the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 17 Feb 2026
The changing mass of the Antarctic Ice Sheet during ENSO-dominated periods in the GRACE era (2002–2022)
John Bright Ayabilah
Matt King
Danielle Udy
Tessa Vance
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- Final revised paper (published on 17 Feb 2026)
- Supplement to the final revised paper
- Preprint (discussion started on 14 Apr 2025)
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2025-1187', Anonymous Referee #1, 20 May 2025
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AC1: 'Reply on RC1', John Bright Ayabilah, 14 Jul 2025
Reviewer 1
SUMMARY
The study presents the impact that different ENSO-induced atmospheric circulation changes have on Antarctic ice sheet mass changes and analyze teleconnections with the southern annular mode. The authors show that there is strong event-to-event spatial variability between ENSO events using GRACE observed mass changes, regional climate model output and ERA5. This work fits well within the scope of the journal and provides a contribution to the field. The manuscript is generally well written, but some paragraphs can be somewhat lengthy. The following comments should help with solving the remaining issues before publication, with e.g. L1 referring to line 1.
Author’s response: We thank you for your thoughtful and constructive comments, which have contributed to improving the clarity, structure, and scientific integrity of the manuscript. All major and minor points have been carefully addressed.
General comments:
Reviewer comment
- Recently, a new version of the regional climate model RACMO2.4p1 was published for the Antarctic ice sheet (Van Dalum et al., 2025, https://doi.org/10.5194/egusphere-2024-3728), which includes new physics (in particular relevant here are changes in precipitation). Importantly, RACMO2.4p1 also has a higher horizontal resolution of 11 km compared to the 27 km resolution used in RACMO2.3p2. Using the SMB of RACMO2.4p1 would improve the comparisons done in this study and I suggest the authors to use this version instead of RACMO2.3p2. RACMO2.4p1 data can be found here: https://doi.org/10.5281/zenodo.14217231
Author’s response: In this study, we are primarily interested in the broad patterns associated with ENSO and the impact of the update of RACMO needs exploration. We will examine the differences produced by RACMO2.4p1 and, if they are substantial, we will update the results. If they are not, we will make note of their similarity.
Reviewer comment
- In the manuscript, basal melting is mentioned but SMB and mass changes are not studied on the ice shelves, hence relating the results to basal melting is difficult. Therefore, consider to include ice shelves in the comparison with RACMO SMB in e.g. Fig. 3b and elsewhere, and if possible also for GRACE, or explain why that cannot be done. Furthermore, it is also interesting to see how the SMB changes over the major ice shelves for each ENSO period.
Reviewer comment
Author’s response: We did not examine basal melting in this study. However, as GRACE data cannot distinguish between mass changes due to atmospheric forcing and those due to ice dynamics, our mention of basal melting refers to components of ice mass change that are potentially not explained by atmospheric processes. We will revise this section of the manuscript for better clarity and to avoid any confusion.
Reviewer comment
- I think it is valuable for this study to mention whether an ENSO event is central or eastern and discuss if and how such events differ, as it may explain some of the patterns that are identified in this study and therefore increase understanding. The authors shortly discuss the potential importance in the manuscript, like on L486-495, but I think a more in-depth analysis will improve the manuscript. Other work, like Macha et al. (2024), may provide information about whether an ENSO event is central or eastern, or it can be determined by following methods described by Ren and Jin (2011).
Author’s response: The use of cumulatively summed ENSO indices allows us to capture the net influence of all ENSO events within a period, including transitions between central and eastern Pacific events. This means that our ENSO periods may cover a single ENSO event, or they may cover a series of events, such as two or three La Niña events in a 2-3 year period. Because of this, it is a different technique to that of Macha et al., as one of our ‘ENSO events’ may cover both central and eastern Pacific events. In addition the Niño3.4 index does not distinguish between central and eastern-type ENSO events, however we acknowledge the value of more detailed classification. We will expand our discussion of the Macha et al work. We agree that it would be helpful to indicate whether the El Niño–dominated periods included Central or Eastern Pacific events. Rather than assigning events on a month-by-month basis, we will refer to established classifications in the literature to identify which periods include Central or Eastern Pacific El Niño events. This will provide useful context without implying monthly resolution that our data do not support.
Reviewer comment
- Not all locations that are discussed in the manuscript are shown on a map, like the Wedell Sea, Ross Sea, location of the ASL or the various ocean sectors. Including the locations mentioned in the manuscript will improve clarity, making it easier to follow.
Author’s response: As suggested, we will revise the manuscript to include more regional delineation on the maps, improving clarity and ease of interpretation.
Reviewer comment
- Including maps where the SMB changes are shown in percentage of the total SMB for the considered periods will help to understand how big the impact of ENSO/SAM is on the various regions that are considered, as some changes may seem large in for example high precipitation areas, while they are only relatively small. An alternative could be to report the integrated SMB values in Gt yr-1 for the ENSO events for the whole domain and smaller regions and compare them to the reference period.
Author’s response: Since we are interested in the total mass of the ice sheet we are interested in both absolute and relative impacts. To address the relative impact, we will include maps showing SMB changes expressed as a percentage of the climatological mean SMB for each ENSO-dominated period. For each period (e.g., the 2009–2010 El Niño-dominated period), the mean SMB will be computed and compared to the long-term climatological mean at each grid point, then expressed as a percentage. These maps will highlight regions where ENSO-related atmospheric circulation changes result in substantial deviations in SMB. However, our objective is to capture the absolute mass change rather than the relative mass change.
Specific comments:
Reviewer comment: L18: As you also use regional climate model output in your study, it should be mentioned in the abstract as well.
Author’s response: We will include the model output in the next revised text.
Reviewer comment: L23-26: “… and its influence on the ASL and the Southern Ocean circulation can be equally (and in some cases more) important to AIS variability.” Please specify with respect to what or rephrase this sentence.
Author’s response: We will rephrase this sentence for better clarity.
Reviewer comment: Abstract: I think it is also important to shortly mention the uncertainties in the abstract that you also mention in the text, such as the relatively short time period that you use and the various teleconnections that may have not happened yet within this time period, or other processes like atmospheric rivers.
Author’s response: We agree with the suggestion and will include it in the abstract.
Reviewer comment: L29-30: “The drivers of inter-annual to decadal Antarctic Ice Sheet (AIS) mass variability are complex and not yet fully understood”. Please add a reference to this.
Author’s response: Reference will be added to this statement in the revised manuscript
Reviewer comment: L35: Not only precipitation, but also riming can add to the SMB.
Author’s response: We will revise the manuscript accordingly.
Reviewer comment: L43: Can you specify here what typically the time scale is that the SAM changes from positive to negative, or vice versa and why the SAM happens?
Author’s response: We will elaborate on the timescale of the SAM changes and provide further explanation of the underlying mechanisms driving these variations.
Reviewer comment: L50: Is the total reduction of precipitation in the East AIS typically comparable to the precipitation increase in West Antarctica and the western Antarctic Peninsula? In other words, looking at the AIS as a whole, does a positive SAM increase or decrease the SMB?
Author’s response: Overall, positive SAM phases are associated with a net reduction in SMB over the AIS, while negative SAM phases are linked to a net increase in SMB. We will revise this paragraph to more clearly reflect the overall impact of SAM on AIS SMB.
Reviewer comment: L67-75: Please add the location of the ASL, sectors like the Pacific sector, Indian sector etc. and other names in a map (for example in Fig. 2), which would help visualize the processes described the paper.
Author’s response: We will include the mean locations of the ASL, as well as the Pacific, Atlantic, and Indian sectors, in Fig. 2 for clarity.
Reviewer comment: L76-83: Mention here why your study is different than the studies that you mention.
Author’s response: We will clarify in the revised manuscript why this study is unique compared to previous studies, highlighting its novel contributions.
Reviewer comment: L87: As GRACE observes mass changes, the mass loss due to processes like runoff and sublimation are also included in the signal and should be mentioned here, even though they are relatively small compared to discharge.
Author’s response: We will revise the manuscript as suggested.
