Synchronous δ¹³C shifts oceans and atmosphere

In conjunction with the end-Permian biotic crisis, the most conspicuous geochemical event is the worldwide negative shift in the carbon isotopic composition (¹³δC) of both carbonates and sedimentary organic matter. Despite its approximate coincidence, it can not directly be interpreted as proof for drastic changes in the atmospheric carbon reservoir. The δ¹³C-org values can reflect the carbon-isotopic composition of a mixture of marine and land-derived material. A further complicating factor is the wide variation among the ¹³C-content of individual organic compounds in plants. These complicating factors are overcome by comparative analysis of carbon-isotope data (fig. 1) for carbonates and compound-specific carbon-isotopic signatures of n-alkanes (δ¹³C-alkane) characteristic of leaf cuticles (fig. 2) from land plants, from a marine P-Tr transition section in the Southern Alps, Italy. The comparison substantiates that the end-Permian δ¹³C disturbance was both large (>6‰) and rapid. The data confirm an approximately synchronous primary chemical change occurring in oceanic and atmospheric chemistry during the end-Permian ecologic crisis. The ¹³δC excursion appears to be a consequence of the ecological crisis, and the global reservoir of soil organic matter may be the only plausible source of ¹³δC-depleted carbon.

Sephton M.A., Looy C.V., Veefkind R.J., Visscher H., Brinkhuis H. and De Leeuw J.W., 2002. Synchronous record of δ¹³C shifts in the oceans and atmosphere at the end of the Permian. Geological Society of America Special Paper 356: 455-462.