Ocean Drilling Program, United States

The Paleocene/Eocene Thermal Maximum (PETM) was a transient interval of global warming approximately 55 m.y. ago associated with transformation of ecosystems and changes in carbon cycling. The event was caused by the input of massive amounts of CO (sub 2) or CH (sub 4) to the ocean-atmosphere system. Rapid shoaling of the lysocline and calcite compensation depth (CCD) is a predicted response of CO (sub 2) or CH (sub 4) input; however, the extent of this shoaling is poorly constrained. Investigation of Ocean Drilling Program (ODP) Sites 1209-1212 at Shatsky Rise, which lies along a depth transect, suggests a minimum lysocline shoaling of approximately 500 m in the tropical Pacific Ocean during the PETM. The sites also show evidence of CaCO (sub 3) dissolution within the sediment column, carbonate "burn-down" below the level of the carbon isotope excursion, and a predicted response to a rapid change in deepwater carbonate saturation. Close examination of several foraminiferal preservation proxies (i.e., fragmentation, benthic/planktonic foraminiferal ratios, coarse fraction, and CaCO (sub 3) content) and observations of foraminifers reveal that increased fragmentation levels most reliably predict intervals with visually impoverished foraminiferal preservation as a result of dissolution. Low CaCO (sub 3) content and high benthic/planktonic ratios also mirror intervals of poorest preservation.