Award: OPP-1023351

Melting of the Greenland Ice Sheet releases a large amounts of water to the surrounding oceans and it is expected that these fluxes are increasing. While this meltwater is created on the surface of the Ice Sheet, part of it is funneled to the base at the Ice Sheet margin and/or through proglacial deposits (moraines) where it can react with rocks and sediments and become enriched in dissolved and particulate material. Our study focuses on processes that release solutes, nutrients and nanoparticles to meltwater. We were especially interested to evaluate the dependence of these processes on glacial setting, lithology and microbial communities at the western margin of the Greenland Ice Sheet (GrIS). Special interest was paid to identify the amount of bioavailable iron that is transported with the meltwater to the ocean. The study was performed at two different locations: in northwest Greenland at the Thule Airbase (76º N, 68°W) where summer temperatures are low and the Greenland Ice Sheet is frozen to its base (cold based); in southwest Greenland, Kangersussuaq (67°N, 50°W) where summer temperatures are warmer and where parts of the base of the Ice Sheet are at its melting point (polythermal). Both locations are underlain by different lithology. In the north, bedrock is mostly composed of sedimentary rocks with some gneiss and basalt, and in the south, bedrock is mostly gneiss with some amphibolite lenses. At both locations, samples of meltwater streams were taken on a regular basis between May and September in 2011 (Thule) and 2012 (Kangerlsussuaq) and analyzed for solute composition, iron species and microbial communities. The iron concentrations measured in both locations are not very different and, when related to the meltwater flux from the entre Greenland Ice Sheet, they would in average be comparable to iron that is contributed by atmospheric dust to the surrounding oceans. The source and kind of iron varies between both locations. In the north, most of the iron is coming from proglacial areas in front of the ice sheet. This iron has a different structure and it is less available to phytoplankton to be used as nutrient. It is assumed that this kind of iron is more related to soil processes. In southwestern Greenland, the iron is in a chemical form that is more available to phytoplankton and its source areas are located underneath the ice sheet. At this location where the base of the ice sheet is above freezing point, surface meltwater flows through cracks (crevasses) and channels (moulins) to the base of the Ice Sheet which is in contact with rocks and sediments. In these areas dissolution of the minerals leads to the formation of dissolved iron that very quickly aggregates to nanoparticles. These iron aggregates are then flushed out with meltwater and transported by streams to the fjord. The microorganisms that were found in the subglacial water together with the iron appear to be suitable to catalyze the dissolution of iron releasing minerals, such as pyrite, and contribute to the formation of bioavailable iron aggregates such as ferrihydrate. This project supported one graduate and one undergraduate geology student. We gave a number of presentations about the Greenland Ice Sheet and its potential role as supplier for micronutrients to 160 middle school students, and presented at public workshops and at teacher conferences in Anchorage, Alaska. Scientific presentations were given at International Conferences in the US and Europe and manuscripts were published in peer review journals. Last Modified: 10/31/2014 Submitted by: Birgit Hagedorn