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Source and development of large manganese enrichments above eastern Mediterranean sapropel S1

Source and development of large manganese enrichments above eastern Mediterranean sapropel S1
Source and development of large manganese enrichments above eastern Mediterranean sapropel S1
The residual dark unit of the most recent eastern Mediterranean sapropel (S1) is usually overlain by sediments with enhanced concentrations of MnOx in two separated layers. The variability and magnitude of the Mn enrichment at different locations and water depths indicate that Mn must have been added preferentially to sediments at intermediate (1–2 km) water depths. We propose a two-stage mechanism for the Mn enrichment that involves decreasing oxygenation with increasing water depth. This mechanism involves the loss of reduced Mn2+ from the deepest sediments (>2 km water depth) into overlying anoxic waters and a variable gain of MnOx in sediments in contact with oxygenated waters at shallower depth. In the S1 unit that receives the extra MnOx input, an upper higher Mn-enriched zone (>3 wt %) is maintained continuously at the top of the accumulating S1 unit because the pore waters are anoxic at shallow sediment depth while bottom waters are oxic to some degree. In a reactive-transport model, the Mn enrichment in the upper zone could not be supported by normal sediment diagenesis. Thus the MnOx in the upper Mn horizon must have formed mainly in the water column. The MnOx in the upper Mn-enriched zone adsorbed Mo and Li from seawater in a similar manner as other Mn-enriched oxic sediments, nodules, and crusts, with a Mn:Mo ratio of ~600:1, a Mn:Li ratio of ~750:1, and a ?98/95MoMOMO of ?2.5 ‰
manganese, sapropel SI, eastern Mediterranean, molybdenum, lithium
0883-8305
PA3007
Reitz, A.
e25f1ee0-d381-435f-8991-faa8b1df8a13
Thomson, J.
3395054f-e507-4841-9758-a06ed37f7d6b
de Lange, G.J.
f3a5a890-cb53-44e6-b3b0-77f53bc04dac
Hensen, C.
8bce9be3-c232-49b2-9ec7-9cceb32d5988
Reitz, A.
e25f1ee0-d381-435f-8991-faa8b1df8a13
Thomson, J.
3395054f-e507-4841-9758-a06ed37f7d6b
de Lange, G.J.
f3a5a890-cb53-44e6-b3b0-77f53bc04dac
Hensen, C.
8bce9be3-c232-49b2-9ec7-9cceb32d5988

Reitz, A., Thomson, J., de Lange, G.J. and Hensen, C. (2006) Source and development of large manganese enrichments above eastern Mediterranean sapropel S1. Paleoceanography, 21 (3), PA3007. (doi:10.1029/2005PA001169).

Record type: Article

Abstract

The residual dark unit of the most recent eastern Mediterranean sapropel (S1) is usually overlain by sediments with enhanced concentrations of MnOx in two separated layers. The variability and magnitude of the Mn enrichment at different locations and water depths indicate that Mn must have been added preferentially to sediments at intermediate (1–2 km) water depths. We propose a two-stage mechanism for the Mn enrichment that involves decreasing oxygenation with increasing water depth. This mechanism involves the loss of reduced Mn2+ from the deepest sediments (>2 km water depth) into overlying anoxic waters and a variable gain of MnOx in sediments in contact with oxygenated waters at shallower depth. In the S1 unit that receives the extra MnOx input, an upper higher Mn-enriched zone (>3 wt %) is maintained continuously at the top of the accumulating S1 unit because the pore waters are anoxic at shallow sediment depth while bottom waters are oxic to some degree. In a reactive-transport model, the Mn enrichment in the upper zone could not be supported by normal sediment diagenesis. Thus the MnOx in the upper Mn horizon must have formed mainly in the water column. The MnOx in the upper Mn-enriched zone adsorbed Mo and Li from seawater in a similar manner as other Mn-enriched oxic sediments, nodules, and crusts, with a Mn:Mo ratio of ~600:1, a Mn:Li ratio of ~750:1, and a ?98/95MoMOMO of ?2.5 ‰

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More information

Published date: 2006
Keywords: manganese, sapropel SI, eastern Mediterranean, molybdenum, lithium

Identifiers

Local EPrints ID: 44166
URI: http://eprints.soton.ac.uk/id/eprint/44166
ISSN: 0883-8305
PURE UUID: 904c7444-23b1-40be-bc54-53519a7f8c4d

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Date deposited: 16 Feb 2007
Last modified: 15 Mar 2024 09:01

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Contributors

Author: A. Reitz
Author: J. Thomson
Author: G.J. de Lange
Author: C. Hensen

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