09:15 〜 09:30
[MIS20-02] Hot-water drilling and subglacial measurement at Langhovde Glacier in East Antarctica
キーワード：南極、氷河、熱水掘削、接地線、棚氷
The Antarctic ice sheet is losing mass under the influence of increasing rates of iceshelf basal melting and ice discharge into the ocean. Acceleration of outlet glaciers is a key to project future evolution of the ice sheet, as well as to understand the mechanism driving ongoing changes. Ice dynamics and its variations are controlled by subglacial process, such as basal sliding and sediment deformation that are affected by basal water pressure. Nevertheless, in-situ data from subglacial measurement are sparse because access to the glacier bed is difficult. To investigate subglacial conditions and ice dynamics of an Antarctic outlet glacier, we performed hot-water drilling and subglacial measurement at 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 was the focus of our previous drilling campaigns in 2011/12 and 2017/18 (Sugiyama et al., 2014; Minowa et al., 2021). During the 2021/22 austral summer season, we drilled five boreholes at three locations in the upper reaches from the previous drilling sites. These drilling sites are distributed near the grounding line, including the upper most site situated approximately 1 km upglacier from the grounding line.
By using a hot-water drilling system, two 550-m long bottom reaching boreholes were drilled at the upper most drilling site (Boreholes 1-3 in Figure 1). One borehole was equipped with a ploughmeter (three-axis accelerometer and water pressure sensor) at the glacier bed, whereas the other one was used for installation of a water pressure sensor at the bed and seven thermistors for ice temperature measurement. A 200-m long borehole was drilled at the same location for englacial installation of a borehole seismometer. In close vicinity of the grounding line, a water pressure sensor was installed at 470 m below the ice surface in a 2-m thick sea-water cavity (Borehole 5 in Figure 4). These boreholes were inspected by a borehole video camera and a conductivity/temperature/depth profiler. On the glacier surface and nearby mountain peaks, GNSS receivers, seismometers and timelapse cameras were installed to monitor the glacier motion (Figure 1).
Water pressure at the glacier bed showed short-term fluctuations in response to atmospheric conditions as well as ocean tides. This result evinced that subglacial environment was hydraulically connected to the surface and to the ocean. The pressure variations were associated with changes in surface ice motion to the horizontal and vertical directions. Therefore, ice dynamics of Langhovde Glacier is connected to the glacier surface and ocean conditions through subglacial hydraulics. Inner-most part of the subshelf cavity at Borehole 5 was filled with cold water (<−2 degree C) and inhabited by fauna similar to sea anemone and stalked taxa. This observation provides unique information to understand subshelf environment very close to the grounding line.
In the presentation, we introduce the overview of the field campaign and report initial results of the subglacial observations.
Acknowledgement:
The field activity on Langhovde Glacier was a scientific program of the 63rd Japanese Antarctic Research Expedition (JARE63). The research was funded by the Research of Ocean-ice BOundary InTeraction and Change around Antarctica (ROBOTICA) project under the JARE framework, JSPS KAKENHI Grant Number JP17H06316 (2017–2022) and 20H00186 (2020–2025). The authors acknowledge the support in the field by JARE63 and JARE62 members with special thanks to Akira Watanabe for his contribution to the drilling activity.
References:
Minowa, M., S. Sugiyama, M. Ito, S. Yamane and S. Aoki. 2021. Thermohaline structure and circulation beneath the Langhovde Glacier ice shelf in East Antarctica. Nature Communications, 12, 3929.
Sugiyama, S., T. Sawagaki, T. Fukuda and S. Aoki. 2014. Active water exchange and life near the grounding line of an Antarctic outlet glacier. Earth and Planetary Science Letters, 399C, 52-60.
Figure 1. Satellite image of Langhovde Glacier (Landsat 8 on January 23, 2020), showing he locations of the boreholes and instruments for surface measurements.
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 was the focus of our previous drilling campaigns in 2011/12 and 2017/18 (Sugiyama et al., 2014; Minowa et al., 2021). During the 2021/22 austral summer season, we drilled five boreholes at three locations in the upper reaches from the previous drilling sites. These drilling sites are distributed near the grounding line, including the upper most site situated approximately 1 km upglacier from the grounding line.
By using a hot-water drilling system, two 550-m long bottom reaching boreholes were drilled at the upper most drilling site (Boreholes 1-3 in Figure 1). One borehole was equipped with a ploughmeter (three-axis accelerometer and water pressure sensor) at the glacier bed, whereas the other one was used for installation of a water pressure sensor at the bed and seven thermistors for ice temperature measurement. A 200-m long borehole was drilled at the same location for englacial installation of a borehole seismometer. In close vicinity of the grounding line, a water pressure sensor was installed at 470 m below the ice surface in a 2-m thick sea-water cavity (Borehole 5 in Figure 4). These boreholes were inspected by a borehole video camera and a conductivity/temperature/depth profiler. On the glacier surface and nearby mountain peaks, GNSS receivers, seismometers and timelapse cameras were installed to monitor the glacier motion (Figure 1).
Water pressure at the glacier bed showed short-term fluctuations in response to atmospheric conditions as well as ocean tides. This result evinced that subglacial environment was hydraulically connected to the surface and to the ocean. The pressure variations were associated with changes in surface ice motion to the horizontal and vertical directions. Therefore, ice dynamics of Langhovde Glacier is connected to the glacier surface and ocean conditions through subglacial hydraulics. Inner-most part of the subshelf cavity at Borehole 5 was filled with cold water (<−2 degree C) and inhabited by fauna similar to sea anemone and stalked taxa. This observation provides unique information to understand subshelf environment very close to the grounding line.
In the presentation, we introduce the overview of the field campaign and report initial results of the subglacial observations.
Acknowledgement:
The field activity on Langhovde Glacier was a scientific program of the 63rd Japanese Antarctic Research Expedition (JARE63). The research was funded by the Research of Ocean-ice BOundary InTeraction and Change around Antarctica (ROBOTICA) project under the JARE framework, JSPS KAKENHI Grant Number JP17H06316 (2017–2022) and 20H00186 (2020–2025). The authors acknowledge the support in the field by JARE63 and JARE62 members with special thanks to Akira Watanabe for his contribution to the drilling activity.
References:
Minowa, M., S. Sugiyama, M. Ito, S. Yamane and S. Aoki. 2021. Thermohaline structure and circulation beneath the Langhovde Glacier ice shelf in East Antarctica. Nature Communications, 12, 3929.
Sugiyama, S., T. Sawagaki, T. Fukuda and S. Aoki. 2014. Active water exchange and life near the grounding line of an Antarctic outlet glacier. Earth and Planetary Science Letters, 399C, 52-60.
Figure 1. Satellite image of Langhovde Glacier (Landsat 8 on January 23, 2020), showing he locations of the boreholes and instruments for surface measurements.