Research Activities

High-resolution subglacial topography around Dome Fuji, Antarctica, based on ground-based radar surveys

The retrieval of continuous ice core records of more than 1 Myr is an important challenge in palaeo-climatology. For identifying suitable sites for drilling such ice, the knowledge of the subglacial topography and englacial layering is crucial. For this purpose, extensive ground-based ice radar surveys were done over Dome Fuji in the East Antarctic plateau during the 2017–2018 and 2018–2019 austral summers by the Japanese Antarctic Research Expedition, on the basis of ground-based radar surveys conducted over the previous ~30 years. High-gain Yagi antennae were used to improve the antenna beam directivity thereby significantly decreasing hyperbolic features of unfocussed along-track diffraction hyperbolae in the echoes from mountainous ice-bedrock interfaces. We combined the new ice thickness data with the previous ground-based data, recorded since the 1980s, to generate an accurate high-spatial-resolution (up to 0.5 km between survey lines) ice thickness map. This map revealed a complex landscape composed of networks of subglacial valleys and highlands. Based on the new map, we examined the roughness of the ice-bed interface, bed surface slope, the driving stress of ice, and the subglacial hydrological condition. These new products and those analyses set substantial constraints for identifying possible locations for new drilling. In addition, our map was compared with a few bed maps compiled by earlier independent efforts based on airborne radar data to examine the difference in features between datasets. Our analysis suggests that widely available bed topography products should be validated with in-situ observations where it is possible.

Figure. (Left) Photographs showing the JARE snow vehicles with various radar antennae (The 16-element antenna used in 2018–2019). (right) Gridded ice thickness (0.5 km horizontal resolution) and contours with intervals of 100 m.

Publication

• Tsutaki, S., K. Fukui, H. Motoyama, A. Hattori, J. Okuno, S. Fujita, and K. Kawamura (2021): Surface heights over a traverse route from S16 to Dome Fuji, East Antarctica as measured by kinematic GNSS surveys in 2012–2013 and 2018–2019. Polar Data Journal, 5, 144-156.

• Tsutaki, S., S. Fujita, K. Kawamura, A. Abe-Ouchi, K. Fukui, H. Motoyama, Y. Hoshina, F. Nakazawa, T. Obase, H. Ohno, I. Oyabu, F. Saito, K. Sugiura, and T. Suzuki (2022): High-resolution subglacial topography around Dome Fuji, Antarctica, based on ground-based radar surveys conducted over 30 years. The Cryosphere, 16, 2967-2983.

Press release

• 過去30年にわたる観測データから南極ドームふじ地域の詳細な基盤地形を解明 〜100万年超のアイスコア掘削に向けて〜, 大学共同利用機関法人情報・システム研究機構 国立極地研究所, 2022年10月20日 [Link]

Surface elevation changes of marine and land-terminating glaciers in northwestern Greenland

To quantify recent thinning of marine-terminating outlet glaciers in northwestern Greenland, we carried out field and satellite observations near the terminus of marine-terminating Bowdoin Glacier. These data were used to compute the change in surface elevation during 2007–2013, and this rate of thinning was then compared with that of the adjacent land-terminating Tugto Glacier. Comparing DEMs of 2007 and 2010 shows that Bowdoin Glacier is thinning more rapidly than Tugto Glacier. The observed negative surface mass balance accounts for <40% of the elevation change of Bowdoin Glacier, meaning that the thinning of Bowdoin Glacier cannot be attributable to surface melting alone. The ice speed of Bowdoin Glacier increases down-glacier. This flow regime causes longitudinal stretching and vertical compression. It is likely that this dynamically-controlled thinning has been enhanced by the acceleration of the glacier since 2000. Our measurements indicate that ice dynamics indeed plays a predominant role in the rapid thinning of Bowdoin Glacier.