Reviewer comment: L139: Please mention that the index is normalized in Fig. 1a.
Author’s response: We will revise the manuscript as suggested.
Reviewer comment: L149: Also mention that the climate indices are detrended in Fig. 1c.
Author’s response: We will revise the manuscript as suggested.
Reviewer comment: L155-161: Consider moving this paragraph such that it is mentioned before the paragraph of L148-154.
Author’s response: We will revise the manuscript as suggested.
Reviewer comment: L162-164: “...where the positive phase of ENSO dominates the negative ENSO phase until a positive peak in the cumulative index is reached…”. I think that I know what the authors mean, but consider reformulating this to improve clarity. Also, do you apply a minimum length that an ENSO period has to last?
Author’s response: The sentence will be revised to improve clarity. We did not apply a minimum length criterion but were instead focused on the total mass change over the duration of each ENSO-dominated period.
Reviewer comment: Fig. 1: Please add a description to the Y-axis of the figures. In Figure 1.d, consider adding ENSO and in Figure 1.e SAM in the top of the figure, which would help reading the figure more quickly.
Author’s response: We will revise the manuscript as suggested.
Reviewer comment: Section 2.3: It has not been mentioned in the paper before why you want to use a regional climate model and why it is necessary, which should be explained in e.g. the introduction before explaining what regional climate model you are going to use.
Author’s response: A brief explanation of the rationale for using a regional climate model will be included in the revised manuscript.
Reviewer comment: L189: .”..at its lateral and ocean boundaries…” → at its lateral boundaries and SST and sea ice extent at the sea surface boundary…
Author’s response: We will revise the manuscript as suggested.
Reviewer comment: Section 2.4: The authors should mention here why it is necessary to use ERA5 over RACMO output for the 10 m wind speeds and sea level pressure.
Author’s response: We will provide a justification for using ERA5 instead of RACMO output for the wind and sea level pressure fields in the revised manuscript.
Reviewer comment: L225: Capital letter is missing in ‘key’.
Author’s response: We will revise the manuscript as suggested.
Reviewer comment: L227-229: Also mention here that you plot ERA5 and RACMO in Figure 3.
Author’s response: We will revise the manuscript as suggested.
Reviewer comment: Fig. 3: I do not fully understand what is shown here. Is this the SLP and winds, SMB and GRACE mass loss averaged over the ENSO events? If this is the average over the ENSO events, including both El Nino and La Nina, would they not compensate each other?
Author’s response: We will reword the methods section and corresponding figure captions to improve clarity, and we will take special care to ensure consistent and precise use of terminology throughout the manuscript. The figure shows the regression coefficient of sea level pressure (SLP) and winds anomalies (cumulatively summed), surface mass balance (SMB, cumulatively summed), and GRACE anomalies onto the cumulatively summed ENSO index. The results illustrate the atmospheric and mass patterns associated with El Niño events; conversely, the opposite pattern is generally observed during La Niña conditions. We will review the description and improve the clarity
Reviewer comment: Regarding Figures 4 and 5, we agree that interpreting the results would be easier with additional context on the SAM phase. We will revise the figure captions and/or figure panels to indicate whether the SAM index during each ENSO event was positive, negative, or neutral. This will help clarify how the combined phase of ENSO and SAM influences the observed spatial patterns.
Author’s response: The manuscript will be amended accordingly.
Reviewer comment: Fig. 4i-l: Do you know why the north-south striping is so much more pronounced in Fig. 4j and Fig. 4l compared to Fig. 4i and Fig. 4k?
Author’s response: It is possible that the north-south stripping is much more pronounced over shorter periods of time. Furthermore, due to instrument degradation toward the end of the GRACE mission, the observational error increases, which likely contributes to the more noticeable north–south striping in Fig. 4j and Fig. 4l.
Reviewer comment: L310: Do you mean Fig. 4g instead of Fig. 4c?
Author’s response: Fig. 4c instead.
Reviewer comment: L311-312: “Note that the 2002-2005 SMB anomaly is only marginally positive (Fig. 4a).” → Note that the 2002-2005 SMB anomaly is only marginally positive for the Antarctic Peninsula (Fig. 4e).
Author’s response: We will revise the manuscript as suggested.
Reviewer comment: L313, 314: Fig. 4f → Fig 4f, h and also Fig. 4j → Fig. 4j, l.
Author’s response: We will revise the manuscript as suggested.
Reviewer comment: L323: Please also show these sectors on a map, e.g. Fig. 2.
Author’s response: We will revise the manuscript as suggested.
Reviewer comment: L330-353: Link the pressure anomalies and wind changes to moisture transport and their consequent impact on SMB and mass changes. These paragraphs can also be shortened.
Author’s response: The paragraphs will be rewritten for clarity and improved flow.
Reviewer comment: L380-381: Fig. 5f, g-h → Fig 5f-h and also Fig. 5j, k-l → Fig. 5j-l
Author’s response: We will revise the manuscript as suggested.
Reviewer comment: L385-387: Can you explain more how the northerly winds from the Pacific and southerly winds from the continent can lead to convection? And how it may result in positive mass anomalies?
Author’s response: We attribute the positive mass anomalies to the convergence zone formed where northerly and southerly winds meet, enhancing convection and leading to increased precipitation.
Reviewer comment: L393-398: Similarly, as before, link the pressure and wind anomalies to moisture transport and then to SMB and mass changes.
Author’s response: We will revise the manuscript as suggested.
Reviewer comment: L421-426: How much of the 2020-2022 La Nina SMB signal is caused by this atmospheric river event? Is it possible that it is (almost) completely dominated by it?
Author’s response: This was not included in our initial analysis, but we will incorporate an assessment to determine the extent to which the March 2022 ice mass anomaly influenced the 2020–2022 La Niña-dominated period.
Reviewer comment: Fig. 6: How did you calculate the average of the anomalies shown here? Did you weigh them by the length of the El Nino or La Nina-dominated periods? Or did you simply take the average of the maps that you have shown in Fig. 4 and 5?
Author’s response: We simply averaged the anomaly maps presented in Figures 4 and 5 without weighting by period length. Our aim was to highlight the mean spatial response of ENSO. We will clarify this in the figure caption and in the results section and note it in discussion.
Reviewer comment: 459-461: Can you elaborate about these unusual climate dynamics? Does this have any impact on ENSO/SAM related SMB changes that you have discussed in the paper?
Author’s response: We will expand on the unusual climate dynamics and explain how they influence the observed ENSO/SAM-related SMB variability. This will be included in the revised manuscript to provide a clearer context for the observed mass change anomalies.
Reviewer comment: L474-476: I am not sure if I fully understand how your results support the findings that increased basal melt is compensated by higher SMB. If I am not mistaken, you do not include ice shelves in your analysis where basal melt can occur, so how do you know that the positive SMB anomalies and increased mass that you show compensate for increased basal melt?
Author’s response: We agree with your comment, and this statement will be omitted in the revised manuscript.
Reviewer comment: L477: “… El Nino-dominated period in the Amundsen sector differ” → “… El Nino-dominated periods in the Amundsen sector differs”
Author’s response: We will revise the manuscript as suggested.
Reviewer comment: L483-485: As you include the complete events, doesn’t it make your methods more vulnerable for irregular events, such as atmospheric rivers, that may overshadow the ENSO signals?
Author’s response: Our methodology is vulnerable to irregular events such as atmospheric rivers (ARs). However, we can't exclude ARs from the methodology (there are multiple each year), but we can provide additional context and strengthen the discussion the likely contribution of ARs to SMB anomalies during ENSO dominating periods, using some key examples (e.g. 2009 in DML and 2022 in Wilkes Land) from the ENSO-dominated period by accounting the proportion of the signal to that AR. We will ensure that our discussion remains measured and is clearly framed within the context of Shields et al. (2022) and related work.
Reviewer comment: L508-510: Considering moving this to the la nina part.
Author’s response: We will revise the manuscript as suggested.
Reviewer comment: L524: “tie” → “tied”
Author’s response: We will revise the manuscript as suggested.
