Global carbon isotope records and carbon cycle feedbacks following the PETM perturbation (Invited)

Global warming during the Paleocene-Eocene Thermal Maximum is associated with a transient, multi-phase negative carbon isotope excursion documented throughout the global exogenic carbon cycle. The precipitous drop in carbon isotope ratios at the onset of the event is widely accepted to reflect a massive addition of 13C-depleted carbon to the ocean/atmosphere system and resultant increases in atmospheric pCO2 and ocean water acidity. But what, if anything, does the pattern of continued carbon isotope change tell us about the patterns and mechanisms of carbon cycle change during the subsequent 170 kyr? Carbon isotope ratios remain relatively stable and low for some 60 kyr following the initiation of the event, suggesting either continued perturbation of the system away from its pre-PETM state or a change in the rate or net isotopic composition of the carbon burial flux during this interval. The interval of δ13C stability ended abruptly ca. 80 kyr after the beginning of the PETM, when carbon isotope ratios rapidly increased by at least 2‰ over no more than 30 kyr. The rebound rate of δ13C values was an order of magnitude faster than expected based on the residence time of carbon in the exogenic system, and implies either a dramatic decrease in residence time or a substantial change in the isotopic composition of carbon fluxes between this system and the lithosphere. The isotopic record of the PETM carbon cycle oscillates between stability and instability, suggesting discrete changes in global carbon fluxes at points throughout the event. Understanding whether these changes were driven by variation in bulk carbon fluxes or ‘isofluxes’ will be necessary to accurately interpret the carbon isotope record to better understand lithospheric carbon burial feedbacks, CO2 drawdown, and the termination of the PETM hyperthermal climate.