Morphology shapes microbial ecosystems and carbon cycling within cryoconite holes on a Greenland outlet glacier

Cryoconite holes, small water-filled cylindrical pits on glacier surfaces, are crucial microbial habitats and play a pivotal role in darkening the Greenland Ice Sheet, potentially accelerating ice melt. To understand how their morphology influences microbial ecosystems and biogeochemical functions, we investigated cryoconite hole dimensions, microbial communities, and cryoconite characteristics across Issunguata Sermia (Glacier), southwest Greenland. Our findings reveal distinct morphological gradients: cryoconite holes were shallower in the rough crevasse zone near the glacier margin and significantly deeper in the flat ice zone at the glacier’s midline. These morphological differences were strongly linked to disparities in phototrophic community composition and relative abundance, including filamentous cyanobacteria and glacier algae, between the deeper and shallower holes. Furthermore, cryoconite from deeper holes exhibited significantly higher organic content and enriched carbon stable isotope signatures, suggesting enhanced in-situ microbial productivity, despite consistent meltwater geochemistry and mineral compositions across all sites. Our results unequivocally demonstrate that glacier surface topography primarily drives cryoconite hole development, critically shaping localized microbial communities, carbon cycling, and albedo feedbacks. This study highlights the complex physical-biological interplay in glaciers, offering crucial insights into ice sheet melt and carbon dynamics in a changing polar region. Glacier surface topography primarily drives cryoconite hole development, critically shaping localized microbial communities, carbon cycling, and albedo feedback, according to a field investigation across the Issunguata Sermia (Glacier), southwest Greenland.