169-5 Every P Pool Has a Story

Session: Phantastic Phosphorus and Its Historical Biogeochemistry

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Abstract:

The first published study combining sequential chemical extraction of specific phosphorus (P) pools from marine sediments (Ruttenberg,1992) with oxygen isotope analysis (d¹⁸O_P ) of each pool in 2010 (Jaisi and Blake, 2010), presented a new investigative tool and opened new avenues of inquiry and discovery. This coupled analytical approach-- d¹⁸O_P  analysis of individually extracted and separate P pools was quickly adopted across distinct environmental matrices, primarily by the soil /agricultural sciences and environmental engineering communities.Their assimilation of sequential extraction (e.g., SEDEX, Hedley) coupled to d¹⁸O_P has provided significant new insights into P cycling, transport, and transformations in soils and marine sediments by microbiota, and more recently by plants (Pfahler et al., 2013). Although studies of marine sediments are relatively sparser, they have firmly demonstrated the utility of d¹⁸O_P analysis of separate sediment P pools.  Moreover, geochemical modeling of coupled marine sediment P_i -d¹⁸O_P and co-existing pore fluid dissolved phosphate d¹⁸O_P data further indicates a direct link between rates of dissolved P_i-water O isotope exchange and rates of sedimentary organic carbon respiration. This, for the first time, anchors measured dissolved P_i d¹⁸O_P values (which also reflect specific microbial metabolic activities) to rates of microbial metabolism and the amount of biodegradable organic carbon in sediments (Zhao et al., 2021). Here, we detail the story behind each P pool. Both adsorbed P (includes Fe and Al--oxy-hydroxides/oxides) and authigenic P pools reflect formerly dissolved P_i which carries signatures of its sources (e.g., regeneration from organic matter) and P cycling pathways (e.g., microbial P_i uptake, or P_i cycling/turnover with resetting to new ambient T and d¹⁸O-water).  Marine water column (paleo)temperature is reflected in d¹⁸O_P values of bioapatite and also of dissolved P_i in the water column that becomes adsorbed to/ occluded within non-biogenic hydrothermal iron oxides/oxy-hydroxides. Finally, the detrital P pool reflects sediment P provenance (e.g, riverine or airborne input), and the residual organic P pool (in the case of SEDEX) derives primarily from surface organic matter.

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