CHARACTERIZATION OF MICROBIAL CARBON IN CRYOCONITE HOLES ON TWO SOUTHERN ALASKAN GLACIERS

Albedo, or glacier reflectivity, has been steadily declining due to the increasing amount of dark-colored snow on glacier surfaces. This dark colored material tends to accumulate in depressions in the ice surface called cryoconite holes. Since the increasing amount of dark snow causes glaciers to melt more rapidly, the characterization and source of dark material in cryoconite holes must be determined. Export from glaciers contains old carbon, which suggests a fossil carbon source, such as the combustion of fossil fuels. However, the chemical composition of exported material is microbial in nature. To understand what carbon microbes on the surface of glaciers are using, we collected cryoconite material in August of 2015 from Matanuska and Spencer glaciers in southern Alaska and isolated the phospholipid fatty acids (PLFAs), which are biomarkers of the viable microbial community and are quickly hydrolyzed after death, using solvent extraction. The amount of PLFA was converted to cell abundances and was between 2x10⁹ and 1x10¹⁰ cells per gram of sample, which is similar to surrounding soils. PLFA abundances were found to be very similar on both glaciers, with around 40% saturated, 40% monounsaturated, 10% branched, and 10% polyunsaturated, cyclic, and other structures, which will allow for the identification of a broad class of microorganisms present in cryoconite holes. Additionally, the radiocarbon content of the PLFA will be used to determine the source of carbon to microorganisms in cryoconite holes, which will indicate carbon inputs into the cryoconite material. Characterizing the microbial composition of cryoconite holes and determining the source of carbon to microorganisms residing in the holes will help in investigating why dark material continues to populate glaciers, reducing albedo and increasing glacier melt.