The Middle Eocene Climatic Optimum
The cooling trend reverses for half a million years, and nobody is quite sure why.
- When
- —
- Duration
- 500 thousand years
- Known to
- ± 300 thousand years
- Era
- Eocene, Cenozoic
Around 40 million years ago the steady Eocene cooling is interrupted by several degrees of warming lasting roughly 500,000 years, accompanied by a rise in carbon dioxide and a shoaling carbonate compensation depth that makes the deep ocean corrosive. Unlike the PETM, MECO has no sharp negative carbon isotope spike, which rules out a rapid methane or organic-carbon release and points instead to something slower — metamorphic decarbonation as the Tethys closed is a leading candidate. It is the clearest example of a carbon perturbation that is not a hyperthermal.