Carbon System Controls on CO2

Increase biologicIncrease biologiccarbon pump incarbon pump incoastal andcoastal andtropical oceantropical ocean

Increase carbonIncrease carbonpump in Antarcticpump in Antarctic

Change chemistry ofChange chemistry ofAntarctic surface waterAntarctic surface water

Change chemistry of shallowChange chemistry of shallowSouthern Ocean subsurface waterSouthern Ocean subsurface water

High Latitude Stratification Sigman Sigman et alet al. (2004; . (2004;

NatureNature 428, 59-63) 428, 59-63) Cold climates Cold climates

promote polar ocean promote polar ocean stratificationstratification

Opal MAR decreased at Opal MAR decreased at ~2.7 mya~2.7 mya Fewer diatomsFewer diatoms

1515NNOMOM increased or did increased or did not changenot change Greater NOGreater NO33

2-2- utilization or no utilization or no change in NOchange in NO33

2-2- utilizationutilization

Indicates stratificationIndicates stratification

Density at Cold Temperatures Variation in seawater Variation in seawater

density as a function of density as a function of temperature, with temperature, with salinity at 35‰salinity at 35‰

Density of sea water Density of sea water increases less rapidly as increases less rapidly as the temperature drops the temperature drops towards freezing pointtowards freezing point

High latitude SST cold High latitude SST cold enough so winter enough so winter cooling did not have cooling did not have enough of an effect to enough of an effect to overcome salinity overcome salinity gradientsgradients

From Francois (2004; Nature 428 31-32)

Salinity Variations Today

Density (cooling)

Density as a function of depth in the modern wintertime Density as a function of depth in the modern wintertime Antarctic and changes in this density structure for Antarctic and changes in this density structure for uniform changes in seawater temperatureuniform changes in seawater temperature. Cooling . Cooling entire water column nearly doubles the vertical density entire water column nearly doubles the vertical density difference.difference.

Effect of Stratification on PCO2

Global cooling an important factor promoting Global cooling an important factor promoting high-latitude stratificationhigh-latitude stratification

Polar ocean stratification prevents deep ocean Polar ocean stratification prevents deep ocean ventilationventilation Traps more carbon in the deep seaTraps more carbon in the deep sea

During Quaternary climatic cyclesDuring Quaternary climatic cycles Interglacial periods sufficiently warm to allow Interglacial periods sufficiently warm to allow

deep water convection in Antarcticdeep water convection in Antarctic Not the North PacificNot the North Pacific

During glacial periodsDuring glacial periods Stratification in Antarctica and North PacificStratification in Antarctica and North Pacific Contribute to lower atmospheric COContribute to lower atmospheric CO22

Six factors may Six factors may contribute to glacial contribute to glacial atmospheric COatmospheric CO22 change change Four factors tied to Four factors tied to

carbon cycle through carbon cycle through changes inchanges in

Nutrient upwellingNutrient upwelling Antarctic surface Antarctic surface

water chemistrywater chemistry Factors contributing Factors contributing

most to drop in COmost to drop in CO22

Lower SSTLower SST Stronger biological Stronger biological

carbon pumpcarbon pump Increased COIncreased CO33

2-2- linked linked to changes in deep to changes in deep ocean circulationocean circulation

Ice-Driven Climate Responses Ice sheets can become drivers of climate Ice sheets can become drivers of climate

within the system becausewithin the system because Large heightLarge height

Influences wind direction and Influences wind direction and temperaturetemperature

Bright surfaceBright surfaceMajor albedo contrastMajor albedo contrast

Calve icebergsCalve icebergsDeliver cold fresh water to oceansDeliver cold fresh water to oceans

Glacier Climate Interactions Regions in close geographic proximity to Regions in close geographic proximity to

ice sheetice sheet The tempo of climate change is set by The tempo of climate change is set by

the change in ice sheetthe change in ice sheet Ice sheet has highest thermal inertiaIce sheet has highest thermal inertia

Ice-Driven Responses Orbital scale ice sheet Orbital scale ice sheet

rhythmsrhythms Quickly transferred Quickly transferred

to other parts of the to other parts of the climate systemclimate systemAtmosphereAtmosphereOceansOceans

Ice sheets respond Ice sheets respond to solar insolationto solar insolationOther systems Other systems

respond quickly respond quickly to change in ice to change in ice sheetssheets

Ocean Surface Temperature N. Atlantic SST should N. Atlantic SST should

respond to change in N. respond to change in N. Hemisphere glaciationsHemisphere glaciations SST track ice volume with SST track ice volume with

no lagno lag SST reconstruction from SST reconstruction from

faunal assemblagesfaunal assemblages Ice volume and SST follow Ice volume and SST follow

41,000 year cycles41,000 year cycles Similar relationships found Similar relationships found

in younger coresin younger cores Correlate with 100,000 Correlate with 100,000

year cyclesyear cycles

Mechanisms for Ocean Cooling Calving icebergs undoubtedly Calving icebergs undoubtedly

importantimportant Changes in windsChanges in winds

GCM sensitivity testsGCM sensitivity tests Clockwise flow of winds Clockwise flow of winds

initiated over ice sheetsinitiated over ice sheets• Cold winds blown over Cold winds blown over

