SIMULATED WARM POLAR CURRENTS DURING THE LATE PERMIAN PERIOD

During Permian Stage 6 (Wordian, Kazanian) the Pangaean supercontinent was surrounded by a superocean - Panthalassa. An ocean general circulation model is coupled to an atmospheric energy balance model to simulate the sensitivity of the Wordian climate (~268 million years ago) to changes in greenhouse gas concentrations, the ocean gate ways and earth orbital configurations. The model shows a high sensitivity of the ocean circulation to changes in the greenhouse gas forcing, ranging from a forceful southern circulation at low CO2 concentration (present level) to a more symmetric circulation cell with deep water formation in both hemisphere at high CO2 concentration (8 x present level). In addition, variations of orbital configurations yield significantly different annual temperature ranges implying different possible biome classes. Strong subtropical gyres with similarities to the modern South Pacific circulation are consistent with geological evidence from reconstructions of climate-sensitive sediments. Moderate surface temperatures on the southern continent Gondwana, resulting from a strong poleward heat transport in the ocean, are in a good agreement with climate-sensitive sediments and phytogeographic patterns if a four times present level CO2 concentration is used. An even more moderate climate can be generated if ocean gateways at the poles allow circumpolar currents or if orbital configurations favor high summer insolation over Gondwana.