MEPS 508:53-66 (2014)  -  DOI:

Isotopic fractionation of carbon in the coccolithophorid Emiliania huxleyi 

Dan Tchernov1,*, David F. Gruber2, Andrew Irwin3

1Marine Biology Department, The Leon H. Charney School of Marine Sciences, University of Haifa, Mount Carmel, Haifa 31905, Israel
2Department of Natural Sciences, Baruch College, City University of New York and Sackler Institute for Comparative Genomics, American Museum of Natural History, New York, NY, USA
3Department of Mathematics and Computer Science, Mount Allison University, Sackville, New Brunswick, Canada
*Corresponding author:

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.

KEY WORDS: Emiliania huxleyi · Calcifying phytoplankton · Isotopic fractionation of carbon · Vital effects · Paleo-CO2 reconstruction · Temperature · Carbon-concentrating mechanism

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Cite this article as: Tchernov D, Gruber DF, Irwin A (2014) Isotopic fractionation of carbon in the coccolithophorid Emiliania huxleyi . Mar Ecol Prog Ser 508:53-66.

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