Reviewer comment: L550-551: “ENSO impacts West Antarctica through modulation of the ASL via Rossby wave propagation, though the ASL’s influence on East Antarctica remains unclear”, please add a reference to this.
Author’s response: Reference will be added to this statement.
Reviewer comment: L583-585: Consider reformulating this sentence.
Author’s response: We will revise the manuscript as suggested.
Reviewer comment: L595: The reference to Fig. 1c seems to be larger than the surrounding text.
Author’s response: We will revise the manuscript as suggested.
Reviewer comment: L631: “However, the timescale of the response of the upstream ice to the positive SAM forcing is unclear and would involve a substantial lag”. Please also describe how substantial this lag is what it would mean to the GRACE signal that you have used in this study.
Author’s response: We will revise the manuscript to include a brief discussion of the potential lag in the response of upstream ice to positive SAM forcing. This lag, which may range from months to several years depending on regional ice dynamics, suggests that the GRACE signal may reflect a delayed response rather than an immediate reaction to SAM variability. We will clarify this point to help interpret the relationship between SAM and GRACE-derived mass changes more accurately.
Reviewer comment: L649: “This dynamical signal is stronger in West than in East Antarctica.”. Add a citation to this.
Author’s response: We will revise the manuscript as suggested.
Reviewer comment: L 658-659: The authors should add the time period that is considered in this study here. Also mention that you used ERA5 and RACMO.
Author’s response: We will revise the manuscript as suggested.
Reviewer comment: L676-683: As it is the last concluding paragraph of the paper, remove references to figures and citations in this paragraph.
Author’s response: We will revise the manuscript as suggested.
Reviewer comment: L676-683: Similar to my comment about the abstract, consider to shortly mention the uncertainties that have been discussed, such as the relatively short time period that you use and the various teleconnections that may have not happened yet within this time period, or other processes like atmospheric rivers.
Author’s response: We will include it in the conclusion.
Reviewer comment: L690: This citation does not lead to the correct RACMO2.3p2 SMB data, as it refers to a newer version of RACMO: RACMO2.3p3.
Author’s response: We will make the necessary correction.
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AC1: 'Reply on RC1', John Bright Ayabilah, 14 Jul 2025
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RC2: 'Comment on egusphere-2025-1187', Anonymous Referee #2, 27 May 2025
SUMMARY
“The changing mass of the Antarctic Ice Sheet during ENSO-dominated periods in the GRACE era (2002-2022)” presents a comprehensive analysis of the circulation, surface mass balance, and ice mass variation patterns associated during four different periods of El Nino and La Nina phases of ENSO over two decades. The study ties together a number of prior studies on how ENSO impacts Antarctic surface mass balance by highlighting that the spatial impacts of this mode of variability vary strongly depending on the periods considered. It brings together observational, reanalysis, and model datasets to produce a compelling argument that the ENSO signal in Antarctica is dependent on event-specific atmospheric circulation patterns. I look forward to the publication of this manuscript; however, I have some major comments about the presentation of results without indications of statistical significance, the structure of the results, and the wording around association versus causation when establishing the occurrence of circulation and SMB/mass variability patterns during periods of El Nino and La Nina. Please see major and minor comments below.
MAJOR COMMENTS
Statistical significance of trends and anomalies – many of the figures and corresponding analyses in this manuscript describe trends and anomalies in circulation, surface mass balance, and short-term mass change of the Antarctic Ice Sheet. However, the figures and discussion are missing critical information on the statistical significance of the results shown. For example, Fig. 2 shows the linear trend in ice mass change based on GRACE data, and here it would be very useful to add hatching or another indicator of where the trend is statistically significant. For Fig. 3, does the regression output p-values? If so, this would be another example of where it would be important to show where the statistically significant regions are. Same for Fig. 4 and 5 - for the composite maps, it would be key to add an indication for where the mean anomaly in sea level pressure is statistically significant (or exceeds the standard deviation among the different anomalies, for example). Without an indication on the maps for which regions exhibit statistically significant anomalies, readers cannot know which patterns are robust.
For the analyses of figure 4 and 5, I recommend structuring the text either by region (then compare different periods) or by period (and go through each region). The current structure of the text alternates between period and region, and that makes it hard to follow.
There are several instances of language that implies causation rather than correlation throughout the paper. For example on L229, “the results show that ENSO influences circulation over Antarctica, driving short-term fluctuation in AIS mass…” – rather, the results show that ENSO periods are correlated with certain meridionally-oriented circulation patterns conducive to the flow of marine air masses onto the AIS. Furthermore, since there is not an analysis of the individual events that are contributing precipitation during the time periods in question, I would avoid using the word “driving” when it comes of the ENSO phase/circulation pattern and the associated SMB signals. As mentioned later in the text, precipitation can be driven by a few impactful events or many smaller snowfall events, or a mix of the two, and this study does not address the link between individual snowfall events and the large-scale circulation patterns. Furthermore, some of the language such as “that weakened the Antarctic high” or “a developing low-pressure system” or “leading to…” implies that this study examined the time-evolution of sea level pressure anomalies during the periods in question. My understanding of the methods is that this was not done – in which case, I would strongly recommend to the authors to remove any suggestions of the temporal evolution of anomalies throughout the text, unless there are figures to back up the claims.
L421-426 – I would be careful presenting the March 2022 event here as if it were the only extreme event/atmospheric river that occurred here over the time period studied. Certainly, this event was a standout and had a huge impact on the surface. At the same time, there are multiple atmospheric rivers impacting each location along the Antarctic coastline every year – meaning that there is the opportunity to assess the relationship between extremes, ENSO, and SAM. I would encourage the authors to discuss their results in the context of Shields et al. 2022 (https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2022GL099577) – which examined the associated between different modes of variability and atmospheric river occurrence and precipitation. Please see Fig. 3 of the Shields paper in reference to L565-566 of the Discussion as well – which shows the correlation between atmospheric river days and negative SAM.
MINOR COMMENTS
Abstract – would recommend removing/reducing the number of acronyms, including AIS, ASL, SAM, and SST.
L17 – “… we investigate AIS mass variability” (add mass? Same for L26)
L22 – “anticyclonic circulation anomalies” (add circulation)
L23-26 – sentence is a bit confusing, consider shortening or clarifying
L27 – what does “event-scale” mean? Synoptic-scale?
L43 – Add “The” to beginning of sentence, and “is regionally dependent and affects different regions” is redundant
L57 – it may be helpful to mention Pacific South American mode 1 (PSA1) in the Introduction, since this is another term used to describe the second most-dominant mode of variability around Antarctica, associated with ENSO.
L65 – impact of ASL on East Antarctica – is there any evidence that the ASL influences East Antarctic circulation? This is also mentioned at the end of the manuscript, and I think it would be helpful to clarify (a) whether any links have been found between the ASL and East Antarctic circulation (to support the statement that “the impact” exists) and (b) what those links could be.
L73 – “reducing precipitation and SMB in West Antarctica” – please be specific about which regions of West Antarctica
L84-105 – really nice summary here, framing the motivation for this study in the context of prior literature
L112 – clarify what COST-G RL-01 V0003 50km is, and please add a discussion either here or in the Discussion section about the spatiotemporal resolution of GRACE observations. How well do these observations capture spatial variability in accumulation? Is there a tendency to under/overestimate surface mass balance anomalies given the 300km resolution?
L128 – Is the linear trend sufficient for capturing ice mass variation over 2002-2022? Is the 7-month moving median specifically applied for the linear trend removal, or do all results shown include the 7-month-averaged signals? Are there regions where the trend is/isn’t statistically significant, by grid point? Is the trend removed everywhere or only where it is significant?
L132 – do you know if there is a lag between the initiation of an El Nino or La Nina event and the teleconnection that impacts Antarctic surface mass balance? Do you know the timescale of the teleconnection?
Fig. 1 – “shows the cumulatively summed normalised raw indices after which it is renormalized" – I’m having a hard time understanding what the method is.
