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| Titel |
Morphological, geochemical, and ecological differences of two extant menardiform globorotaliid planktonic foraminifera |
| VerfasserIn |
Marcus Regenberg, Sven N. Nielsen, Wolfgang Kuhnt, Ann Holbourn |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250043506
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| Zusammenfassung |
| Taxonomic consistency is the basic prerequisite for any foraminiferal study. In particular,
interpretation of planktonic foraminiferal geochemical data requires consistent selection of
monospecific tests, since different species are adapted to different ecological niches and
hence different calcification depths. Recording stable isotope signals and temperatures of
ambient seawater during calcification, species-specific planktonic foraminiferal oxygen
isotope values (δ18O) and Mg/Ca ratios reflect environmental conditions at different depth
levels of the upper water column, which makes them suitable for paleoceanographic and
climate reconstructions. However, since slight morphological differences may reflect
different life habitats, the geochemical composition of a foraminiferal sample is
highly dependent on the selection of morphologically alike specimens used for
analysis. In order to exemplify the impact of unintended mixing of slightly varying
species on δ18O values and Mg/Ca ratios, this study investigates morphological
characteristics and geochemical signatures of Globorotalia cultrata (d’Orbigny, 1839) and
Globorotalia menardii (Parker, Jones & Brady, 1865). Both species are often assembled as
“G. menardii” group or referred to as synonyms and are commonly suggested to
represent seasonal thermocline habitats. In general, both nonspinose species precipitate
circular to oval, lobulate, and low trochospiral tests showing 5–6 chambers in the final
whorl. The perforate chambers meet at limbate sutures, which are straight on the
umbilical side and curved on the spiral side. Tests are rimmed with an imperforate
keel. The umbilical extra-umbilical aperture is furnished with an imperforate lip. In
contrast, tests of G. cultrata differ from G. menardii in surface and keel. The surface
of G. cultrata is smooth and shiny, at shallow sites transparent, and shows only
few subconical pustules of sizes |
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