Open AccessCalcium isotope fractionation during coccolith formation in Emiliania huxleyi: Independence of growth and calcification rate
Author(s) -
Langer Gerald,
Gussone Nikolaus,
Nehrke Gernot,
Riebesell Ulf,
Eisenhauer Anton,
Thoms Silke
Publication year - 2007
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2006gc001422
Subject(s) - emiliania huxleyi , coccolithophore , coccolith , fractionation , calcium , isotope fractionation , seawater , isotopes of calcium , oxygen isotope ratio cycle , geology , calcite , mineralogy , chemistry , oceanography , phytoplankton , carbonate , chromatography , nutrient , organic chemistry
Recently, calcium isotope fractionation in the coccolithophore Emiliania huxleyi was shown to exhibit a significant temperature dependency. An important subsequent question in this context is whether the observed fractionation patterns are caused by temperature itself or related growth rate changes. In order to separate growth and calcification rate effects from direct temperature effects, batch culture experiments with the coccolithophore E. huxleyi were conducted under varying light intensities. Despite large changes in cellular growth and calcification rates, calcium isotope fractionation remained constant. Independence of calcium isotope fractionation on growth and calcification was also obtained in two additional sets of experiments in which growth rates changed in response to varying calcium concentration and seawater salinity. These experiments also showed no direct effects of calcium concentration and salinity on calcium isotope fractionation. Values for calcium isotope fractionation of E. huxleyi coccoliths fell within a range of −1.0 to −1.6 (1000 ln α ), confirming earlier results. This range is similar to that observed in several foraminiferal species and coccolith oozes, suggesting a rather homogeneous calcium isotopic composition in marine biogenic calcite. Our data further show that the calcium isotope fractionation does not change with changing isotopic composition of seawater. This is a basic requirement for reconstructing the calcium isotopic composition of the ocean over time.