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