A glacier respires: Quantifying the distribution and respiration Co₂ flux of cryoconite across an entire Arctic supraglacial ecosystem

This paper quantifies the mass distribution of cryoconite at the glacier scale using photographic surveys conducted either at ground level, or at 20 m elevation using a novel uninhabited aerial vehicle (UAV). Image acquisition allowed three key deposits to be quantified: cryoconite holes, cryoconite in streams (“stream cryoconite”), and dispersed cryoconite granules (detectable only in the ground-based images). Cryoconite was found all over the snow-free parts of the glacier in one or more of these forms, covering about 0.42% (4600 kg km−2 dry weight) as holes and stream cryoconite deposits (>0.25 cm2 and thus visible in the UAV images), or 1% (10600 kg km−2) when smaller dispersed granules were included (using the ground images). No spatial patterns in the distribution of cryoconite cover were apparent, although cryoconite holes were far more common than stream cryoconite at high altitude due to lower melt rates. Measurements of respiration and bacterial carbon production estimated from in situ incubations of cryoconite–water mixtures indicated rates of 1.174 ± 0.182 (1 standard deviation) and 0.040 ± 0.019 μg C g−1 h−1, respectively. The respiration measurements then yielded glacier-wide CO2 fluxes for 1998 and 2000 of 6.3 and 5.1 kg C km−2 a−1 when the loci and duration of activity were defined using the UAV images and a degree day model, respectively. These fluxes increased to 14 and 12 kg C km−2 a−1 when the dispersed cryoconite detected in the ground-based images were also considered. The measurements therefore show that cryoconite ecosystems clearly have the capacity to impact upon carbon cycling in glacial environments.