the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 20 Dec 2021
Uncertainties in mass balance estimation of the Antarctic Ice Sheet using the input and output method
Abstract. The input-output method (IOM) is one of the most popular methods of estimating the ice sheet mass balance (MB), with a significant advantage in presenting the dynamics response of ice to climate change. Assessing the uncertainties of the MB estimation using the IOM is crucial to gaining a clear understanding of the Antarctic ice-sheet mass budget. Here, we introduce a framework for assessing the uncertainties in the MB estimation due to the methodological differences in the IOM, the impact of the parameterization and scale effect on the modeled surface mass balance (SMB, input), and the impact of the uncertainties of ice thickness, ice velocity, and grounding line data on ice discharge (D, output). For the assessment of the D’s uncertainty, we present D at a fine scale. Compared with the goal of determining the Antarctic MB within an uncertainty of 15 Gt yr−1, we found that the different strategies employed in the methods cause considerable uncertainties in the annual MB estimation. The uncertainty of the RACMO2.3 SMB caused by its parameterization can reach 20.4 Gt yr−1, while that due to the scale effect is up to 216.7 Gt yr−1. The observation precisions of the MEaSUREs InSAR-based velocity (1–17 m yr−1), the airborne radio-echo sounder thickness (±100 m), and the MEaSUREs InSAR-based grounding line (±100 m) contribute uncertainties of 17.1 Gt yr−1, 10.5 ± 2.7 Gt yr−1 and 8.0~27.8 Gt yr−1 to the D, respectively. However, the D’s uncertainty due to the remarkable ice thickness data gap, which is represented by the thickness difference between the BEDMAP2 and the BedMachine reaches 101.7 Gt yr−1, which indicates its dominant cause of the future D’s uncertainty. In addition, the interannual variability of D caused by the annual changes in the ice velocity and ice thickness are considerable compared with the target uncertainty of 15 Gt yr−1, which cannot be ignored in annual MB estimations.
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Interactive discussion
Status: closed
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RC1: 'Comment on tc-2021-325', Anonymous Referee #1, 21 Jan 2022
General comments
This manuscript assesses some of the uncertainty in estimating mass balance of the Antarctic Ice Sheet using the input/output (IO) method. The authors distinguish between method uncertainty (model resolution, scaling discharge, etc.) and data uncertainty (e.g. which data products are used for velocity, grounding line, ice thickness, etc.).
I'm a big fan of proper treatment and discussion of uncertainty. I like the idea behind this paper. Unfortunately I have significant issues with the implementation of the idea. Specifically, the work is incomplete, and difficult to understand. All work could be considered incomplete because any effort can always be done a bit more or better, but by my understanding of uncertainty analysis this work leaves out a lot of sources of uncertainty, and ignores ways that many scientist reduce uncertainty. Or maybe it is there, but suffers from my second issue - it is difficult to understand.
I think there needs to be a significant effort added to the discussion of random errors vs. systematic bias. Many scientists assume errors are random, and then use this and the mathematical treatment of uncertainty to reduce errors by summing or averaging over many small regions with random error. This may or may not be correct, but should be discussed in detail in this paper. Limited discussion on the distinction between these two types uncertainty, and their treatments in other works, is problematic.
Other general comments include,
+ The authors make some questionable decisions on use of data to assess uncertainty. For example, they use BedMachine and BedMap, but do not address the uncertainty field provided by BedMachine.
+ The authors continually refer to an 'uncertainty analysis framework'. What is this? Is 'framework' just a different way of saying 'method'? An "introduction" suggests something new or not seen before. I do not see anything particularly novel in this work. Therefore, if it is not novel, it should at least be comprehensive, but it is not that either.
+ Finally, I feel that the summary of this work could be a simple and clear table showing the uncertainty from different sources in both absolute (Gt/decade?) and relative (% of total uncertainty) terms. Table 3 lists "data uncertainties" but not "method uncertainties" and not relative amounts.
