quaternary intro

• when did the quaternary start?

  2.6 ma
• Based on the appearance of homo habilis and the first appearance of large cobbles resting in and on deep sea deposits - floating ice carried them there. 
• There have been frequent and rapid changes in climate. 
• In the last 2.5 million years there were 50 warm cold cycles 
• There is evidence of the formation of ice caps in Iceland towards the end of the Neogene. 

  • Glacial deposits are easy to date radiometrically due to the lava flows 
• Obliquity:

  • Tilt of the axis 
  • If upright - radiation is evenly distributed between summer and winter 
  • Cooler summers so less ice melt 
  • Warmer winter so more evaporation that falls as snow 
  • more likely to get glacial
  • 41000 years 
• Precession:

  • Wobble changes angle of tilt - making it larger or smaller than without wobble 
  • Now at perihelion so northern hemisphere points away from the sun - warmer winter 
  • Southern hemisphere gets hotter summer 
• Our climate is affected by a combination of the cycles. There is a complex interplay of different factors. 

  • Feedback mechanisms 
  • Variation in solar output 
  • Plate tectonics 
  • Volcanic activity 
  • Ocean circulation
  • Mountain building 
• When the cycles combine to give reduced radiation during summer at 60 - 65 degrees north. Then less snow melts during summer 

  • Snow accumulates and radiation is reflected to space 
  • Positive feedback 
• Milankovitch cycles produce half a degree of temperature change. 
• In the cold phases ice covered land and sea at higher latitudes but the effects were felt in low latitudes. 
• Eccentricity:

  • Shape of orbit - distance from sun 
  • Very small changes in insolation 
  • 100000 years 
• Milankovitch cycles were not accepted, only with the study of ocean sediment cores to obtain oxygen isotope data did proof of variation impacting climate be found.