Fig. 1 – please clarify what metrics where used to determine the ENSO phases shaded in (d) and (e). Also, I would recommend moving the legend from (c) to (a) and because there is no text labeling the figure axes, I’d recommend adding titles to each figure.
L211/212 – “relative strengthening” and “relative weakening”
Fig. 3 – how was the regression of 10m wind anomalies performed? For u and v separately, or did you use the wind vectors? For detrending the variables, did you use a linear trend? I think it would be helpful to have more information on the methods used here.
L240 – It could be helpful to readers if you present some Antarctic Ice Sheet-integrated SMB values when discussing the precipitation anomalies during El Nino and La Nina.
L242 – in Fig. 3, the W. Antarctic winds look more along-shore than onshore except over the Antarctic Peninsula – can you clarify? As a general comment, it is quite difficult to see the wind vectors along the Antarctic coast, meaning it’s not always clear if/when a figure supports the conclusions in the text about wind directions at the coast.
L273 – for the different periods of El Nino events presented, it would perhaps be helpful as added context to know whether these events were central or eastern.
L274 – “representing a weakened an/or shifted ASL” rather than an actual high-pressure system” – how do you know? Do you have a figure to show this?
L276 – “influencing meridional circulation, thus driving distinct spatial patterns in SMB” – could add a mention of “marine intrusions”/marine air masses here to link these two processes (the meridional circulation and the SMB)
L278 – “West Antarctica as two regions” – I’m very confused about what region is actually meant by the Amundsen Sea sector. Are you including all of Marie Byrd Land and the Ross coast in the Amundsen Sea? Where does the Bellingshausen fall? I would recommend adding region names to one of your early maps, and being very specific in your description of regional patterns.
L280 – “different signs but broadly uniform” – I am slightly confused by the wording in this sentence
L286 – “influences” – please use language of association and not causation
L296 – “… over the continent that weakened the Antarctic high” – again, use “associated with a weakened Antarctic high” or similar
L298 – “observed positive anomalies” – from GRACE?
L298 – “A low-pressure anomaly” – I see a low-pressure anomaly all along the coast, but not specifically between these two sites?
L301-307 – do you have a hypothesis for why this pattern occurred? Other modes of variability and/or teleconnections?
L308 – “two distinct mass variability responses” – I’ve seen this wording several times in the text and there are only two possible responses, right? Mass gain or loss? Please clarify.
L327 – “western Dronning Maud Land” – please be specific about the region, and label on a map
L333 – “southerly wind flow” and “northerly winds” – these are wind anomalies, right? If so, please refer to them as anomalies throughout the text. Also, these wind vectors are very hard to see in the figure. Perhaps I am misunderstanding the text, but I find it a bit confusing regarding the generating of “northerly winds into western regions, supporting slight positive anomalies”. I expect northerly winds to occur on the eastern flank of the low-pressure anomaly and I also see a convergence of northerly and southerly winds at the coast.
L339 – “central-eastern Dronning Maud Land”
L340 – “mid-latitude blocking pattern” – I would not necessarily call a high-pressure anomaly a mid-latitude block, without first looking at the mid-upper level geopotential height patterns and sea level pressure (not the anomaly).
L344-347 – this sentence is long and a bit confusing, recommend breaking it into two
L345 – 4c or 4b?
L348 – I don’t know that I see mid-latitude westerlies in 4c? (also these are wind anomalies, right?) – maybe more like the polar jet?
L351 – “pressure anomalies” – specify low or high
L351 – “developing” implies time-evolution
Fig. 5 - I am slightly concerned that the striping in Fig. 5k, for example, which extends all the way from the interior to the coast (especially because the patterns exhibit spatial continuity). I would recommend to the authors that they mask out the interior region most affected by the striping.
L373 – “strengthening” – implies time-evolution
L378 – these low-pressure anomalies all look pretty elongated to me?
L379 – “enhanced southerly wind anomalies” – in 5d, I see northeasterly onshore wind anomalies and positive SMB here in RACMO2?
L386 – “potentially can support convection and positive mass anomalies” – reference for this?
L400 – again, here it would be very helpful to show what the regions of statistically significant positive/negative SMB are on the RACMO2 SMB maps.
L409 – “resulting in uniform northerly winds and positive mass anomalies” – are you talking about the coast only? From the figure I see westerly and northwesterly winds, not purely northerly – though I would re-iterate that the wind vectors are so small in the maps that they are really hard to see. Finally, also mentioning once more that if these are wind anomalies they should always be referred to as such, and not presented as if they were the actual wind field.
L413 – “two distinct” – again, there are only two possible SMB responses, right?
L419 – “deepening” implies temporal evolution
L419-421 – these two features (low-pressure anomaly in the Pacific and wind anomalies over Wilkes Land) seem far apart spatially – I’m missing the connection here with respect to the circulation?
Fig. 6 – again, there needs to be information on the statistical significance of the patterns in this figure, which will presumably support the authors’ claims that different ENSO events are associated with different circulation and surface mass balance patterns.
L430 – Amundsen Sea sector and Marie Byrd Land
L446-447 – language suggests causation
L453 – might help to remind readers what the bi-polar pattern is
L454 – what is meant by “underlying”? Most common, strongest, dominant?
L470 – “coastal easterlies” – could you clarify this? I see coastal westerly wind anomalies in 4a, c, and d.
L479 – western Ross Sea sector is not mentioned earlier in the text, nor is the Ross ice shelf shown in any figures. Could you clarify what is meant here?
L490 – “the anomalous response can be attributed to altered Rossby wave propagation” – surely Rossby wave propagation influences almost all ENSO-associated circulation patterns around Antarctica?
L524 – “isolating ENSO signals” – I would be careful with stating that you are isolating ENSO signals here, because as was already mentioned, there are a number of different weather patterns and extremes that occurred during the periods over which the circulation and SMB patterns were composited.
L525 – “convergence zone that enhances precipitation” – reference for this? And can you be specific about exactly where you see the convergence occurring? Do you see this in the actual wind fields too, not only the anomalies?
L4545-548 – reference?
L550 – “ASL’s influence on East Antarctica remains unclear” – as mentioned earlier, this implies that there is an influence but we don’t know what it is – is that the conclusion from Li et al. 2022, as cited?
L559 – can use “significant” if you show statistical significance of mass changes in the figure
L574-579 – it’s probably important to add there that it’s equally likely that certain modes of variability and their associated circulation patterns may be conducive to atmospheric river landfall in certain regions.
L598 – “structure of the westerlies was altered” implies causation, and refers to the winds rather than the wind anomalies.
Discussion – general comment: this is a very long section, and while it is interesting, I think it comes across as somewhat redundant following the results and before the conclusion. I would recommend shortening it where possible, to make the section more concise and less repetitive.
Citation: https://doi.org/10.5194/egusphere-2025-1187-RC2 -
AC2: 'Reply on RC2', John Bright Ayabilah, 14 Jul 2025
RC 2.
SUMMARY
“The changing mass of the Antarctic Ice Sheet during ENSO-dominated periods in the GRACE era (2002-2022)” presents a comprehensive analysis of the circulation, surface mass balance, and ice mass variation patterns associated during four different periods of El Nino and La Nina phases of ENSO over two decades. The study ties together a number of prior studies on how ENSO impacts Antarctic surface mass balance by highlighting that the spatial impacts of this mode of variability vary strongly depending on the periods considered. It brings together observational, reanalysis, and model datasets to produce a compelling argument that the ENSO signal in Antarctica is dependent on event-specific atmospheric circulation patterns. I look forward to the publication of this manuscript; however, I have some major comments about the presentation of results without indications of statistical significance, the structure of the results, and the wording around association versus causation when establishing the occurrence of circulation and SMB/mass variability patterns during periods of El Nino and La Nina. Please see major and minor comments below.
Author’s response: We appreciate your constructive feedback and believe that your suggestions will significantly enhance the clarity and scientific rigor of our study. We have carefully addressed each of the major and minor comments you raised.
