Phosphorus burial and diagenesis in the central Bering Sea (Bowers Ridge, IODP Site U1341): Perspectives on the marine P cycle

• Published in: Chemical Geology
• Main Authors: März, C, Poulton, SW, Wagner, T, Schnetger, B, Brumsack, H-J
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2014
• Subjects: Bering Sea; Bowers
• Online Access: https://eprints.whiterose.ac.uk/80330/; https://eprints.whiterose.ac.uk/80330/1/Phosphorus%20burial%20and%20diagenesis%20in%20the%20central%20Bering%20Sea%20Bowers%20Ridge,%20IODP%20Site%20U1341%20Perspectives%20on%20the%20marine%20P%20cycle.pdf; https://doi.org/10.1016/j.chemgeo.2013.11.004

To reconstruct the cycling of reactive phosphorus (P) in the Bering Sea, a P speciation record covering the last ~4Ma was generated from sediments recovered during Integrated Ocean Drilling Program (IODP) Expedition 323 at Site U1341 (Bowers Ridge). A chemical extraction procedure distinguishing between different operationally defined P fractions provides new insight into reactive P input, burial and diagenetic transformations. Reactive P mass accumulation rates (MARs) are ~20-110μmol/cm/ka, which is comparable to other open ocean locations but orders of magnitude lower than most upwelling settings. We find that authigenic carbonate fluorapatite (CFA) and opal-bound P are the dominant P fractions at Site U1341. An overall increasing contribution of CFA to total P with sediment depth is consistent with a gradual "sink switching" from more labile P fractions (fish remains, Fe oxides, organic matter) to stable authigenic CFA. However, the positive correlation of CFA with Al content implies that a significant portion of the supposedly reactive CFA is non-reactive "detrital contamination" by eolian and/or riverine CFA. In contrast to CFA, opal-bound P has rarely been studied in marine sediments. We find for the first time that opal-bound P directly correlates with excess silica contents. This P fraction was apparently available to biosiliceous phytoplankton at the time of sediment deposition and is a long-term sink for reactive P in the ocean, despite the likelihood for diagenetic re-mobilisation of this P at depth (indicated by increasing ratios of excess silica to opal-bound P). Average reactive P MARs at Site U1341 increase by ~25% if opal-bound P is accounted for, but decrease by ~25% if 50% of the extracted CFA fraction (based on the lowest CFA value at Site U1341) is assumed to be detrital. Combining our results with literature data, we present a qualitative perspective of terrestrial CFA and opal-bound P deposition in the modern ocean. Riverine CFA input has mostly been reported from continental shelves and ...