Isotopic fractionation of carbon in the coccolithophorid Emiliania huxleyi

Marine Ecology Progress Series

David F. Gruber¹  Dan Tchernov¹  Andrew Irwin¹ 

关键词: Emiliania huxleyi;    Calcifying phytoplankton;    Isotopic fractionation of carbon;    Vital effects;    Paleo-CO2 reconstruction;    Temperature;    Carbon-concentrating mechanism;   

DOI  :  10.3354/meps10840

学科分类：海洋学与技术

来源: Inter-Research

【 摘 要 】

ABSTRACT: Relating atmospheric CO₂ to β¹³C of calcifying phytoplankton is often used as a proxy to reconstruct paleo-CO₂. Therefore, a firm undertanding of how living cells fractionate carbon under different environmental conditions (known as vital effects) is necessary when interpreting δ¹³C values. In this study, we measured the isotopic fractionation of carbon in organic matter (ε_p) in the globally distributed, bloom-forming coccolithophorid Emiliania huxleyi grown in continuous culture under nutrient-replete conditions with growth rate limited by light or temperature. At a constant temperature of 18°C, growth followed a hyperbolic function of irradiance. At low irradiance levels, changes in ε_p were highly correlated with growth rate. However, as growth became light-saturated, ε_p declined with increasing light intensities. When temperature was increased from 7 to 18°C at a constant photon flux density, equilibrium partial pressure CO₂ concentrations ([pCO₂]) decreased from 17 to 13 µM, and ε_p values declined from 25 to 19‰. As temperature was increased further to 26°C, [pCO₂] declined to 10 µM and ε_p increased to 25‰. This non-linear pattern in isotopic fractionation is consistent with the induction of a carbon-concentrating mechanism at low [pCO₂] that replenishes the internal inorganic carbon pool with isotopically lighter carbon. In this study, we present an empirical model that predicts this non-linear behavior, and we validate this model with experimental data. These results suggest extreme variability in the isotopic fractionation of carbon in the bulk organic pool in E. huxleyi that precludes the reconstruction of pCO₂ from isotopic measurements without a priori knowledge of temperature.

【 授权许可】

Unknown