Download Chapter 14--Part 3

Chapter 14—Part 3
Younger Dryas Period/
CO2-climate feedbacks
CO2 Variations
Bubbles in ice cores provide samples of ancient air.
These samples tell us that CO2 levels track the
changes in temperature
CO2
T
CH4
http://www.pbs.org/wgbh/warming/stories/
Temperature and CO2 change together
Temperature
http://www.env.leeds.ac.uk/envi2150/lecture6/lecture6.html
CO2
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?
The Weathering Cycle is TOO SLOW!
The weathering cycle operates over millions of years
Glacial climate changes take place over thousands of years
CaSiO3 + CO2
CaCO3 + SiO2
The Biological Pump (marine organic carbon cycle)
transfer of CO2 to the deep ocean:
North Atlantic
Pacific Ocean
Transfer of carbon
Deep water
surface
water
Photosynthesis
CO2 + H2O  CH2O + O2
sinking particles
Respiration
CH2O + O2  CO2 + H2O
deep
water
Changes in the Biological Pump:
Atmospheric CO2 can decrease if more CO2 is stored
in deep waters
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
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
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
Redfield Ratios
These are the ratios of different elements in
living organisms
Element
C
N
P
Fe
Relative # of atoms
106
15
1
0.01-0.1
Nitrogen in organisms
• Amino acids (shown
at left) are the
building blocks of
proteins
• Nitrogen is part of
the amino (NH2)
group
Diagram from Wikipedia
Phosphorus in organisms
• Phosphorus is a key
component of
nucleic acids, i.e.,
DNA and RNA
• Nucleic acids also
contain nitrogen
http://www.isof.cnr.it/ppage/capob/synth.html
Iron in organisms
• Iron is used as part
of various catalysts
• There evidently is
some iron in
chlorophyll, but not
much (main metal
atom is Mg)
– But, iron is required
for the synthesis of
chlorophyll
http://chaitanya1.wordpress.com/2007/07/09/strawberries/
Possible glacial-interglacial
CO2/climate feedback loops
• Broecker’s “shelf hypothesis” (P)
• Martin’s “iron hypothesis” (Fe)
• “Coral reef hypothesis” (carbonate
saturation state)
Broecker’s “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
The Shelf Hypothesis Feedback Loop
Start here
Atm.
CO2
Surf. Temp.
Ts
Continental
Ice Sheets
(+)
Biological
Pump
P to
ocean
Shelf
exposure
 Positive feedback loop!
Sea
Level
Martin’s “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
Iron Fertilization Feedback Loop
Start here
Atm.
CO2
Surf. Temp.
Ts
Equator to pole
Temp. gradient
(+)
Biological
Pump
Iron in Dust
to Ocean
 Positive feedback loop!
Wind
Speeds
Coral Reef Hypothesis
Interglacial sea level
Coral
reef
(CaCO3)
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
Coral reef feedback loop
Start here
Surf. temp
Ts
Continental
glaciers
Sea
level
(+)
Atmospheric
CO2
Surface
ocean CO2
 Positive feedback loop!
Reef
formation
• 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
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
Younger Dryas Period
• Temperatures
come from O
and H isotopes
in ice cores
• High 18O (or high
D/H)  warmer
temperatures
Younger Dryas
The Atlantic Conveyor
• Did the oceanic thermohaline circulation shut down
during the Younger Dryas Period?
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?