FLUSHING THE SYSTEM: COUPLING LITHIUM ISOTOPES AND CLIMATE MODEL OBSERVATIONS DURING THE PETM

Climate model simulations of the PETM warming have mainly focused on replicating the global thermal response through greenhouse forcing, i.e. CO₂, at levels compatible with observations. Comparatively less effort has gone into assessing the skill of models in replicating the response of the hydrologic cycle to the warming, particularly on regional scales. This study couples lithium isotopes of the clay-sized fraction of siliciclastic sediment to high-resolution model output of changes in precipitation and runoff in the Mid-Atlantic coast during the PETM. Lithium isotopes of siliciclastic sediment are a novel proxy that provide insight into the “weathering congruency” of a region, i.e. the ratio of chemical weathering to physical erosion. Lithium isotope data obtained from two locations in the Mid-Atlantic demonstrate a 2-3‰ decrease indicating an increase in physical erosion relative to chemical weathering, with one site demonstrating a lithium isotope excursion occurring prior to the carbon isotope excursion. Modeled output utilized a two by two experimental design to test the effects both of orbital and CO₂ forcing on precipitation and runoff. Both forcings independently led to an increase in seasonal precipitation in the region, suggesting orbital changes may have driven changes in the regional hydrology before the release of carbon that defines the PETM.