Paper No. 9
Presentation Time: 3:45 PM
CLIMATE SENSITIVITY TO TOPOGRAPHIC CHANGES DURING THE LATE PERMIAN AND IMPLICATIONS FOR MASS EXTINCTIONS
Evidence from stratigraphic sections of the Panthalassa, Paleo- and Neo-Tethys, suggests that oceans incurred wide spread anoxia during the Late Permian that likely contributed to the extinction of more than 90% of marine species. A carbon isotope shift indicates significant perturbations in the carbon cycle occurred during the Late Permian and persisted into the Early Triassic. Bathymetric features of the Panthalassic Ocean are not well known since the ocean floor from 252 Ma has been subducted. Tectonic reconstructions indicate that subduction zones were active along the borders of Pangaea, thus requiring an active ridge or rift system. Most climate simulations have assumed a flat bottom ocean, because the exact location of a mid ocean ridge was uncertain. In this study, two different bathymetric configurations are being considered in the comprehensive climate simulation model (CCSM-3): a ridge simulation where a mid-ocean ridge was placed within the Panthalassa Ocean and a simulation in which the deep Tethys Ocean was topographically separated from the Panthalassa Ocean by a sill. Comparisons between the flat bottom control and the ridge experiment indicate that the addition of a north-south mid-ocean ridge would likely disrupt of the deep Panthalassa Ocean circulation, causing remarkable changes in vertical mixing. Warm saline water masses from the subtropical region transported into the equatorial zone in the area east of the mid ocean ridge lead to higher water temperatures (by as much as 1.0 °C) as well as a decrease in dissolved oxygen concentration. In the experiment with a sill between the Paleo-Tethys and Panthalassa, deep water increased in salinity (by ~0.5 psu) and temperature (~5.0°C). Circulation restriction within the Paleo-Tethys caused by the sill enhanced stratification, leading to a reduced oxygen concentration of these water masses. Both sensitivity experiments indicate that changes in bathymetric features may have been a contributing factor to the Permian-Triassic mass extinction by altering global and regional circulation patterns.