15:00 〜 15:15
[ACG39-18] Supraglacial lakes evolution on Tracy and Heilprin Glaciers, northwestern Greenland
キーワード：グリーンランド、氷河上湖、リモートセンシング
Supraglacial lakes are widely distributed near the margin of the Greenland ice sheet during the melt season. Generally, they form when meltwater ponds in ice surface depressions, and influence ice surface melt by lowing the albedo. Drainage of lake water into the glacier bed reduces basal friction and causes ice flow acceleration. Therefore, studying the evolution of supraglacial lakes sheds new light on understanding the effect of meltwater on the ice sheet. Here, we report a satellite-based study on supraglacial lakes on Tracy and Heilprin, marine-terminating glaciers in northwest Greenland (Fig. 1). Although these two glaciers have similar dimensions and flow into the same fjord, Inglefield Bredning, lakes on the glaciers exhibit remarkably different behaviors.
Taking advantage of Google Earth Engine (GEE), we compiled about 300 Sentinel-2 level-1C (S2) scenes at 10 m resolution, covering the two glaciers with sun elevation angles greater than 20°. These S2 scenes cover the period from May to August during 2016–2020. Glacier masks were generated in this study to eliminate sea and land areas from the analysis. By the integrated random forest algorithm in GEE, we distinguished water pixels from the glacier surface for all the selected S2 scenes. The water body smaller than 5 pixels and narrower than 2 pixels were removed by assuming they are slush or streams rather than lakes.
For both of the glaciers (Fig. 2), relatively small lakes (< 0.5 km2) account for the vast majority (> 95%) of all observed over the five-year period. Lakes larger than 0.5 km2 were distributed mostly in higher altitude (> 400 m a.s.l). Although the basin areas of Heilprin and Tracy glaciers are similar (653.45 km2 and 538.82 km2), lake surface area on Heilprin glacier (21.13 km2) was three times greater than that on Tracy glacier (6.87 km2). Considering water tend to store in flat and slower-moving ice, we attribute the smaller lake area on Tracy to its faster ice speed (1740 m a-1 in 2014) and steeper surface slope (4.0°) as compared to these of Heilprin glacier (1360 m a-1 in 2014 and 3.1°). Despite the difference in the lake areas, temporal patterns were similar during the observation period. In general, lakes began formation in the middle of May, which was followed by substantial increase in area from middle of June. After reaching a maximum thereafter, the lake area decreases in August. Due to annual variations in meteorological conditions, the area peaked in different timing every year. In 2016, 2019, and 2020, lake area reached peak values between late June and beginning of July. In 2017 and 2018, however, the peaks were observed later in late July because of cold summer temperature (Fig. 3). A possible impact of lake drainage on the ice dynamics is under investigation using ice velocity time series.
Taking advantage of Google Earth Engine (GEE), we compiled about 300 Sentinel-2 level-1C (S2) scenes at 10 m resolution, covering the two glaciers with sun elevation angles greater than 20°. These S2 scenes cover the period from May to August during 2016–2020. Glacier masks were generated in this study to eliminate sea and land areas from the analysis. By the integrated random forest algorithm in GEE, we distinguished water pixels from the glacier surface for all the selected S2 scenes. The water body smaller than 5 pixels and narrower than 2 pixels were removed by assuming they are slush or streams rather than lakes.
For both of the glaciers (Fig. 2), relatively small lakes (< 0.5 km2) account for the vast majority (> 95%) of all observed over the five-year period. Lakes larger than 0.5 km2 were distributed mostly in higher altitude (> 400 m a.s.l). Although the basin areas of Heilprin and Tracy glaciers are similar (653.45 km2 and 538.82 km2), lake surface area on Heilprin glacier (21.13 km2) was three times greater than that on Tracy glacier (6.87 km2). Considering water tend to store in flat and slower-moving ice, we attribute the smaller lake area on Tracy to its faster ice speed (1740 m a-1 in 2014) and steeper surface slope (4.0°) as compared to these of Heilprin glacier (1360 m a-1 in 2014 and 3.1°). Despite the difference in the lake areas, temporal patterns were similar during the observation period. In general, lakes began formation in the middle of May, which was followed by substantial increase in area from middle of June. After reaching a maximum thereafter, the lake area decreases in August. Due to annual variations in meteorological conditions, the area peaked in different timing every year. In 2016, 2019, and 2020, lake area reached peak values between late June and beginning of July. In 2017 and 2018, however, the peaks were observed later in late July because of cold summer temperature (Fig. 3). A possible impact of lake drainage on the ice dynamics is under investigation using ice velocity time series.