Fraction distribution and dynamic cycling of phosphorus in lacustrine sediment at Inexpressible Island, Antarctica

Phosphorus (P) chemistry and its dynamic cycling are essential for understanding aquatic primary productivity and ecosystem structure. However, there is a lack of knowledge on P chemistry in pristine aquatic ecosystems, such as in Antarctica. Here, we applied the Standards, Measurements and Testing Program (SMT) procedure and nuclear magnetic resonance spectroscopy (NMR) to reveal P speciation in two types of lacustrine sediment cores collected from Inexpressible Island, Ross Sea, East Antarctica. The Positive Matrix Factorization Model and Generalized Additive Models were applied to quantitatively identify the P sources and estimate relative effects of various environmental factors on the speciation. Our results demonstrate that orthophosphate, mainly as Ca-P, is the major component and the ortho-monoesters are the predominant organic phosphorus (OP) form in lacustrine sediments. Ornithogenic lacustrine sediments have a higher content of P as Ca-P than sediments with little or no penguin influence. Our model further suggests that penguin guano is the most important source for Ca-P, accounting for 80%, while detrital input is the predominant source for Fe/Al-P (up to 90%). The content of orthomonoesters, as revealed by NMR, declines with depth, reflecting mineralization process of OP in the sediments. Moreover, we observed higher relative proportions of organic P in the sediments with little guano influence and the deposition of organic P are likely facilitated by microbial mats. Overall, our data suggest that burial of P in Antarctic lakes is sensitive to different P sources and sedimentary environments. The relatively higher bioavailable phosphorus in lacustrine sediments largely controls growth of aquatic microbial mats in oligotrophic lakes and ponds in Antarctica. The sediment profile data also indicate that P burial increased during the Medieval Climate Anomaly period, and climate warming is more conducive to P burial through the expansion of penguin populations and productivity of microbial mats. Our findings represent the first systematic understanding of natural P cycling dynamics and its main controlling factors in pristine ponds with different organic sources in Antarctica.