Paper No. 11
Presentation Time: 4:45 PM
CORAL CONSTRAINTS ON ATMOSPHERIC CARBON DIOXIDE LEVELS AT THE TRIASSIC-JURASSIC BOUNDARY, A POTENTIAL OCEAN ACIDIFICATION EVENT
MARTINDALE, Rowan1, BERELSON, William M.
2, CORSETTI, Frank A.
2, BOTTJER, David
2 and WEST, A. Joshua
2, (1)Department of Earth Sciences, University of Southern California, Los Angeles, CA 90089-0470, (2)Department of Earth Sciences, University of Southern California, Los Angeles, CA 90089, rmartind@usc.edu
Ocean acidification associated with Central Atlantic Magmatic Province (CAMP)-derived CO
2 has been hypothesized as a probable kill mechanism for the Triassic-Jurassic (T-J) extinction (~200Ma), but few direct proxies for ancient atmospheric CO
2 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 CO
2 limitations derived from modern scleractinian coral biomineralization to test pCO
2 reconstructions and the plausibility of ocean acidification across the T-J boundary.
Three scenarios for ocean ΩArag 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.
