ALBERT

Description: The late Palaeocene Thermal Maximum (LPTM) was a brief interval at c. 55 Ma characterized by a −2.5 to −3‰ shift in the δ13C of global carbon reservoirs. The geochemical perturbation probably represents a massive input of 12C-rich carbon to the exogenic carbon cycle. Largely unresolved issues concerning this carbon injection during the LPTM are the rates of carbon input and removal. Simple expressions are developed here to describe a δ13C excursion in the exogenic carbon cycle after carbon input. A change in global δ13C (dδEx/dt) can be explained to a first approximation by a set of parameters: the initial mass and isotopic composition of the global carbon cycle (MEx(o), δEx(o)), and the fluxes and isotopic compositions of external carbon inputs, outputs and injected carbon (FIn, δIn, FOut, δOut, FAdd, δAdd). In general, for a given exogenic carbon cycle, a large FAdd or low δAdd results in a larger δ13C excursion. Likewise, for a given negative δ13C excursion, a large MEx or low δEx requires a greater input of 12C. Differences in FIn, δIn, FOut and δOut cause changes in the response of δEx over time. For a negative δ13C excursion of given magnitude, a greater FIn requires a greater input of 12C and lessens the time for δEx to return to initial conditions. A decrease in δOut (caused by an increase in the relative output of organic matter and carbonate) has a similar effect. Variable dMAdd/dt produces transients in δEx that are related to the source function but modified by carbon removal. In theory, a well-dated and representative global δ13C excursion could be used to derive the carbon inputs and ouputs. Ocean Drilling Program (ODP) Site 1051 has an expanded early Palaeogene section, and recent work at this location has provided a well-dated δ13C record across the LPTM. This δ13C record contains transient variations of apparently global nature. These observed transients are best explained by a pulsed injection of CH4 into an exogenic carbon cycle with a greater carbon throughput or enhanced burial of organic matter after carbon addition.