INFLUENCE OF CLOUD FEEDBACKS ON THE END-PERMIAN MARINE MASS EXTINCTION

In this paper we discuss a major feedback associated with the change of cloud condensation nuclei (CLAW hypothesis) that could have contributed to the extinction of the marine species at the Permian Triassic boundary. The extinction of organisms on land lowered the burning of biomass and could, together with the warming of the ocean and reduced marine primary production, have decreased the emissions of dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) in to the atmosphere. The reduced DMS and DMDS emissions would have ultimately reduced the concentration of cloud condensations nuclei and enhanced the water droplet size in clouds.

Here, the climate model CCSM-3 is applied to investigate the climate feedback of a reduction of the concentration of cloud condensation nuclei over the ocean and over the land on the climate at the Permian-Triassic boundary. The climatic response to the changes in cloud properties is remarkable, with a warming over the ocean of ~4 K and over Gondwanaland exceeding 10 K. As a consequence, high-latitude water masses become more stratified with an increase in the vertical thermal gradient, whereas the formation of saline and warm subtropical water masses near the east coast of Pangea is intensified. In response to these changes, the ventilation of the deep Panthalassa is significantly reduced and deep-sea temperature rises by ~3 K.

The changes in the ocean circulation influence the export production and oxygen distribution in the deep sea. The equatorial productivity is decreased by a decline in the wind-driven upwelling, leading to a reduced carbon export into the deep sea. Oxygen in the deep sea is diminished because of its lower solubility in warmer water and because of a more stagnant ocean circulation. The environmental stress associated with the ocean warming, shift in water masses, and decrease in the oxygen concentration could have contributed to the extinction of marine organisms.