Regional Paleoprecipitation Records from the Late Eocene and Oligocene of North America

The marine δ18O record indicates precipitous cooling or significant expansion of Antarctic ice volume across the Eocene‐Oligocene epoch boundary at 33.7 Ma. This climatic step is also found in estimates of decreased paleoprecipitation from paleosols in Oregon, Montana, and Nebraska but is only a part of a long‐term decline across the Eocene‐Oligocene transition rather than a sudden shift. This suggests that climate was driven by a gradual process rather than a single perturbation. Paleoprecipitation levels stabilized during the Oligocene, coincident with a stabilization in δ18O values, possibly indicating a new climatic steady state.