MICROFOSSIL δ11B AS A PROXY FOR ORBITAL-SCALE pCO2 CHANGE IN THE EARLY PLEISTOCENE (Invited Presentation)

Atmospheric CO₂ concentrations in the late Pleistocene have been characterized from ancient air bubbles trapped within polar ice sheets which demonstrate the glacial-interglacial relationship between the global carbon cycle and climate. However, continuous ice core records 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 to earlier time periods, when glacial cycles instead occurred approximately every 41-ky. We present new high-resolution records of planktic foraminiferal δ¹¹B, Mg/Ca (a sea surface temperature proxy), and δ¹⁸O. Combined with reasonable assumptions for ocean alkalinity, these data allow us to estimate pCO₂ over three of the 41-ky climate cycles at ~1.5 Ma. Our results provide new constraints for studies of long-term CO₂ storage and release, regional controls on the early Pleistocene carbon cycle, and pCO₂ variability before the mid-Pleistocene transition.