is deposited in Greenland. I am therefore not clear what you mean about wet deposition and precipitation. Please explain but for now I will assume you present simple back trajectories.
The next issue is that you describe launching trajectories from 4 different altitudes, but you don’t say which is shown in your figures. I assume it’s all 4 mixed together but this is an odd thing to do without first discussing what are the differences for different altitudes of launch.
Then Figure 2 is useless to the reader as the trajectory densities shown are nearly all over the ocean which cannot be a source of dust. You need to treat the trajectories in a different way: so we can judge where they might pick up dust. But there are a number of subtleties that are not well treated here. Firstly, of course every trajectory passes over the Greenland coast where there might be rock. But what matters is (a) how long the air spent over a source and (b) whether it was at low altitude where it could pick up fresh material (bearing in mind that as Schupbach discussed there could be places where air is lofted to altitude from the surface but at scales that Hysplit doesn’t capture). The reason I mention this in respect of Fig 2 is that the Figure gives the impression of a high input from the Greenland coast, but the reality is that the air probably only spends an hour or less over the thin coastal strip of sediment/soil, and probably not at ground level (as the air has to have reached high altitude by the time it reaches EGRIP). The figure is therefore misleading about the potential influence of local material, and completely unsuited (because the trajectories are too short) to showing which distant continent could have contributed.
Page 7 re dating. This is OK but I’d like to have seen your assignment of the ages near the bottom of your section confirmed by deeper volcanic matches (ie ones below the ice you used). Motjabavi et al 2020 have presented a chronology for EGRIP, so it would be helpful if you compared your chronology to theirs.
Line 215. “The mode values showed an increasing trend over the 100-year period except for the 1910–1920 sample”. This is not an acceptable statement. With that first sample, there is no trend, and even without it, I doubt the trend is statistically significant.
Fig 6. I again emphasise that if each decade is really only represented by a count of the types of 200 particles then most differences are likely to be statistically insignificant so again please clarify in methods, and if I have understood correctly please don’t overinterpret counts that have large uncertainties on them.
Fig 7 should be removed. It simply doesn’t represent what you say for the reasons I outlined above. These are not the “contributions of air masses” unless you weight them by the length of time they spend over a location (in fact I am very unclear what is plotted here anyway but it certainly isn’t what it says). Fig 8 is slightly more helpful and could possibly be used to interpret your data if we also had information about altitudes (where did trajectories last intersect with the ground?).
Section 4.1 eg line 263. Again I doubt the significance of any variability here given the number of particles of each sort counted.
Line 282. “The morphological properties of the EGRIP ice-core dust also suggest a small supply of minerals from local source areas”. This is not correctly written. It suggests evidence that there is a local supply albeit small. What you actually have is no evidence for a local supply. Please reword.
Page 15/16. While I agree that prior data suggest an East Asian source I cannot agree that you have added new evidence for that. As your Table 1 shows, 4 of your dust types could originate from East Asia but none of them uniquely so. Indeed both Asia and North America are mentioned for types A, B, C. This method is simply incapable to differentiate the long range sources.
The discussion of trajectories on page 16 is also incapable of differentiating sources as discussed above (and also for the reasons given by Schupbach).
Page 17. I simply can’t see the possible changes (more after 1980) in proportion of medium sized particles in Figure 11. Please either make a clear statistical case or remove this implication. Additionally changes in the proportion of 2 micron particles have not been shown to indicate a local source, but more likely a change in transport strength (if significant).
Section 4.3 adds nothing and should be removed.
The conclusions need to be changed to reflect the changes in the text, eg lines 432-4 are not shown in the data.
Citation: https://doi.org/10.5194/egusphere-2023-1666-RC2 - AC4: 'Reply on RC2', Naoko Nagatsuka, 19 Dec 2023
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RC3: 'Comment on egusphere-2023-1666', Anonymous Referee #3, 20 Oct 2023
Dear authors, the two reviews you already receive present most of my perplexities and doubts about your methodology and robusteness of conclusions.
My appreciation is that the paper presents interesting data, and could deserve publication if the treatement was better presented and justified. I only have a few additional suggestions with respect to the points rose by my colleagues.
