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

Christian März, Simon W. Poulton, Thomas Wagner, B. Schnetger, H.-J. Brumsack

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Abstract

To reconstruct the cycling of reactive phosphorus (P) in the Bering Sea, a P speciation record covering the last similar to 4 Ma 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 similar to 20-110 mu mol/cm(2)/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 PMARs at Site U1341 increase by similar to 25% if opal-bound P is accounted for, but decrease by similar to 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 margins draining P-rich lithologies, while eolian CFA input is found across wide ocean regions underlying the Northern Hemispheric "dust belt". Opal-bound P burial is important in the Southern Ocean, North Pacific, and likely in upwelling areas. Shifts in detrital CFA and opal-bound P deposition across ocean basins likely occurred over time, responding to changing weathering patterns, sea level, and biogenic opal deposition. (C) 2013 Elsevier B.V. All rights reserved.

Original languageEnglish
Pages (from-to)270-282
Number of pages13
JournalChemical Geology
Volume363
DOIs
Publication statusPublished - 10 Jan 2014

Keywords

  • Integrated Ocean Drilling Program
  • Bering Sea
  • Phosphorus
  • Sequential extraction
  • Biogenic opal
  • Carbonate fluorapatite
  • CONTINENTAL-MARGIN SEDIMENTS
  • SEQUENTIAL EXTRACTION METHOD
  • BLACK SHALE FORMATION
  • WATER-COLUMN ANOXIA
  • GULF-OF-CALIFORNIA
  • ORGANIC-CARBON
  • BALTIC SEA
  • SOUTHERN-OCEAN
  • SILICA INTERFERENCE
  • PARTICULATE MATTER

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