The cryoconite ecosystem on the Greenland ice sheet

This paper presents an assessment of biological activity associated with ice surface debris (cryoconite) at the ice-sheet scale. Estimates of the mass distribution of cryoconite over the Greenland ice sheet (GIS) and the biological activity associated with it are presented and then coupled with a surface mass-balance model to estimate total carbon fluxes due to respiration and photosynthesis. We find an average loading of 66 g m -2 at Kangerlussuaq, southwest Greenland, which compares well with recent estimates from Kronprins Christians Land (17-440 g m -2 : Boggild and others, 2010) in northeast Greenland. We also report a significant microbial biomass in cryoconite at both these places (10 3 -10 4 cells mg -1 ) and carbon fluxes of the order of 1-3 m MCg -1 d -1 for both respiration and photosynthesis. The modelling indicates that total respiration and photosynthesis fluxes are likely to be � 10 1 -10 2 Gg C a -1 and thus far from trivial. However, estimation of the net ecosystem impact across the entire ice sheet on atmospheric CO2 concentrations is problematic because photosynthesis rates were almost certainly low during our field campaign. Therefore, like its water balance, the carbon balance of the GIS is now known to be important, but its accurate quantification will remain elusive until more data are forthcoming.