A Global Warming Event in Magnetochron C19r: New evidence from the Atlantic Ocean

Abstract:

The Chron C19r event in the late middle Eocene was first described at ODP Site 1260 in the equatorial Atlantic. It is characterized by strong dissolution expressed in a dark, clay-rich layer and a distinct peak in X-ray fluorescence (XRF) scanning Fe intensities as well as by a negative carbon isotope excursion (CIE) in bulk sediment. All similar to early Paleogene hyperthermal events - the Chron C19r event could also be a hyperthermal event but in the late middle Eocene. The dissolution of carbonate at Site 1260 prevented so far to retrieve a benthic stable isotope record with a typical CIE and warming of deep water. The C19r event occurred ~1.0 myr prior to the onset of the Middle Eocene Climate Optimum (MECO, 40.5 Ma) and several million years after the Early Eocene Climate Optimum (EECO, 51 Ma) during a slightly cooler climate. No significant CCD changes have been observed one million years before and after the event as expressed by regular Fe cycles at Site 1260. The duration of the event estimated by orbital calibration is in the order of 40-50 kyr, similar to other transient hyperthermals in the early to middle Eocene.

Here we present new high-resolution bulk and benthic stable isotope data revealing the widespread nature of the event. We investigated ODP Sites 702B (~2200m) near the crest of the Islas Orcadas Rise in the southern South Atlantic, 1263 (~1800 m) on Walvis Ridge in the SE Atlantic, and 1051 (2100 m) on Blake Nose in the NW Atlantic. The position of the event was initially narrowed by careful analysis of magnetostratigraphy and XRF scanning data. First results of stable isotope data show a ~0.7 δ¹³C and ~0.4‰ δ¹⁸O excursion very similar to the pattern observed at Site 1260. Although the magnitude of the bulk δ¹³C excursion is comparable, the bulk δ¹⁸O excursion at Site 702B is only a third of that observed at Site 1260 which might be related to diagenetic and/or latitudinal effects. 702B benthic isotope data show a ~0.75 ‰ CIE and a ~0.4‰ shift in δ¹⁸O. For the first time the new records validate the C19r event in the southern South Atlantic and its ocean-wide if not global nature with a ~2°C deep sea warming. The magnitudes of the CIE and δ¹⁸O excursion are comparable to the H2 event (53.6 Ma) suggesting a similar response of the climate system to carbon cycle perturbations even in relatively cooler climate.