MAJOR COMMENTS
Reviewer comment:
Statistical significance of trends and anomalies – many of the figures and corresponding analyses in this manuscript describe trends and anomalies in circulation, surface mass balance, and short-term mass change of the Antarctic Ice Sheet. However, the figures and discussion are missing critical information on the statistical significance of the results shown. For example, Fig. 2 shows the linear trend in ice mass change based on GRACE data, and here it would be very useful to add hatching or another indicator of where the trend is statistically significant. For Fig. 3, does the regression output p-values? If so, this would be another example of where it would be important to show where the statistically significant regions are. Same for Fig. 4 and 5 - for the composite maps, it would be key to add an indication for where the mean anomaly in sea level pressure is statistically significant (or exceeds the standard deviation among the different anomalies, for example). Without an indication on the maps for which regions exhibit statistically significant anomalies, readers cannot know which patterns are robust.
Author’s response: We agree with the reviewer that indicating statistical significance is important for a robust interpretation of our results. We are currently implementing statistical significance tests for the trends and anomalies presented in the manuscript. Significant regions will be highlighted on the maps to help readers identify which observed patterns are robust.
Reviewer comment
For the analyses of figure 4 and 5, I recommend structuring the text either by region (then compare different periods) or by period (and go through each region). The current structure of the text alternates between period and region, and that makes it hard to follow.
Author’s response: We will also restructure the text to enhance flow and readability, following your suggestion to present each region individually before making comparisons across regions.
Reviewer comment
There are several instances of language that implies causation rather than correlation throughout the paper. For example on L229, “the results show that ENSO influences circulation over Antarctica, driving short-term fluctuation in AIS mass…” – rather, the results show that ENSO periods are correlated with certain meridionally-oriented circulation patterns conducive to the flow of marine air masses onto the AIS. Furthermore, since there is not an analysis of the individual events that are contributing precipitation during the time periods in question, I would avoid using the word “driving” when it comes of the ENSO phase/circulation pattern and the associated SMB signals. As mentioned later in the text, precipitation can be driven by a few impactful events or many smaller snowfall events, or a mix of the two, and this study does not address the link between individual snowfall events and the large-scale circulation patterns. Furthermore, some of the language such as “that weakened the Antarctic high” or “a developing low-pressure system” or “leading to…” implies that this study examined the time-evolution of sea level pressure anomalies during the periods in question. My understanding of the methods is that this was not done – in which case, I would strongly recommend to the authors to remove any suggestions of the temporal evolution of anomalies throughout the text, unless there are figures to back up the claims.
Author’s response: Regarding the language used, we will refine it to avoid implying causation or temporal evolution that is not supported by our methods. Although much of this language was revised in earlier drafts, we acknowledge that some instances still remain. We will carefully review the manuscript to ensure that all wording clearly reflects correlation rather than causation and avoids terms that may suggest otherwise.
Reviewer comment
L421-426 – I would be careful presenting the March 2022 event here as if it were the only extreme event/atmospheric river that occurred here over the time period studied. Certainly, this event was a standout and had a huge impact on the surface. At the same time, there are multiple atmospheric rivers impacting each location along the Antarctic coastline every year – meaning that there is the opportunity to assess the relationship between extremes, ENSO, and SAM. I would encourage the authors to discuss their results in the context of Shields et al. 2022 (https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2022GL099577) – which examined the associated between different modes of variability and atmospheric river occurrence and precipitation. Please see Fig. 3 of the Shields paper in reference to L565-566 of the Discussion as well – which shows the correlation between atmospheric river days and negative SAM.
Author’s response: We will ensure that our discussion remains measured and is clearly framed within the context of Shields et al. (2022) and related work.
MINOR COMMENTS
Reviewer comment: Abstract – would recommend removing/reducing the number of acronyms, including AIS, ASL, SAM, and SST.
Author’s response: We will reduce the number of acronyms used throughout the manuscript for improved readability.
Reviewer comment: L17 – “… we investigate AIS mass variability” (add mass? Same for L26)
Author’s response: Mass will be added to this line.
Reviewer comment: L22 – “anticyclonic circulation anomalies” (add circulation)
Author’s response: We will add the term “circulation” as suggested.
Reviewer comment: L23-26 – sentence is a bit confusing, consider shortening or clarifying
Author’s response: The sentence will be rewritten to improve clarity.
Reviewer comment: L27 – what does “event-scale” mean? Synoptic-scale?
Author’s response: In this instance, “event-scale” refers to synoptic-scale events. We recognize that the term “event-scale” may cause confusion given our use of the term “ENSO events” elsewhere in the manuscript. To avoid ambiguity, we will revise the text and change it to “synoptic-scale”.
Reviewer comment: L43 – Add “The” to beginning of sentence, and “is regionally dependent and affects different regions” is redundant
Author’s response: We will edit the manuscript as suggested.
Reviewer comment: L57 – it may be helpful to mention Pacific South American mode 1 (PSA1) in the Introduction, since this is another term used to describe the second most-dominant mode of variability around Antarctica, associated with ENSO.
Author’s response: We will edit the manuscript as suggested.
Reviewer comment: L65 – impact of ASL on East Antarctica – is there any evidence that the ASL influences East Antarctic circulation? This is also mentioned at the end of the manuscript, and I think it would be helpful to clarify (a) whether any links have been found between the ASL and East Antarctic circulation (to support the statement that “the impact” exists) and (b) what those links could be.
Author’s response: There is no clear evidence of a direct ASL impact in East Antarctica; however, it is possible that the ASL indirectly influences the region. Our analysis of the 2020–2022 La Niña period suggests that the ASL may have contributed to moisture inflow into Dronning Maud Land. We will revise the text to clarify this point and include supporting references, as suggested.
Reviewer comment: L73 – “reducing precipitation and SMB in West Antarctica” – please be specific about which regions of West Antarctica
Author’s response: Okay, we will revise the language to be more regionally specific to improve clarity and accuracy.
Reviewer comment: L84-105 – really nice summary here, framing the motivation for this study in the context of prior literature
Author’s response: We thankful to the reviewer.
Reviewer comment: L112 – clarify what COST-G RL-01 V0003 50km is, and please add a discussion either here or in the Discussion section about the spatiotemporal resolution of GRACE observations. How well do these observations capture spatial variability in accumulation? Is there a tendency to under/overestimate surface mass balance anomalies given the 300km resolution?
Author’s response: We will expand the discussion of the GRACE dataset to include a description of its effective spatial resolution (~300 km) and the implications for detecting surface mass balance anomalies.
Reviewer comment: L128 – Is the linear trend sufficient for capturing ice mass variation over 2002-2022? Is the 7-month moving median specifically applied for the linear trend removal, or do all results shown include the 7-month-averaged signals? Are there regions where the trend is/isn’t statistically significant, by grid point? Is the trend removed everywhere or only where it is significant?
Author’s response: A 7-month moving median is used to smooth the GRACE data before computing the ice mass variation trend over the period 2002–2022. No significance test was conducted, but it will be included in our future analysis. The results for ENSO-dominated periods include the 7-month moving median signals, which are then detrended to focus on variability. The choice of a 7 month filter follows King et al. 2023 and is a subjective choice to dampen GRACE month-to-month noise only.
Reviewer comment: L132 – do you know if there is a lag between the initiation of an El Nino or La Nina event and the teleconnection that impacts Antarctic surface mass balance? Do you know the timescale of the teleconnection?
Author’s response: King et al 2003 looked at it and we can’t resolve it with our method as it is likely ~6 months.
Reviewer comment: Fig. 1 – “shows the cumulatively summed normalised raw indices after which it is renormalized" – I’m having a hard time understanding what the method is.
Author’s response: We will reword the methods section and corresponding figure captions to improve clarity, and we will take special care to ensure consistent and precise use of terminology throughout the manuscript.
Reviewer comment: Fig. 1 – please clarify what metrics where used to determine the ENSO phases shaded in (d) and (e). Also, I would recommend moving the legend from (c) to (a) and because there is no text labeling the figure axes, I’d recommend adding titles to each figure.
