ice cores

• Ice cores are studied in Greenland and antarctica. 
• Vostok ice cores go back 420,000 years and covers 4 pleistoscene glacial periods across a depth of over 3000 metres. 

  • Far away from human influence of pollution in the middle of the Antarctic ice sheet. 

   
• Data obtained:

  • Oxygen isotope from ice 
  • Hydrogen isotopes from the ice 
  • Analysis of gas bubbles within the ice 
  • Dust particles - size and composition 
• Oxygen isotope ratios:

  • Enriched in O16 relative to O18 during colder periods 
  • Record is opposite to ocean sediment isotope ratios 
• Hydrogen isotopes:

  • Deuterium is heavy hydrogen 
  • So hydrogen isotopes behave in a similar way to oxygen 
• Gas bubbles:

  • Age of gas bubbles is different to ice age 
  • Gas trapped at depth below surface when pores in ice close up 
  • So ice age is older than gas age 
• Gas bubbles:

  • Record past atmosphere composition 
  • Can measure composition of greenhouse gases to see how they have changed 
• Dust:

  • Larger particles = exposed land closer 
  • Smaller particles = exposed land further away 
  • Larger particles mean that climate in that region is warmer 
• Dating ice cores:

  • Count number of seasonal layers - yearly variation of temperature makes wiggles that tell the age of the ice 
  • But layers get thinner with depth and ice starts to flow - so mathematical model is used 
• Dating:

  • Analysing dust component for volcanic ash 
  • Each eruption has a unique chemical composition 
  • The eruption can be dated 
  • So dust from volcanic activity can be correlated with age 
• Dating:

  • Radioactive decay of elements within dust 
  • Uranium found in samples 
• Short major glacial periods are called stadials. 

  • Ice advanced to lower latitudes 
  • First major glaciation seen at 2.4 mya - shown by extinction of some tree species 
  • Shorter interglacials are called interstadials 
• Only evidence for three most recent glacials:

  • 450,000, 250,000 - older drift and 18,000 - newer drift years ago 
  • Early evidence destroyed in later glacials 
• 13000 years ago, almost all the ice had disappeared from Britain. There was a small stadial 11500 years ago called the loch Lomond re-advance. 
• There are brief stadials and interstadials imposed on the longer period of glacials and interglacials.