the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 13 Nov 2024
Satellite data reveal details of glacial isostatic adjustment in the Amundsen Sea Embayment, West Antarctica
Abstract. The instability of the West Antarctic ice sheet (WAIS) is a tipping element in the climate system and it is mainly dictated by changes in the ice flow behavior of the outflow glaciers in the Amundsen Sea Embayment (ASE). Recent studies postulated that vertical uplift of bedrock can delay the collapse of glaciers in this region. In West Antarctica, bedrock motion is largely caused by a fast viscoelastic response of the upper mantle to changes in ice loads during the last centuries. This glacial isostatic adjustment (GIA) effect is poorly understood so far, since Earth's rheology and the ice-loading history are both subject to large uncertainties in simulations. Moreover, results from data-driven approaches have not yet resolved GIA at a sufficient spatial resolution. We present a data-driven GIA estimate, based on data from GRACE/GRACE-FO, CryoSat-2 altimetry, regional climate modelling, and firn modelling, that is the first to agree with independent GNSS-derived vertical velocities in West Antarctica. Our data combination yields a maximum GIA bedrock-motion rate of 43 ± 7 mm a-1 in the Thwaites Glacier region and agrees within uncertainties of the GNSS-derived rate. The data-driven present-day GIA result may be used in future simulation runs to quantify a potential delay of the collapse of the West Antarctic ice sheet due to the stabilization effects induced by GIA. Furthermore it may be used for testing rheological models with a low upper-mantle viscosity in conjunction with centennial loading histories.
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RC1: 'Comment on egusphere-2024-3086', Matt King, 16 Dec 2024
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The authors present an analysis of altimetry, GRACE and firn datasets using a much-improved methodology in the Amundsen Sea area and produce estimates of GIA bedrock uplift that are spatially continuous. This work is a substantial advance on prior work by others and produces the first realistic spatially continuous GIA uplift field as verified by GNSS time series in the Amundsen Sea Embayment. It is a significant and exciting result that will be critical in advancing understanding of GIA in this region, and by result ice sheet mass change. The technique will be relevant for application in other regions.
The paper is generally very well written and the figures are well drawn. My only substantial comments regard a desire for a little more discussion or detail on a few key points. There are a few sentences where I did not understand the meaning and I suggest these are rewritten.
Methodology:
Please add a note on the origin of the various frames of GPS and the empirical model.
I was also very confused by the text before Equation 2 and Eq2 also. The first part of equation 2 is the daily formal errors. These are well known to be over-optimistic but also entirely dependent on choices in the analysis that are subjective. How were these scaled? The first part of Eq2 sums these in quadrature but there is no multiplier of 1/D. Is that correct? I do not understand the rationale for the two components of Eq2 so a larger explanation would be welcome.
P9L5: I was unsure if the spatial mask is exactly the values of Riva et al or something else 'according to' is ambiguous.
Section 4: please define the meaning of Gaussian width. there are various definitions used such as half height or 6 sigma or 1 sigma.
Discussion: please come back to the potential origin of the bias with the GNSS of ~1mm/yr. Where may this come from? Some informed speculation is appropriate. Please also discuss a little more what GIA modelling went into the Riva mask and if that explored low viscosity mantle and if not, what impact that could have.
General: I think spatial high resolution is not the right term but spatially continuous. Consider changing throughout.
Detailed remarks
P2L5 add the Gomez et al 2024 study (Science Advances)
P6L5-7 I did not understand what was meant here.
P6 L23 "At some" -> "Some"
P13L21 should be Fig S4 I think
P13L39 please repeat the data period given the trend is limited to that for IMC
P5L6 well, it is tuned to GNSS in terms of filter width
P15L8 this sentence is only for ASE. I note Wolstencroft et al found good agreement in the southern peninsula, updated by Koulali et al 2023
L16L6 'as a the'
P16L10 add bedrock locations to Fig4c? and 100W meridian?
P18L7 not sure what 'no dominant magnitudes of viscous effects' means
Data: need link to GNSS
Matt King, Dec 16, 2024
Citation: https://doi.org/10.5194/egusphere-2024-3086-RC1 -
RC2: 'Comment on egusphere-2024-3086', Anonymous Referee #2, 17 Dec 2024
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“Satellite data reveal details of glacial isostatic adjustment in the Amundsen Sea Embayment, West Antarctica” by Matthias Willen and co-authors.
Summary:
The authors present a data-driven GIA estimate for West Antarctica, with focus on the Amundsen Sea Embayment, using a combination of GRACE/FO, CryoSat2, regional climate modelling and firn modelling. They compare their results with GNSS vertical velocities and find agreement within the uncertainties. The authors present the improvements in the methods of deriving a data-driven GIA estimate, with the results predicting twice as much GIA uplift as previous methods. The content of the paper is significant. It is of particular note that the authors present time series of data-derived GIA uplift rather than rates, highlighting that time series may reveal short-term changes. The paper is well-written, and my comments relate to clarifications needed in the text.
Comments:
Throughout: where the text mentions “GIA result” or “estimated present-day GIA” e.g. p18,L15, it would be better to clarify which part of GIA you’re talking about. GIA uplift, or GIA-related mass changes etc. There are several places where this clarification would be beneficial.
Pg1L12: “GIA result” – do you mean bedrock uplift?
Pg2L5: is Groh et al 2012 the right reference here?
Pg2L16: “Global GIA models” change to “Global 1D GIA models”
Figure 1c: It would be useful to be able to see on this map which GNSS are continuous, and which are campaign. I suggest using a different symbol for each.
Pg7L8: “GIA effects” what specific effects – GIA related mass change? Uplift?
Pg9L9: “based on findings from GIA modelling” What GIA modelling? This could do with some further explanation as Figure S2 also does not clarify. Also, previous line – “GIA at each location” do you mean the 20x20km grid, or what locations?
Pg15L28: how low is the upper mantle viscosity used in that study?
Pg15L29 – correct reference format
Pg16L2: “GIA rates” > “GIA uplift rates”
Pg16L6: remove “but” or “however”
Pg18L7-10: not sure I understand– “no dominant magnitudes” – also I would expect to see viscous effects on a 10-year time scale in the ASE due to low viscosity.
Citation: https://doi.org/10.5194/egusphere-2024-3086-RC2
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