Micromorphological features of mineral matter from cryoconite holes on Arctic (Svalbard) and alpine (the Alps, the Caucasus) glaciers

Mineral grain micromorphology is a useful proxy for reconstructing the history of mineral matter deposited on glaciers. In this study, we focus on the grain shape and micromorphology of mineral particles collected from cryoconite holes on glaciers in the Alps, the Caucasus and Svalbard. We use the scanning electron microscopy (SEM) to better understand the origin, transport regime, depositional processes, biofilm formations, degradation and grain transformation. Our results show that chemical and physical weathering are equally relevant in shaping mineral grains, although in polar and cold regions physical processes dominate. Grains with smooth edges owing to chemical weathering in some of the investigated samples, represent more than 60-70%. Comparison of main grain-type abundance helped to establish that climate is not the most important factor affecting grain micromorphology on glaciers, but local rock sources and supraglacial processes. We hypothesize that grain surface roughness plays an essential role with respect to biofilm formation, while at the same time bacteria-enhanced weathering enriches micromorphology (we observed polymeric substances on some of grains) and release critical compounds for nutrient-poor glacial systems. Thus, grain type and morphology might be an important factor influencing cryoconite granules formation and productivity of cryoconite holes.