THE LATE PALEOZOIC CARBON CYCLE - EVIDENCE FROM TERRESTRIAL ORGANIC MATTER

Profound changes occur throughout the late Paleozoic, notably the formation of Pangea, a change from greenhouse to icehouse conditions, and the rapid colonization of terrestrial environments by land plants. Based on diverse evidence, a substantial decline in the abundance of atmospheric carbon dioxide has been postulated. Carbon isotopes have been utilized as proxy signals for monitoring the temporal evolution of the global carbon cycle. Numerous studies have focussed on the Phanerozoic carbon cycle, studying both carbonates and organic carbon from marine sediments. Few systematic studies have concentrated on the carbon isotopic composition of terrestrial carbonates and/or organic matter. Substantial variations in the carbon isotope record are clearly recorded in marine carbonates. Based on an isotope mass balance, these are generally attributed to the enhanced burial of organic matter. Specifically, a rise in d¹³C during the late Paleozoic is frequently seen in connection with the burial of organic matter in terrestrial ecosystems. Based on a systematic survey of terrestrial organic matter (carbonized plant fossils, bulk organic matter from terrestrial sediments, coal), a carbon isotope record is presented for the late Paleozoic. Our results are supplemented by data from the literature. The terrestrial organic carbon isotope record (running mean, 20 Ma time window, 5 Ma time steps) is in overall agreement with the respective dataset for marine carbonates, although less well constrained. The average isotopic composition varies between –27 and –23 ‰ with a band width of 2 – 5 ‰ as defined by the standard deviation. Values are quite comparable to modern C3 plants and imply a similar isotope fractionation. The overall agreement between the marine and terrestrial carbon isotope records clearly documents the linkage via atmospheric carbon dioxide.