September 30, 2013
Earth System History
GEOL 1020
[15]
Announcements
More about global geochemical cycles
About plants and carbon
fixation….
THIS DIFFERENCE IN BEHAVIOR OF THE BOND STRENGTHS,
CAN BE TRACED USING CARBON ISOTOPES!!
The photosynthesis-respiration cycle in plants.
KNOW THIS
BIOLOGICAL SYSTEMS PREFER THE
LIGHT ISOTOPE OF CARBON (12C) OVER
THE HEAVY ISOTOPE (13C).
The CO2 and O2 system
What is the relationship between burial of
plant debris and atmospheric chemistry?
CO2 DOWN  O2 UP
CO2 UP  O2 DOWN
Respiration “BURNS” organic matter back to CO2
And consumes Oxygen in the process…
OXIDATION
CO2 formation
Rapid burial of organic
KNOW THIS:
matter cuts it off from
oxygen, therefore no feedback to CO2!!
13C
/ 12C ratio in
atmosphere
13C
/ 12C ratio in
atmosphere
is steady here.
is increasing here!
Case Study: Increased plant growth and/or increased carbon burial
PREFERS
CARBON-12
Carbon-12 gets
Depleted in atmosphere
Oxygen starts
to build up.
Carbon-12 enriched
Organic matter gets
Buried.
The CO2 and O2 system
What is the relationship between burial of
plant debris and atmospheric chemistry?
CO2 DOWN  O2 UP
CO2 UP  O2 DOWN
Amount of
CO2 in
atmosphere
Case Study: Decreased plant growth and/or decreased carbon burial
TEMPERATURE??
Time (samples from bottom to top)
IS IT GETTING HOTTER OR COLDER WITH TIME?
A. COLDER
B. HOTTER
CO2 in
atmosphere
Case Study: Decreased plant growth and/or decreased carbon burial
TEMPERATURE!!
time
IS IT GETTING HOTTER OR COLDER OUTSIDE?
A. COLDER
B. HOTTER
BECAUSE CO2 IS A GREENHOUSE GAS, IT
TRAPS WARMTH AND WARMS THE AIR
Case Study: Decreased plant growth and/or decreased carbon burial
A.
OXYGEN
LEVELS?
B.
time
OXYGEN LEVELS?
13C/12C
In atmosphere & sediments
C.
time
OXYGEN
LEVELS?
Case Study: Decreased plant growth and/or decreased carbon burial
time
OXYGEN LEVELS?
13C/12C
In atmosphere & sediments
C.
time
OXIDATION
CO2 formation
Returns
Carbon-12 to
atmosphere
Rapid burial of organic
KNOW THIS:
matter cuts it off from
oxygen, therefore no feedback to CO2!!
13C
/ 12C ratio in
atmosphere
13C
/ 12C ratio in
atmosphere
is steady here.
is increasing here!
Mid-Cretaceous
RECALL:
if CO2 goes down, O2 goes up
if O2 goes down, CO2 goes up
More organic carbon burial = left-over HEAVY carbon in
atmospheric CO2.
With increasing burial of organic matter, or increasing
FLUX (input) into sedimentary reservoir, CO2 level goes
DOWN
13C
/
12C
ratio in atmosphere
is steady.
/
12C
ratio in atmosphere
is increasing!
COLD
WARM
13C/12C
13C
ratio changes over time
In the marine system, the same relationship
between increased burial of organic matter
in INCREASE in the stable carbon isotope
ratio (13C/12C) holds!