26th May 2014 | Posted by: Admin |
Microbial abundance in Antarctic glacier ice is estimated to be 1014-1017 cells per km-3, making it the largest freshwater reservoir of microorganisms on Earth (Priscu and Christner, 2004). However, snow and ice remain among the most poorly understood habitats globally. Ice covers 99.7% of the Antarctic landscape, but the biology of these snow and ice-bound ecosystems has been largely overlooked compared to other Antarctic terrestrial and freshwater habitats (Bergstrom et al, 2006). It is known that microorganisms living on the surface of glaciers and ice sheets are active throughout the melt season, and can readily transform inorganic nutrients and CO2 from the atmosphere into organic biomass (Hodson et al, 2008). Part of the organic matter produced is then transported to the surrounding terrestrial or marine ecosystems in meltwater. Due to the recent rapid regional warming in West Antarctica and around the Antarctic Peninsula in particular, large masses of ice and snow have been lost into the surrounding ocean (~180 Gt of ice year-1: Rignot et al, 2009). With this ice, we estimate around 16 Gg of organic carbon are also released every year and transferred into the ocean, but the ecological implications of this transfer for the marine ecosystem remain unclear. Furthermore, iron lost from melting glaciers has been recently shown to stimulate phytoplankton production in the Southern Ocean (Alderkamp et al, 2012), which can potentially partially offset the negative effect of the warming in the region by leading to enhanced uptake of atmospheric CO2.
We aimed to study internal production and biogeochemistry of snow and ice habitats on Signy Island (South Orkney Island group) and Livingston Island (South Shetland Island group) in the maritime Antarctic. Microbiology, nutrient economy and productivity of snow and ice surface habitats were assessed at sites representative of different melting and nutrient conditions. Microbial community structure and biomass changes were studied in snowpack, slush and superimposed ice during the summers of 2012/13 and 2013/14, using molecular, biogeochemical and conventional microbiological techniques. Fluxes of nutrients such as carbon, nitrogen, phosphorus, silica and iron were also monitored throughout the season within snowpacks and the runoff they produced. Net ecosystem production, respiration and photosynthesis of the Signy ice-bound ecosystems were evaluated using radioisotope labelling (14C and 3H) and CO2 flux measurements. Meltwater runoff was monitored continuously in order to estimate microbial and nutrient loss from glaciated areas into the ocean. At Livingston we developed several techniques for assessing microbial activity in snow that were based upon more portable technologies, including gas measurements of CO2 within the snow matrix and fluorescence detection of photosynthesizing microorganisms.
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