Evidence for past climate

• • Tree rings - form due to variations in growth rate in seasonal climates. Lack of tree rings indicates equatorial climate zone and narrow tree rings indicate dry conditions
  • Height of plants - Exceptional heights suggest a hot and humid climate
  • Leaf shape - smooth suggests higher temperatures whilst jagged suggests lower temperatures
  • Pollen - resists chemical weathering. Identified and assigned to specific plants so fossils can reveal a plant assemblage which can in turn be used to estimate climatic conditons
• Reef coral - reef coral require warm, shallow oxygenated marine environments so fossils indicate a specific paleoclimate. Solitary coral are less useful as they can survive a wider range of environments.
• Microfossils - Important in borehole cores where chances of finding macro fossils is remote - used for zoning and palaeoclimate studies.
• • Oxygen isotope ratios are indicative of temperature of ancient ocean waters. The ratio is incorporated into carbonate shells of foraminifera. Higher 18O in fossils = cooler. Lower 18O in fossils = warmer.
  • This works because 18O is heavier than 16O. When evaporation occurs, more 18O remains. The 16O becomes locked in ice during glacial periods so a colder ocean is more rich in 18O. During warmer periods, ice melts and 16O is returned to ocean via runoff.
• Glacial varves - associated with fresh water. Annual layers - lighter layers are deposited in summer thaw and darker layers are deposited in winter freeze over, more carbonaceous material. Each pair of summer and winter beds represents a year.
• Dropstones - larger particles are dropped out of a glacier into finer marine sediment when the glacier melts. Tells us how extensive glaciation was when coupled with palaeomagnetism.
• Ice cores - provide a record of past climate up to 800Ka