- 著者
- Shin Sugiyama Masahiro Minowa
- 雑誌
- JpGU-AGU Joint Meeting 2020
- 巻号頁・発行日
- 2020-03-13
Subglacial environment of the Antarctic ice sheet is one of the least investigated areas on the Earth. Base of the ice sheet forms an important boundary, which controls ice dynamics and thermal conditions. Existence of subglacial channels and lakes poses important questions about basal hydrology and microbial ecosystem under several-kilometer-thick ice. Recent mass loss of the ice sheet is driven by the melting of ice shelves, which occurs at the basal boundary of floating ice. Sensing physical properties beneath the ice is possible by using seismic and electromagnetic waves, but in-situ measurements and sampling are required to answer many of the questions. Hot-water drilling is a powerful tool to provide an access to the bed of glaciers and ice sheets. In this contribution, I introduce recent progress in our understanding of subglacial environment of the Antarctic ice sheet based on direct observations through boreholes, including our project in Langhovde Glacier in East Antarctica.Langhovde Glacier is a 3-km wide outlet glacier located 20 km south of the Japanese Syowa Station in East Antarctica. Lower 2–3 km of the glacier forms a floating tongue, which feeds into the Lützow-holm bay. To study basal melting and subshelf ocean environment, we drilled four boreholes in January 2018 using a hot-water drilling system. The boreholes were utilized to measure spatial variations of temperature, salinity and current under the ice. Two of the boreholes were equipped with a temperature and CTD/current sensors for year-round observations. Potential temperature of the seawater underneath the ice was between −1.4 and −1.1°C, approximately 1°C warmer than the freezing temperature. Water temperature within several hundred meters from the grounding line was −1.2°C in January 2018. Temperature dropped to −1.6°C from January to May, which was followed by gradual warming to −1.55°C in December. The temperature in January 2018 (−1.2°C) was significantly warmer than that in the summer 2019 (−1.55°C), as well as temperature measured at the same location in 2012 and 2013 (−1.55°C). A possible interpretation of the unusually warm water in 2018 was break-up of land-fast sea ice in the Lützow-holm bay in 2016. Presumably, open water near the glacier front facilitated transport of heat to the grounding line. Our subshelf observations implied significant amount of basal melting occurs under the entire ice shelf of Langhove Glacier, and thermal conditions near the grounding line is susceptible to changes in the ocean.
- 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.