Author’s response: We will revise the manuscript according to the suggestion.
Reviewer comment: L211/212 – “relative strengthening” and “relative weakening”
Author’s response: We will modify as suggested.
Reviewer comment: Fig. 3 – how was the regression of 10m wind anomalies performed? For u and v separately, or did you use the wind vectors? For detrending the variables, did you use a linear trend? I think it would be helpful to have more information on the methods used here.
Author’s response: The regression was performed separately for the u and v components. Detrending was done by removing the linear trend. Additional information will be included.
Reviewer comment: L240 – It could be helpful to readers if you present some Antarctic Ice Sheet-integrated SMB values when discussing the precipitation anomalies during El Nino and La Nina.
Author’s response: Okay, we will consider.
Reviewer comment: L242 – in Fig. 3, the W. Antarctic winds look more along-shore than onshore except over the Antarctic Peninsula – can you clarify? As a general comment, it is quite difficult to see the wind vectors along the Antarctic coast, meaning it’s not always clear if/when a figure supports the conclusions in the text about wind directions at the coast.
Author’s response: To address this comment, we will increase the size of the wind vectors in the figure to enhance visibility, particularly along the Antarctic coast. This adjustment will help clarify the wind patterns discussed in the text and more effectively support the conclusions presented.
Reviewer comment: L273 – for the different periods of El Nino events presented, it would perhaps be helpful as added context to know whether these events were central or eastern.
Author’s response: We agree that it would be helpful to indicate whether the El Niño–dominated periods included Central or Eastern Pacific events. Rather than assigning events on a month-by-month basis, we will refer to established classifications in the literature to identify which periods include Central or Eastern Pacific El Niño events. This will provide useful context without implying monthly resolution that our data do not support.
Reviewer comment: L274 – “representing a weakened an/or shifted ASL” rather than an actual high-pressure system” – how do you know? Do you have a figure to show this?
Author’s response: We make this observation in reference to the climatology, which indicates a high-pressure system over Antarctica. This pattern is evident when we compute the climatology over the study period (2002–2022), although it is not shown in the manuscript.
Reviewer comment: L276 – “influencing meridional circulation, thus driving distinct spatial patterns in SMB” – could add a mention of “marine intrusions”/marine air masses here to link these two processes (the meridional circulation and the SMB)
Author’s response: The manuscript will be revised to establish a clearer connection between the two processes.
Reviewer comment: L278 – “West Antarctica as two regions” – I’m very confused about what region is actually meant by the Amundsen Sea sector. Are you including all of Marie Byrd Land and the Ross coast in the Amundsen Sea? Where does the Bellingshausen fall? I would recommend adding region names to one of your early maps, and being very specific in your description of regional patterns.
Author’s response: A more detailed map with additional regional labels will be included to allow for clearer and more specific descriptions of the regional patterns discussed in the text.
Reviewer comment: L280 – “different signs but broadly uniform” – I am slightly confused by the wording in this sentence
Author’s response: The sentence will be restructured for better clarity.
Reviewer comment: L286 – “influences” – please use language of association and not causation
Author’s response: We will review the manuscript carefully to ensure the language is precise and does not imply causation where only correlation is observed.
Reviewer comment: L296 – “… over the continent that weakened the Antarctic high” – again, use “associated with a weakened Antarctic high” or similar
Author’s response: We will review the manuscript carefully to ensure the language is precise and does not imply causation where only correlation is observed.
Reviewer comment: L298 – “observed positive anomalies” – from GRACE?
Author’s response: We will clarify the observed positive anomalies.
Reviewer comment: L298 – “A low-pressure anomaly” – I see a low-pressure anomaly all along the coast, but not specifically between these two sites?
Author’s response: We will clarify the position of the low-pressure anomaly.
Reviewer comment: L301-307 – do you have a hypothesis for why this pattern occurred? Other modes of variability and/or teleconnections?
Author’s response: Again, we will clarify why this pattern occurred and the potential hypothesis. Our hypothesis is linked to that El Nino dominating period coinciding with a central Pacific El Nino event.
Reviewer comment: L308 – “two distinct mass variability responses” – I’ve seen this wording several times in the text and there are only two possible responses, right? Mass gain or loss? Please clarify.
Author’s response: We agree with the reviewer that there are fundamentally two possible responses—mass gain or mass loss. We will revise the wording throughout the manuscript to clarify this and avoid ambiguous phrasing such as “two distinct mass variability responses.”
Reviewer comment: L327 – “western Dronning Maud Land” – please be specific about the region, and label on a map
Author’s response: We will revise as suggested.
Reviewer comment: L333 – “southerly wind flow” and “northerly winds” – these are wind anomalies, right? If so, please refer to them as anomalies throughout the text. Also, these wind vectors are very hard to see in the figure. Perhaps I am misunderstanding the text, but I find it a bit confusing regarding the generating of “northerly winds into western regions, supporting slight positive anomalies”. I expect northerly winds to occur on the eastern flank of the low-pressure anomaly and I also see a convergence of northerly and southerly winds at the coast.
Author’s response: The winds described here are wind anomalies and will be consistently referred to as anomalies throughout the text in a revised document. The wind vectors will be replotted and enlarged where possible to improve visibility for the reader.
We acknowledge the confusion and appreciate the reviewer’s observation. The low-pressure anomaly is located further west of the Dronning Maud Land coast, and the northerly winds anomaly is on the eastern flank of the low-pressure anomaly. The convergence zone is more prominent toward Enderby Land, where a slight positive mass anomaly is observed. We will clarify this description in the text, and we expect the wind patterns to be more easily interpreted with the improved figure.
Reviewer comment: L339 – “central-eastern Dronning Maud Land”
Author’s response: Agree, we will change it to central-eastern Dronning Maud Land.
Reviewer comment: L340 – “mid-latitude blocking pattern” – I would not necessarily call a high-pressure anomaly a mid-latitude block, without first looking at the mid-upper level geopotential height patterns and sea level pressure (not the anomaly).
Author’s response: We will revise the sentence to state that the feature resembles a mid-latitude block, but we have not explicitly categorized it as such.
Reviewer comment: L344-347 – this sentence is long and a bit confusing, recommend breaking it into two
Author’s response: The sentence will be break into two for more clarity.
Reviewer comment: L345 – 4c or 4b?
Author’s response: 4b. We will fix this.
Reviewer comment: L348 – I don’t know that I see mid-latitude westerlies in 4c? (also these are wind anomalies, right?) – maybe more like the polar jet?
Author’s response: These winds are anomalies, and the westerly jet observed primarily influences the AIS and the Southern Ocean, rather than the mid-latitudes as noted in the comment. It is more likely associated with the polar front jet. We will revise to indicate this.
Reviewer comment: L351 – “pressure anomalies” – specify low or high
Author’s response: A weak high-pressure anomaly over the continent. We will revise to...
Reviewer comment: L351 – “developing” implies time-evolution
Author’s response: The language will be revised to: “accompanied by a low-pressure anomaly in the adjacent ocean.”
Reviewer comment: Fig. 5 - I am slightly concerned that the striping in Fig. 5k, for example, which extends all the way from the interior to the coast (especially because the patterns exhibit spatial continuity). I would recommend to the authors that they mask out the interior region most affected by the striping.
Author’s response: We will take this into consideration and assess how to define the boundary of what should or should not be masked, in a way that does not obscure meaningful signals and is feasible to implement. If a suitable method can be identified, we will apply the masking. Otherwise, we will revise the figure caption to guide the reader’s attention toward the more robust signals along the coast.
Reviewer comment: L373 – “strengthening” – implies time-evolution
Author’s response: The language will be revised to: “reflecting an intensification and/or shift of the Amundsen Sea Low (ASL) (Fig. 5a–d).”
Reviewer comment: L378 – these low-pressure anomalies all look pretty elongated to me?
Author’s response: The statement will be deleted in the revised version.
Reviewer comment: L379 – “enhanced southerly wind anomalies” – in 5d, I see northeasterly onshore wind anomalies and positive SMB here in RACMO2?
