A HIGH-RESOLUTION BENTHIC STABLE ISOTOPE RECORD OF THE MIDDLE EOCENE CLIMATIC OPTIMUM FROM THE NEWFOUNDLAND DRIFTS

The long-term global cooling trend of the middle to late Eocene was interrupted by an approximately 500,000-year period of ocean and atmosphere warming termed the Middle Eocene Climatic Optimum (MECO, ~40 million years ago). Records of the stable carbon and oxygen isotopic composition of benthic foraminifera recovered from deep-sea sediments (e.g. Bohaty et al., 2009) have provided the clearest evidence for MECO warming and carbon cycle dynamics, and suggest a global nature for the event. However, the limited temporal resolution imposed by the slow sedimentation rates of existing records hinders a detailed understanding of the orbital and sub-orbital scale climatic variability during the MECO and the phase relationship (if any) between that variability and background orbital cycles. Scientific drilling in the Newfoundland Drifts of the North Atlantic Ocean (IODP Expedition 342, Sites U1408 and U1410) recovered sedimentary records spanning the MECO that accumulated at rapid sedimentation rates (~2-3 cm per thousand years) with exceptional foraminiferal preservation. We have constructed a record of stable isotopes from benthic foraminifera at Site U1408 that documents MECO bottom-water temperature and carbon cycle dynamics at unprecedented temporal resolution (a sample spacing of approximately 2 thousand years). While the broad long-term pattern of gradual warming and more rapid subsequent cooling is similar to other sites, on shorter timescales our record reveals significant variability (of a similar magnitude to high-resolution benthic records of other Eocene intervals). Additionally, there appears to be coupling between short-lived warming events and negative carbon isotope excursions. The improved temporal resolution of our record promises to offer new insight into this enigmatic chapter of Earth’s history.

Bohaty, S. M., Zachos, J. C., Florindo, F., & Delaney, M. L. (2009). Coupled greenhouse warming and deep‐sea acidification in the middle Eocene. Paleoceanography, 24(2).