Pliocene switch in orbital-scale carbon cycle/climate dynamics

Abstract

The high-frequency (periods of ~10 5 -years) relationship between carbon and oxygen isotopes in benthic foraminifera - the two proxies most extensively used to reconstruct past changes in Earth's carbon cycle and climate - shows two distinct patterns across the Cenozoic. The first, "glacial-style," pattern associates negative excursions in δ 13 C with positive excursions in δ 18 O indicative of relatively cold temperatures and greater ice volume. The second, "hyperthermal-style," pattern associates negative excursions in δ 13 C with negative excursions in δ 18 O indicative of warming. Here I assess the coherence and phasing of these high-frequency, orbital-scale cycles (in particular, the ~100 kyr eccentricity period) in δ 13 C and δ 18 O from multiple high-resolution benthic foraminiferal records spanning the last ~65 million years of Earth history in order to identify which of these patterns is most persistent across the Cenozoic and when the switch between these patterns occurred. I find that the glacial-style δ 13 C-δ 18 O pattern is a feature restricted to the Plio-Pleistocene, suggesting a fundamental change in the interplay between the carbon cycle and climate associated with the onset of Northern Hemisphere glaciation. This relative stability of the high-frequency relationship between δ 13 C and δ 18 O across most of the Cenozoic persists despite significant secular changes in climate and may suggest a dichotomous response of terrestrial carbon cycle dynamics to orbital forcing with a switch occurring in the last ~5 Myr. Key Points Two Cenozoic patterns in the orbital-scale relationship between δ 13 C and δ 18 O With onset of Northern Hemisphere ice, δ 13 C and δ 18 O phase relationship changes Terrestrial biosphere response to climate may drive δ 13 C and δ 18 O pattern