Soil phosphorus cycling in an Antarctic polar desert

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Soil phosphorus distribution and cycling in the McMurdo Dry Valleys is poorly understood despite its importance for contemporary Antarctic ecosystem processes. We present data from sequential chemical extractions of phosphorus pools from dry valley soils and sediments on tills across a gradient of surface exposure ages, and across potential weathering gradients in stream channels. The geologically old, but poorly weathered, soils of the dry valleys have large phosphorus pools relative to in situ biological requirements. These pools are dominated by unweathered P fractions, comprising between 60 and 90% of total soil phosphorus among sites occurring on tills ranging in surface exposure ages of approximately 10 3–10 6 yrs. Variation in total phosphorus concentration and availability are related to differences in the initial P content of these tills; Ross Sea tills contain basalts and kenyte which contribute to higher concentrations of phosphorus relative to soils developing on tills deposited by advances of the Taylor Glacier. At local scales, physicochemical gradients contribute to variation in weathering rates, altering the distribution of phosphorus among chemical fractions, which differ in their potential mobility and availability to microorganisms. For example, hyporheic stream sediments exhibit evidence of phosphorus weathering from primary minerals and loss relative to upland soils adjacent to stream channels. Dry valley landscapes (glaciers, lakes streams, soils) are hydrologically connected, providing a mechanism for phosphorus weathering and mobilization in soils and sediments to contribute to the nutrient budgets of adjacent aquatic ecosystems. We suggest that landscape history (till composition) and contemporary subsurface and stream hydrology are the primary controls over phosphorus cycling in the McMurdo Dry Valleys.