Journal
GEOCHIMICA ET COSMOCHIMICA ACTA
Volume 66, Issue 7, Pages 1171-1184Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/S0016-7037(01)00848-1
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Phosphorus regeneration and burial fluxes during and after formation of the most recent sapropel Sl were determined for two deep-basin, low-sedimentation sites in the eastern Mediterranean Sea. Organic C/P ratios and burial fluxes indicate enhanced regeneration of P relative to C during deposition of sapropel S1. This is largely due to the enhanced release of P from organic matter during sulfate reduction. Release of P from Fe-bound P also increased, but this was only a relatively minor source of dissolved P. Pore-water HPO42- concentrations remained too low for carbonate fluorapatite formation. An increased burial of biogenic Ca-P (i.e., fish debris) was observed for one site. Estimated benthic fluxes of P during sapropel formation were elevated relative to the present day (similar to900 to 2800 vs. similar to70 to 120 mumol m(-2) yr(-1)). The present-day sedimentary P cycle in the deep-basin sediments is characterized by two major zones of reaction: (1) the zone near the sediment-water interface where substantial release of HPO42- from organic matter takes place, and (2) the oxidation front at the top of the S1 where upward-diffusing HPO42- from below the sapropel is sorbed to Fe-oxides. The efficiency of aerobic organisms in retaining P is reflected in the low organic C/P ratios in the oxidized part of the sapropel. Burial efficiencies for reactive P were significantly lower during Sl times compared with the present day (similar to7 to 15% vs. 64 to 77%), Budget calculations for the eastern Mediterranean Sea demonstrate that the weakening of the antiestuarine circulation and the enhanced regeneration of P both contributed to a significant increase in deep-water HPO42- concentrations during sapropel S1 times. Provided that sufficient vertical mixing occurred, enhanced regeneration of P at the seafloor may have played a key role in maintaining increased productivity during sapropel S1 formation. Copyright (C) 2002 Elsevier Science Ltd.
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