Global mapping of carbon isotope ratios in coal

We present stable carbon isotope ratios (delta C-13) in 95 coals from 10 countries on a global delta C-13 map and trace the relationship between delta C-13 and coal production over geologic time. In addition, we compare delta C-13 trends in coal as determined from samples and as calculated independently from trends in the delta C-13 of atmospheric carbon dioxide (CO2). We show that the delta C-13 values measured in coal display a wide range (-27.4 parts per thousand to -23.7 parts per thousand). Furthermore, the delta C-13 values in Cenozoic coals are systematically lighter than those in Paleozoic coals. We made independent estimates of delta C-13 values in coal by tracing the derivation of carbon from atmospheric CO2, from its incorporation in plants to the resulting coals. The resulting delta C-13 histories in coal also show a trend toward lighter values. We suggest that the history of delta C-13 in coal may reflect isotopic changes in atmospheric CO2 caused by interactions of the short-term and long-term carbon cycles, in addition to factors in the photosynthetic process. (C) 2016 Elsevier B.V. All rights reserved.