Specific comments
+ The 15 gt/yr target has a reference, but it is not clear that this target is necessary. Furthermore, the reference for that states,
Determine the changes in total ice-sheet mass balance to within 15 Gton/yr over the course of a decade and the changes in surface mass balance and glacier ice discharge with the same accuracy over the entire ice sheets, continuously, for decades to come.
And it isn't clear to me how to parse that. Is this 15 Gt/year average over a decade? Or 150 Gt/decade? Or 15 Gt/decade? Something else?
+ Authors use terms without defining them. For example "scale effect" on L22.
+ What does it mean to have an uncertainty on an uncertainty? For example, L24 reports "Uncertainties of [...] X +- Y Gt/yr".
+ There is often reference to "future D". But everything else is using present or historical data. Why is "D" discussed predictively?
+ L73 is a motivation for the entire work, "the dominant factors influencing the uncertainties in the MB estimation of the
AIS remain unclear." I disagree, the dominant factors are known. Perhaps not their relative scales?+ L83 "We introduce an uncertainty analysis framework" <-- where?
+ L96 "SMB (input)" SMB is output too (runoff, sublimation, evaporation) although runoff is small in Antarctica.
+ L104 D equation also uses ice density.
+ L168 Which "original raster" is extended? The velocity raster? thickness? Both?
+ L190-195: This sentence seems out-of-place. It's not about your methods or results of your methods, it is instead about anomalous years. I am unable to see the relevance to the surrounding text or the paper.
+ L447-449: "The strategy of using the yearly averaged SMB instead of the annual SMB is acceptable for decadal MB estimation to constrain variability when the long-term trend is required. However, if the research is related to short-term, regional snowfall events, it is better to use the annual SMB to determine the annual variability." <-- but the motivation for this whole paper is about a 15 Gt/year decade average. In several places there is mention of "annual variation" (see also L467). It isn't clear to me that annual variation matters based on the target "15 Gt/year over the course of a decade". Can these annual variations be considered random and therefore reduce when averaged over a decade?
+ L454 - again mention of "future D". Why not also mention "future SMB"?
+ L464 "Even ice thickness data with a 100-m precision" What is 100 m precision? Is that like "thick_100 = round(thick/100)*100" ?
TC review questions
1. Does the paper address relevant scientific questions within the scope of TC?
Yes
2. Does the paper present novel concepts, ideas, tools, or data?
No
3. Are substantial conclusions reached?
No
4. Are the scientific methods and assumptions valid and clearly outlined?
Yes, but they are incomplete.
5. Are the results sufficient to support the interpretations and conclusions?
Yes
6. Is the description of experiments and calculations sufficiently complete and precise to allow their reproduction by fellow scientists (traceability of results)?
Yes
7. Do the authors give proper credit to related work and clearly indicate their own new/original contribution?
Mostly, except the "introduce a new framework" suggests something original which I could not find.
8. Does the title clearly reflect the contents of the paper?
Yes
9. Does the abstract provide a concise and complete summary?
Yes
10. Is the overall presentation well structured and clear?
No
11. Is the language fluent and precise?
No
12. Are mathematical formulae, symbols, abbreviations, and units correctly defined and used?
Yes
Citation: https://doi.org/10.5194/tc-2021-325-RC1 -
AC1: 'Reply on RC1', Yijing Lin, 14 Mar 2022
Dear Reviewer,
We sincerely thank the editor and two reviewers for their insightful and constructive comments and suggestions. They were of great assistance in improving the quality of the manuscript. In the attached file, we respond to the general comments and give point-to-point answers to the specific comments.
We have given more comprehensive uncertainty estimations in the revised version. We have assessed: (1) the (combined) standard uncertainty based on the uncertainty field of the data sets and the given measurement precision, (2) the Monte Carlo uncertainty based on the uncertainty field of the data sets and the given measurement precision, (3) the uncertainty due to system error, (4) the uncertainty presented by the difference between two datasets and between two methods and between two studies.
Again, many thanks for pointing us into directions where our consideration was not sufficiently comprehensive. This helped a lot to improve the manuscript.
