Sediment-moss interactions on a temperate glacier: Falljökull, Iceland

This paper presents the results of preliminary investigations of globular moss growth on the surface of Falljökull, a temperate outlet glacier of the Vatnajökull ice cap, Southern Iceland. Supraglacial debris has provided a basis for moss colonisation and several large (>500m) patches of moss growth (Racomitrium spp.) are observed on the surface of the glacier. Each area of moss-colonised supraglacial debris shows a down-slope increase in sphericity and moss cushion size and a decrease in percentage surface coverage of moss-colonised and bare clasts. It is suggested that moss growth on supraglacial debris allows preferential down-slope movement of clasts through an associated increase in both overall mass and sphericity. Thermal insulation by moss cushions protects the underlying ice surface from melt, and the resulting ice pedestals assist in down-slope sliding and toppling of moss cushions. The morphology and life cycle of supraglacial globular mosses is therefore not only closely linked to the presence and distribution of supraglacial debris, but also appears to assist in limited down-glacier transport of this debris. This research highlights both the dynamic nature of the interaction of mosses with supraglacial sedimentary systems and the need for a detailed consideration of their role within the wider glacial ecosystem.