Post on 04-Jan-2016
Chapter 11Chapter 11Orbital-Scale Changes in Orbital-Scale Changes in
Carbon Dioxide and Carbon Dioxide and MethaneMethane
Reporter : Yu-Ching ChenDate : May 22, 2003 (Thursday)
OutlineOutline IntroductionIntroduction Ice Cores Ice Cores Drilling and Dating Ice Cores Trapping Gases in the Ice Orbital-Scale Change in MethaneOrbital-Scale Change in Methane Methane and the monsoon Orbital-Scale Change in COOrbital-Scale Change in CO22
Physical Oceanographic Explanations of CO2 Changes Orbital-Scale Carbon Reservoirs Tracking Carbon through the Climate System Can δ13C Evidence Detect Glacial Changes in Carbon Reservoirs? Pumping of Carbon into the Deep Ocean during Glaciations Changes in the Circulation of Deep Water during Glaciations ConclusionConclusion
IntroductionIntroduction Methane (CHMethane (CH44) and carbon dioxide (CO) and carbon dioxide (CO22) have varied ) have varied
over orbital time scales.over orbital time scales.
Methane levels have fluctuated mainly at the 23,000-year Methane levels have fluctuated mainly at the 23,000-year orbital rhythm of precession, and we will evaluate the orbital rhythm of precession, and we will evaluate the hypothesis that these changes are linked to fluctuations hypothesis that these changes are linked to fluctuations in the strength of monsoons in Southeast Asia.in the strength of monsoons in Southeast Asia.
During glaciations, atmosphere CODuring glaciations, atmosphere CO2 2 value have value have repeatedly dropped by 30 . repeatedly dropped by 30 .
00000
0
Ice Cores Ice Cores Drilling and Dating Ice CoresDrilling and Dating Ice Cores
Ice CoresIce Cores Trapping Gases in the Ice
Air moves freely through snow and ice in
the upper 15m of an ice sheet, but flow is
increasingly restricted below this level.
Bubbles of old air are eventually sealed off
completely in ice 50 to 100m below the
surface.
Figure 11-3. Sintering: Sealing air bubbles in ice
Ice CoresIce Cores
Measurements of CO2 (top) and methane (bottom) taken on bubbles in ice cores merge perfectly with measurements of the atmosphere in recent decades.
Figure 11-4. Ice core and instrumental CO2 and CH4 .
Orbital-Scale Change in MethaneOrbital-Scale Change in Methane
550~770 maxima
350~450 minima
12500-10000/5=23000 years/cycle
Methane record from Vostok ice in Antarctica shows regular cycles at Intervals near 23,000 years (left).
This signal closely resembles the monsoon- response signal driven by low-latitude insolation (right).
Figure 11-5. Methane and the monsoon
How would changes in the strength ofHow would changes in the strength of
low-latitude monsoons producelow-latitude monsoons produce
changes in atmospheric methanechanges in atmospheric methane
concentrations?concentrations?
Heavy rainfall in such regions saturates the ground, reduces its ability to absorb water, and thereby increases
the amount of standing water in bogs.
Decaying vegetation uses up any oxygen in the water and creates the oxygen-free conditions needed to generate methane.
The extent of these boggy areas must have expanded during wet monsoon maxima and shrunk during dry monsoon minima.
Orbital-Scale Change in COOrbital-Scale Change in CO22
A 400,000-year record of CO2 from Vostok ice in Antarctica shows four large-scale cycles at a period of 100,000 years similar to those in the marine δ18O record.
280-300ppm maxima 180-190 minima
Abrupt increases in CO2 occur during time of rapid ice melting.
Figure 11-6. Long-term CO2 changes
Orbital-Scale Change in COOrbital-Scale Change in CO22
A record of the last 160,000
years of CO2 variations from Vostok ice in Antarctica (left)resembles the marine δ18O record (right).
CO2 concentrations in the
atmosphere changed by 30
just a few thousand years.