Best regards,
Yijing Lin
-
AC1: 'Reply on RC1', Yijing Lin, 14 Mar 2022
-
RC2: 'Comment on tc-2021-325', Anonymous Referee #2, 02 Feb 2022
The study from Lin et al touches on a very important topic that certainly would fit well within the remit of The Cryosphere. The manuscript provides an in depth assessment on the uncertainties associated with calculating ice sheet mass balance using the input (SMB) and output (ice discharge) method. It is true that some aspects of the uncertainty analysis has been covered in some detail in other studies, but I feel that this study has the added benefit of combing all of this analysis into one paper, but also includes some novel analysis on factors not considered/addressed in other studies e.g. grounding line position.
Therefore, I do think the concept of the study presented has the potential to be a nice contribution to The Cryosphere. However, at the moment I do not think that the manuscript has reached this potential and there are some major issues that need to be addressed before publication can be considered, that are detailed below.
Difficult to follow
My main concern with the manuscript is that I found it very difficult to follow and I feel that the manuscript could benefit from a slight restructuring and having a greater focus on hammering home the key points.
- Small things such as re-structuring the manuscript so it goes through all the uncertainties associated with ice discharge first (e.g. scaling, velocity, ice thickness and grounding line) and then the SMB stuff could make the manuscript easier to follow. At the moment the manuscript is ordered: ice discharge scaling -> SMB -> and then back to other ice discharge stuff, sometimes individual paragraphs contain information on both ice discharge and SMB methods, that makes it difficult to follow.
- For example in the methods section you could have new subsections 2.3 Ice Discharge – where you would go through systemically, paragraph by paragraph, what the manuscript focusses regarding ice discharge (e.g. scaling, velocity, ice thickness and grounding line). You could also do the same for a new subsection (2.4) on SMB. You could then structure the results section in a similar manor.
- The results section should stick to results and not wonder off into speculative discussions
- I think the discussion needs to be more streamlined and more to the point. At the moment it is lengthy and contains a lot of numbers and other bits of text that really don’t add anything. I do not think it hammers home the key points. Which brings me to the question what are the key points? Is scaling suitable? What is the dominant source of uncertainty, SMB? Is it imperative that even small grounding line changes are accounted for? Please let the reader know in a concise manor.
Unclear on some aspects of the methodologies/ important omissions
Discharge scaling factor
You compare discharge using the full pixel values and using a scaling method. I think this is potentially a valuable contribution and I agree there is an unknown impact of using this scaling, particularly going back in time where velocity data is more sparse. But I am not entirely sure how you have done this:
- Presumably in the innterannual mosaics used for this experiment there are plenty of data gaps, with some regions presumably having no data at some time periods. How do you account for this? How do you get a seemingly ice sheet wide estimate of ice discharge using the pixel value when some of the mosaics will have very large data gaps. More precisely what is a pixel scale estimate, is this simply taking the velocity value directly at the grounding line. A better explanation is needed here.
- Why did you choose only 100 m, what is the reason for this? For me 100 m yr is still relatively slow flowing ice.
- How do you treat the Antarctic Peninsula which has some difficult topography (e.g. narrow fjords) and how does this compare to other studies e.g. (Gardner et al., 2018).?
SMB
What about other SMB models apart from RACMO? I think some analysis of this has already been done, so it is not necessary to repeat. But I am certainly surprised not to see any mention of the below paper at all in the manuscript, it seems highly relevant.
Mottram, R., Hansen, N., Kittel, C., van Wessem, J. M., Agosta, C., Amory, C., Boberg, F., van de Berg, W. J., Fettweis, X., Gossart, A., van Lipzig, N. P. M., van Meijgaard, E., Orr, A., Phillips, T., Webster, S., Simonsen, S. B., and Souverijns, N.: What is the surface mass balance of Antarctica? An intercomparison of regional climate model estimates, The Cryosphere, 15, 3751–3784, https://doi.org/10.5194/tc-15-3751-2021, 2021.
Ice thickness
I agree with reviewer 1 that it is odd not include some analysis on the uncertainty product associated with BedMachine.
