Higher Resolution Modeling of the Global Terrestrial Biosphere for the PETM

Abstract:

The Paleocene-Eocene Thermal Maximum (PETM) was a rapid climactic warming event at ~55.5 Ma associated with abrupt warming of surface temperatures (5-8 °C), massive input of carbon into the ocean-atmosphere system, and negative carbon isotope excursions (CIE) across nearly every terrestrial and oceanic carbon pool. Whereas there is ubiquitous evidence for CIEs across sites, differences in magnitude and duration of these shifts among records highlight an incomplete characterization of initial carbon injections and of ecosystem feedbacks in response to such perturbations. Numerical modeling of global carbon cycling has thus been utilized to reconcile differences between isotope records, and to also check for agreement with other constraints like carbon release scenarios and oceanic acid-base chemistry. Here, we present a carbon cycle box model that addresses oversimplification in previous quantification of terrestrial carbon cycling by introducing a soil organic and inorganic soil carbon reservoirs. The new model calculates the carbon isotope compositions of both soil organic carbon and pedogenic carbonate and considers the seasonality of calcium carbonate formation, productivity/respiration rates. Coupling this more resolved terrestrial carbon model to a global carbon flux model with established oceanic-atmospheric interaction (LOSCAR) provides a compatibility check given recent paleosol CIE records in the Bighorn Basin (Wyoming, USA). Moreover, the more highly resolved model is used in an effort to address previously irreconcilable differences between organic carbon, surface oceanic, and pedogenic CIE records. Changes in ocean and atmospheric chemistry from such rapid carbon perturbations provided in the model output ultimately serves as an important analog for modern climate change.