QUANTIFYING PINNACLE MORPHOLOGY USING 3-DIMENSIONAL RECONSTRUCTIONS OF MICROBIAL MATS IN LAKE VANDA, ANTARCTICA

Benthic microbial pinnacles grow in ice-covered Lake Vanda, McMurdo Dry Valleys, Antarctica. They extend from the base of the ice to more than 50m water depth. Three-dimensional models of these pinnacles at 21.8m and 23.6m water depths were reconstructed using underwater videos and Agisoft Photoscan. The resolution of reconstructions varies with the heights of the pinnacles. More abundant tall pinnacles in the 23.6m mats led to shadowing in the input photos, and small pinnacles are harder to resolve in the reconstructions. Reconstructions are being analyzed in UCD KeckCAVES (http://keckcaves.org), where interactive exploration and analysis of three-dimensional data allows us to measure pinnacle locations, heights, and density. At 21.8m depth, measured pinnacle heights ranged over an order of magnitude in relative size. Short pinnacles can be measured in this reconstruction due to excellent resolution with less shadowing from tall pinnacles. At 23.6m depth, measurable pinnacle heights range over a factor of 3. Abundant smaller pinnacles are also present, but reconstruction quality was sufficiently poor that they were not measured. Results collected through these methods are being compared to nutrient diffusion model predictions to study constraints on the growth of microbial communities in Lake Vanda and the resulting pinnacle morphology. These results suggest an inverse correlation between heights of pinnacles and water depth. The youngest and shortest pinnacles are at 21.8m depth, where flow rates of up to 0.1 m/s may induce nutrient transport by convection. At depths greater than 23.2m, there is negligible flow in the water column, therefore, nutrient delivery occurs only through diffusion. Significant differences in pinnacle growth rate and morphology may be affected by the water depth, nutrient delivery mode, and age of the microbial mats.