Geochemical events documented in inorganic carbon isotopes

Screening of sampling and analytical data is crucial for the detection of real global shifts in marine δ13C, against the noise of diagenesis. The real global shifts of 13C are of two types: (1) long-term secular shifts caused by changes in the fractional burial of organic carbon, and (2) transient shifts caused by abrupt changes of biological productivity in the surface photic zone. Both are applicable to stratigraphic correlation, but differ in their application to modelling of changes in oceanographic or atmospheric composition. A recent compilation found 34 carbon isotope events in the Phanerozoic and Neoproterozoic, equally distributed among positive and negative shifts. This in itself attests to a variety of proximate causes of the shifts.