Carbon Isotopic Fractionation of Alkenones and <i>Gephyrocapsa</i> Coccoliths Over the Late Quaternary (Marine Isotope Stages 12–9) Glacial‐Interglacial Cycles at the Western Tropical Atlantic

The sensitivity of coccolithophores to changing CO2 and its role modulating cellular photosynthetic carbon isotopic fractionation (εp) is crucial understand the future adaptation these organisms higher world assess reliability εp for past estimation. Here, we present measured on natural fossil samples across glacial-interglacial (G-I) variations marine isotope stages 12 9 interval (454–334 ka) at western tropical Atlantic Ocean Drilling Program Site 925 together with a set organic inorganic geochemical, micropaleontological morphometrical data from Gephyrocapsa coccoliths in same samples. ∼2‰ variation significantly correlated CO2[aq] concentrations calculated assumption air-sea equilibrium ice core pCO2 concentrations. similar that derived multiple regression model culture observations not well simulated classical purely diffusive algal acquisition. range cell sizes insufficient explain non-CO2 effects this location, via either direct size effect or growth rate size. Primary productivity, potentially triggered by shifting rates light levels, may also affect εp. Proposed productivity proxies % Florisphaera profunda ratio between C37 C38.et alkenone (C37/C38.et ratio) both correlates modestly When observed G-I site used estimate since Miocene, inferred declines are larger amplitude compared theoretical model. We find oxygen stable vital near monogeneric-separated (respectively Δδ18OGephyrocapsa–Trilobatus sacculifer εcoccolith) coupled through time series, but origins readily explained existing models.