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Recent and imminent calving events do little to impair Amery ice shelf’s stability
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Teng Li1, 4, Yan Liu1, 3, 4, *, Xiao Cheng2, 3, 4
Acta Oceanologica Sinica | 2020, 39(5) : 168 - 170
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Acta Oceanologica Sinica | 2020, 39(5): 168-170
• News and Views •
Recent and imminent calving events do little to impair Amery ice shelf’s stability
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Teng Li1, 4, Yan Liu1, 3, 4, *, Xiao Cheng2, 3, 4
Affiliations
  • 1 College of Global Change and Earth System Science , and State Key Laboratory of Remote Sensing Science, Beijing Normal University, Beijing 100875, China
  • 2 School of Geospatial Engineering and Science, Sun Yat-Sen University, Zhuhai 519000, China
  • 3 Southern Marine Science and Engineering Guangdong Laboratory, Zhuhai 519000, China
  • 4 University Corporation for Polar Research (UCPR), Beijing 100875, China
Published: 2020-05-25 doi: 10.1007/s13131-020-1600-6
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Teng Li, Yan Liu, Xiao Cheng. Recent and imminent calving events do little to impair Amery ice shelf’s stability[J]. Acta Oceanologica Sinica, 2020 , 39 (5) : 168 -170 . DOI: 10.1007/s13131-020-1600-6
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Accounting for about half of mass loss in Antarctic, glacier calving is an important ablation process for the ice sheet (Liu et al., 2015). Thanks to the revolutionized era of satellite remote sensing, the 21st century witnessed dozens of prominent calving events. However, calving could occur as a natural behavior of the glacier to maintain itself in a steady state, rather than forced by external environment factors.
At the end of September 2019, another spectacular calving event took place in East Antarctic, shedding an iceberg coded as D28 from the Amery Ice Shelf (the AIS, see Fig. 1). Considering the 60–70 year’s calving cycle of the AIS and it has been 56 years since last separation in 1963–1964 (Fricker et al., 2002), we propose the recent and imminent calvings are part of the normal advance-retreat-advance loop, therefore would not do harm to its balance state. To test the above hypothesis, this study quantifies the dynamic response of the AIS to these events by a set of modeling experiments.
The two-dimensional finite-element ice flow model Úa is employed as the experiment platform (Gudmundsson, 2013). To capture the stream-shelf flow dynamics, we select Shallow Shelf Approximation (SSA) with refined unstructured mesh up to 500 m nearby the grounding line. A group of five simulations is conducted, with the first inverse and second control run to eliminate the residual effect of initialization. Afterward the other three calving runs are implemented to mimic the gradual recession of the AIS front, with each following the previous one subsequently after 15 years.
Three diagnostic variables, i.e. volume-above-flotation (VAF), grounded area and discharge flux, are selected to represent the system dynamics, and their temporal evolution are displayed in Fig. 2. For VAF, a clear decrease trend can be detected after each one of three events, with the later one declining at a steeper slope consequently ending up with a lower value. Similar patterns appear in Figs 2b and c as well, but with noise fluctuations superimposed on the general decrease or increase background.
Of particular interest is the reverse trend in the last 5 years for both grounded area and flux. This consistent behavior for all three runs implies they are highly correlated and constrained by the parallel stress regime. In terms of absolute magnitude, the calving3 at the end of the run can lead up to about 4 Gt of VAF, 60 km2 of grounded area, and 1 Gt/a of flux as the response to all three calvings in a full cycle. On one hand, by comparing four transient runs our model is able to differentiate the responses of the AIS for each calving in the computation domain. On the other hand, such discrepancies are too weak to be detected by satellite in the physical world. For example, Zhou et al. (2019) quantified the latest flux as (61±5) Gt/a. While our modeling estimations (56–58 Gt/a) fall within such interval, even the largest difference among each other (1 Gt) is well below statistical uncertainty (5 Gt).
To illustrate the spatial-varying backstress exerted on the remaining ice shelf, we also predicted the ice thickness changes and flow acceleration. Dynamic thinning causes mass re-distribution thus associated surface elevation changes. The thinning mainly spreads within 100 km upstream of calving1, with a quantity of about 2 m after 40 years. Such scale is beyond the detection capability of modern space altimetry, and the variation should be muted into the basal melting signal. Such dynamic responses also express as the acceleration in a more concentrated way. The outlet of calving1 enhance adjacent velocity by 50–70 m/a, but barely noticeable further upstream. Thanks to the funneling geometry and the accompanying greater lateral drag, the front sectors exert minimal backstress to upstream ice flow, although every potential iceberg blocks do serve as the buttressing plug. With that said, geometry changes in the outer boundary essentially have limited influence on glacier dynamics.
With the bedrock underlie at 550–800 m below the AIS front, there is no potential rumple acting as a sticky point nearby. Therefore we infer the AIS can still restructure itself in a healthy state even experiencing further retreat before the Gillock Island; in other words, the AIS has at least 150 km "safe distance" upstream, which agrees with the findings from the progressive retreat (Gong et al., 2014).
In this study we attempt to assess the effects of the latest and impending iceberg calving on AIS. Given the order of magnitude and spatial distribution of response signals make sense, we assume they are directly resulted from the physical variations rather than the numerical artifacts. Not unexpectedly, we find that velocity acceleration (70 m/a), grounding line retreat (–60 km2), thinning (–2 m) and dynamic mass loss (–4 Gt) all occur as the responses for the front cutting-off. Although our model can resolve such tiny reactions, from a pragmatic point of view, we doubt whether they are measurable by contemporary observational technology if considering uncertainties.
