Eastern Tropical Pacific Ocean Climate Variability in the 12th Century

Supervisor: Thierry Correge (Univ. Bordeaux)
Reconstructing past climatic variability is an important step for understanding the Earth responses to climatic changes and improving climate prediction models. The tropical Pacific Ocean is a major contributor to Earth’s climate, and is under the influence of the interannual ENSO phenomenon. To reconstruct past climate variability in the tropical Pacific Ocean, we use massive corals as they have the advantage of recording highly resolved climate records. Porites species from Clipperton Atoll, located in the eastern Pacific, were analysed. Their aragonitic skeleton contains trace metals and stable isotopes, such as Sr/Ca and δ18O, and these can provide an insight into the past sea surface temperature and salinity, respectively. Palaeo-reconstructions were applied on a fossil coral record dating back to the Medieval Warm Period (800 – 1200 A.D.). A multi-proxy approach was employed to better identify the main environmental trend of the period under study and sea surface temperatures were estimated via calibration equations, revealing they were colder than in modern times. Furthermore, variability at different frequencies was analysed, including ENSO, and a comparison between the temperature proxies Li/Mg and Sr/Ca was made in order to assess their relative reliability.

Keywords: Corals, metal tracers, oxygen isotopes, salinity, temperature, ENSO, paleoclimatology, Eastern Pacific Ocean, Clipperton Atoll