James C. Zachos
Univ. of California, Santa Cruz
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Astronomically tuned, high-resolution marine carbon and oxygen isotope records are essential for identifying the underlying causes of past changes in climate (e.g., the origin of glacial - interglacial cycles). While such records have been available for the Plio-Pleistocene for over 3 decades, only recently have records of similar quality been extended back into the early Cenozoic, specifically for intervals characterized by major climatic transitions or extremes such as the Eocene-Oligocene and the Paleocene-Eocene boundaries. The perspective provided by these high-resolution records, has altered our understanding of how various forcing factors can interact to drive changes in climate on a variety of time scales. They have also created new opportunities to study the coupling between climate and carbon cycle through various feedbacks, both positive and negative.
In this presentation, I focus on high-resolution pelagic and hemi-pelagic 18O and 13C and lithologic records from the Atlantic and Pacific that span the upper Paleocene and lower Eocene. These records resolve the orbital scale variability in both climate and the carbon cycle showing pronounced concentration of variance at periods associated with precession (21 kyr) and eccentricity (100 and 400-kyr), as well as obliquity (41 kyr). The records also capture the Eocene "hyperthermals", as represented by extreme minima in 18O and 13C, which appear to be in phase with maxima in eccentricity, implying orbital pacing of these events. The magnitude of the hyperthermals relative to background variability, however, suggests amplification by feedbacks involving the carbon cycle. Here I discuss the possible nature of these feedbacks, specifically the potential coupling of climate with the large exogenic marine and continental reduced carbon reservoirs.