2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 68-6
Presentation Time: 2:55 PM

OCEAN ACIDIFICATION AND THE PERMO-TRIASSIC MASS EXTINCTION: PROCESS AND MANIFESTATION


KASEMANN, Simone A.1, WOOD, Rachel A.2, CLARKSON, Matthew3, LENTON, Timothy4, DAINES, Stuart4, RICHOZ, Sylvain5, MEIXNER, Anette6, POULTON, Simon W.7 and TIPPER, Edward8, (1)Department of Geosciences & MARUM-Center for Marine Environmental Sciences, University of Bremen, Leobener Str, Bremen, 28359, Germany, (2)School of GeoSciences, University of Edinburgh, Grant Institute, The King's Buildings, West Mains Road, Edinburgh, EH9 3JW, United Kingdom, (3)Department of Chemistry, University of Otago, Union Street, Dunedin, 9016, New Zealand, (4)College of Life and Environmental Sciences, University of Exeter, North Parks Road, Exeter, EX4 4QE, United Kingdom, (5)Institute of Earth Sciences, University of Graz, Heinrichstra├če 26, Graz, 8010, Austria, (6)Department of Geosciences & MARUM-Center for Marine Environmental Sciences, University of Bremen, Bremen, 28334, Germany, (7)School of Earth and Environment, Univ. of Leeds, Leeds, LS2 9JT, United Kingdom, (8)Department. of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, United Kingdom, simone.kasemann@uni-bremen.de

Ocean acidification triggered by Siberian Trap volcanism was a possible kill mechanism for the Permian Triassic Boundary (PTB) mass extinction, but direct evidence for an acidification event is lacking. We present a high resolution seawater pH record across this interval, utilizing boron isotope data (╬┤11B) combined with petrographic analysis and quantitative modeling approach. Through this integration we are able to produce an envelope that encompasses the most realistic range in pH, which then allows us to resolve three distinct chronological phases of carbon cycle perturbation, each with very different environmental consequences for the Late Permian-Early Triassic Earth system. In the latest Permian, increased ocean alkalinity, primed the Earth system with a low level of atmospheric CO2and a high ocean buffering capacity. The first phase of extinction was coincident with a slow injection of carbon into the atmosphere and ocean pH remained stable. During the second extinction pulse, however, a rapid and large injection of carbon caused an abrupt acidification event that drove the preferential loss of heavily calcified marine biota.

The boron signal cuts across primary lithological boundaries, including micritic carbonates, grainstones, and intervals with calcispheres. Boron isotope trends are therefore both facies and fabric independent but the short-lived acidification event is manifest in a loss of any biotic component, and unusual and anomalous carbonate precipitates that may indicate profound carbon cycle disruption.