Line comments
Line 63-69: It is not clear to me what the ‘maximum difference’ is here? The difference to what exactly?
Line 67-69: Over what time periods are these comparisons made? Are you directly comparing the average mass balance from the entire rignot record (1979-2017) to the much shorter record of Shen or Gardner (2008-2015), I can not tell? For example, for Pine Island because it is changing so rapidly different estimates of mass balance would be expected over different timescales. So this is not really a fair comparison.
Line 83: I am not sure what you mean by an uncertainty analysis framework.
Line 125: More detail on the scaling factor is needed (See main comments)
Line 133: New paragraph as you move onto SMB
Line 167: What is the source for the original flux gate
Line 176-177: Probably a point for the discussion. Also, this is a large number, why is this? I presume it is something to do with the ice thickness used to calculate D – Rignot uses SMB as a base ice flux from the 1970s where there is no suitable ice thickness data?
Line 188 – discharge, not ‘mass balance’
Line 195: This sentence seems out of place
Figure 3: Specify in caption on figure that the multi-year average is 12 years
Line 255: ‘cannot be ignored’ – or confirms internal variation in ice discharge driven by climatological factors
Line 279 – 285: This is speculative discussion and should not be in the results. Also I would certainly disagree that ice shelves such as the Ross Ronne and Amery are ‘significantly thickening’, likewise for ‘significantly thinning’ ice shelves in Wilkes Land – much depends on what timescales you are referring too. I do not think this is a valid conclusion.
Line 303: I was not aware that the Measures grounding line covers the whole ice sheet? Are there not gaps? What did you use for the gaps?
Line 308-310: Again this is discussion. Furthermore, I don’t think I understand what you are trying to say in this point
Line 318-329; Example of text that is arguably not needed, most of it is repeated elsewhere in the manuscript
Line 336-337: I am not sure of the relevance of this sentence. Slow flowing ice only accounts for a small portion of the total discharge of Antarctica, So in absolute terms faster flowing ice is always going to have larger interannual variability.
Line 343: ‘The annual SMB data are probably closer to the real values’ – I do not understand what you mean here
Line 318-435: In general this discussion needs to be more streamlined and have less of a focus on repeating points made earlier in the manuscript.
Citation: https://doi.org/10.5194/tc-2021-325-RC2 -
AC2: 'Reply on RC2', Yijing Lin, 14 Mar 2022
Dear Reviewer,
We sincerely thank the editor and two reviewers for their insightful and constructive comments and suggestions. They were of great assistance in improving the quality of the manuscript. In the attached file, we respond to the general comments and give point-to-point answers to the specific comments.
We have restructured the manuscript and deleted the repeating points and make the discussion more streamlined in the revised version. We also have clarified some omissions of the scaling factor, SMB, and ice thickness, which are raised in the RC.
Again, many thanks for pointing us into directions where our consideration was not sufficiently comprehensive. This helped a lot to improve the manuscript.
Best regards,
Yijing Lin
Interactive discussion
Status: closed
-
RC1: 'Comment on tc-2021-325', Anonymous Referee #1, 21 Jan 2022
General comments
This manuscript assesses some of the uncertainty in estimating mass balance of the Antarctic Ice Sheet using the input/output (IO) method. The authors distinguish between method uncertainty (model resolution, scaling discharge, etc.) and data uncertainty (e.g. which data products are used for velocity, grounding line, ice thickness, etc.).
I'm a big fan of proper treatment and discussion of uncertainty. I like the idea behind this paper. Unfortunately I have significant issues with the implementation of the idea. Specifically, the work is incomplete, and difficult to understand. All work could be considered incomplete because any effort can always be done a bit more or better, but by my understanding of uncertainty analysis this work leaves out a lot of sources of uncertainty, and ignores ways that many scientist reduce uncertainty. Or maybe it is there, but suffers from my second issue - it is difficult to understand.