- is the X-ray self attenuation for light elements taken into account for the EDS analysis? this can be severe for elements such as Al when large particles are present and could false the mineralogical attribution
- there is too little description of the way by which the size distributions are obtained
- I would suggest to present the size distribution as number of particles per unit size class and use a log scale for the x-axis
- the calcium depletion could be due to size sorting and not solubility, have you considered that?
- back trajectories are only showing provenance but need to be complemented by precipitation fields if you want to obtain deposition. Dry deposition can be approximated (roughly) by gravitational settling if you know the size distribution
Citation: https://doi.org/10.5194/egusphere-2023-1666-RC3 - AC2: 'Reply on RC3', Naoko Nagatsuka, 19 Dec 2023
Status: closed
-
RC1: 'Comment on egusphere-2023-1666', Anonymous Referee #1, 14 Sep 2023
In this manuscript Nagatsuka and colleagues analyze the mineral content of dust particles in a shallow ice core from central Greenland, and estimate the potential source contribution through backtrack trajectory modeling. They compare their results with a similar core drilled further west and published previously.
The main contribution of this manuscript are the detailed mineralogical analyses of this new shallow core since 1910. Although the results are new, they are rather incremental and it is not clear how these new data are improving our knowledge of Central Greenland dust advection or source contribution. That dust in central Greenland mostly originates from distant sources (mostly in East Asia) and not local ones was already known from other cores. This study mostly repeats this result at higher resolution. In addition, the authors imply links between their results with recent warming in Greenland, which is poorly supported since any kind of analyses including Atlantic and Pacific oscillations are missing. Finally, the discussion of volcanic particles is mostly a literature review without any contribution from this manuscript.
For these reasons I suggest to reject this manuscript as it does not include sufficient scientific advances for Climate of the Past. Instead, I suggest to publish these results in a more specialized journal.
Major Comments:
The authors mostly compare their results with an ice core from northeast Greenland (sigma-d) for which similar data are available. However, the comparison to central Greenland, east Greenland (Renland) and southeast Greenland (Dye-3) should be included in the discussion. In particular, the comparison with NGRIP should be made, as the claim that EGRIP represents Eastern Greenland and NGRIP central Greenland is a bit shaky, considering both sites are at similar altitudes and quite close to each other.
The authors group Europe and NorthEast Asia, as well as Africa and SouthEast Asia into single potential source areas in their analysis. Considering the long debate about Asian, European and African dust sources for Greenland, these should probably be split into four, unless the authors can justify their choice.
The authors talk about trends in the data in various sections of the manuscript, in particular comparing the last 20 years with the mid-section of the core. In particular, the authors imply that the recent warming has been responsible for various changes in dust mineralogy and concentrations. But looking at the complete record, these look more like multidecadal oscillations to me and should not be described as trends. Although recent warming in Greenland may have been responsible for some of the observed changes, such a hypothesis has to be put in context with the complete oscillations shown in the records. The authors briefly mention NAO at some point, but the link between their record and various Atlantic and Pacific oscillations should be discussed in much more details.
Minor Comments:
Line 18: Abstract could benefit from a more general introductory phrase at the beginning.
Line 33-34: Since Greenland is an island, all air masses must come from a coast. Be more precise.
Line 38: 100,000 years seems a bit short for the geological timescale, although I am not a geologist and may be wrong. Maybe Milankovitch timescale?
Line 42: “ice-core dust shows…”. Also this is only shown for Central Greenland, not the whole of Greenland.
Line 44-45: This is not at all the message of Svensson et al., 2000. Generally, I very much doubt that the seasonal variability in dust advection to Greenland is due to climate change…
Line 46: Not “predict”. “estimate” maybe.
Line 47: “partly responsible”. Grain size and partial melt is very important as well for albedo.
Line 53-58: The message of these phrases is unclear. Are you suggesting to collect dust from outcropped ice in the ablation zone to measure old dust? Or just dust in fresh snow on the surface? Then why talk about the movement of ice and dust through the ice sheet?
Line 60: Ujvari et al. used Hf not Pb.
