Open AccessCharacterization of Mg/Ca distributions in planktonic foraminifera species by electron microprobe mapping
Author(s) -
Sadekov Aleksey Yu.,
Eggins Stephen M.,
De Deckker Patrick
Publication year - 2005
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2005gc000973
Subject(s) - foraminifera , electron microprobe , seawater , globigerinoides , geology , calcification , water column , plankton , mole , oceanography , mineralogy , chemistry , medicine , biochemistry , pathology , benthic zone
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.