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1 0 0 0 OA Acceleration and retreat of Langhovde Glacier, East Antarctica, after the breakup of land-fast sea ice in 2016

著者: 近藤研杉山慎
雑誌: JpGU-AGU Joint Meeting 2020
巻号頁・発行日: 2020-03-13

The Antarctic ice sheet drains ice into the ocean through floating ice shelves and outlet glaciers, which play key roles in the mass balance of the Antarctic ice sheet. Since iceberg calving and ice shelf basal melting are major ablation processes of the ice sheet, understanging the dynamics of floating ice is important. Land-fast sea ice affects the stability of ice shelves by exerting battressing force on the ice front. For example, previous studies reported glacier front retreat, disintegration of ice shelves and ice flow acceleration after breakup of sea ice in front of glaciers (e.g. Miles et al., 2017). Lützow-Holm Bay located in East Antarctica is usually covered with land-fast sea ice all year round, but a large portion of sea ice broke up in April 2016 (Aoki et al., 2017). In order to investigate the impact of the sea ice break up on outlet glaciers in the region, we carried out satellite observations on Langhovde Glacier, one of the outlet glaciers terminating in Lützow-Holm Bay. Glacier terminus position was deliniated from 2000 to 2020, using Landsat 7 Enhanced Thematic Mapper Plus (ETM+) and Landsat 8 Operational Land Imager (OLI) imagery. Changes in glacier surface area near the calving front were devided by the width of the calving front to obtain mean retreat/advance distance. Ice flow velocity field from 2014 to 2020 was measured, by applying a feature tracking method (Sakakibara and Sugiyama, 2014) to Landsat 8 OLI image pairs.Terminus position has been relatively stable from 2000 to 2012, with only small fluctuations within a range of 200 m. The glacier then advanced by 400 m from 2012 to 2016. After 2016, the year of the land-fast sea ice break up, the terminus retreated rapidly by 720 m by 2020 as a result of large calving events in 2016 and 2019. The glacier front reached the most retreated position since 2000. After the sea ice breakup, ice speed increased from 110 m a−1 in 2017 to 135 m a−1 in 2019. The results of this study suggest the glacier had been stabilized by the land-fast sea ice by 2016. Rapid retreat and acceleration after the breakeup indicate significant influence of sea ice on the dynamics of outlet glaciers in Antarctica.ReferencesMiles, B.W.J. and Stokes, C.R. and Jamieson, S.S.R (2017), Simultaneous disintegration of outlet glaciers in Porpoise Bay (Wilkes Land), East Antarctica, driven by sea ice break-up, The Cryosphere, 11, 427-442.Aoki, S. (2017), Breakup of land-fast sea ice in Lützow-Holm Bay, East Antarctica, and its teleconnection to tropical Pacific sea surface temperatures, Geophys. Res. Lett., 44, 3219–3227.Sakakibara, D., and S. Sugiyama (2014), Ice-front variations and speed changes of calving glaciers in the Southern Patagonia Icefield from 1984 to 2011, J. Geophys. Res. Earth Surf., 119, 2541–2554.

2020-07-16 10:18:59
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https://confit.atlas.jp/guide/event/jpgu2020/subject/MIS15-P19/detail

1 0 0 0 OA <strong>Surface elevation changes of glaciers along the coast of Prudhoe Land, northwestern Greenland, from 1985 to 2018</strong>

著者: YEFAN WANG Shin Sugiyama Daiki Sakakibara
雑誌: JpGU-AGU Joint Meeting 2020
巻号頁・発行日: 2020-03-13

