Fig. 4.

Stable carbon and oxygen isotopes of O. neapolitana compared to other coccolithophore species. Atmospheric pCO₂ vs. Δ¹³C_PIC (a), Δ¹³C_POC (b), and Δ¹⁸O_PIC (c) for O. neapolitana (black solid circles) and other coccolithophore species. Δ¹⁸O_PIC and most Δ¹³C_POC data for O. neapolitana fall within the range reported for other species, with Δ¹³C_PIC being markedly higher. Offsets may be attributable to differences in species and/or method of acidification, as most past studies manipulate seawater pH via acid–base addition (labeled in gray), while the present study varied seawater pH via CO₂ gas manipulation. Both the trends and absolute values of stable carbon and oxygen isotopes of O. neapolitana are compatible with the framework recently proposed by McClelland et al.⁵², as expanded on in Fig. 5 and the main text