Line 75: Can you give some references to support that hypothesis?
Line 117: Is the Beckman CC located in a normal laboratory or a clean room or a laminar flow bench? What kind of aperture tube was used?
Line 145, Table 1: Why is South America included as a possible source for Type A particles? I’m not saying it’s wrong (although I do doubt it), but I wonder why it was included in the list.
Lines 171-174: Snow cover fractions vary substantially from one model to another. Please provide and uncertainty estimate due to the choice of the model.
Lines 209-216: What do the numerical ranges indicate? 1-sigma range? If so how were the mean and standard deviations calculated?
Citation: https://doi.org/10.5194/egusphere-2023-1666-RC1 - AC1: 'Reply on RC1', Naoko Nagatsuka, 23 Sep 2023
- AC3: 'Reply on RC1', Naoko Nagatsuka, 19 Dec 2023
-
RC2: 'Comment on egusphere-2023-1666', Anonymous Referee #2, 18 Oct 2023
This paper documents analyses of dust particles in the EGRIP Greenland ice core. The analyses consist of size information, and a set of SEM observations that have allowed mineralogical classification to be made. The work covers only the last century in 10 decade-long bins. The data are certainly worthwhile to make available, and a significant amount of work has gone into the SEM study. However it must be said that the new insights gained from this study are quite minor. I appreciate the authors’ point that isotopic analyses would be demanding in terms of sample size (though not with modern instruments quite as demanding as implied); however the coarse mineralogical separation here is simply not capable of defining source areas. It might (as in the previous work from SIGMA-D) be capable of defining the appearance of local sources but in this work no evidence of any local material is presented. Additionally the time series all appear flat (within statistical variation) meaning that there is no story about changing sources here. The back trajectory work is used in a way I think is inappropriate to try to define source areas (I will elaborate later). The work about volcanic material presents nothing new – we would not expect to see tephra from most eruptions, and indeed we don’t. In summary, there are data here that are worthwhile to make available, but there is no scientific story, and the data are not capable of defining source areas. It is therefore for the editor to decide: the authors could be encouraged to strip the paper down and correct/remove unsupported statements so that a correct but unexciting paper appears in CP: this would be a major revision as there are some issues that are conceptually wrong (especially regarding back trajectories) at present. Or they could recommend submission of a stripped down version to a journal such as ESSD that takes datasets without expecting too much in the way of interpretation.
Detailed comments
Abstract. There are a couple of sentences I don’t think are supported by the data and text. On lines 26-27 (local dust), I don’t think the case is made at all for a local dust source. On lines 31-33, the back trajectories really don’t make this case as presented. And the last sentence is contradictory as written.
Section 2.3: please be more precise with this explanation. As written, my reading is that you collected a total of 11 filters, and analysed 200 particles on each. However was each sample an average of all the vials from the 10 year interval or is it a spot measurement from one or more vials within the section? This is crucial to whether the samples are representative. And if you only analysed 200 particles per filter, then how are you later giving mineralogies to 0.1% accuracy (Table 3)? If this is really what was done (I hope not) then most of the differences between time periods would be completely statistically insignificant, so it’s really important to understand this.
Back trajectories: Starting with lines 153-5. I don’t understand what you are telling us about wet deposition here? Standard HYSPILT trajectories are simply that – trajectories of air masses, which take no account of the contents of the air and therefore take no account of what is lost en route or how it is deposited in Greenland. I am therefore not clear what you mean about wet deposition and precipitation. Please explain but for now I will assume you present simple back trajectories.
The next issue is that you describe launching trajectories from 4 different altitudes, but you don’t say which is shown in your figures. I assume it’s all 4 mixed together but this is an odd thing to do without first discussing what are the differences for different altitudes of launch.