In recent decades, the Greenland Ice Sheet has been a major contributor to global sea-level rise as a consequence of accelerating mass loss. Numerous studies have described spatiotemporal heterogeneity in glacier terminus retreat, flow speed variations, surface elevation change in a scale covering the entire ice sheet. However, details of the changes and heterogeneity of individual glaciers remain uncertain. Therefore, detailed investigations in a finer spatial scale are required. Here we show the surface elevation changes of 16 outlet glaciers along the coast of Prudhoe Land, northwestern Greenland, derived from multi-source DEMs (digital elevation models) (1985 (t0) aerial photograph DEM, ASTER DEMs in 2001–2003 (t1) and 2016–2018 (t2)), for the last 30 years.We observed a mean surface lowering rate of −0.55±0.22 m a−1 over the past three decades (t0–t2) for the whole studied glaciers. The most rapid surface lowering (−3.08 m a−1) was observed near the glacier termini (elevation band 0–50 m), and the slowest surface lowering rate (−0.14 m a−1) is found on the elevation band 800–850 m. The rates varied among the periods. The mean rate showed a slightly positive value of 0.14±0.16 m a−1 during t0 – t1, and no distinct altitudinal variations was observed in this period. Strongly negative elevation change rates (−1.31±0.19 m a−1) were detected during the second subperiod (t1– t2). The most rapid thinning (−5.47 m a−1) occurred near the frontal areas (elevation band 0–50 m), and slower but significant thinning at a rate −0.57 m a−1 was observed inland areas (elevation band 800–850 m). For individual glaciers, most glaciers have exhibited no significant change or slight surface thickening during the period t0 – t1. Obvious thinning happened only in the frontal areas of Tracy, Farquhar, Sharp and Sun Glaciers. During the period t1– t2, all the studied glaciers experienced thinning in different magnitudes. Tracy (−3.91±0.12 m a−1) and Farquhar (−2.91±0.15 m a−1) Glaciers experienced most significant thinning, while Heilprin Glacier, adjacent to Tracy, showed a moderate thinning rate (−0.51±0.12 m a−1). Interestingly, there is no obvious change at Verhoeff Glacier both in t0 – t1 and t1– t2. Outlet glaciers terminating in Inglefield Bredning showed a mean thinning rate of −1.07 ± 0.18 m a−1, which was 67% greater than those of glaciers terminating in Baffin Bay (−0.64 ± 0.24 m a−1) during t1–t2.The elevation changes are generally correlated with atmospheric and oceanic warming in the region. Nevertheless, considerably large heterogeneity was observed among individual glaciers, which may be attributed to the control of the fjord bathymetry and glacier bed topography on the submarine melting and ice dynamics.

2020-07-16 10:17:49
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https://confit.atlas.jp/guide/event/jpgu2020/subject/ACG57-P06/detail

1 0 0 0 OA Reduced mass loss from the Greenland ice sheet under stratospheric aerosol injection

著者: Ralf Greve John C. Moore Thomas Zwinger Chao Yue Liyun Zhao
雑誌: JpGU-AGU Joint Meeting 2020
巻号頁・発行日: 2020-03-13

Sea level rise from the ice sheets is one of the chief impacts of greenhouse gas emissions. The Greenland ice sheet is expected to contribute some ten centimetres to ~1 metre of global sea level equivalent (SLE) this century (Goelzer et al., 2020, doi: 10.5194/tc-2019-319). In the longer term, Greenland will likely lose more than 90% of its ice sheet unless summer temperatures are kept to less than 2°C above pre-industrial levels (Pattyn et al., 2018, doi: 10.1038/s41558-018-0305-8). Stratospheric aerosol injection (SAI) has been proposed as a potential method of meeting the IPCC 1.5°C or 2°C global temperature rise targets. In this study, we use the SICOPOLIS (www.sicopolis.net) and Elmer/Ice (elmerice.elmerfem.org) dynamic models driven by changes in surface mass balance and temperature to estimate the sea level rise contribution from the Greenland ice sheet under the IPCC RCP4.5, RCP8.5 and GeoMIP G4 (Kravitz et al., 2013, doi: 10.1002/2013JD020569) scenarios. The G4 scenario adds 5 Tg/yr sulfate aerosols to the equatorial lower stratosphere (equivalent of ~1/4 of the 1991 Mt. Pinatubo SO2 emission rate) to the IPCC RCP4.5 scenario, which itself approximates to the Paris NDC (Nationally Determined Contributions) greenhouse gas emission commitments. The figure shows the mass loss of the Greenland ice sheet under the three scenarios with four earth system models (BNU-ESM, HadGEM2-ES, MIROC-ESM, MIROC-ESM-CHEM), simulated with the SICOPOLIS model. Relative to a constant-climate control run (ctrl_proj), the losses from 2015 to 2090 are 63 [53, 76] mm SLE for RCP8.5, 45 [38, 52] mm SLE for RCP4.5 and 28 [18, 38] mm SLE for G4 (mean and full range). Thus, the mean mass loss under G4 is about 38% smaller than that under RCP4.5 and 55% smaller than that under RCP8.5. We aim to repeat all simulations with the full-stress Elmer/Ice model to assess model-induced uncertainty.