Record of Climate Change

• Oxygen Isotope Ratios (O18/O16):

  • fixed amount of each isotope - variation in each isotope ratio in each store - isotopic composition of each ice layer, record of isotopic composition of precipitation which produces it
  • oxygen isotopes preserve record of effects of Milankovitch Cycles on climate change during Quaternary
• Oxygen Isotope Ratios:

  • as water evaporates from ocean surface, small mass difference means O16 evaporates more readily than O18 into water vapour (remaining water enriched in O18/depleted in O16)
  • condensation reverses process/restores equilibrium - if large, continental ice masses exist, return flow diminished as water locked up as ice; more extensive ice sheets = heavier isotopic water composition of sea water
  • measuring isotopic enrichment in heavy oxgen in sea water and depletion in precipitation indicator of extent of global ice masses

  
• Oxygen Isotope Ratios:

  • in glacials, O16 evaporates from colder oceans leaving heavier O18 - larger ice sheet has higher O16 ratio; at poles more O16 left to precipitate (more O16 enrichment) + more O18 left behind in oceans - cores enriched in O16 in colder climatic glacials
  • as ice melts during interglacials, O16 within ice returns to oceans; interglacials have high ratio of O16 in oceans - in glacials, O16 evaporated from colder oceans leaving heavier O18 - ice cores on land enriched in heavier O18 during interglacials (more energy for evaporation of heavier isotope)
• Foraminifera combine dissolved oxygen with carbon/calcium to build calcium carbonate shells (incorporating temperature dependent O18:O16 ratio) - organisms die and settle on sea bed preserving record of global climate change.

  • High O18 in oceans = Low Temperature
  • Low O18 in oceans = High Temperature
• Records of Climate Change:

  • terrestrial record more fragmentary; glacial, fluvio-glacial, periglacial and coastal landforms only represent most recent advances/retreat of quaternary glaciers
  • oceanic sediments present more complete record of quaternary climate change + varves are more continuous record, but limited in temporal/spatial extent (same with tree rings)
• Proxies

  • Tree Rings - 10,000 years
  • Ice Cores - 400,000 years
  • Microfossils/Foraminafera - millions of years >
  • Pollen - thousands of years >
• Ice Cores:

  • ice cores contain trapped air bubbles, wind blown dust, volcanic ash and radioactive substances - youngest parts of core show greatest details
  • provide information on temperature, ocean volume, precipitation, chemistry, gas composition of lower atmosphere, volcanic eruptions, solar variability, extent of deserts and forest fires
  • over last 800,000 years interglacials occured every 10,000 years + over last 400,000 years interglacials lasted around 10,000 years (before they were less warm/lasted longer)