Phosphorus (P) availability varies considerably throughout the McMurdo Dry Valleys, Antarctica. For instance, in upper Taylor Valley (Lake Bonney basin), soils have a much lower total P content than in lower Taylor Valley (Lake Fryxell basin). As an essential nutrient, P content and weathering have significant implications for the diversity and functioning of biota in soils, streams, and lakes. We hypothesize that the striking contrast in soil P availability is related to differences in glacial drift source and weathering rates.
To address this question of P availability, we use multiple approaches. First, at the landscape scale, we are measuring the total and soluble P content in soils developing on different glacial deposits and in multiple valleys, to understand how glacial history may play a role in P availability. Second, at the grain scale, we quantified the morphologies and surface etching features of individual apatite grains separated from Taylor Valley soils to investigate the grain-scale weathering processes resulting in the release of P into streams and adjacent soils. Finally, to trace individual apatite grains back to their source rocks, we are measuring the Rare Earth Element (REE) composition of apatite grains using laser ablation ICP-MS.
At the landscape scale, preliminary results point to the importance of glacial processes in depositing distinct parent materials, which in turn leads to differences in soil P availability. Within the Fryxell Basin of Taylor Valley, glacial landforms with high concentrations of basalt and kenyte tend to have high P availability. At the grain scale, a higher degree of grain roundness and surface etching on apatite grains in the Fryxell basin suggests a higher rate of weathering as compared to the Bonney basin. Finally, preliminary results from the laser ablation ICP-MS show that apatite grains from different source rocks have unique REE signatures, giving us confidence that this method will reveal the provenance of soil apatite grains.
As the climate warms, more liquid water is expected to be available within the soils of the McMurdo Dry Valleys. This increase in water will likely lead to higher rates of P weathering and cycling, potentially altering nutrient limitation in both the terrestrial and aquatic systems. Understanding how the P cycle will respond to a changing Antarctica climate is contingent on understanding the current weathering processes and controls on P availability.