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doi:10.2204/iodp.proc.336.205.2015

Introduction

Phosphorus (P) is an essential nutrient for life and is present in a wide range of organic and inorganic compounds, which are characterized by different bioavailability and reactivity (Björkman and Karl, 1994; Paytan and McLaughlin, 2007). Elucidating P geochemistry in open-ocean sediments is important, considering little is known about the nature of P compounds fueling microbial life in the deep subseafloor environment. This environment is estimated to contain up to 1% of Earth’s total biomass and includes significant prokaryotic populations at depths greater than 1 km (Kallmeyer et al., 2012; Roussel et al., 2008). The existence and activity of these microbial populations may have implications on global biogeochemical cycles and our understanding of the limits of life. This study aims to characterize the solid-phase P reservoirs in sediment samples collected from North Pond, a sediment pond on the western flank of the Mid-Atlantic Ridge sampled during Integrated Ocean Drilling Program (IODP) Expedition 336 (Fig. F1), using the sedimentary extraction (SEDEX) sequential extraction scheme (Ruttenberg, 1992; Ruttenberg et al., 2009). The appeal of the SEDEX method is that it has been successfully used in numerous studies in the field of P biogeochemistry (Ruttenberg, 2003). Furthermore, it is the only procedure that allows for the separation of carbonate fluorapatite from the detrital apatite pool (Ruttenberg, 1992). This is critical because authigenic apatite represents a sink for reactive P, whereas detrital apatite does not (Delaney, 1998).

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