Organic Phosphorus in the Deep Subseafloor Environment

Monday, 15 December 2014
Delphine Defforey, University of California Santa Cruz, Santa Cruz, CA, United States and Adina Paytan, UCSC-Inst Marine Sciences, Santa Cruz, CA, United States
Phosphorus (P) is a macronutrient involved both in functional and structural components of all living cells. This makes it an essential nutrient for life, including microbial life in the deep subseafloor habitat. P availability in this environment is limited since organic matter is scarce and P is thought to be mainly present in refractory mineral phases. However, recent estimates suggest that the deep biosphere may contain up to 1% of Earth’s total biomass, which implies that microorganisms may possess mechanisms to harvest recalcitrant phosphorus compounds in this environment. In addition, the role of the organic P pool in this setting is poorly understood and could be of great importance should it represent an important P pool fueling the deep biosphere. This study aims to identify and quantify organic P compounds in open ocean sediments using our newly developed sequential extraction procedure for 31P nuclear magnetic resonance spectroscopy (31P NMR). This method amplifies the signal of organic P in spectra by increasing its concentration and quantitatively removing the majority of inorganic P. Briefly, P bound to iron oxyhydroxides is removed from sediment samples during a reductive step; then, P in authigenic and biogenic apatite is solubilized over the course of an extraction in an acidic buffer. These two steps remove the majority of inorganic P from the sample. Lastly, the residue is extracted in 0.25M NaOH+ 0.05M Na2EDTA and the supernatant is frozen and lyophilized prior to 31P NMR analysis. This method will be applied to sediment samples from North Pond (IODP expedition 336), an isolated sediment pond on the western flank of the Mid-Atlantic ridge. This work will provide valuable insight into the diagenetic processes affecting organic P in open ocean sediments and into possible nutrient sources to the deep biosphere.