Abstract. Coccolithophore responses to changes in carbonate chemistry speciation such
as CO2 and H+ are highly modulated by light intensity and
temperature. Here, we fit an analytical equation, accounting for simultaneous
changes in carbonate chemistry speciation, light and temperature, to
published and original data for Emiliania huxleyi, and compare the
projections with those for Gephyrocapsa oceanica. Based on our
analysis, the two most common bloom-forming species in present-day
coccolithophore communities appear to be adapted for a similar fundamental
light niche but slightly different ones for temperature and CO2,
with E. huxleyi having a tolerance to lower temperatures and higher
CO2 levels than G. oceanica. Based on growth rates, a
dominance of E. huxleyi over G. oceanica is projected below
temperatures of 22 ∘C at current atmospheric CO2 levels.
This is similar to a global surface sediment compilation of E. huxleyi and G. oceanica coccolith abundances suggesting
temperature-dependent dominance shifts. For a future Representative
Concentration Pathway (RCP) 8.5 climate change scenario (1000 µatm
fCO2), we project a CO2 driven niche contraction for
G. oceanica to regions of even higher temperatures. However, the
greater sensitivity of G. oceanica to increasing CO2 is
partially mitigated by increasing temperatures. Finally, we compare
satellite-derived particulate inorganic carbon estimates in the surface ocean
with a recently proposed metric for potential coccolithophore success on the
community level, i.e. the temperature-, light- and
carbonate-chemistry-dependent CaCO3 production potential (CCPP).
Based on E. huxleyi alone, as there was interestingly a better
correlation than when in combination with G. oceanica, and excluding
the Antarctic province from the analysis, we found a good correlation between
CCPP and satellite-derived particulate inorganic carbon (PIC) with an R2
of 0.73, p < 0.01 and a slope of 1.03 for austral winter/boreal
summer and an R2 of 0.85, p < 0.01 and a slope of 0.32 for
austral summer/boreal winter.