000
Figure 11-7. The most recent CO2 cycle
What factors could explain the What factors could explain the observed 90-ppm drop in COobserved 90-ppm drop in CO22 levels levels during glacial Intervals from the during glacial Intervals from the levels observed Interglacial intervals?levels observed Interglacial intervals?
Physical Oceanographic Explanations Physical Oceanographic Explanations of COof CO22 Changes Changes
One possibility is that changes in the physical oceanographic One possibility is that changes in the physical oceanographic characteristics of the surface ocean-its temperature and salicharacteristics of the surface ocean-its temperature and salinity.nity.
COCO22 dissolves more readily in colder seawater, atmospheric dissolves more readily in colder seawater, atmospheric
COCO22 levels will drop by 9 ppm for each 1 of ocean cooling.℃ levels will drop by 9 ppm for each 1 of ocean cooling.℃ COCO2 2 dissolves more easily in seawater with a lower dissolves more easily in seawater with a lower
salinity.salinity. During glaciations, the average salinity of entire ocean During glaciations, the average salinity of entire ocean
increased by about 1.2increased by about 1.2oo//oooo, atmospheric CO, atmospheric CO22 levels increase levels increase
11 ppm .11 ppm . 000
Physical Oceanographic Explanations Physical Oceanographic Explanations of COof CO22 Changes Changes
Orbital-Scale Carbon ReservoirsOrbital-Scale Carbon Reservoirs
Figure 11-8. Exchange of carbon The large changes in atmospheric CO2 in ice cores over intervals of a few thousand years must involve rapid exchanges of carbon among the near-surface reservoirs.
Orbital-Scale Carbon ReservoirsOrbital-Scale Carbon Reservoirs
Figure 11-9. Interglacial-glacial changes in carbon reservoirs During the glacial maximum 20,000 years ago, large reductions of carbon occurred in the atmosphere, in vegetation and soils on land, and in the surface ocean. The total amount of carbon removed from these reservoirs (> 1000 gigatons) was added to much larger reservoir in the deep ocean.
Tracking Carbon through the Climate SystemTracking Carbon through the Climate System
Figure.11-11 Photosynyhesis and carbon isotope factionation Photosyntheis on land and in the surface ocean converts inorganic carbon to organic form and causes large negative shifts in δ1
3C values of the organic carbon produced.
Tracking Carbon through the Climate SystemTracking Carbon through the Climate System
Figure 11-10. Carbon reservoir δ13C values The major reservoirs of carbon on Earth have varying amounts of organic and inorganic carbon, and each type of carbon has characteristic carbon isotope values.
Tracking Carbon through the Climate STracking Carbon through the Climate Systemystem
1000)/(
)/()/(
tan1213
tan12131213
13
dards
dards
CC
CCCCC sample 1000
)/(
)/()/(
tan1213
tan12131213
13
dards
dards
CC
CCCCC sample
1000)/(
)/()/(
tan1213
tan12131213
13
dards
dardssample
CC
CCCCC
BOX 11-1. Carbon Isotope Ratios
)000(
Can δCan δ1313C Evidence Detect Glacial Changes C Evidence Detect Glacial Changes in Carbon Reservoirs?in Carbon Reservoirs?
We can use a mass balance calculation to estimate the We can use a mass balance calculation to estimate the effect of adding very negative carbon to the inorganic effect of adding very negative carbon to the inorganic carbon already present in the deep sea:carbon already present in the deep sea:
(38,000) (0%) + (530) (-25%) = (38,530) (x%)(38,000) (0%) + (530) (-25%) = (38,530) (x%)
Inorganic C Mean C added Mean Glacial ocean MeanInorganic C Mean C added Mean Glacial ocean Mean
in ocean δin ocean δ1313C from land δC from land δ1313C carbon total δC carbon total δ1313C C
x=-0.34x=-0.34
Can δCan δ1313C Evidence Detect Glacial Changes C Evidence Detect Glacial Changes in Carbon Reservoirs?in Carbon Reservoirs?
