Collapsed upwelling and intensified euxinia in response to climate warming during the Capitanian (Middle Permian) mass extinction

Abstract

The Middle Permian was marked by a major biotic crisis, in the Capitanian, and the termination of the long-lasting Gondwanan glaciation, which began in the Carboniferous. Eruption of the Emeishan large igneous province (ELIP) in South China may have been linked with this event and contemporary changes of ocean circulation. However, causal mechanisms linking the extinction with potential ELIP-climate-ocean co-variations remain poorly constrained. Here we have examined these themes by studying a deep-water section on the margin of the South China continent (lower Yangtze platform margin) region. Our results show chemical weathering increased from the Roadian to the Capitanian suggesting a change from a warm-humid to a hot-humid climate. This trend was enhanced at the time of ELIP eruption in the middle Capitanian. Using the Cd/Mo and Co x Mn proxies reveals that a strong coastal upwelling system with anoxic (but not euxinic) conditions and moderate-high productivity persisted for at least 10 m.y. on the Yangtze Platform margin. However, it abruptly collapsed in the middle Capitanian and then shifted to a relatively restricted but nutrient-enriched system with increased productivity and intensified anoxia. Climate warming slightly precedes these changes, making it likely that it was a primary trigger. Not only does warming slow down ocean circulation, it also promotes the delivery nutrients to the ocean through accelerated continental weathering. All contributed to the intensification and expansion of ocean anoxia-euxinia which occurred immediately prior to the Capitanian biotic crisis. Large-scale volcanic activity of the ELIP likely triggered these decoupled climate-ocean changes. An upwelling regime was re-established in the late Capitanian flowing a cooling that may have been caused by chemical weathering of the Emeishan flood basalts.