Then Figure 2 is useless to the reader as the trajectory densities shown are nearly all over the ocean which cannot be a source of dust. You need to treat the trajectories in a different way: so we can judge where they might pick up dust. But there are a number of subtleties that are not well treated here. Firstly, of course every trajectory passes over the Greenland coast where there might be rock. But what matters is (a) how long the air spent over a source and (b) whether it was at low altitude where it could pick up fresh material (bearing in mind that as Schupbach discussed there could be places where air is lofted to altitude from the surface but at scales that Hysplit doesn’t capture). The reason I mention this in respect of Fig 2 is that the Figure gives the impression of a high input from the Greenland coast, but the reality is that the air probably only spends an hour or less over the thin coastal strip of sediment/soil, and probably not at ground level (as the air has to have reached high altitude by the time it reaches EGRIP). The figure is therefore misleading about the potential influence of local material, and completely unsuited (because the trajectories are too short) to showing which distant continent could have contributed.
Page 7 re dating. This is OK but I’d like to have seen your assignment of the ages near the bottom of your section confirmed by deeper volcanic matches (ie ones below the ice you used). Motjabavi et al 2020 have presented a chronology for EGRIP, so it would be helpful if you compared your chronology to theirs.
Line 215. “The mode values showed an increasing trend over the 100-year period except for the 1910–1920 sample”. This is not an acceptable statement. With that first sample, there is no trend, and even without it, I doubt the trend is statistically significant.
Fig 6. I again emphasise that if each decade is really only represented by a count of the types of 200 particles then most differences are likely to be statistically insignificant so again please clarify in methods, and if I have understood correctly please don’t overinterpret counts that have large uncertainties on them.
Fig 7 should be removed. It simply doesn’t represent what you say for the reasons I outlined above. These are not the “contributions of air masses” unless you weight them by the length of time they spend over a location (in fact I am very unclear what is plotted here anyway but it certainly isn’t what it says). Fig 8 is slightly more helpful and could possibly be used to interpret your data if we also had information about altitudes (where did trajectories last intersect with the ground?).
Section 4.1 eg line 263. Again I doubt the significance of any variability here given the number of particles of each sort counted.
Line 282. “The morphological properties of the EGRIP ice-core dust also suggest a small supply of minerals from local source areas”. This is not correctly written. It suggests evidence that there is a local supply albeit small. What you actually have is no evidence for a local supply. Please reword.
Page 15/16. While I agree that prior data suggest an East Asian source I cannot agree that you have added new evidence for that. As your Table 1 shows, 4 of your dust types could originate from East Asia but none of them uniquely so. Indeed both Asia and North America are mentioned for types A, B, C. This method is simply incapable to differentiate the long range sources.
The discussion of trajectories on page 16 is also incapable of differentiating sources as discussed above (and also for the reasons given by Schupbach).
Page 17. I simply can’t see the possible changes (more after 1980) in proportion of medium sized particles in Figure 11. Please either make a clear statistical case or remove this implication. Additionally changes in the proportion of 2 micron particles have not been shown to indicate a local source, but more likely a change in transport strength (if significant).
Section 4.3 adds nothing and should be removed.
The conclusions need to be changed to reflect the changes in the text, eg lines 432-4 are not shown in the data.
Citation: https://doi.org/10.5194/egusphere-2023-1666-RC2 - AC4: 'Reply on RC2', Naoko Nagatsuka, 19 Dec 2023
-
RC3: 'Comment on egusphere-2023-1666', Anonymous Referee #3, 20 Oct 2023
Dear authors, the two reviews you already receive present most of my perplexities and doubts about your methodology and robusteness of conclusions.
My appreciation is that the paper presents interesting data, and could deserve publication if the treatement was better presented and justified. I only have a few additional suggestions with respect to the points rose by my colleagues.
- is the X-ray self attenuation for light elements taken into account for the EDS analysis? this can be severe for elements such as Al when large particles are present and could false the mineralogical attribution
- there is too little description of the way by which the size distributions are obtained
- I would suggest to present the size distribution as number of particles per unit size class and use a log scale for the x-axis
- the calcium depletion could be due to size sorting and not solubility, have you considered that?
- back trajectories are only showing provenance but need to be complemented by precipitation fields if you want to obtain deposition. Dry deposition can be approximated (roughly) by gravitational settling if you know the size distribution
Citation: https://doi.org/10.5194/egusphere-2023-1666-RC3 - AC2: 'Reply on RC3', Naoko Nagatsuka, 19 Dec 2023
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