I think there needs to be a significant effort added to the discussion of random errors vs. systematic bias. Many scientists assume errors are random, and then use this and the mathematical treatment of uncertainty to reduce errors by summing or averaging over many small regions with random error. This may or may not be correct, but should be discussed in detail in this paper. Limited discussion on the distinction between these two types uncertainty, and their treatments in other works, is problematic.
Other general comments include,
+ The authors make some questionable decisions on use of data to assess uncertainty. For example, they use BedMachine and BedMap, but do not address the uncertainty field provided by BedMachine.
+ The authors continually refer to an 'uncertainty analysis framework'. What is this? Is 'framework' just a different way of saying 'method'? An "introduction" suggests something new or not seen before. I do not see anything particularly novel in this work. Therefore, if it is not novel, it should at least be comprehensive, but it is not that either.
+ Finally, I feel that the summary of this work could be a simple and clear table showing the uncertainty from different sources in both absolute (Gt/decade?) and relative (% of total uncertainty) terms. Table 3 lists "data uncertainties" but not "method uncertainties" and not relative amounts.
Specific comments
+ The 15 gt/yr target has a reference, but it is not clear that this target is necessary. Furthermore, the reference for that states,
Determine the changes in total ice-sheet mass balance to within 15 Gton/yr over the course of a decade and the changes in surface mass balance and glacier ice discharge with the same accuracy over the entire ice sheets, continuously, for decades to come.
And it isn't clear to me how to parse that. Is this 15 Gt/year average over a decade? Or 150 Gt/decade? Or 15 Gt/decade? Something else?
+ Authors use terms without defining them. For example "scale effect" on L22.
+ What does it mean to have an uncertainty on an uncertainty? For example, L24 reports "Uncertainties of [...] X +- Y Gt/yr".
+ There is often reference to "future D". But everything else is using present or historical data. Why is "D" discussed predictively?
+ L73 is a motivation for the entire work, "the dominant factors influencing the uncertainties in the MB estimation of the
AIS remain unclear." I disagree, the dominant factors are known. Perhaps not their relative scales?+ L83 "We introduce an uncertainty analysis framework" <-- where?
+ L96 "SMB (input)" SMB is output too (runoff, sublimation, evaporation) although runoff is small in Antarctica.
+ L104 D equation also uses ice density.
+ L168 Which "original raster" is extended? The velocity raster? thickness? Both?
+ L190-195: This sentence seems out-of-place. It's not about your methods or results of your methods, it is instead about anomalous years. I am unable to see the relevance to the surrounding text or the paper.
+ L447-449: "The strategy of using the yearly averaged SMB instead of the annual SMB is acceptable for decadal MB estimation to constrain variability when the long-term trend is required. However, if the research is related to short-term, regional snowfall events, it is better to use the annual SMB to determine the annual variability." <-- but the motivation for this whole paper is about a 15 Gt/year decade average. In several places there is mention of "annual variation" (see also L467). It isn't clear to me that annual variation matters based on the target "15 Gt/year over the course of a decade". Can these annual variations be considered random and therefore reduce when averaged over a decade?
+ L454 - again mention of "future D". Why not also mention "future SMB"?
+ L464 "Even ice thickness data with a 100-m precision" What is 100 m precision? Is that like "thick_100 = round(thick/100)*100" ?
TC review questions
1. Does the paper address relevant scientific questions within the scope of TC?
Yes
2. Does the paper present novel concepts, ideas, tools, or data?
No
3. Are substantial conclusions reached?
No
4. Are the scientific methods and assumptions valid and clearly outlined?
Yes, but they are incomplete.
5. Are the results sufficient to support the interpretations and conclusions?
Yes
6. Is the description of experiments and calculations sufficiently complete and precise to allow their reproduction by fellow scientists (traceability of results)?
Yes
7. Do the authors give proper credit to related work and clearly indicate their own new/original contribution?
Mostly, except the "introduce a new framework" suggests something original which I could not find.
