Productivity and Biogeochemistry of terrestrial ice-bound ecosystems of the maritime Antarctic.

The most poorly understood terrestrial habitat in Antarctica is its ice: a significant microbial resource that collectively constitutes the largest single freshwater reservoir of bacteria on the Earth's surface. The total bacterial cell biomass in the Antarctic ice sheet is thought to amount to ~ 2.44 Tg (Priscu and Christner, 2004) and so mass losses from West Antarctic and the Peninsula (~ 180 Gt ice a-1: Ringnot et al, In Press: Nature Letters) mean major biomass and organic carbon fluxes (~ 16 GgC a-1) are taking place whose ecological implications have been completely overlooked. Furthermore, these are viable microorganisms that are so active when melting takes place that they sequester between 50% and 75% of the inorganic snowpack nutrient reservoir (Hodson, 2006) and fix ~ 10 mgC m-2 d-1 from the atmosphere by photosynthesis (Fogg, 1968). Thus snow and ice-bound microorganisms transform enormous quantities of inorganic nutrients and CO2 from the atmosphere into organic biomass while they are in transit to the coast. Here, there is now evidence that glacial and snowmelt runoff can increase marine plankton blooms up to 100 km offshore (Dierssen et al, 2002). A systematic study of the internal biological production and biogeochemistry of snow and ice habitats in the maritime Antarctic is therefore long overdue. Further, since extreme responses to climate change are already being observed here in its soil, lake and coastal ecosystems, we believe that an investigation of the relationship between these changes and those occurring in snow and ice habitats is urgently required. Measurements of the nutrient content of snow and ice prior to melt cannot be used to predict enhanced production in terrestrial, freshwater and marine ecosystems at the ice margin because this neglects the internal nutrient demands imposed by its own biological production. It also offers no insights into the biological CO2 pump in icy habitats, which will dominate the terrestrial ecosystem CO2 budget, yet has never been measured. The net impact of biological production within snow and ice is most likely a significant regional CO2 source, but this flux will become far greater if other parts of coastal Antarctica begin to melt to the same extent as the northern Peninsula and Scotia arc. This project will therefore quantify the microbiology, nutrient economy and productivity of snow and ice surface habitats as they melt in the maritime Antarctic. Our approach will be to establish transects upon Signy Island (South Orkney Islands) that are representative of the broad range of melting and nutrient gradients found along much of the Antarctic Peninsula's west coast and associated archipelagos. These sites will encompass nutrient-rich, high melt rate coastal snowpacks and nutrient impoverished, cold snowpacks at altitudes where melting is sporadic and typically restricted to the surface. We will also follow the retreat of the snowpack up our transects and examine the glacier surface habitats exposed as a consequence. At each site we will establish the microbial community structure and biomass throughout the summer and track the fate of microorganisms as melting removes them from the snow and ice. We will also track nutrients at the same time and measure the melt energy fluxes that drive the whole system. This tight integration of physical, chemical and biological process measurements and also the range of sites being considered are important because they will then enable us to assess other parts of the Antarctic Peninsula not subject to detailed monitoring. For these areas, we will use existing meteorological data and estimates of melt extent to calculate the westward flux of melt, nutrients and microbial biomass that might be expected under current and future melt scenarios. At the same time we will establish the CO2 fluxes as a result of biological activity within Antarctic snow and ice habitats for the first time.