Figure. (Left) Photograph showing the terminus of Bowdoin Glacier on 9 July 2015. (Middle) The rate of surface elevation change over Bowdoin and Tugto Glaciers between 20 August 2007 and 4 September 2010. The glacier margin was determined from the 2010 satellite image. The background is an ALOS PRISM image taken on 4 September 2010. (Right) Annual mean surface velocity (arrows) and its magnitude (color scale) of Bowdoin and Tugto Glaciers in 2007. Background is an ALOS PRISM image acquired on 20 August 2007.

Publication

• Tsutaki, S., S. Sugiyama, D. Sakakibara and T. Sawagaki (2016): Surface elevation changes during 2007–13 on Bowdoin and Tugto Glaciers, northwestern Greenland. Journal of Glaciology, 62(236), 1083–1092.

• Tsutaki, S., S. Sugiyama and D. Sakakibara (2017): Surface elevations on Qaanaaq and Bowdoin Glaciers in northwestern Greenland as measured by a kinematic GPS survey from 2012-2016. Polar Data Journal, 1, 1–16.

Press release

• 論文掲載：グリーンランド北西部における海洋性カービング氷河の氷損失, 北海道大学北極域研究センター, 2016年11月29日 [Link]

Surface mass balance, ice velocity and ice temperature on Qaanaaq Ice Cap in northwestern Greenland

To better understand the processes controlling recent mass loss of peripheral glaciers and ice caps in northwestern Greenland, we measured surface mass balance, ice velocity and near-surface ice temperature on Qaanaaq Ice Cap in the summers of 2012–2016. The measurements were performed along a survey route spanning the terminus of an outlet glacier to the upper reaches. The glacier-wide surface mass balance ranged from −1.10 ± 0.29 to −0.13 ± 0.26 m w.e. a⁻¹ for the years from 2012–2013 to 2015–2016. Mass balance showed substantially large fluctuations over the study period under the influence of summer temperature and snow accumulation. Ice velocity showed seasonal speed-up only in the summer of 2012, suggesting an extraordinary amount of meltwater penetrated to the bed and enhanced basal ice motion. Ice temperature at a depth of 13 m was −8.0°C at 944 m a.s.l., which was 2.5°C warmer than that at 243 m a.s.l., suggesting that ice temperature in the upper reaches was elevated by refreezing and percolation of meltwater. Our study provided in-situ data from a relatively unstudied region in Greenland, and demonstrated the importance of continued monitoring of these processes for longer timespans in the future.

Figure. (Left) Photograph showing Qaanaaq Ice Cap (QIC) on 30 June 2014. (Middle) (a) Measured SMB at Q1201–Q1206 (cross) and the SMB gradient every 100 m bin for the balance years 2012/13–2015/16. (b) Hypsometry of Qannaq Glacier (QG: blue) and QIC (purple) with altitude bands of 100 m. (Right) The glacier-wide SMB (black), summer (June–August) mean air temperature (SMT: red) and snow accumulation (blue). The solid line in temperature indicates the periods included in the temperature calculation.

Publication

• Tsutaki, S., S. Sugiyama, D. Sakakibara, T. Aoki and M. Niwano (2017): Surface mass balance, ice velocity and near-surface ice temperature on Qaanaaq Ice Cap, northwestern Greenland, from 2012 to 2016. Annals of Glaciology, 58(75-2), 181–192.

Contrasting thinning patterns between lake and land-terminating glaciers in the Bhutanese Himalaya