8. Does the title clearly reflect the contents of the paper?
Yes
9. Does the abstract provide a concise and complete summary?
Yes
10. Is the overall presentation well structured and clear?
No
11. Is the language fluent and precise?
No
12. Are mathematical formulae, symbols, abbreviations, and units correctly defined and used?
Yes
Citation: https://doi.org/10.5194/tc-2021-325-RC1 -
AC1: 'Reply on RC1', Yijing Lin, 14 Mar 2022
Dear Reviewer,
We sincerely thank the editor and two reviewers for their insightful and constructive comments and suggestions. They were of great assistance in improving the quality of the manuscript. In the attached file, we respond to the general comments and give point-to-point answers to the specific comments.
We have given more comprehensive uncertainty estimations in the revised version. We have assessed: (1) the (combined) standard uncertainty based on the uncertainty field of the data sets and the given measurement precision, (2) the Monte Carlo uncertainty based on the uncertainty field of the data sets and the given measurement precision, (3) the uncertainty due to system error, (4) the uncertainty presented by the difference between two datasets and between two methods and between two studies.
Again, many thanks for pointing us into directions where our consideration was not sufficiently comprehensive. This helped a lot to improve the manuscript.
Best regards,
Yijing Lin
-
AC1: 'Reply on RC1', Yijing Lin, 14 Mar 2022
-
RC2: 'Comment on tc-2021-325', Anonymous Referee #2, 02 Feb 2022
The study from Lin et al touches on a very important topic that certainly would fit well within the remit of The Cryosphere. The manuscript provides an in depth assessment on the uncertainties associated with calculating ice sheet mass balance using the input (SMB) and output (ice discharge) method. It is true that some aspects of the uncertainty analysis has been covered in some detail in other studies, but I feel that this study has the added benefit of combing all of this analysis into one paper, but also includes some novel analysis on factors not considered/addressed in other studies e.g. grounding line position.
Therefore, I do think the concept of the study presented has the potential to be a nice contribution to The Cryosphere. However, at the moment I do not think that the manuscript has reached this potential and there are some major issues that need to be addressed before publication can be considered, that are detailed below.
Difficult to follow
My main concern with the manuscript is that I found it very difficult to follow and I feel that the manuscript could benefit from a slight restructuring and having a greater focus on hammering home the key points.
- Small things such as re-structuring the manuscript so it goes through all the uncertainties associated with ice discharge first (e.g. scaling, velocity, ice thickness and grounding line) and then the SMB stuff could make the manuscript easier to follow. At the moment the manuscript is ordered: ice discharge scaling -> SMB -> and then back to other ice discharge stuff, sometimes individual paragraphs contain information on both ice discharge and SMB methods, that makes it difficult to follow.
- For example in the methods section you could have new subsections 2.3 Ice Discharge – where you would go through systemically, paragraph by paragraph, what the manuscript focusses regarding ice discharge (e.g. scaling, velocity, ice thickness and grounding line). You could also do the same for a new subsection (2.4) on SMB. You could then structure the results section in a similar manor.
- The results section should stick to results and not wonder off into speculative discussions
- I think the discussion needs to be more streamlined and more to the point. At the moment it is lengthy and contains a lot of numbers and other bits of text that really don’t add anything. I do not think it hammers home the key points. Which brings me to the question what are the key points? Is scaling suitable? What is the dominant source of uncertainty, SMB? Is it imperative that even small grounding line changes are accounted for? Please let the reader know in a concise manor.
Unclear on some aspects of the methodologies/ important omissions
Discharge scaling factor
You compare discharge using the full pixel values and using a scaling method. I think this is potentially a valuable contribution and I agree there is an unknown impact of using this scaling, particularly going back in time where velocity data is more sparse. But I am not entirely sure how you have done this:
- Presumably in the innterannual mosaics used for this experiment there are plenty of data gaps, with some regions presumably having no data at some time periods. How do you account for this? How do you get a seemingly ice sheet wide estimate of ice discharge using the pixel value when some of the mosaics will have very large data gaps. More precisely what is a pixel scale estimate, is this simply taking the velocity value directly at the grounding line. A better explanation is needed here.
- Why did you choose only 100 m, what is the reason for this? For me 100 m yr is still relatively slow flowing ice.
