Abstract:
The Paleocene is marked by secular variations in climate that appear to be strongly coupled to prominent variations in the carbon cycle as inferred from carbon isotope and other data. Here we use new high-resolution, orbitally-tuned stable isotope records from the South Atlantic to evaluate the nature of coupling on both long and short-time scales. The records were constructed using cores from 3 holes drilled at Site 1262 on Walvis Ridge during ODP Leg 208. The records, which have a approximately 3 k.y. resolution and are stratigraphically continuous from 53 to 61 Mya., were orbitally tuned to an astronomical model (see Westerhold et al., 2007). The carbon isotope time series shows the well-characterized long-term decline from a late Paleocene maximum (57.4 Ma) to the early Eocene minimum (53.6 Ma). Superimposed on the long-term C-isotope trend are prominent cycles along with several distinct negative excursions including the PETM and ELMO. The cycle variance is largely concentrated in the precession and eccentricity bands (100, 400 k.y.). The carbon isotope minima generally correspond with minima in carbonate content and oxygen isotopes implying increased input of isotopically depleted (reduced) carbon, lower ocean pH, and greenhouse induced global warming. The cycle amplitudes appear to increase from the mid to late Paleocene. These patterns imply enhanced coupling between the carbon cycle and climate throughout this period, possibly involving exchange of carbon with a large reduced carbon reservoir (e.g., methane hydrate capacitor of Dickens (2003)). Several possible mechanisms for this coupling are discussed.