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Distribution of diatoms, coccolithophores and planktic foraminifers along a trophic gradient during SW monsoon in the Arabian Sea

Distribution of diatoms, coccolithophores and planktic foraminifers along a trophic gradient during SW monsoon in the Arabian Sea
Distribution of diatoms, coccolithophores and planktic foraminifers along a trophic gradient during SW monsoon in the Arabian Sea
The distribution of diatoms, coccolithophores and planktic foraminifers mirrored the hydrographic and trophic conditions of the surface ocean (0–100 m) across the upwelling area off the Oman coast to the central Arabian Sea during May/June 1997 and July/August 1995. The number of diatoms was increased in waters with local temperature minimum and enhanced nutrient concentration (nitrate, phosphate, silicate) caused by upwelling. Vegetative cells of Chaetoceros dominated the diatom assemblage in the coastal upwelling area. Towards the more nutrient depleted and stratified surface waters to the southeast, the number of diatoms decreased, coccolithophore and planktic foraminiferal numbers increased, and floral and faunal composition changed. In particular, the transition between the eutrophic upwelling region off Oman and the oligotrophic central Arabian Sea was marked by moderate nutrient concentration, and high coccolithophore and foraminifer numbers. Florisphaera profunda, previously often referred as a ‘lower-photic-zone-species’, was frequent in water depths as shallow as 20 m, and at high nutrient concentration up to 14 mol NO3 l?1 and 1.2 mol PO4 l?1. To the oligotrophic southeast of the divergence, cell densities of coccolithophores declined and Umbellosphaera irregularis prevailed throughout the water column down to 100 m depth. In general, total coccolithophore numbers were limited by nutrient threshold concentration, with low numbers (<10×103 cells l?1) at high [NO3] and [PO4], and high numbers (>70×103 cells l?1) at low [NO3] and [PO4]. The components of the complex microplankton succession, diatoms, coccoliths and planktic foraminifers (and possibly others), should ideally be used as a combined paleoceanographic proxy. Consequently, models on plankton ecology should be resolved at least for the seasonality, to account for the bias of paleoceanographic transfer calculations.

coccoliths, diatom flora, foraminifera, nutrients, oceanography, paleoceanography
0377-8398
345-371
Schiebel, R.
e3ee9c3f-ae96-4523-8ec2-2ed7acdfb83a
Zeltner, A.
6bd508e5-fb58-46b0-9393-b0756caa7973
Treppke, U.F.
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Waniek, J.J.
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Bollmann, J.
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Rixen, T.
dc65e23d-a115-4dbd-8aa8-7b1d402d6c66
Hemleben, C.
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Schiebel, R.
e3ee9c3f-ae96-4523-8ec2-2ed7acdfb83a
Zeltner, A.
6bd508e5-fb58-46b0-9393-b0756caa7973
Treppke, U.F.
7236501d-06b6-4adc-8a5d-ca3e5e9ed2d9
Waniek, J.J.
749b55a4-c736-4961-a522-37645dd73b45
Bollmann, J.
412078c1-7dac-43cc-88a8-5c327a339d76
Rixen, T.
dc65e23d-a115-4dbd-8aa8-7b1d402d6c66
Hemleben, C.
0f45ede4-dfec-457e-8a64-b96a5b8c71f0

Schiebel, R., Zeltner, A., Treppke, U.F., Waniek, J.J., Bollmann, J., Rixen, T. and Hemleben, C. (2004) Distribution of diatoms, coccolithophores and planktic foraminifers along a trophic gradient during SW monsoon in the Arabian Sea. Marine Micropaleontology, 51 (3-4), 345-371. (doi:10.1016/j.marmicro.2004.02.001).

Record type: Article

Abstract

The distribution of diatoms, coccolithophores and planktic foraminifers mirrored the hydrographic and trophic conditions of the surface ocean (0–100 m) across the upwelling area off the Oman coast to the central Arabian Sea during May/June 1997 and July/August 1995. The number of diatoms was increased in waters with local temperature minimum and enhanced nutrient concentration (nitrate, phosphate, silicate) caused by upwelling. Vegetative cells of Chaetoceros dominated the diatom assemblage in the coastal upwelling area. Towards the more nutrient depleted and stratified surface waters to the southeast, the number of diatoms decreased, coccolithophore and planktic foraminiferal numbers increased, and floral and faunal composition changed. In particular, the transition between the eutrophic upwelling region off Oman and the oligotrophic central Arabian Sea was marked by moderate nutrient concentration, and high coccolithophore and foraminifer numbers. Florisphaera profunda, previously often referred as a ‘lower-photic-zone-species’, was frequent in water depths as shallow as 20 m, and at high nutrient concentration up to 14 mol NO3 l?1 and 1.2 mol PO4 l?1. To the oligotrophic southeast of the divergence, cell densities of coccolithophores declined and Umbellosphaera irregularis prevailed throughout the water column down to 100 m depth. In general, total coccolithophore numbers were limited by nutrient threshold concentration, with low numbers (<10×103 cells l?1) at high [NO3] and [PO4], and high numbers (>70×103 cells l?1) at low [NO3] and [PO4]. The components of the complex microplankton succession, diatoms, coccoliths and planktic foraminifers (and possibly others), should ideally be used as a combined paleoceanographic proxy. Consequently, models on plankton ecology should be resolved at least for the seasonality, to account for the bias of paleoceanographic transfer calculations.

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More information

Published date: 2004
Keywords: coccoliths, diatom flora, foraminifera, nutrients, oceanography, paleoceanography

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Local EPrints ID: 9868
URI: http://eprints.soton.ac.uk/id/eprint/9868
ISSN: 0377-8398
PURE UUID: 9fef0951-2d72-4075-91d7-56b45630217c

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Date deposited: 14 Oct 2004
Last modified: 15 Mar 2024 04:57

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Contributors

Author: R. Schiebel
Author: A. Zeltner
Author: U.F. Treppke
Author: J.J. Waniek
Author: J. Bollmann
Author: T. Rixen
Author: C. Hemleben

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