Surface temperatures coupled with carbon dioxide concentrations during the Paleozoic Era

Appropriateness of the inorganic Δ47-temperature calibration for brachiopods and molluscs Ghosh et al. (2006) 1 determined the relationship between Δ47 and temperature (Eq 4) by analyzing the CO2 extracted from synthetic calcites grown in the laboratory at known, controlled temperatures. In addition, they analyzed natural surface-dwelling corals (Porites) and deep-sea corals (D. dianthus), which grew at known, approximately constant temperatures 1. Their results indicate that the vital effects that influence the δ18O and δ13C of surface-dwelling and deep-sea corals do not influence the Δ47 values of the CO2 extracted from that carbonate 1. This result is consistent with models for vital effects 2, 3, which describe the δ18O and δ13C offsets as reservoir effects, rather than kinetic fractionations. Recent calibration work 4 reveals that fish otolith carbonate, which also suffers from vital effects in δ18O and δ13C, does not exhibit a significant offset from the Ghosh et al. (2006) 1 calibration of the relationship between growth temperature and the ∆47 of CO2. As part of the current study, we analyzed naturally occurring brachiopods and molluscs (the two phyla from which we obtained Paleozoic temperatures based on carbonate clumped isotope thermometry) that grew at known temperatures in the modern ocean (see Supplementary Table 1 and Supplementary Figure 1). The ∆47 values of CO2 extracted from brachiopod carbonate are plotted vs. mean annual temperatures 5, whereas the ∆47 values of CO2 extracted from mollusc carbonate,