Fig. 11-12Fig. 11-12
Pumping of Carbon into the Deep Pumping of Carbon into the Deep Ocean during GlaciationsOcean during Glaciations
During glaciations(A), 12C-enriched from the land to the ocean at the same time that 16O-enriched water vapor is extracted from the ocean and stored in ice sheets.
During interglaciations (B), 12C-rich carbon returns to the land as 16O- rich water flows back into the ocean.
Figure 11-13. Glacial transfer ofFigure 11-13. Glacial transfer of 12 12C and C and 1616OO
Pumping of Carbon into the Deep Pumping of Carbon into the Deep Ocean during GlaciationsOcean during Glaciations
Ocean carbon pump hypothesisOcean carbon pump hypothesis
Carbon was exported from surface watersCarbon was exported from surface waters
to the deep ocean by higher rates of to the deep ocean by higher rates of
photosynthesis and biologic productivity.photosynthesis and biologic productivity.
COCO22+H+H22O CHO CH22O+OO+O22
Pumping of Carbon into the Deep Pumping of Carbon into the Deep Ocean during GlaciationsOcean during Glaciations
Figure 11-14. Annual carbon production in the modern surface oceanFigure 11-14. Annual carbon production in the modern surface ocean
DO wind Fertilize the Glacial Ocean?DO wind Fertilize the Glacial Ocean?BOX 11-2. Iron fertilization of ocean surface waters
Pumping of Carbon into the Deep Pumping of Carbon into the Deep Ocean during GlaciationsOcean during Glaciations
Photosynthesis in ocean surface waters sends 12C rich organic matter to the deep sea, leaving surface waters enriched in 13C (left).
At the same time, photosynthesis extracts nutrients like phosphate (PO4-
-2) from surface waters and sends them to deep sea. As a result, seawater δ13C values and phosphate concentrations are closely correlated (right).
Figure. 11-17. Link between nutrients and δ13C values
Pumping of Carbon into the Deep Ocean during Pumping of Carbon into the Deep Ocean during GlaciationsGlaciations
Figure 11-16. Measuring changes in the ocean carbon pumpFigure 11-16. Measuring changes in the ocean carbon pump
Pumping of Carbon into the Deep Ocean during Pumping of Carbon into the Deep Ocean during GlaciationsGlaciations
Figure 11-17. Past changes in the carbon pump
If the ocean carbon pump
affects atmospheric CO2 levels,
the net difference between
surface and deep-water δ13C
values should increase when
CO2 levels are low.
Measured δ13C differences
show some correlation with
past changes in atmospheric
CO2
Changes in the Circulation of Deep Changes in the Circulation of Deep Water during GlaciationsWater during Glaciations
Figure 11-18 Modern deepocean δδ1313CC patterns
Changes in the Circulation of Deep Water during Changes in the Circulation of Deep Water during GlaciationsGlaciations
Present-Day Controls on Regional δ13C Values
Figure 11-19. Regional δFigure 11-19. Regional δ1313C differenceC difference
Changes in the Circulation of Deep Water during Changes in the Circulation of Deep Water during GlaciationsGlaciations
Past Changes in Regional δ13C Values
Figure 11-20. Change in deep Atlantic circulation during glaciationFigure 11-20. Change in deep Atlantic circulation during glaciation
Changes in the Circulation of Deep Water during Changes in the Circulation of Deep Water during GlaciationsGlaciations
Figure 11-21 Changing sources of Atlantic deep water.
The percentage of deep water
Originating in the North
Atlantic and flowing to the
equator during the last1.25
Myr has been consistently
lower during glaciations than
during interglaciations.
Changes in the Circulation of Deep Water during Changes in the Circulation of Deep Water during GlaciationsGlaciations
Changes in Ocean Chemistry
Figure 11-22. Carbon system controls on COFigure 11-22. Carbon system controls on CO22 in the glacial atmosphere in the glacial atmosphere
ConclusionConclusion
Thanks For Your Thanks For Your AttentionAttention