Equatorial Pacific "stable isotope reference curve" for the Oligocene

Abstract

We present an uninterrupted chronology of climate and ocean carbon chemistry from ODP Site 1218 recovered in the equatorial Pacific, from the Eocene / Oligocene to the Oligocene / Miocene boundary, ~34 to 23 Ma. Using astronomically age calibrated data we find a strong imprint of the 405, 127 and 96-thousand-year (kyr) Earth's eccentricity as well as a dominant influence of the 1.2 million year (Myr) obliquity amplitude modulation cycles on periodically re-occurring Oligocene glacial and carbon cycle events. In combination, these astronomical modulations act as the "heartbeat" of the Oligocene climate system. The response of the climate system to intricate orbital variations is striking and suggests a fundamental role of the carbon cycle in the interaction between solar forcing and climate. Our record provides a new high-resolution view of the Oligocene climate system, prompts a re-evaluation of the previously hypothesised late Oligocene deglaciation, and sheds new light on Oligocene inter-ocean isotope gradients. Salient observations include foraminiferal benthic stable oxygen and carbon isotopes that co-vary, a phase lag of δ¹³C w.r.t. δ¹⁸O for the 405 kyr cycle, preferential filtering of longer orbital periods in δ¹³C, presumably due to σCO₂ reservoir buffering. We then use simple orbitally forced carbon cycle box models and manage to re-create the patterns observed in our data, including the overall strong amplitude of 405 kyr cycles in δ¹³C. Depending on ice-sheet presence and pCO₂ concentrations, our model predicts re-occurring conditions favouring glaciations every 2.4 Myr, including the Eocene/Oligocene transition.

More information

Identifiers

ORCID for P.A. Wilson: orcid.org/0000-0001-6425-8906

Catalogue record

Export record