A High‐Fidelity Benthic Stable Isotope Record of Late Cretaceous–Early Eocene Climate Change and Carbon‐Cycling. Issue 4 (30th April 2019) - Barnet, J. S. K.
Abstract: The Late Cretaceous–Early Paleogene is the most recent period in Earth history that experienced sustained global greenhouse warmth on multimillion year timescales. Yet, knowledge of ambient climate conditions and the complex interplay between various forcing mechanisms are still poorly constrained. Here we present a 14.75 million‐year‐long, high‐resolution, orbitally tuned record of paired climate change and carbon‐cycling for this enigmatic period (~67–52 Ma), which we compare to an up‐to‐date compilation of atmospheric p CO2 records. Our climate and carbon‐cycling records, which are the highest resolution stratigraphically complete records to be constructed from a single marine site in the Atlantic Ocean, feature all major transient warming events (termed "hyperthermals") known from this time period. We identify eccentricity as the dominant pacemaker of climate and the carbon cycle throughout the Late Maastrichtian to Early Eocene, through the modulation of precession. On average, changes in the carbon cycle lagged changes in climate by ~23, 000 years at the long eccentricity (405, 000‐year) band, and by ~3, 000–4, 500 years at the short eccentricity (100, 000‐year) band, suggesting that light carbon was released as a positive feedback to warming induced by orbital forcing. Our new record places all known hyperthermals of the Late Maastrichtian–Early Eocene into temporal context with regards to evolving ambient climate of the time. We constrain potential carbon cycle influences of Large Igneous Province volcanism associated with the Deccan Traps and North Atlantic Igneous Province, as well as the sensitivity of climate and the carbon‐cycle to the 2.4 million‐year‐long eccentricity cycle. Plain Language Summary: The study of globally warm climates and short‐lived warming events in Earth's past can provide unrivaled insights into the challenges that mankind may face over the next few generations. Using samples recovered from an ocean drill core in the deep South Atlantic, we have generated continuous temperature and carbon cycle records from the calcite shells of a single microfossil species, spanning a period of globally warm climate from 67 to 52 million years ago, before the development of permanent large‐scale polar ice sheets. Our record contains a number of rapid warming events, allowing us to determine their origin. We find that changes in the shape of Earth's orbit around the Sun initiated warming at Earth's surface, which was then amplified by the release of greenhouse gases from temperature‐ or climate‐sensitive carbon stores (e.g., peat, permafrost, or methane hydrates). These rapid warming events increased in frequency and magnitude during the warmer climate intervals characterized by significant volcanic activity, suggesting that such carbon stores become more unstable during warmer climates. As our climate warms at unprecedented rates, the release of greenhouse gases from naturally occurring temperature‐ or climate‐sensitive carbon stores could also form an additional and largely unconstrained contribution to future climate change. Key Points: 405‐ and 100‐kyr eccentricity forced the climate and carbon cycle, with carbon cycle perturbations lagging climate during this time Elevated global temperatures and atmospheric p CO2 during LIP volcanism increased climate and carbon cycle sensitivity to orbital forcing The frequency of hyperthermals suggests that carbon was periodically released from a dynamic reservoir which could be replenished quickly