Initiation of Northern Hemisphere Glaciation

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Initiation of Northern Hemisphere Glaciation
Present day ice sheet on Svalbard Islands

• The Role of the North Pacific

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(No Transcript)
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Role of the Subarctic Pacific Ocean
Westerly winds
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Data

• Foram data shows a cooling at 2.7Ma
• Opal accumulation decreases at 2.7Ma
• Alkenone unsaturation ratios
• Diatom d18O
• IRD/magnetic susceptibility

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Alkenone unsaturation ratios

• Coccoliths ratio of organic molecules
  (alkenones) varies with temperature
• Shows a 7C warming at 2.7 Ma
• problems possible lateral transport and
  exhumation, diagenesis, light and nutrient changes

2.7Ma
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Diatom d18O

• Shows 5 decrease - 1 halocline development,
  0.5 inc for ice volume
• 4.5 for temperature
• Shows 9C warming at 2.7Ma

2.7Ma
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Contradictory evidence?

• Forams and IRD-cooing, Diatoms/alkenones-warming
• Forams-late winter/spring, Diatoms/coccoliths-late
  summer/autumn
• Recording an increase in seasonality
• Why? development of seasonal thermocline at
  2.7Ma

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Conditions in modern Subarctic Pacific
Seasonal thermocline
Permanent halocline in upper 300m
Less salty, less dense
300m
Saltier, denser
Summer/Autumn SST 12c
Winter/Spring SST 1c
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Past conditions

• Pre 2.7 Ma destratified ocean, more difficult
  to warm surface ocean
• Cooling causes development of halocline
• Post 2.7Ma stratified ocean, sea surface can
  warm
• Lag between continental and oceanic cooling
  allows snow accumulation in North America
• Change due to increase in amplitude of 41kyr
  obliquity cycle

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Climate model

• Set up model with stratified and destratified
  oceans
• Stratified model produces greater seasonal
  variation in SST and more ice over North America
• Model stratification by changing freshwater input?

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Summary

• Orbital cycles
• Stratification in Subarctic Pacific
• Increased moisture supply
• Lower summer temps
• Formation of Ice on North America
• Ice albedo feedback
• Initiation of northern hemisphere glaciation