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Living (Rose-Bengal-stained) benthic foraminiferal faunas along a strong bottom-water oxygen gradient on the Indian margin (Arabian Sea)

Living (Rose-Bengal-stained) benthic foraminiferal faunas along a strong bottom-water oxygen gradient on the Indian margin (Arabian Sea)
Living (Rose-Bengal-stained) benthic foraminiferal faunas along a strong bottom-water oxygen gradient on the Indian margin (Arabian Sea)
Rose-Bengal-stained foraminiferal assemblages (> 150 ?m) were analysed along a five-station bathymetric transect across the core and the lower part of the oxygen minimum zone (OMZ) on the Indian margin of the Arabian Sea. Sediment cores were collected using the manned submersible Shinkai 6500 during the RV Yokosuka cruise YK08-11 in the post-monsoon season (October 2008) at water depths ranging from 535 to 2000 m, along a gradient from almost anoxic to well-oxygenated (0.3 to 108 ?M) bottom waters. Stained benthic foraminifera were investigated from two different size fractions (150–300 ?m and > 300 ?m). Stained foraminiferal densities were very high in the core of the OMZ (at 535 and 649 m) and decreased at deeper sites. The faunas (> 150 ?m) were dominated (40–80 %) by non-calcareous taxa at all stations. These were mainly species of Reophax and Lagenammina but also included delicate monothalamous taxa (organic-walled "allogromiids", agglutinated saccamminids, psammosphaerids and tubular forms). These new data from the Indian margin are compared to previous studies from the Murray Ridge, the Pakistan margin and the Oman margin. The fact that similar species were found at sites with comparable bottom-water oxygen concentrations but with very different surface water productivity suggests that, within the strongly developed Arabian Sea OMZ, bottom-water oxygen concentration, and not the organic flux to the sea floor, is the main factor controlling the species composition of the foraminiferal communities. Several foraminiferal species (e.g. Praeglobobulimina sp. 1, Ammodiscus sp. 1, Bolivina aff. dilatata) were confined to the core of the OMZ. These species are presently known only from the Arabian Sea. Because of their association with extremely low oxygen concentrations, these species may be good markers for very low oxygen concentrations, and could be used to reconstruct past OMZ variability in the Arabian Sea.
1726-4170
5005-5019
Caulle, C.
c5173a99-ddf9-4ae5-bc30-b0b26f1a0e1d
Mojtahid, M.
7aaf70ba-de8e-422e-8905-6ba3affdc143
Gooday, A.J.
d9331d67-d518-4cfb-baed-9df3333b05b9
Jorissen, F.J.
5e9da85b-8b77-465e-8816-0ed4acf2da63
Kitazato, H.
aeaa64e4-279a-4089-b0af-a733500f2e3b
Caulle, C.
c5173a99-ddf9-4ae5-bc30-b0b26f1a0e1d
Mojtahid, M.
7aaf70ba-de8e-422e-8905-6ba3affdc143
Gooday, A.J.
d9331d67-d518-4cfb-baed-9df3333b05b9
Jorissen, F.J.
5e9da85b-8b77-465e-8816-0ed4acf2da63
Kitazato, H.
aeaa64e4-279a-4089-b0af-a733500f2e3b

Caulle, C., Mojtahid, M., Gooday, A.J., Jorissen, F.J. and Kitazato, H. (2015) Living (Rose-Bengal-stained) benthic foraminiferal faunas along a strong bottom-water oxygen gradient on the Indian margin (Arabian Sea). Biogeosciences, 12 (16), 5005-5019. (doi:10.5194/bg-12-5005-2015).

Record type: Article

Abstract

Rose-Bengal-stained foraminiferal assemblages (> 150 ?m) were analysed along a five-station bathymetric transect across the core and the lower part of the oxygen minimum zone (OMZ) on the Indian margin of the Arabian Sea. Sediment cores were collected using the manned submersible Shinkai 6500 during the RV Yokosuka cruise YK08-11 in the post-monsoon season (October 2008) at water depths ranging from 535 to 2000 m, along a gradient from almost anoxic to well-oxygenated (0.3 to 108 ?M) bottom waters. Stained benthic foraminifera were investigated from two different size fractions (150–300 ?m and > 300 ?m). Stained foraminiferal densities were very high in the core of the OMZ (at 535 and 649 m) and decreased at deeper sites. The faunas (> 150 ?m) were dominated (40–80 %) by non-calcareous taxa at all stations. These were mainly species of Reophax and Lagenammina but also included delicate monothalamous taxa (organic-walled "allogromiids", agglutinated saccamminids, psammosphaerids and tubular forms). These new data from the Indian margin are compared to previous studies from the Murray Ridge, the Pakistan margin and the Oman margin. The fact that similar species were found at sites with comparable bottom-water oxygen concentrations but with very different surface water productivity suggests that, within the strongly developed Arabian Sea OMZ, bottom-water oxygen concentration, and not the organic flux to the sea floor, is the main factor controlling the species composition of the foraminiferal communities. Several foraminiferal species (e.g. Praeglobobulimina sp. 1, Ammodiscus sp. 1, Bolivina aff. dilatata) were confined to the core of the OMZ. These species are presently known only from the Arabian Sea. Because of their association with extremely low oxygen concentrations, these species may be good markers for very low oxygen concentrations, and could be used to reconstruct past OMZ variability in the Arabian Sea.

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Published date: 25 August 2015
Organisations: Marine Biogeochemistry

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Local EPrints ID: 382541
URI: https://eprints.soton.ac.uk/id/eprint/382541
ISSN: 1726-4170
PURE UUID: aad31e12-8434-4b80-830d-f765c3cbef53

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Date deposited: 06 Oct 2015 16:12
Last modified: 17 Jul 2017 20:20

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Contributors

Author: C. Caulle
Author: M. Mojtahid
Author: A.J. Gooday
Author: F.J. Jorissen
Author: H. Kitazato

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