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The role of mat-forming diatoms in formation of Mediterranean sapropels

The role of mat-forming diatoms in formation of Mediterranean sapropels
The role of mat-forming diatoms in formation of Mediterranean sapropels
The origins of sapropels (sedimentary layers rich in organic carbon) are unclear, yet they may be a key to understanding the influence of climate on ocean eutrophication, the mechanisms of sustaining biological production in stratified waters and the genesis of petroleum source rocks. Recent microfossil studies of foraminifera and calcareous nannofossils have focused attention on a deep chlorophyll maximum as a locus for the high production inferred for sapropel formation, but have not identified the agent responsible. Here we report the results of a high-resolution, electron-microscope-based study of a late Quaternary laminated sapropel in which the annual flux cycle has been preserved. We find that much of the production was by diatoms, both mat-forming and other colonial forms, adapted to exploit a deep nutrient supply trapped below surface waters in a stratified water column. Reconstructed organic-carbon and opal fluxes to the sediments are comparable to those at high-productivity sites in today's oceans, and calculations based on diatom Si/C ratios suggest that the high organic-carbon content of sapropels may be entirely accounted for by sedimenting diatoms. We propose that this style of production may have been common in ancient Palaeogene and Cretaceous seas, environments for which conventional appeals to upwelling-driven production to account for the occurrence of diatomites, and some organic-carbon-rich sediments, have never seemed wholly appropriate.
0028-0836
57-61
Kemp, A.E.S.
131b479e-c2c4-47ae-abe1-ad968490960e
Pearce, R.B.
7d772b25-3ad0-4909-9a96-3a1a8111bc2f
Koizumi, I.
fcdf4306-ce72-421b-a3db-e2deac3da850
Pike, J.
a752c052-98ae-4c4c-967d-051bc9586219
Rance, S.J.
b3b2b523-351c-44ff-8d57-57a50c6ded99
Kemp, A.E.S.
131b479e-c2c4-47ae-abe1-ad968490960e
Pearce, R.B.
7d772b25-3ad0-4909-9a96-3a1a8111bc2f
Koizumi, I.
fcdf4306-ce72-421b-a3db-e2deac3da850
Pike, J.
a752c052-98ae-4c4c-967d-051bc9586219
Rance, S.J.
b3b2b523-351c-44ff-8d57-57a50c6ded99

Kemp, A.E.S., Pearce, R.B., Koizumi, I., Pike, J. and Rance, S.J. (1999) The role of mat-forming diatoms in formation of Mediterranean sapropels. Nature, 398 (6722), 57-61. (doi:10.1038/18001).

Record type: Article

Abstract

The origins of sapropels (sedimentary layers rich in organic carbon) are unclear, yet they may be a key to understanding the influence of climate on ocean eutrophication, the mechanisms of sustaining biological production in stratified waters and the genesis of petroleum source rocks. Recent microfossil studies of foraminifera and calcareous nannofossils have focused attention on a deep chlorophyll maximum as a locus for the high production inferred for sapropel formation, but have not identified the agent responsible. Here we report the results of a high-resolution, electron-microscope-based study of a late Quaternary laminated sapropel in which the annual flux cycle has been preserved. We find that much of the production was by diatoms, both mat-forming and other colonial forms, adapted to exploit a deep nutrient supply trapped below surface waters in a stratified water column. Reconstructed organic-carbon and opal fluxes to the sediments are comparable to those at high-productivity sites in today's oceans, and calculations based on diatom Si/C ratios suggest that the high organic-carbon content of sapropels may be entirely accounted for by sedimenting diatoms. We propose that this style of production may have been common in ancient Palaeogene and Cretaceous seas, environments for which conventional appeals to upwelling-driven production to account for the occurrence of diatomites, and some organic-carbon-rich sediments, have never seemed wholly appropriate.

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Published date: March 1999

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Local EPrints ID: 37572
URI: http://eprints.soton.ac.uk/id/eprint/37572
ISSN: 0028-0836
PURE UUID: 751a37b9-568c-4e67-800b-8c884f3b5942

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Date deposited: 23 May 2006
Last modified: 15 Jul 2019 19:04

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