The ice sheet breathes
Antarctic ice advances and retreats on orbital rhythms, leaving a metronome in the sediment record.
- When
- —
- Duration
- 7 million years
- Known to
- ± 2 million years
- Era
- Oligocene, Cenozoic
Through the Oligocene the East Antarctic Ice Sheet is not static: oxygen isotope records show it expanding and contracting in step with the 41,000-year obliquity cycle and the 100,000- and 400,000-year eccentricity cycles. This is the first sustained interval in which orbital forcing translates directly into global ice volume and sea level, and reading those cycles in drill cores is what makes the Oligocene timescale so precisely tuned. The same machinery, amplified by northern ice, will later produce the glacial-interglacial cycles.