- How do you treat the Antarctic Peninsula which has some difficult topography (e.g. narrow fjords) and how does this compare to other studies e.g. (Gardner et al., 2018).?
SMB
What about other SMB models apart from RACMO? I think some analysis of this has already been done, so it is not necessary to repeat. But I am certainly surprised not to see any mention of the below paper at all in the manuscript, it seems highly relevant.
Mottram, R., Hansen, N., Kittel, C., van Wessem, J. M., Agosta, C., Amory, C., Boberg, F., van de Berg, W. J., Fettweis, X., Gossart, A., van Lipzig, N. P. M., van Meijgaard, E., Orr, A., Phillips, T., Webster, S., Simonsen, S. B., and Souverijns, N.: What is the surface mass balance of Antarctica? An intercomparison of regional climate model estimates, The Cryosphere, 15, 3751–3784, https://doi.org/10.5194/tc-15-3751-2021, 2021.
Ice thickness
I agree with reviewer 1 that it is odd not include some analysis on the uncertainty product associated with BedMachine.
Line comments
Line 63-69: It is not clear to me what the ‘maximum difference’ is here? The difference to what exactly?
Line 67-69: Over what time periods are these comparisons made? Are you directly comparing the average mass balance from the entire rignot record (1979-2017) to the much shorter record of Shen or Gardner (2008-2015), I can not tell? For example, for Pine Island because it is changing so rapidly different estimates of mass balance would be expected over different timescales. So this is not really a fair comparison.
Line 83: I am not sure what you mean by an uncertainty analysis framework.
Line 125: More detail on the scaling factor is needed (See main comments)
Line 133: New paragraph as you move onto SMB
Line 167: What is the source for the original flux gate
Line 176-177: Probably a point for the discussion. Also, this is a large number, why is this? I presume it is something to do with the ice thickness used to calculate D – Rignot uses SMB as a base ice flux from the 1970s where there is no suitable ice thickness data?
Line 188 – discharge, not ‘mass balance’
Line 195: This sentence seems out of place
Figure 3: Specify in caption on figure that the multi-year average is 12 years
Line 255: ‘cannot be ignored’ – or confirms internal variation in ice discharge driven by climatological factors
Line 279 – 285: This is speculative discussion and should not be in the results. Also I would certainly disagree that ice shelves such as the Ross Ronne and Amery are ‘significantly thickening’, likewise for ‘significantly thinning’ ice shelves in Wilkes Land – much depends on what timescales you are referring too. I do not think this is a valid conclusion.
Line 303: I was not aware that the Measures grounding line covers the whole ice sheet? Are there not gaps? What did you use for the gaps?
Line 308-310: Again this is discussion. Furthermore, I don’t think I understand what you are trying to say in this point
Line 318-329; Example of text that is arguably not needed, most of it is repeated elsewhere in the manuscript
Line 336-337: I am not sure of the relevance of this sentence. Slow flowing ice only accounts for a small portion of the total discharge of Antarctica, So in absolute terms faster flowing ice is always going to have larger interannual variability.
Line 343: ‘The annual SMB data are probably closer to the real values’ – I do not understand what you mean here
Line 318-435: In general this discussion needs to be more streamlined and have less of a focus on repeating points made earlier in the manuscript.
Citation: https://doi.org/10.5194/tc-2021-325-RC2 -
AC2: 'Reply on RC2', Yijing Lin, 14 Mar 2022
Dear Reviewer,
We sincerely thank the editor and two reviewers for their insightful and constructive comments and suggestions. They were of great assistance in improving the quality of the manuscript. In the attached file, we respond to the general comments and give point-to-point answers to the specific comments.
We have restructured the manuscript and deleted the repeating points and make the discussion more streamlined in the revised version. We also have clarified some omissions of the scaling factor, SMB, and ice thickness, which are raised in the RC.
Again, many thanks for pointing us into directions where our consideration was not sufficiently comprehensive. This helped a lot to improve the manuscript.
Best regards,
Yijing Lin
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