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[ACG52-08] Collapse of Cryoconite Hole: A novel darkening process of Greenland Ice Sheet
Keywords:Cryoconite holes, Greenland Ice Sheet, Darkening
Darkening processes in Greenland Ice Sheet (GrIS) are concerning as they accelerate ice melting. Known causes of darkening include increases in impurities such as black carbon and mineral dust and microbial activities. Here we propose a previously unrecognized darkening process caused by the collapse of cryoconite holes.
Cryoconite holes (CCHs) form when microbially derived dark material called “cryoconite” selectively absorbs radiative heat. We developed a heat balance model (CryHo) that considers the geometric structure of CCHs (Onuma et al., 2023). In this study, we applied CryHo to the entire GrIS and calculated the effect of albedo lowering when CCHs become shallower and collapse, and the cryoconite inside CCHs spreads on the surrounding surface. For the input data for CryHo, we used NHM-SMAP (Niwano et al.d, 2018), and then calculated the change in CCH depth at a hourly interval. We accumulated the time of CCH collapse each summer, and calculated the effect of albedo reduction using an observational result by Takeuchi et al. (2018), which revealed that the albedo decreased by 0.1 when a cryoconite hole collapsed.
Annual variation in the albedo reduction due to the CCH collapse was calculated for the period 2000-2020, and compared with the MODIS-derived albedo, revealing a high correlation over 0.4 along coastal regions of GrIS. Compared with the interannual variability of the MODIS albedo, we find that the albedo reduction due to the CCH collapse contributed about 8%.
Niwano et al. (2018) Cryosphere, doi: 10.5194/tc-12-635-2018
Onuma et al. (2023) Cryosphere, doi: 10.5194/tc-17-3309-2023
Takeuchi et al. (2018) Annals of Glaciology, doi: 10.1017/aog.2018.19
Cryoconite holes (CCHs) form when microbially derived dark material called “cryoconite” selectively absorbs radiative heat. We developed a heat balance model (CryHo) that considers the geometric structure of CCHs (Onuma et al., 2023). In this study, we applied CryHo to the entire GrIS and calculated the effect of albedo lowering when CCHs become shallower and collapse, and the cryoconite inside CCHs spreads on the surrounding surface. For the input data for CryHo, we used NHM-SMAP (Niwano et al.d, 2018), and then calculated the change in CCH depth at a hourly interval. We accumulated the time of CCH collapse each summer, and calculated the effect of albedo reduction using an observational result by Takeuchi et al. (2018), which revealed that the albedo decreased by 0.1 when a cryoconite hole collapsed.
Annual variation in the albedo reduction due to the CCH collapse was calculated for the period 2000-2020, and compared with the MODIS-derived albedo, revealing a high correlation over 0.4 along coastal regions of GrIS. Compared with the interannual variability of the MODIS albedo, we find that the albedo reduction due to the CCH collapse contributed about 8%.
Niwano et al. (2018) Cryosphere, doi: 10.5194/tc-12-635-2018
Onuma et al. (2023) Cryosphere, doi: 10.5194/tc-17-3309-2023
Takeuchi et al. (2018) Annals of Glaciology, doi: 10.1017/aog.2018.19