Geological Society of America

T131 Ocean Acidification and Other Societally Relevant Environmental Changes: Using the Past to Infer Our Future (Cushman Session)

Monday, 1 November 2010
1:30 PM - 5:30 PM
Room 603

CORAL CONSTRAINTS ON ATMOSPHERIC CARBON DIOXIDE LEVELS AT THE TRIASSIC-JURASSIC BOUNDARY, A POTENTIAL OCEAN ACIDIFICATION EVENT

Paper number: T131-13
Program: Technical Sessions
Time: 4:45 PM – 5:00 PM

Authors

Rowan Martindale Presenting Author
University of Southern California, Los Angeles, CA
Will Berelson
USCEarth Sciences, Los Angeles, CA
Frank Corsetti
University of Southern California, Los Angeles, CA
David Bottjer
University of Southern California, Los Angeles, CA
A. Joshua West
University of Southern California, Los Angeles, CA

Abstract

Ocean acidification associated with Central Atlantic Magmatic Province (CAMP)-derived CO₂ has been hypothesized as a probable kill mechanism for the Triassic-Jurassic (T-J) extinction (~200Ma), but few direct proxies for ancient atmospheric CO₂ or ocean acidity are available. The presence of fossil corals provides some constraint on ocean acidity, as modern corals struggle to biomineralize below aragonite saturation states (Ω_Arag) of 2 and coral reefs are restricted to environments with Ω_Arag> 3. Here, we use CO₂ limitations derived from modern scleractinian coral biomineralization to test pCO₂ reconstructions and the plausibility of ocean acidification across the T-J boundary.

Three scenarios for ocean Ω_Arag were calculated using T-J carbonate parameter outputs from models of Phanerozoic global biogeochemical cycles. The highest calculated pCO₂ that would permit coral preservation is 2650 ppm, allowing us to reject the highest estimates of pCO₂ during the Rhaetian and mid to late Hettangian. With respect to the extinction interval, CAMP-related pCO₂ could have risen as high as 6500 ppm in the very earliest Hettangian. Our results suggest that it is extremely unlikely that corals could have secreted a skeleton under these conditions, and such high pCO₂ may have caused the ocean to be undersaturated with respect to carbonate. Short but extreme acidification would satisfactorily explain the T-J marine extinction and Early Hettangian coral gap.