8. Evidence for Lysocline Shoaling at the Paleocene/Eocene Thermal Maximum on Shatsky Rise, Northwest Pacific1

Amanda B. Colosimo,2 Timothy J. Bralower,3 and James C. Zachos4

ABSTRACT

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 CO2 or CH4 to the ocean-atmosphere system. Rapid shoaling of the lysocline and calcite compensation depth (CCD) is a predicted response of CO2 or CH4 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 CaCO3 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 CaCO3 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 CaCO3 content and high benthic/planktonic ratios also mirror intervals of poorest preservation.

1Colosimo, A.B, Bralower, T.J., and Zachos, J.C., 2006. Evidence for lysocline shoaling at the Paleocene/Eocene Thermal Maximum on Shatsky Rise, northwest Pacific. In Bralower, T.J., Premoli Silva, I., and Malone, M.J. (Eds.), Proc. ODP, Sci. Results, 198 [Online]. Available from World Wide Web: <http://www-odp.tamu.edu/publications/198_SR/112/112.htm>. [Cited YYYY-MM-DD]

2Department of Chemistry and Geology, Monroe Community College, 1000 East Henrietta Road, Rochester NY 14623, USA.

3Department of Geosciences, Pennsylvania State University, University Park PA 16802, USA. bralower@geosc.psu.edu

4Department of Earth Sciences, University of California, Santa Cruz CA 95064, USA.

Initial receipt: 8 March 2004
Acceptance: 8 September 2005
Web publication: 31 January 2006
Ms 198SR-112

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