[A-CG68] Science in the Arctic Region

[ACG68-P05] Formation mechanisms of stripe patterns of dark ice surfaces on Qaanaaq Glacier, Northwest Greenland

*Kaho Miyazaki¹, Masato Ono², Kenshiro Arie⁴, Sumito Matoba³, Rigen Shimada⁴, Motoshi Nishimura⁵, Takumi Suzuki⁴, Kino Kobayashi¹, Nozomu Takeuchi⁶ (1.Graduate School of Science and Engineering, Chiba University , 2.Center for Ecological Research, Kyoto University, 3.Pan-Okhotsk Research Center, Institute of Low Temperature Science, Hokkaido University, 4.Earth Observation Research Center, Japan Aerospace Exploration Agency (JAXA), 5.Institute for Mountain Science, Research Cluster for Social Implementation, Shinshu University, 6.Center for Environmental Remote Sensing, Chiba University)

Recent studies have highlighted surface darkening in glacier ablation zones as an important factor enhancing glacier melt through albedo reduction. In the ablation zone of the Greenland Ice Sheet, dark areas often appear as stripe patterns of dark ice surfaces, characterized by alternating dark and white bands oriented approximately perpendicular to ice flow. The stripe patterns suggest that outcropping impurities from ablating glacier ice play a role in forming the dark surface. However, the formation mechanisms of the stripe patterns remain poorly understood. This study aims to characterize glacier ice beneath the stripe patterns and discuss their formation processes in the ablation zone of Qaanaaq Glacier, northwest Greenland. During the summer of 2024, a total of 18 ice cores were drilled from the surface to a depth of approximately 90 cm at dark and adjacent white ice surfaces on the glacier. Stratigraphic observations revealed no clear differences in internal layering between cores from dark and white surfaces. Coulter counter analyses also showed no significant difference in total fine particle concentrations in the ice. In contrast, microscopic observations revealed that mineral particle concentrations were significantly higher in cores from the dark surface, with particularly high concentrations near the surface. Glacier algae and cryoconite granules were also concentrated in surface layers of dark cores, whereas they were scarce in white cores. Chemical analyses revealed that NO₃^- concentrations in the lower sections were significantly higher in the dark cores. Results of the stable water isotope analyses suggested that this ice originated from snowfall during an interglacial period. Based on these findings, the stripe patterns of dark ice surface on Qaanaaq Glacier are considered to have formed as NO₃^- preserved in the dark cores was exposed at the surface through melting, functioning as a nutrient that promoted microbial growth. Furthermore, microbial activity likely enhanced the aggregation of mineral particles, contributing to the development of the dark bands. Future studies should include analyses of deeper ice cores, detailed surface topography, and meltwater dynamics to further clarify the formation mechanisms.