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Perturbing phytoplankton: a tale of isotopic fractionation in two coccolithophore species
R. E. M. Rickaby1,**, J. Henderiks2,*, and J. N. Young1
1Department of Earth Sciences, Oxford University, Parks Road, Oxford, OX1 3PR, UK
2Department of Geology and Geochemistry, Stockholm University, Sweden
*now at: Department of Earth Sciences, Paleobiology Program, Uppsala University, Villavägen 16, 75 236 Uppsala, Sweden
**Invited contribution by R. E. M. Rickaby, one of the EGU Outstanding Young Scientist Award winners 2008.
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Abstract. No two species of coccolithophore appear to respond to perturbations
of carbonate chemistry in the same way. Here, we show that the degree of
malformation, growth rate and stable isotopic composition of organic matter
and carbonate produced by two contrasting species of coccolithophore
(Gephyrocapsa oceanica and Coccolithus pelagicus ssp. braarudii) are
indicative of differences between their photosynthetic and calcification
response to changing dissolved inorganic carbon (DIC) levels (ranging from
~1100 to ~7800 μmol kg−1) at constant pH
(8.13±0.02). G. oceanica thrived under all
conditions of DIC, showing evidence of increased growth rates at higher DIC,
but C. braarudii was detrimentally affected at
high DIC showing signs of malformation, and decreased growth rates. The
carbon isotopic fractionation into organic matter and the coccoliths
suggests that C. braarudii utilises a common
internal pool of carbon for calcification and photosynthesis but
G. oceanica relies on independent supplies for
each process. All coccolithophores appear to utilize bicarbonate as their
ultimate source of carbon for calcification resulting in the release of a
proton. But, we suggest that this proton can be harnessed to enhance the
supply of aqueous dissolved carbon dioxide (CO2(aq)) for
photosynthesis either from a large internal bicarbonate ion
(HCO3-) pool which acts as a pH buffer
(C. braarudii), or pumped externally to aid the
diffusive supply of CO2 across the membrane from the abundant
HCO3- (G. oceanica), likely
mediated by an internal and external carbonic anhydrase, respectively. Our
simplified hypothetical spectrum of physiologies may provide a context to
understand different species response to changing pH and DIC, the
species-specific εp and calcite "vital effects", as well as accounting for geological trends in coccolithophore
cell size.
 Notice on Discussion StatusThe requested discussion paper has a corresponding peer-reviewed
final revised paper in the journal Climate of the Past (CP). You are
encouraged to refer to the final revised version. Final Revised Paper (CP) Discussion Paper (PDF, 2130 KB)
Citation: Rickaby, R. E. M., Henderiks, J., and Young, J. N.: Perturbing phytoplankton: a tale of isotopic fractionation in two coccolithophore species, Clim. Past Discuss., 6, 257-294, doi:10.5194/cpd-6-257-2010, 2010. Bibtex EndNote Reference Manager XML
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