Characterization of Mg/Ca distributions in planktonic foraminifera species by electron microprobe mapping

Aleksey Yu Sadekov, Stephen M. Eggins, Patrick De Deckker

Research output: Contribution to journalArticle

111 Citations (Scopus)

Abstract

The distribution of Mg/Ca within the tests of eight modern planktonic foraminifer species has been characterized using electron microprobe mapping. Species include several that are commonly used for estimation of past seawater temperatures (Globigerinoides ruber, G. sacculifer, Neogloboquadrina incompta (synonym of N. pachyderma dex.), N. dutertrei, and G. truncatulinoides). Each of the investigated species displays large variations in Mg/Ca composition within individual tests. However, the pattern of Mg/Ca variation is notably different between symbiont-bearing and symbiont-free species. In symbiotic species, cyclic Mg/Ca compositional banding occurs that is characterized by narrow (<1-3 μm), high-Mg/Ca (typically 8-11 mmol/mol) bands, intercalated between broader low Mg/Ca (typically 1-5 mmol/mol) bands. This factor of 2-3 difference equates to an apparent calcification temperature change of 10°C or more. Such temperature changes are considered highly improbable and suggest vital effects significantly modify the incorporation of Mg/Ca into the tests of symbiont-bearing species. These vital effects remain poorly understood and demand further careful evaluation as they may need to be accounted for when making reliable reconstructions of past oceanic temperatures. Symbiont-free species typically have fewer and broader compositional bands that may reflect more closely changes in calcification temperature as these species migrate within a water column.

Original languageEnglish
Article numberQ12P06
JournalGeochemistry, Geophysics, Geosystems
Volume6
Issue number12
DOIs
Publication statusPublished - Dec 2005
Externally publishedYes

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planktonic foraminifera
electron probe analysis
Bearings (structural)
Electrons
calcification
symbiont
electrons
Temperature
temperature
Seawater
distribution
broadband
Water
evaluation
Chemical analysis
water column
water
seawater
test

Cite this

@article{8846571320c344f19cd4254fec138c07,
title = "Characterization of Mg/Ca distributions in planktonic foraminifera species by electron microprobe mapping",
abstract = "The distribution of Mg/Ca within the tests of eight modern planktonic foraminifer species has been characterized using electron microprobe mapping. Species include several that are commonly used for estimation of past seawater temperatures (Globigerinoides ruber, G. sacculifer, Neogloboquadrina incompta (synonym of N. pachyderma dex.), N. dutertrei, and G. truncatulinoides). Each of the investigated species displays large variations in Mg/Ca composition within individual tests. However, the pattern of Mg/Ca variation is notably different between symbiont-bearing and symbiont-free species. In symbiotic species, cyclic Mg/Ca compositional banding occurs that is characterized by narrow (<1-3 μm), high-Mg/Ca (typically 8-11 mmol/mol) bands, intercalated between broader low Mg/Ca (typically 1-5 mmol/mol) bands. This factor of 2-3 difference equates to an apparent calcification temperature change of 10°C or more. Such temperature changes are considered highly improbable and suggest vital effects significantly modify the incorporation of Mg/Ca into the tests of symbiont-bearing species. These vital effects remain poorly understood and demand further careful evaluation as they may need to be accounted for when making reliable reconstructions of past oceanic temperatures. Symbiont-free species typically have fewer and broader compositional bands that may reflect more closely changes in calcification temperature as these species migrate within a water column.",
keywords = "Electron microprobe, Mg/Ca thermometry, Paleoceanography, Planktonic foraminifera, Vital effect",
author = "Sadekov, {Aleksey Yu} and Eggins, {Stephen M.} and {De Deckker}, Patrick",
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Characterization of Mg/Ca distributions in planktonic foraminifera species by electron microprobe mapping. / Sadekov, Aleksey Yu; Eggins, Stephen M.; De Deckker, Patrick.

In: Geochemistry, Geophysics, Geosystems, Vol. 6, No. 12, Q12P06, 12.2005.

Research output: Contribution to journalArticle

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AB - The distribution of Mg/Ca within the tests of eight modern planktonic foraminifer species has been characterized using electron microprobe mapping. Species include several that are commonly used for estimation of past seawater temperatures (Globigerinoides ruber, G. sacculifer, Neogloboquadrina incompta (synonym of N. pachyderma dex.), N. dutertrei, and G. truncatulinoides). Each of the investigated species displays large variations in Mg/Ca composition within individual tests. However, the pattern of Mg/Ca variation is notably different between symbiont-bearing and symbiont-free species. In symbiotic species, cyclic Mg/Ca compositional banding occurs that is characterized by narrow (<1-3 μm), high-Mg/Ca (typically 8-11 mmol/mol) bands, intercalated between broader low Mg/Ca (typically 1-5 mmol/mol) bands. This factor of 2-3 difference equates to an apparent calcification temperature change of 10°C or more. Such temperature changes are considered highly improbable and suggest vital effects significantly modify the incorporation of Mg/Ca into the tests of symbiont-bearing species. These vital effects remain poorly understood and demand further careful evaluation as they may need to be accounted for when making reliable reconstructions of past oceanic temperatures. Symbiont-free species typically have fewer and broader compositional bands that may reflect more closely changes in calcification temperature as these species migrate within a water column.

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