Chapter 14Part 3

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Chapter 14Part 3

• Younger Dryas Period/
• CO2-climate feedbacks

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CO2 Variations Bubbles in ice cores provide
samples of ancient air. These samples tell us
that CO2 levels track the changes in temperature
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CO2
T
CH4
http//www.pbs.org/wgbh/warming/stories/
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Temperature and CO2 change together
CO2
Temperature
http//www.env.leeds.ac.uk/envi2150/lecture6/lectu
re6.html
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CO2 Variations Bubbles in ice cores provide
samples of ancient air. These samples tell us
that CO2 levels track the changes in
temperature This suggests CO2 can amplify
climate change that is initiated by orbital
variations. How?
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The Weathering Cycle is TOO SLOW! The weathering
cycle operates over millions of years Glacial
climate changes take place over thousands of years
Weathering
CaSiO3 CO2
CaCO3 SiO2
Volcanism
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The Biological Pump (marine organic carbon
cycle) transfer of CO2 to the deep ocean
North Atlantic
Pacific Ocean
Transfer of carbon
Deep water
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surface water
Photosynthesis CO2 H2O ? CH2O O2
sinking particles Respiration CH2O O2 ? CO2
H2O
deep water
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Changes in the Biological Pump Atmospheric CO2
can decrease if more CO2 is stored in deep waters
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Changes in the Biological Pump Atmospheric CO2
can decrease if more CO2 is stored in deep
waters. This could be due to 1) slower deep
ocean circulation
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Changes in the Biological Pump Atmospheric CO2
can decrease with more storage of CO2 in deep
waters. This could be due to 1) slower deep
ocean circulation or 2) greater photosynthesis
in surface waters
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Changes in the Biological Pump Atmospheric CO2
can decrease with more storage of CO2 in deep
waters. This could be due to 1) slower deep
ocean circulation or 2) greater photosynthesis
in surface waters More nutrients to the
ocean? Limiting nutrients N, P, and Fe
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Redfield Ratios
These are the ratios of different elements
in living organisms
Element Relative of atoms C 106 N
15 P 1 Fe 0.01-0.1
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Possible glacial-interglacial CO2/climate
feedback loops

• Broeckers shelf hypothesis (P)
• Martins iron hypothesis (Fe)
• Coral reef hypothesis (carbonate
• saturation state)

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Broeckers Shelf hypothesis
Interglacial sea level
-Weathering releases P from rocks -Some of
this P accumulates in sediments on the shelves
P-rich sediments
Glacial sea level

• When sea level falls, P-rich sediments on the
  continental
• shelves are washed into the deep ocean, raising
  productivity

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The Shelf Hypothesis Feedback Loop
Start here
Atm. CO2
Continental Ice Sheets
Surf. Temp. Ts
()
Sea Level
Shelf exposure
Biological Pump
P to ocean
? Positive feedback loop!
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Martins Iron hypothesis

• Iron is a limiting nutrient in parts of the
  ocean, especially the southern oceans near
  Antarctica
• Iron is supplied to the oceans by windblown dust
  from the continents
• Wind strength increases when the climate becomes
  glacial because the poles cool more than does the
  equator

Saharan dust plume
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Iron Fertilization Feedback Loop
Start here
Surf. Temp. Ts
Atm. CO2
Equator to pole Temp. gradient
()
Wind Speeds
Iron in Dust to Ocean
Biological Pump
? Positive feedback loop!
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Coral Reef Hypothesis
Interglacial sea level
CaCO3 CO2 H2O ? Ca 2 HCO3?
Glacial sea level

• Reefs form when sea level goes up ? CO2 goes up

• Reefs weather and dissolve when sea level goes
  down
• ? CO2 goes down

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Coral reef feedback loop
Start here
Continental glaciers
Sea level
Surf. temp Ts
()
Reef formation
Surface ocean CO2
Atmospheric CO2
? Positive feedback loop!
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• So, there are several positive feedback loops
  that may cause atmospheric CO2 to go up and down
  in concert with the glacial-interglacial cycles
• Some combination of these feedback loops,
  combined with changes in ocean circulation, is
  probably responsible for the CO2 fluctuations
  seen in the Vostok ice core

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Younger Dryas Period

• Towards the end of the last Ice Age, climate
  warmed, then suddenly cooled again for almost
  1000 yrs
• The evidence comes from the reappearance of the
  Dryas flower in the Alps, which flourishes in
  glacial climates

Image from Wikkipedia
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Younger Dryas Period

• Temperatures
• come from O
• and H isotopes
• in ice cores
• High 18O (or high
• D/H) ? warmer
• temperatures

Younger Dryas
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The Atlantic Conveyor

• Did the oceanic thermohaline circulation shut
  down
• during the Younger Dryas Period?

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Atlantic Conveyor Shutdown

• As the Laurentide ice sheet retreated, melt water
  was diverted from the Mississippi River to the
  St. Lawrence River
• North Atlantic ocean became capped with
  freshwater ? not dense enough to sink ?
  thermohaline circulation shut down for 1000 yrs
• Could this happen again as a result of global
  warming?