Author’s response: The focus was on the Amundsen Embayment, which led to the generalization of southerly wind anomalies. However, during our defined 2020–2022 La Niña-dominated period, the wind anomalies across the embayment are more northeasterly, potentially transporting moisture onshore—particularly along the western part of the embayment. This likely explains the positive SMB signal seen in the RACMO data. We will revise the manuscript to reflect this more accurate description.
Reviewer comment: L386 – “potentially can support convection and positive mass anomalies” – reference for this?
Author’s response: The statement was a deduction intended to explain the observed positive mass anomaly. We will include a suitable reference to support this explanation in the revised manuscript.
Reviewer comment: L400 – again, here it would be very helpful to show what the regions of statistically significant positive/negative SMB are on the RACMO2 SMB maps.
Author’s response: Statistical significance tests will be performed to define....
Reviewer comment: L409 – “resulting in uniform northerly winds and positive mass anomalies” – are you talking about the coast only? From the figure I see westerly and northwesterly winds, not purely northerly – though I would re-iterate that the wind vectors are so small in the maps that they are really hard to see. Finally, also mentioning once more that if these are wind anomalies they should always be referred to as such and not presented as if they were the actual wind field.
Author’s response: As noted previously, the font size in the wind plots will be increased to improve the visibility of wind direction. The term "northerly wind anomalies" was used in reference to the coastal region; however, further inland the anomalies exhibit more westerly to northwesterly flow. We will revise the text to consistently refer to these as wind anomalies throughout.
Reviewer comment: L413 – “two distinct” – again, there are only two possible SMB responses, right?
Author’s response: The current wording suggests a range of possibilities; however, there are only two possible outcomes. We will revise the text to more accurately reflect this conclusion.
Reviewer comment: L419 – “deepening” implies temporal evolution
Author’s response: The language will be revised to: “due to the unusually deep low-pressure anomaly in the Pacific.”
Reviewer comment: L419-421 – these two features (low-pressure anomaly in the Pacific and wind anomalies over Wilkes Land) seem far apart spatially – I’m missing the connection here with respect to the circulation?
Author’s response: The low-pressure anomaly appears to direct northwesterly winds toward Dronning Maud Land, rather than specifically over Wilkes Land. However, the co-occurrence of La Niña and a positive SAM phase seems to alter the atmospheric circulation pattern. Instead of the expected zonally symmetric flow over the Antarctic Ice Sheet (AIS), the circulation becomes more asymmetric, resulting in northerly to northwesterly wind anomalies over Wilkes Land. We will revise the paragraph to improve clarity and accurately reflect these circulations.
Reviewer comment: Fig. 6 – again, there needs to be information on the statistical significance of the patterns in this figure, which will presumably support the authors’ claims that different ENSO events are associated with different circulation and surface mass balance patterns.
Author’s response: We agree with this suggestion and will perform a statistical significance test to support the conclusions presented in this study.
Reviewer comment: L430 – Amundsen Sea sector and Marie Byrd Land
Author’s response: We will edit the manuscript accordingly.
Reviewer comment: L446-447 – language suggests causation
Author’s response: The sentence will be rewritten to suggest a correlation rather than causation.
Reviewer comment: L453 – might help to remind readers what the bi-polar pattern is
Author’s response: We will edit the manuscript accordingly.
Reviewer comment: L454 – what is meant by “underlying”? Most common, strongest, dominant?
Author’s response: The “underlying” used here represent the dominant ENSO impact.
Reviewer comment: L470 – “coastal easterlies” – could you clarify this? I see coastal westerly wind anomalies in 4a, c, and d.
Author’s response: There is weaken coastal easterlies (actual winds), which is shown by the observed coastal westerly wind anomalies.
Reviewer comment: L479 – western Ross Sea sector is not mentioned earlier in the text, nor is the Ross ice shelf shown in any figures. Could you clarify what is meant here?
Author’s response: More geographical regions will be included and mention the manuscript going forward.
Reviewer comment: L490 – “the anomalous response can be attributed to altered Rossby wave propagation” – surely Rossby wave propagation influences almost all ENSO-associated circulation patterns around Antarctica?
Author’s response: We will revise to clarify and highlight the differences in the propagation pathways of the Rossby waves during Central versus Eastern Pacific. Rossby wave propagation influences ENSO-associated circulation patterns around Antarctica. However, the source location of Rossby wave trains tends to be 20°–30° farther west during Central Pacific El Niño events compared to Eastern Pacific El Niño events. These differing propagation pathways result in a westward and latitudinal shift of the ASL during Central El Niño events relative to Eastern El Niño events.
Reviewer comment: L524 – “isolating ENSO signals” – I would be careful with stating that you are isolating ENSO signals here, because as was already mentioned, there are a number of different weather patterns and extremes that occurred during the periods over which the circulation and SMB patterns were composited.
Author’s response: We will reword to prevent any potential confusion.
Reviewer comment: L525 – “convergence zone that enhances precipitation” – reference for this? And can you be specific about exactly where you see the convergence occurring? Do you see this in the actual wind fields too, not only the anomalies?
Author’s response: References will be added, and the identified convergence zones will be cross-checked against the actual wind fields.
Reviewer comment: L4545-548 – reference?
Author’s response: A reference will be added to support this statement.
Reviewer comment: L550 – “ASL’s influence on East Antarctica remains unclear” – as mentioned earlier, this implies that there is an influence but we don’t know what it is – is that the conclusion from Li et al. 2022, as cited?
Author’s response: The influence of the ASL is primarily centred over West Antarctica but can also indirectly affect atmospheric circulation over East Antarctica. Zhang et al. (2021) analysed 500 hPa geopotential height anomalies during La Niña periods and suggested that the ASL facilitates moisture advection into East Antarctica. Similarly, our analysis of the 2020–2022 La Niña period shows a comparable pattern, with the ASL advecting north-westerly winds into Dronning Maud Land. Reference changed to Zhang et al. 2021.
Reviewer comment: L559 – can use “significant” if you show statistical significance of mass changes in the figure
Author’s response: That was an incorrect use of the term 'significant' in this context.
Reviewer comment: L574-579 – it’s probably important to add there that it’s equally likely that certain modes of variability and their associated circulation patterns may be conducive to atmospheric river landfall in certain regions.
Author’s response: We are in agreement with this suggestion and will incorporate it into the revised manuscript.
Reviewer comment: L598 – “structure of the westerlies was altered” implies causation, and refers to the winds rather than the wind anomalies.
Author’s response: We will rephrase the wording to indicate a correlation rather than imply causation.
Reviewer comment: Discussion – general comment: this is a very long section, and while it is interesting, I think it comes across as somewhat redundant following the results and before the conclusion. I would recommend shortening it where possible, to make the section more concise and less repetitive.
Author’s response: Thank you for the helpful suggestion. We agree that the Discussion section is a bit long and, at times, overlaps with the Results. We'll work on tightening the section to make it more concise and focused, while still capturing the key interpretations.
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AC2: 'Reply on RC2', John Bright Ayabilah, 14 Jul 2025
Peer review completion
The study presents the impact that different ENSO-induced atmospheric circulation changes have on Antarctic ice sheet mass changes and analyze teleconnections with the southern annular mode. The authors show that there is strong event-to-event spatial variability between ENSO events using GRACE observed mass changes, regional climate model output and ERA5. This work fits well within the scope of the journal and provides a contribution to the field. The manuscript is generally well written, but some paragraphs can be somewhat lengthy. The following comments should help with solving the remaining issues before publication, with e.g. L1 referring to line 1.
