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Geological Society, London, Special Publications; 2001; v. 183; p. 293-305;
DOI: 10.1144/GSL.SP.2001.183.01.14
© 2001 Geological Society of London

Carbon addition and removal during the Late Palaeocene Thermal Maximum: basic theory with a preliminary treatment of the isotope record at ODP Site 1051, Blake Nose

Gerald R. Dickens

School of Earth Sciences, James Cook University, Townsville, Old 4811, Australia
Department of Geology & Geophysics, Rice University, Houston, TX 77251, USA Jerry{at}geophysics.rice.edu

The late Palaeocene Thermal Maximum (LPTM) was a brief interval at c. 55 Ma characterized by a –2.5 to –3{per thousand} shift in the {delta}13C 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 {delta}13C excursion in the exogenic carbon cycle after carbon input. A change in global {delta}13C (d{delta}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 (MEx(o), {delta}Ex(o)), and the fluxes and isotopic compositions of external carbon inputs, outputs and injected carbon (FIn, {delta}In, FOut, {delta}Out, FAdd, {delta}Add). In general, for a given exogenic carbon cycle, a large FAdd or low {delta}Add results in a larger {delta}13C excursion. Likewise, for a given negative {delta}13C excursion, a large MEx or low {delta}Ex requires a greater input of 12C. Differences in FIn, {delta}In, FOut and {delta}Out cause changes in the response of {delta}Ex over time. For a negative {delta}13C excursion of given magnitude, a greater FIn requires a greater input of 12C and lessens the time for {delta}Ex to return to initial conditions. A decrease in {delta}Out (caused by an increase in the relative output of organic matter and carbonate) has a similar effect. Variable dMAdd/dt produces transients in {delta}Ex that are related to the source function but modified by carbon removal. In theory, a well-dated and representative global {delta}13C 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 {delta}13C record across the LPTM. This {delta}13C 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.