T43 Biotic Response to Global Environmental Change: Analogs for the Future of Life on Earth

Sunday, 22 October 2006
1:30 PM - 5:30 PM

A NEW ROLE FOR ELEVATED CO2 IN THE PROLONGED PERMIAN-TRIASSIC BIOTIC CRISIS

Paper number: T43-4
Program: Technical Sessions
Time: 2:40 PM – 2:55 PM

Authors

Abstract

Atmospheric CO2 has risen continuously since the Industrial Era primarily due to anthropogenic input. As CO2 diffuses into the oceans, the pH and CaCO3 saturation state of seawater decrease, and experiments and observations indicate that small changes measured in surface ocean chemistry today are causing a physiological and biocalcification crisis for Earth's calcareous marine biota. The degree and rate of calcification among corals, coccolithophores, foraminiferans, and coralline red algae decrease as the CaCO3 saturation state of seawater decreases, and low-metabolism organisms may experience reduced growth and reproductive potential and even death if acid-base imbalance is not achieved. Atmospheric CO2 has been elevated at intervals in Earth's history, and it has been hypothesized to have played a role in some ancient biotic crises. Elevated CO2 is hypothesized to have caused the extinction of metabolically slow organisms and reef organisms; a decrease in nannoplankton size and calcification; and extinction and dissolution of calcareous microorganisms during the end-Triassic mass extinction, the early Toarcian crisis, and the Paleocene-Eocene Thermal Maximum, respectively.

Elevated atmospheric CO2 has been hypothesized to have played a critical role in causing the end-Permian mass extinction, too, by facilitating development of a vertically stratified, low O2, H2S-rich deep ocean. However, biotic crisis continued for 5- to 6- million years after the extinction, and some stressed Early Triassic shallow marine faunas do not exhibit any indications of influence from toxic deep water. The absence of metazoan reefs and the numerical dominance of bivalves and tiny adult gastropods in Early Triassic shallow marine environments may indicate that the direct effects of increased atmospheric CO2 on ocean surface waters and biota during this time have been underappreciated previously. We propose that elevated atmospheric CO2 was an important mechanism for sustained ecological degradation in Early Triassic shallow-marine environments. Future research is necessary to test this hypothesis further, but it is likely that the elevated level of atmospheric CO2 during the latest Permian-Early Triassic had detrimental effects on the Earth's shallow-marine biota.