CHARACTERIZATION OF TRAPPED AND BOUND SILICICLASTICS IN VARIABLE MORPHOLOGY MICROBIAL MATS USING MICRO X-RAY CT IN LAKE FRYXELL, MCMURDO DRY VALLEYS, ANTARCTICA

Lake Fryxell, a perennially ice-covered lake in the McMurdo Dry Valleys, Antarctica, is home to a large community of benthic microbial mats, composed chiefly of cyanobacteria. The benthic mat morphology varies with depth, with zones of pinnacle (defined by mm to cm-scale tufts of filaments), honeycomb (defined by ridges and pits), and flat or prostrate (defined by minimal vertical relief) morphologies. In shallow water (< 8.5 m during the 2022-23 season), the supersaturation of dissolved gasses can lead to partial or complete delamination of benthic mats. These lift-off mats migrate through the ice cover and are exported to surrounding soils by the wind, contributing to the carbon cycling within the Dry Valleys. Simultaneously, aeolian sediment deposited on the ice cover melts through the ice and is trapped and bound by the benthic mats. To better characterize how siliciclastic sedimentation through ice cover impacts mat morphology and potential buoyant export, we imaged mats of varying morphologies using micro X-Ray CT (XCT) and Dragonfly image analysis software. XCT was used to scan four frozen mats sampled from Lake Fryxell in January 2023, with a minimum resolution of 20µm. Dragonfly was then implemented to process and segment these scans in order to produce volumetric comparisons of biomass, carbonate, and siliciclastic components, as well as grain-size analysis of trapped and bound sand. These results were then compared with expected sedimentation patterns, grain-size analysis of sediment on the ice cover, and lift-off studies in order to gain a better understanding of the interdependency between siliciclastic sedimentation, mat morphology, and buoyant carbon export in Lake Fryxell. A clearer understanding of how mats trap and bind sediment, and how those processes impact mat lift-off and eventual melt-through of the ice cover, will lead to a better understanding of the carbon cycle in extreme polar environments like the McMurdo Dry Valleys.