THE EOCENE-OLIGOCENE TRANSITION

Abstract

A diverse array of fossil, geochemical and sedimentary data shows patterns of major change at or near the Eocene-Oligocene boundary, indicating a period of fundamental climatic and biotic reorganization on Earth. Multiple lines of evidence support the hypothesis that these changes signal major global cooling, especially at high latitudes, and rapid growth of semi-permanent ice-sheet on Antarctica in the early Oligocene. The quality and temporal resolution of Eocene-Oligocene fossil and sediment records and the diversity of climatic proxy tools have increased enormously in recent years, bringing a new level of detail to the study of this transition. The higher-resolution records have revealed that the climatic shifts across the Eocene-Oligocene boundary occurred in multiple stages that can be calibrated on orbital timescales. Coupled with incresasingly sophisticated computer models, these records have led to significant advances in our understanding of possible causal mechanisms and feedbacks driving this global shift. Here we review the wealth of evidence for Eocene-Oligocene climate change, summarize the current state of understanding, and highlight the key areas still requiring work that might guide the direction of future research. Obtaining a thorough understanding of this critical climatic transition is important for highlighting the mechanisms and sensitivities of Cenozoic climate, and addressing topical questions relating to the dynamics of global change during greenhouse-icehouse climate switching.