Controls on Alkenone Carbon Isotope Fractionation in the Modern Ocean

Abstract

Past field observations have shown that ε p is related to the growth environment, including ambient CO 2 concentrations, temperature, and irradiance, as well as algal physiology (

Atmospheric CO2 Concentration Based on Boron Isotopes Versus Simulations of the Global Carbon Cycle During the Plio‐Pleistocene

“…Another study, although focusing on deeper times, suggests that the calibration of the alkenone-based approach requires a revision (Rae et al, 2021). Phelps et al (2021) recently argued that the theory for the alkenone carbon isotope fractionation model is not supported by field data and should not be used to reconstruct past CO 2 changes before further studies successfully account for the effects of irradiance and cell size variations on isotopic fractionation. Furthermore, a recent review on carbon isotope fractionation in marine phytoplankton (Brandenburg et al, 2022) shows that ɛ p can vary significantly between different phytoplankton species and groups, but also as a result of different culturing methods and differences in daylength.…”

Proxy‐Model Comparison for the Eocene‐Oligocene Transition in Southern High Latitudes

“…The absolute p CO 2 levels are uncertain in the past, due to factors such as boron isotope seawater uncertainties; however, the boron isotope is better at assessing relative change (Raitzsch & Hönisch, 2013). For the alkenone p CO 2 estimates, uncertainties derive from the “b” parameter associated with growth rate and diffusion (Y. G. Zhang et al., 2020) as well as the effects of irradiance on the carbon isotope fractionation (Phelps et al., 2021). The boron and alkenone isotopes are well studied for the EOT and have a high amount of data relative to other p CO 2 proxies.…”

Alkenone-derived estimates of Cretaceous pCO2

“…We note that the alkenone paleobarometer methodology is in a period of flux (e.g., Phelps et al, 2021;Stoll et al, 2019). As alkenone pCO2 estimation methodology evolves, the values presented here will likely be updated.…”