The main argument that there is no direct link between presented calving events and global climate change, is also in accordance with the researcher’s opinions from Scripps Institution of Oceanography (Amos, 2019). Despite that the AIS front appears much like its "passive" counterpart in Larsen-C Ice Shelf (Hogg and Gudmundsson, 2017), the response of the remaining section is linked with how strongly the removed iceberg restrained ice flow upstream. This kind of structural support depends on particular bedrock topography in a complex spatio-temporal evolution, which suggests our analysis is fairly case-by-case and cannot be over-interpreted.
Based on the above discussion, we conclude that front geometry variations do not noticeably affect the holistic integrity of the AIS. Combining with the fact that the AIS has appeared roughly in balance with its surroundings ever since 1970 (King et al., 2009), we can safely infer these calving events are natural phenomena rather than an indicator of climate change. Since little information is available about the last major calving about 60 years ago, these events (would) still offer us an excellent opportunity to understand what is starting to happen within one complete calving cycle. In fact, since D28 could pose a threat for shipping, most polar-orbit satellites will keep tracking this particular area, and we would collect relevant data for further investigation.
Acknowledgements
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We greatly thank ESA for providing Sentinel-1 satellite radar imagery (https://scihub.copernicus.eu/), NSIDC for providing the MOA, MEaSUREs and grounding line datasets (https://nsidc.org). The Úa ice flow program is freely available as open-source code from https://github.com/GHilmarG/UaSource. Gratitude ought to be expressed to Hilmar Gudmundsson at Northumbria University for the software support.
Funding
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  • The National Natural Science Foundation of China under contract Nos 41830536, 41925027 and 41676182; the UK-China Joint Research and Innovation Partnership Fund PhD Placement Program of China Scholarship Council (CSC).
References
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Amos J. 2019. 315 billion-tonne iceberg breaks off Antarctica. https://www.bbc.co.uk/news/science-environment-49885450. [2020-03-15]
Fricker H A, Young N W, Allison I, et al. 2002. Iceberg calving from the Amery ice shelf, East Antarctica. Annals of Glaciology, (34): 241–246, doi: 10.3189/172756402781817581
Gong Y, Cornford S L, Payne A J. 2014. Modelling the response of the Lambert Glacier-Amery ice shelf system, East Antarctica, to uncertain climate forcing over the 21st and 22nd centuries. The Cryosphere, 8(3): 1057–1068, doi: 10.5194/tc-8-1057-2014
Gudmundsson G H. 2013. Ice-shelf buttressing and the stability of marine ice sheets. The Cryosphere, 7(2): 647–655, doi: 10.5194/tc-7-647-2013
Hogg A E, Gudmundsson G H. 2017. Impacts of the Larsen-c ice shelf calving event. Nature Climate Change, 7(8): 540–542, doi: 10.1038/nclimate3359
King M A, Coleman R, Freemantle A, et al. 2009. A 4-decade record of elevation change of the Amery ice shelf, East Antarctica. Journal of Geophysical Research, 114(F01010): 1–13, doi: 10.1029/2008jf001094
Liu Y, Moore J C, Cheng X, et al. 2015. Ocean-driven thinning enhances iceberg calving and retreat of Antarctic ice shelves. Proceedings of the National Academy of Sciences, 112(11): 3263–3268, doi: 10.1073/pnas.1415137112
Zhou C, Liang Q, Chen Y, et al. 2019. Mass balance assessment of the Amery ice shelf basin, East Aantarctica. Earth and Space Science, 6(10): 1987–1999, doi: 10.1029/2019ea000596
Appendix
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Year 2020 volume 39 Issue 5
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37
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Article Info
doi: 10.1007/s13131-020-1600-6
  • Receive Date：2020-03-03
  • Online Date：2026-03-31
  • Published：2020-05-25
Article Data
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History
  • Received：2020-03-03
  • Accepted：2020-03-18
Funding
The National Natural Science Foundation of China under contract Nos 41830536, 41925027 and 41676182; the UK-China Joint Research and Innovation Partnership Fund PhD Placement Program of China Scholarship Council (CSC).
Affiliations
    1 College of Global Change and Earth System Science , and State Key Laboratory of Remote Sensing Science, Beijing Normal University, Beijing 100875, China
    2 School of Geospatial Engineering and Science, Sun Yat-Sen University, Zhuhai 519000, China
    3 Southern Marine Science and Engineering Guangdong Laboratory, Zhuhai 519000, China
    4 University Corporation for Polar Research (UCPR), Beijing 100875, China

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表12种不同金属材料的力学参数
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Family		 属数
Number of
genus		 种数
Number of
species		 占总种数比例
Percentage of
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Genus		 种数
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鹅膏菌科Amanitaceae 2 11 5.26 鹅膏菌属 Amanita 10 4.78
小菇科 Mycenaceae 2 12 5.74 丝盖伞属 Inocybe 5 2.39
多孔菌科 Polyporaceae 8 14 6.70 蜡蘑属 Laccaria 5 2.39
红菇科 Russulaceae 3 23 11.00 小皮伞属 Marasmius 6 2.87
小菇属 Mycena 11 5.26
光柄菇属 Pluteus 5 2.39
红菇属 Russula 17 8.13
栓菌属 Trametes 5 2.39
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