LONG-TERM ORBITAL SCALE PALEOCEANOGRAPHIC VARIABILITY ACROSS THE PALEOCENE-EOCENE BOUNDARY IN THE CENTRAL PACIFIC: INFERENCES FROM ISOTOPE AND GEOCHEMICAL CORE LOG DATA

Much focus has been placed on documenting and understanding extreme climate events such as the Paleocene Eocene Thermal Maximum (PETM). However, practical constraints have limited the temporal scope of investigations conducted at high resolution to several hundreds of thousands of years spanning each event. As such, the natural, long-term background variability of certain key paleoceanographic properties (deep water temperature, ocean chemistry) and the timing of processes on orbital scales during the early Paleogene remain uncharacterized. These parameters are crucial for understanding the timing, origin, and impacts of the PETM (ETM-1) and subsequent hyperthermal events in the early Eocene (ETM-2, ETM-3).

Physical Properties data collected during coring of ODP Site 1209 on Shatsky Rise, north Pacific, exhibit variability on the scale of astronomically forced processes (Milankovitch cycles) over the entire Paleogene. We present here new high-resolution benthic δ¹⁸O and δ¹³C records, along with Wt% coarse fraction (%CF) and geochemical core logging records spanning the upper Paleocene to lower middle-Eocene. These records exhibit pronounced oscillations in the primary orbital bands, and capture all 3 of the early Eocene hyperthermal events, ETM-1, 2, & 3 at 55, 53, and 52 Ma respectively. The carbon isotope and %CF records exhibit power in the eccentricity bands, particularly in the carbon isotope record with power in the 400 k.y. band. In addition to the cyclical and transient signals, there appears to be a long-term shift in the character of carbonate fluxes to the deep-sea that initiates at the P-E boundary as inferred from a rise in the %CF. This might reflect a potential regional reduction in coccolith productivity, an increase in CaCO3 preservation, or a global scale shift in the carbon cycle. These records will be compared to similar records from Walvis Ridge, south Atlantic, ODP Leg 208, where preliminary work reveals similar short- and long-term patterns over the upper Paleocene and lower Eocene.