Enhanced regeneration of phosphorus during formation of the most recent eastern Mediterranean sapropel (S1)

Slomp, C.P.; Thomson, J.; De Lange, G.J.. 2002 Enhanced regeneration of phosphorus during formation of the most recent eastern Mediterranean sapropel (S1). Geochimica et Cosmochimica Acta, 66 (7). 1171-1184. https://doi.org/10.1016/S0016-7037(01)00848-1

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Abstract/Summary

Phosphorus regeneration and burial fluxes during and after formation of the most recent sapropel S1 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 (~900 to 2800 vs. ~70 to 120 mol 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 S1 times compared with the present day (~7 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.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	https://doi.org/10.1016/S0016-7037(01)00848-1
ISSN:	0016-7037
Additional Keywords:	PHOSPHORUS, SAPROPELS, ORGANIC CARBON, MEDITERRANEAN SEA
Date made live:	08 Jun 2004 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/106012

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