1. Paleoclimate Lida Teneva, Tristan Lindot The proxies: corals, ice cores, tree rings, ocean and lake sediments, cave stalagmites, sedimentary rocks, etc. Information: temperature, atmospheric composition, sea level, vegetation change, precipitation patterns, ocean currents, etc.

2. Corals Can be up to 300 years old Mostly used for last millennium climate studies Sr/Ca ratios and d18O geochemical temperature proxies –Sr/Ca partly controlled by algal symbionts –d18O partly controlled by local hydrography and biofractionation

3. Ice cores Take us to 650,000 yrs BP (soon to 800,000) Isotopic composition (O & H) in ice related to temperature Air bubbles trapped in ice reflect atmospheric composition Issues: –Imprecise dating of layers –Air bubbles younger than surrounding ice

4. Tree rings Bristlecone pine of the Great Basin region of western North America are the oldest known living trees, up to 5,000 years old. Tree growth is generally controlled by climate conditions during the year prior to and including the growing season. Bristlecone pine (Pinus longaeva). Photo Credits: Jonathan Pilcher Palaeoecology Centre, Queen's University, Belfast

5. Tree rings and uncertainties The reconstruction models explain 60-75% of the variance in the gage records. Inevitable decline in tree sample size back in time. The Blue River at Dillon Reservoir reconstruction model (green) and the gaged record (blue) over their common time period (1916-2002).

6. Foraminifera Present in all the oceans, Many in the sediments, Very sensible to their environment, Can give information until 100,000 years ago. Limitations due to uncertainties on the tested sample.

7. Sedimentary rocks Loess are sediments carried by winds, Their compositions change with changes in atmospheric circulation, Until 600,000 before present but geographically limited.

8. Take-home points Many different proxies; use depends on time-scale and climatic factors of interest Precision of dating decreases with age Need to understand all the variables that affect the proxies: climate variability and biological variations