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.