Abstract:
Data set consists of carbonate and stable isotope data across the Eocene
"Greenhouse-Icehouse" climate transition, from tropical Pacific ODP cores 1218
and 1219, and calculated Calcite Compensation Depth and 0% isopleth depth.
The transition from the extreme global warmth of the early Eocene 'greenhouse'
climate, ~55 million years ago to the present glaciated state is one of the
most prominent
... changes in Earth's climatic evolution. It is widely accepted
that large ice sheets first appeared on Antarctica ~34 million years ago,
coincident with decreasing atmospheric carbon dioxide concentrations and a
deepening of the calcite compensation depth in the world's oceans, and that
glaciation in the Northern Hemisphere began much later, between 10 and 6
million years ago. Here we present records of sediment and foraminiferal
geochemistry covering the greenhouse Sicehouse climate transition. We report
evidence for synchronous deepening and subsequent oscillations in the calcite
compensation depth in the tropical Pacific and South Atlantic oceans from ~42
million years ago, with a permanent deepening 34 million years ago. The most
prominent variations in the calcite compensation depth coincide with changes
in seawater oxygen isotope ratios of up to 1.5 per mil, suggesting a lowering
of global sea level through significant storage of ice in both hemispheres by
at least 100 to 125 metres. Variations in benthic carbon isotope ratios of up
to ~1.4 per mil occurred at the same time, indicating large changes in carbon
cycling. We suggest that the greenhouse icehouse transition was closely
coupled to the evolution of atmospheric carbon dioxide, and that negative
carbon cycle feedbacks may have prevented the permanent establishment of large
ice sheets earlier than 34 million years ago. 