General comments:
- Recently, a new version of the regional climate model RACMO2.4p1 was published for the Antarctic ice sheet (Van Dalum et al., 2025, https://doi.org/10.5194/egusphere-2024-3728), which includes new physics (in particular relevant here are changes in precipitation). Importantly, RACMO2.4p1 also has a higher horizontal resolution of 11 km compared to the 27 km resolution used in RACMO2.3p2. Using the SMB of RACMO2.4p1 would improve the comparisons done in this study and I suggest the authors to use this version instead of RACMO2.3p2. RACMO2.4p1 data can be found here: https://doi.org/10.5281/zenodo.14217231
- In the manuscript, basal melting is mentioned but SMB and mass changes are not studied on the ice shelves, hence relating the results to basal melting is difficult. Therefore, consider to include ice shelves in the comparison with RACMO SMB in e.g. Fig. 3b and elsewhere, and if possible also for GRACE, or explain why that cannot be done. Furthermore, it is also interesting to see how the SMB changes over the major ice shelves for each ENSO period.
- I think it is valuable for this study to mention whether an ENSO event is central or eastern and discuss if and how such events differ, as it may explain some of the patterns that are identified in this study and therefore increase understanding. The authors shortly discuss the potential importance in the manuscript, like on L486-495, but I think a more in-depth analysis will improve the manuscript. Other work, like Macha et al. (2024), may provide information about whether an ENSO event is central or eastern, or it can be determined by following methods described by Ren and Jin (2011).
- Not all locations that are discussed in the manuscript are shown on a map, like the Wedell Sea, Ross Sea, location of the ASL or the various ocean sectors. Including the locations mentioned in the manuscript will improve clarity, making it easier to follow.
- Including maps where the SMB changes are shown in percentage of the total SMB for the considered periods will help to understand how big the impact of ENSO/SAM is on the various regions that are considered, as some changes may seem large in for example high precipitation areas, while they are only relatively small. An alternative could be to report the integrated SMB values in Gt yr-1 for the ENSO events for the whole domain and smaller regions and compare them to the reference period.
Specific comments:
L18: As you also use regional climate model output in your study, it should be mentioned in the abstract as well.
L23-26: “… and its influence on the ASL and the Southern Ocean circulation can be equally (and in some cases more) important to AIS variability.” Please specify with respect to what or rephrase this sentence.
Abstract: I think it is also important to shortly mention the uncertainties in the abstract that you also mention in the text, such as the relatively short time period that you use and the various teleconnections that may have not happened yet within this time period, or other processes like atmospheric rivers.
L29-30: “The drivers of inter-annual to decadal Antarctic Ice Sheet (AIS) mass variability are complex and not yet fully understood”. Please add a reference to this.
L35: Not only precipitation, but also riming can add to the SMB.
L43: Can you specify here what typically the time scale is that the SAM changes from positive to negative, or vice versa and why the SAM happens?
L50: Is the total reduction of precipitation in the East AIS typically comparable to the precipitation increase in West Antarctica and the western Antarctic Peninsula? In other words, looking at the AIS as a whole, does a positive SAM increase or decrease the SMB?
L67-75: Please add the location of the ASL, sectors like the Pacific sector, Indian sector etc. and other names in a map (for example in Fig. 2), which would help visualize the processes described the paper.
L76-83: Mention here why your study is different than the studies that you mention.
L87: As GRACE observes mass changes, the mass loss due to processes like runoff and sublimation are also included in the signal and should be mentioned here, even though they are relatively small compared to discharge.
L139: Please mention that the index is normalized in Fig. 1a.
L149: Also mention that the climate indices are detrended in Fig. 1c.
L155-161: Consider moving this paragraph such that it is mentioned before the paragraph of L148-154.
L162-164: “...where the positive phase of ENSO dominates the negative ENSO phase until a positive peak in the cumulative index is reached…”. I think that I know what the authors mean, but consider reformulating this to improve clarity. Also, do you apply a minimum length that an ENSO period has to last?
Fig. 1: Please add a description to the Y-axis of the figures. In Figure 1.d, consider adding ENSO and in Figure 1.e SAM in the top of the figure, which would help reading the figure more quickly.
Section 2.3: It has not been mentioned in the paper before why you want to use a regional climate model and why it is necessary, which should be explained in e.g. the introduction before explaining what regional climate model you are going to use.
L189: .”..at its lateral and ocean boundaries…” → at its lateral boundaries and SST and sea ice extent at the sea surface boundary…
Section 2.4: The authors should mention here why it is necessary to use ERA5 over RACMO output for the 10 m wind speeds and sea level pressure.
L225: Capital letter is missing in ‘key’.
L227-229: Also mention here that you plot ERA5 and RACMO in Figure 3.
Fig. 3: I do not fully understand what is shown here. Is this the SLP and winds, SMB and GRACE mass loss averaged over the ENSO events? If this is the average over the ENSO events, including both El Nino and La Nina, would they not compensate each other?
Fig. 4 and 5: Interpreting the results would be easier if you mention in this figure for each ENSO event whether the SAM index is positive, negative or neutral.
Fig. 4i-l: Do you know why the north-south striping is so much more pronounced in Fig. 4j and Fig. 4l compared to Fig. 4i and Fig. 4k?
L310: Do you mean Fig. 4g instead of Fig. 4c?
L311-312: “Note that the 2002-2005 SMB anomaly is only marginally positive (Fig. 4a).” → Note that the 2002-2005 SMB anomaly is only marginally positive for the Antarctic Peninsula (Fig. 4e).
L313, 314: Fig. 4f → Fig 4f, h and also Fig. 4j → Fig. 4j, l.
L323: Please also show these sectors on a map, e.g. Fig. 2.
L330-353: Link the pressure anomalies and wind changes to moisture transport and their consequent impact on SMB and mass changes. These paragraphs can also be shortened.
L380-381: Fig. 5f, g-h → Fig 5f-h and also Fig. 5j, k-l → Fig. 5j-l
L385-387: Can you explain more how the northerly winds from the Pacific and southerly winds from the continent can lead to convection? And how it may result in positive mass anomalies?
L393-398: Similarly as before, link the pressure and wind anomalies to moisture transport and then to SMB and mass changes.
L421-426: How much of the 2020-2022 La Nina SMB signal is caused by this atmospheric river event? Is it possible that it is (almost) completely dominated by it?
Fig. 6: How did you calculate the average of the anomalies shown here? Did you weigh them by the length of the El Nino or La Nina-dominated periods? Or did you simply take the average of the maps that you have shown in Fig. 4 and 5?
459-461: Can you elaborate about these unusual climate dynamics? Does this have any impact on ENSO/SAM related SMB changes that you have discussed in the paper?
L474-476: I am not sure if I fully understand how your results support the findings that increased basal melt is compensated by higher SMB. If I am not mistaken, you do not include ice shelves in your analysis where basal melt can occur, so how do you know that the positive SMB anomalies and increased mass that you show compensate for increased basal melt?
L477: “… El Nino-dominated period in the Amundsen sector differ” → “… El Nino-dominated periods in the Amundsen sector differs”
L483-485: As you include the complete events, doesn’t it make your methods more vulnerable for irregular events, such as atmospheric rivers, that may overshadow the ENSO signals?
L508-510: Considering moving this to the la nina part.
L524: “tie” → “tied”
L550-551: “ENSO impacts West Antarctica through modulation of the ASL via Rossby wave propagation, though the ASL’s influence on East Antarctica remains unclear”, please add a reference to this.
L583-585: Consider reformulating this sentence.
L595: The reference to Fig. 1c seems to be larger than the surrounding text.
L631: “However, the timescale of the response of the upstream ice to the positive SAM forcing is unclear and would involve a substantial lag”. Please also describe how substantial this lag is what it would mean to the GRACE signal that you have used in this study.
L649: “This dynamical signal is stronger in West than in East Antarctica.”. Add a citation to this.
L 658-659: The authors should add the time period that is considered in this study here. Also mention that you used ERA5 and RACMO.
L676-683: As it is the last concluding paragraph of the paper, remove references to figures and citations in this paragraph.
L676-683: Similar to my comment about the abstract, consider to shortly mention the uncertainties that have been discussed, such as the relatively short time period that you use and the various teleconnections that may have not happened yet within this time period, or other processes like atmospheric rivers.
L690: This citation does not lead to the correct RACMO2.3p2 SMB data, as it refers to a newer version of RACMO: RACMO2.3p3.