Glaciers cover 10% of the Earth’s land surface and represent an important, yet very little studied, ecosystem. The biogeochemical cycling of carbon in the glacial ecosystem is largely influenced by microbial communities on glacier surfaces that mainly consist of heterotrophic and photoautotrophic bacteria. They have the potential to play a significant role in regional carbon budgets by means of primary and secondary production and respiration, and it is very important to evaluate their contribution on a large scale. However, to provide a credible supraglacial carbon budget, a study is needed in which C concentration and transformation rates in the supraglacial environment are related to the limiting factors, including the source of microbes and nutrients. Quantification of such a relationship will provide a powerful tool for global carbon budget models. The underlying hypothesis of the proposed research is that the productivity of the supraglacial ecosystem is constrained primarily by the source of microbial cells, and secondarily by rock-derived nutrients. The principal source of microbes and rock-derived nutrients is wind-borne debris originating in deglaciated areas close to the glacier margin. Thus, the main hypothesis to be tested in this study is that there is a relationship between the distance of a site on the glacier surface from the glacier margin and the abundance and activity of the local microbial community. The objectives of this study are to quantify the spatial distribution of surface debris on the Greenland Ice Sheet along a gradient from the glacier edge to the equilibrium line, to determine the quantity and quality of C and the abundance of microbes on the surface, to measure primary and secondary production and respiration of the supraglacial microbial community and to derive a relationship between the position along the gradient and the quantity and quality of C and its transformation rates.