Over the last 540 million years, Earth has, for long intervals of time, lacked large ice sheets like those we see today on Greenland and Antarctica. Warmer intervals in Earth history are called “greenhouse” climates and were characterised by a lack of polar ice, the presence of tropical and sub-tropical floras and faunas at high latitudes and low equator-to-pole temperature gradients. The most recent greenhouse period of Earth history occurred during the Mesozoic and early Cenozoic, and is the focus for research at Oxford. This interval of time is also characterised by geologically brief perturbations of the carbon cycle such as the ‘oceanic anoxic events’ (OAEs) and the hyperthermals of the early Cenozoic (including the Paleocene–Eocene Thermal Maximum, PETM). Such greenhouse intervals of time provide insights into Earth’s natural climate variability, climate sensitivity to CO2. Furthermore, the late Mesozoic and early Cenozoic were important intervals in the early evolution and radiation of key aspects of modern ecosystems, including the flowering plants, and siliceous and calcareous phytoplankton.
We seek to address questions such as…
- How warm was the greenhouse world?
- How and where did deep-water masses form?
- How did the hydrological cycle operate?
- What triggered OAEs and hyperthermals and how did they affect ocean chemistry and environments?
Recent research highlights have included
- Using an organic palaeothermometer (TEX86) to reconstruct global cooling in the Late Cretaceous
- Using neodymium isotopes in fish teeth to identify changes in ocean circulation over short and long timescales
- Using novel metal-isotope proxies (e.g. Ca, Li, & Mo-isotopes) to reconstruct changes in weathering and redox during OAEs
- Documenting the response of carbonate platforms to carbon cycle perturbations
People working in this theme include: Hugh Jenkyns, Stuart Robinson.