Abstract:
The late Palaeocene Thermal Maximum (LPTM) was a brief interval at c. 55 Ma characterized by a -2.5 to -3 per mil shift in the delta (super 13) C of global carbon reservoirs. The geochemical perturbation probably represents a massive input of 12 degrees C-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 delta (super 13) C excursion in the exogenic carbon cycle after carbon input. A change in global delta (super 13) C (ddelta (sub Ex) /dt) can be explained to a first approximation by a set of parameters: the initial mass and isotopic composition of the global carbon cycle (M (sub Ex(O)) , delta (sub Ex(O)) ), and the fluxes and isotopic compositions of external carbon inputs, outputs and injected carbon (F (sub In) , delta (sub In) , F (sub Out) , delta (sub Out) , F (sub Add) , delta (sub Add) ). In general, for a given exogenic carbon cycle, a large F (sub Add) or low delta (sub Add) results in a larger delta (super 13) C excursion. Likewise, for a given negative delta (super 13) C excursion, a large M (sub Ex) or low delta (sub Ex) requires a greater input of (super 12) C. Differences in F (sub In) , delta (sub In) , F (sub Out) and delta (sub Out) cause changes in the response of delta (sub Ex) over time. For a negative delta (super 13) C excursion of given magnitude, a greater delta F (sub In) requires a greater input of (super 12) C and lessens the time for delta (sub Ex) to return to initial conditions. A decrease in delta (sub Out) (caused by an increase in the relative output of organic matter and carbonate) has a similar effect. Variable dM (sub Add) /dt produces transients in delta (sub Ex) that are related to the source function but modified by carbon removal. In theory, a well-dated and representative global delta (super 13) C excursion could be used to derive the carbon inputs and outputs. Ocean Drilling Program (ODP) Site 1051 has an expanded early Palaeogene section, and recent work at this location has provided a well-dated delta (super 13) C record across the LPTM. This delta (super 13) C record contains transient variations of apparently global nature. These observed transients are best explained by a pulsed injection of CH (sub 4) into an exogenic carbon cycle with a greater carbon throughput or enhanced burial of organic matter after carbon addition.