Microbially Mediated Carbon Fluxes on the Surface of Glaciers and Ice Sheets

• Main Author: Cook, Joseph
• Format: Thesis
• Language: English
• Published: University of Sheffield 2012
• Subjects: Arctic; Greenland; Kangerlussuaq; Svalbard; albedo; Ice Sheet
• Online Access: https://etheses.whiterose.ac.uk/2882/; https://etheses.whiterose.ac.uk/2882/1/Thesis_Final.docx

Measurements from Austre Brøggerbreen (Svalbard, 2009) and the Greenland Ice Sheet (GrIS, near Kangerlussuaq, 2010) are used to examine microbially mediated supraglacial carbon fluxes and feedbacks between these fluxes and the abiotic conditions at the ice surface. Linear relationships between mass and area of cryoconite deposits indicate constant sediment layer thicknesses at a range of Arctic locations. This is suggested to result from a tendency for cryoconite to form a layer of single grains, with the thickness determined by grain diameter. A thermodynamic mechanism of single grain layer (SGL) maintenance is proposed, in which holes expand laterally to accommodate increased sediment volumes. This is shown to reduce ice surface albedo and promote photosynthesis because the greatest possible surface area for irradiance of cryoconite is maintained. Since cryoconite only contributes to supraglacial carbon fluxes while it resides upon ice surfaces, two major mechanisms of sediment evacuation are examined: melt-out and hydraulic removal. Energy balance modelling indicates that melt out is unlikely unless high air temperature and low incident radiation persist for multiple days. Stream migration is proposed to be the most likely mechanism of sediment removal; however for the majority of holes, multi-year residence times can be expected. This thesis also provides new estimates of microbially mediated carbon fluxes from the GrIS. New models estimate carbon fluxes from a section of GrIS for which spatially variable parameter values were derived from point-to-point interpolation of field data. An algal ecosystem is included for the first time. The results indicate that cryoconite can fix about four times more carbon than previously predicted, and surface algal ecosystems fix about eleven times more carbon than cryoconite. Biologically mediated carbon fluxes on the GrIS are therefore shown to be much higher than previously thought. Further, the GrIS is shown to be in a relatively stable state of net autotrophy.