The carbonate compensation depth plunges
The level below which shells dissolve drops more than a kilometre, and the deep Pacific starts collecting chalk.
- When
- —
- Duration
- 700 thousand years
- Known to
- ± 300 thousand years
- Era
- Oligocene, Cenozoic
At the Eocene-Oligocene boundary the depth at which calcium carbonate dissolves faster than it accumulates falls abruptly by over a kilometre in the Pacific. Below the old level, seafloor that had been collecting only clay begins collecting carbonate ooze, and drill cores record the switch as a sharp change in sediment colour and composition. It reflects a wholesale reorganisation of ocean carbon chemistry — more alkalinity delivered from a world of falling sea level and increased weathering — and it is one of the sharpest single signals in the deep-sea record.