Spatial variability and possible sources of acetate and formate in the surface snow of East Antarctica

Spatial trends of acetate(Ac~-) and formate(Fo~-) were determined in surface snow samples along a coastal-inland transect(180 km) in the ice cap region at Princess Elizabeth Land and along a coastal transect in the Amery Ice Shelf(130 km),East Antarctica.Variations in both Ac-and Fo-seem to be unrelated to the acidity of snow.Ionic balance determined for the snow samples indicate the availability of HNO3 that could undergo photolysis to produce hydroxyl radical(UOH),one of the major reactants involved in oxidation reactions with organic matter.The strong positive correlations between Ac~- and NO~-_3 in snow from both regions indicate that NO~-_3 mediatedUOH-oxidation of organic compounds in snow could be an important source of Ac-within the snowpack.On the other hand,negative correlation between Fo~- and NO~-_3 might indicate that sources other thanUOH-oxidation of organic matter may be dominant in the case of Fo~-.Higher Ac~- concentrations in the ice cap compared to the ice shelf correspond with long-range transport of biomass burning emissions to the ice cap region.Interaction of Ac~- and Fo~- with alkaline minerals could lead to their stability in the snowpack and minimize their loss from the snow surface.Resident microbial communities could also influence the budget of the carboxylic acids in snow.     

Microbial preference for different size classes of organic carbon: a study from Antarctic snow

Significance of carbon cycling in polar ecosystems is well recognized. Yet, bacteria in surface snow have received less attention in terms of their potential in carbon cycling. Here, we present results on carbon utilization by bacterial communities in three surface snow samples from Antarctica collected along a coastal to inland transect. Microcosm studies were conducted over 8 days at 5?±?1°C to study carbon metabolism in different combinations of added low molecular weight (LMW (glucose, <1 kDa)) and high molecular weight (HMW (starch, >1 kDa)) substrates (final 20 ppm). The total organic carbon (TOC) in the snow samples decreased with time at rates ranging from non-detectable to 1.4 ppm day(-1) with rates highest in snow samples from inland region. In addition, carbon utilization studies were also carried out with bacterial isolates LH1, LH2, and LH4 belonging to the genus Cellulosimicrobium, Bacillus, and Ralstonia, respectively, isolated from the snow samples. Studies with strain LH2 in different amendments of glucose and starch showed that TOC decreased with time in all amendments at a rate of 0.9-1.5 ppm day(-1) with highest rates of 1.4-1.5 ppm day(-1) in amendments containing a higher proportion of starch. The bacterial isolates were also studied to determine their ability to utilize other LMW and HMW compounds. They utilized diverse substrates like carbohydrates, amino acids, amines, amides, complex polymers, etc., of molecular mass <100 Da, 100-500 Da, >500 Da-1 kDa, and >1 kDa preferring (up to 31 times) substrates with mass of >1 kDa than <1 kDa. The ability of bacteria in snow to utilize diverse LMW and HMW substrates indicates that they could be important in the uptake of similar compounds in snow and therefore potentially govern snow chemistry.