Limited Bioweathering by Cyanobacteria in Cold, Nutrient-Limited Conditions: Implications for Microbe-Mineral Interactions and Aquatic Chemistry in Cold Environments

Solute fluxes in Antarctic meltwaters indicate microbial processes influence chemical weathering. Antarctic cyanobacterial mats dominated by Leptolyngbya glacialis enhance weathering rates at 12 degrees C. Yet, their effects on nutrient fluxes in colder, nutrient-limited conditions, similar to the McMurdo Dry Valleys environments, are unknown. Here, we investigate biotic and abiotic weathering rates of glaciofluvial sediments at 4 degrees C and compare results to previous experiments at 12 degrees C. We also examine the effects of nutrient and salt concentrations on weathering fluxes by comparing the effects of different media concentrations (0.1X and 0.001X: 10 and 1000 times diluted) at both temperature conditions. Our results show limited evidence of biologically mediated silica release at 4 degrees C, yet microbe-mineral interactions still affect nutrient fluxes, particularly for Ca, Mg, Mn, P, and N. However, a higher initial salt concentration (0.1X media) increased the concentration of solutes released under abiotic conditions. These results indicate that aqueous solutes, temperature and microbial processes are all important factors controlling weathering rates and nutrient fluxes in cold settings.