An Astronomically-tuned High Resolution Benthic Isotope Stratigraphy for the Late Paleocene and Early Eocene

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TOWARD AN ASTRONOMICALLY-TUNED HIGH-RESOLUTION BENTHIC ISOTOPE STRATIGRAPHY FOR THE PALEOCENE AND EARLY EOCENEJAMES ZACHOS, UNIVERSITY OF CALIFORNIA, SANTA CRUZEAR-0959117ABSTRACTThe late Paleocene to early Eocene (~58 to 52 Mya) represents one of the most climatically dynamic periods of Earth?s past. It is characterized by a gradual long warming trend that culminates in the warmest conditions of the last 90 m.y., the Early Eocene Climatic Optimum. Recent investigations, however, have found that the long-term warming trend was punctuated by several short-lived (transient) warming events (tens of thousands of years in duration), referred to as hyperthermals or Eocene thermal maxima. These events, which include the extreme Paleocene-Eocene Thermal Maximum (PETM, ~56 Mya), are thought to have a common origin, possibly involving orbital forcing amplified by carbon cycle feedbacks. Other proposed driving mechanisms, particularly for the PETM, include volcanic outgassing and/or the decomposition of marine methane hydrates. To assess whether the PETM and other thermal maxima were triggered by orbital or other forcing, we intend to establish the temporal relationship of these events to the long-term background variability (i.e., periodicity) in climate and the cabon cycle. To this end, utilizing a deep sea core recovered from the south Atlantic, we will construct the first high-resolution, astronomically-tuned benthic foraminiferal stable carbon and oxygen isotope time series for a ~5-6 m.y. segment of the upper Paleocene-lower Eocene. These and other records will allow us to establish the relative timing and phasing of the thermal maxima to excursions in the carbon cycle, thus providing constraints for quantitatively evaluating the nature of climate ? carbon cycle coupling during periods of warming. In addition to this application, the astronomically-tuned isotope time-series will serve as a standard isotope reference section by which all other Paleocene and early Eocene deep-sea sequences can be compared. In this capacity, it will be possible to use the carbon isotopes to correlate and calibrate segments of marine sedimentary sections to our tuned record, thereby significantly improving the accuracy of age models. This will facilitate transfer of the astronomical calibrations to sections with exceptional magnetostratigraphy, and thus the geomagnetic polarity time-scale.