REEXAMINING CAUSAL MECHANISMS FOR THE EARLY EOCENE CLIMATIC OPTIMUM

The Early Eocene Climatic Optimum (EECO) was a period of major climatic change during the early Eocene that was caused by large-scale changes in the global carbon cycle. New proxy records from both North and South America demonstrate that the period is characterized by different carbon cycle responses in the terrestrial and marine realms both in terms of the direction and timescale of change, which suggests that traditional causal mechanisms may not adequately explain the dynamics of the EECO. Here we present a summary of terrestrial and marine proxy data, and use them to propose a set of criteria that must be fulfilled to test a series of global carbon model scenarios that represent proposed mechanisms for early Eocene carbon cycle perturbations (e.g., volcanism, methane hydrate releases, carbonate weathering, ocean ventilation). These model simulations use the LOSCAR platform, and collectively indicate that no single causal mechanism sufficiently explains both marine and terrestrial proxy observations. Multi-mechanism scenarios suggest that a preferred carbon cycle scenario involving both increased ventilation of oceanic carbon and increased carbonate weathering are able to fulfill both marine and terrestrial proxy observations of the EECO, and thereby provide a mechanism for global dynamics of the early Eocene. This combination of mechanisms and the timing of carbon cycle events could result from an initial Paleogene carbon cycle instability and early Eocene changes in ocean chemistry and paleogeography.