Evidence for lysocline shoaling at the Paleocene/Eocene Thermal Maximum on Shatsky Rise, northwest Pacific

Amanda B. Colosimo, Timothy J. Bralower, James C. Zachos

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The Paleocene/Eocene Thermal Maximum (PETM) was a transient interval of global warming ∼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 2 or CH 4 to the ocean-atmosphere system. Rapid shoaling of the lysocline and calcite compensation depth (CCD) is a predicted response of CO 2 or CH 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 ∼500 m in the tropical Pacific Ocean during the PETM. The sites also show evidence of CaCO 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 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 3 content and high benthic/planktonic ratios also mirror intervals of poorest preservation.

Original languageEnglish (US)
JournalProceedings of the Ocean Drilling Program: Scientific Results
StatePublished - 2005

All Science Journal Classification (ASJC) codes

  • Oceanography
  • Geology


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