Despite the importance of glacial lake development in ice dynamics and glacier thinning, in situ and satellite-based measurements from lake-terminating glaciers are sparse in the Bhutan Himalaya, where a number of proglacial lakes exist. We acquired in situ and satellite-based observations across lake- and land-terminating debris-covered glaciers in the Lunana region, Bhutan Himalaya. A repeated differential global positioning system survey reveals that thickness change of the debris-covered ablation area of the lake-terminating Lugge Glacier (–4.67 ± 0.07 m a⁻¹) is more than three times more negative than that of the land-terminating Thorthormi Glacier (–1.40 ± 0.07 m a⁻¹) for the 2004–2011 period. The surface flow velocities decrease down-glacier along Thorthormi Glacier, whereas they increase from the upper part of the ablation area to the terminus of Lugge Glacier. Numerical experiments using a two-dimensional ice flow model demonstrate that the rapid thinning of Lugge Glacier is driven by both a negative surface mass balance and dynamically induced ice thinning. However, the thinning of Thorthormi Glacier is minimised by a longitudinally compressive flow regime. Multiple supraglacial ponds on Thorthormi Glacier have been expanding since 2000 and merged into a single proglacial lake, with the glacier terminus detaching from its terminal moraine in 2011. Numerical experiments suggest that the thinning of Thorthormi Glacier will accelerate with continued proglacial lake development.

Figure. (Left) Photograph showing the terminal part of Thorthormi Glacier on 18 September 2011. (Right) Glaciers and glacial lakes in the Lunana region, Bhutan Himalaya, superimposed with the rate of elevation change for the 2004–2011 period. The rate of elevation change is depicted on a 50-m grid, which is averaged from the differentiated 1-m DEMs. The light-green crosses are the benchmark locations used for the GPS surveys in 2004 and 2011. The blue cross is the location of the automatic weather station installed in 2002 (Yamada et al., 2004). The black lines indicate the outline of the glaciers in November 2002. The background image is an ALOS PRISM scene from 2 December 2009.

Publication

• Tsutaki, S., K. Fujita, T. Nuimura, A. Sakai, S. Sugiyama, J. Komori and P. Tshering (2019): Contrasting thinning patterns between lake- and land-terminating glaciers in the Bhutanese Himalaya. The Cryosphere, 13, 2733-2750.

Influence of proglacial lake formation on ice dynamics near the terminus of Rhonegletscher, Switzerland

Rhonegletscher is a temperate valley glacier in the Swiss Alps. In 2005, the ongoing retreat of the glacier led to the formation of a proglacial lake (Lake B). To investigate the influence of proglacial lake formation on ice dynamics and evolution of glaciers, we measured surface elevation change, horizontal flow velocity, vertical ice motion and water levels in boreholes with high spatial resolutions during the summer seasons of 2007–2009. The ice thinning rate in the studied area during 2008–2009 was larger than previous estimates. Annual flow speeds near the terminus (C2) increased by 2.7 times from 2005–2006 to 2007–2008, and exceeded 20 m a⁻¹ in 2009. The velocity increased towards the glacier front, indicating that the ice was thinning under a longitudinally stretching flow regime. Our observations show that the increase in flow speed near the terminus was due to increases in basal motion as a result of ice thinning. We predict that if the current ice thinning continues, the basal water pressure will exceed the pressure exerted by the ice overburden, and the glacier will progressively disintegrate over an expanding area.

Figure. (Left) Photograph showing the terminus of Rhonegletscher on 6 July 2009. (Right) Horizontal flow velocities at the upper reaches (C1) and terminus (C2) from 2000 to 2009. Thin line with open diamonds indicates the thickening rate. Vertical dashed line marks the formation of lake B. The flow velocities in 1999–2000 and 2005–2006 were obtained from aerial photographs (Nishimura et al., 2013).

Publication

• Tsutaki, S. and S. Sugiyama (2009): Development of a hot water drilling system for subglacial and englacial measurements. Bulletin of Glaciological Research, 27, 7–14.

• Tsutaki, S., D. Nishimura, T. Yoshizawa and S. Sugiyama (2011): Changes in glacier dynamics under the influence of proglacial lake formation in Rhonegletscher, Switzerland. Annals of Glaciology, 52(58), 31–36.

• Tsutaki, S., S. Sugiyama, D. Nishimura and M. Funk (2013): Acceleration and flotation of a glacier terminus during formation of a proglacial lake in Rhonegletscher, Switzerland. Journal of Glaciology, 59(215), 559–570.