Climate sensitivity derived from orbital-scale, δ11B-based pCO2 estimates in the early Pleistocene, ~1.5 Ma

Abstract:

Atmospheric CO₂ concentrations in the late Pleistocene have been characterized from ancient air bubbles trapped within polar ice sheets. Ice-core records clearly demonstrate the glacial-interglacial relationship between the global carbon cycle and climate, but they are so far limited to the last 800 ky, when glacial cycles occurred approximately every 100-ky. Boron isotope ratios (δ¹¹B) recorded in the tests of fossil planktic foraminifera offer an opportunity to extend the atmospheric pCO₂ record into the early Pleistocene, when glacial cycles instead occurred approximately every 41-ky. We present a new high-resolution record of planktic foraminiferal d¹¹B, Mg/Ca (a sea surface temperature proxy) and salinity estimates from the deconvolution of δ¹⁸O and Mg/Ca. Combined with reasonable assumptions of ocean alkalinity, these data allow us to estimate pCO₂ over three of the 41-ky climate cycles at ~1.5 Ma. Our results confirm the hypothesis that climate and atmospheric pCO₂ were coupled beyond ice core records and provide new constraints for studies of long-term CO₂ storage and release, regional controls on the early Pleistocene carbon cycle, and estimating climate sensitivity before the mid-Pleistocene transition.