N. AtlanticN. Atlantic• Replaced warm flow Replaced warm flow

from southwestfrom southwest Simulations predict 5-10°C Simulations predict 5-10°C

drop in SSTdrop in SST• Similar to documented Similar to documented

SST changeSST change

Cold Winds Affect Climate Pollen changes in FrancePollen changes in France

N. Europe’s climate N. Europe’s climate changedchanged

Warm and moist (trees)Warm and moist (trees) Cold and dry (herbs)Cold and dry (herbs)

Changes correlate with Changes correlate with ice volumeice volume

Cold winds from Cold winds from Scandinavian ice sheetsScandinavian ice sheets

N. Atlantic ocean colder N. Atlantic ocean colder than todaythan today

Relative warm N. Relative warm N. Atlantic moderates Atlantic moderates Europe’s winter Europe’s winter weatherweather

GCM Test of N. Atlantic SST Boundary conditionBoundary condition

N. Atlantic glacial SSTN. Atlantic glacial SST Output indicated Output indicated

cooling over N. cooling over N. Atlantic, European Atlantic, European maritime regions and maritime regions and central Eurasiacentral Eurasia

Produced lower rainfallProduced lower rainfall N. Hemisphere ice sheet N. Hemisphere ice sheet

growthgrowth Cooled N. AtlanticCooled N. Atlantic Cooled Europe and Cooled Europe and

AsiaAsia• Cooling occurred Cooling occurred

without lagwithout lag

Loess Plateaus Evidence of ice-driven Evidence of ice-driven

response found in Chinaresponse found in China Plateaus of wind-blown Plateaus of wind-blown

siltsilt Deposited by strong Deposited by strong

winds and dry winds and dry conditionsconditions

Loess deposition post-Loess deposition post-date weathered soil at date weathered soil at 2.75 mya2.75 mya Onset of dry conditions Onset of dry conditions

at glacial inceptionat glacial inception 100,000 year cycle 100,000 year cycle

over last 0.5 myover last 0.5 my

Onset of Loess Deposition Loss of N. Atlantic moistureLoss of N. Atlantic moisture

Cold and ice-covered N. AtlanticCold and ice-covered N. AtlanticStop moisture flow to Europe and Stop moisture flow to Europe and AsiaAsia

Siberian high-pressure centerSiberian high-pressure center Today source of strong winter windsToday source of strong winter winds

Could have strengthen during glaciersCould have strengthen during glaciers Windy and dry conditions deposited loessWindy and dry conditions deposited loess

Western N. PacificWestern N. Pacific Greenland ice sheetGreenland ice sheet

Summary Ice volume signal can be transferred far from Ice volume signal can be transferred far from

ice sheetsice sheets Altered wind patternsAltered wind patterns Changes in air and sea surface temperatureChanges in air and sea surface temperature Changes in rainfall over landChanges in rainfall over land

Northern Hemisphere ice sheet growthNorthern Hemisphere ice sheet growth Drives the climate signal on orbital time Drives the climate signal on orbital time

scalesscales Ice sheets respond to orbital forcingIce sheets respond to orbital forcingChanges in ice sheets drive other climate Changes in ice sheets drive other climate

responses in northern latitudesresponses in northern latitudes

Other Effects of N. Ice Sheets Aeolian deposition in Aeolian deposition in

western Indian Oceanwestern Indian Ocean Follows timing of ice Follows timing of ice

sheet growth and sheet growth and meltingmelting

More dust deposited More dust deposited from Arabian desertfrom Arabian desert During glacial intervals During glacial intervals

defined by defined by 1818O O maximamaxima

Less dust deposited Less dust deposited during interglacial during interglacial periodsperiods

Effects in South America Long cores from eastern Long cores from eastern

Columbian lakesColumbian lakes Pollen records that Pollen records that

alternate between alternate between grass and treesgrass and trees

100,000 year cycles100,000 year cyclesTrees grew during Trees grew during rapid warmingrapid warming

Grassland dominated Grassland dominated during slow cooling during slow cooling intervalsintervals

Effects in New Zealand

Marine sediment core Marine sediment core east of New Zealandeast of New Zealand Cyclic variations in tree Cyclic variations in tree

and grass pollenand grass pollen 100,000 year dominant 100,000 year dominant

cyclecycle

Effects in Southern Ocean Marine sediment cores in Marine sediment cores in

Southern OceanSouthern Ocean Assemblages of radiolariansAssemblages of radiolarians

Indicative of ice cover Indicative of ice cover and cold SSTand cold SST

Match well colder Match well colder temperatures in glacialtemperatures in glacial

Appears that only summer Appears that only summer monsoon signal not affected monsoon signal not affected by N. Hemisphere ice volumeby N. Hemisphere ice volume Not expected due to Not expected due to

summer forcing of monsoonsummer forcing of monsoon

Southern Hemisphere Surprises Large Antarctic ice sheets do not appear Large Antarctic ice sheets do not appear

to force S. Hemisphere glacial/interglacial to force S. Hemisphere glacial/interglacial changeschanges Most land mass of Antarctica now Most land mass of Antarctica now

coveredcoveredNot much room to grow so no major Not much room to grow so no major expansion of ice volumeexpansion of ice volume

In contrast, N. Hemisphere ice sheets In contrast, N. Hemisphere ice sheets fluctuated enormouslyfluctuated enormously If climate signals forced by ice sheetsIf climate signals forced by ice sheets

Probably forced by changes in N. Probably forced by changes in N. Hemisphere ice sheetsHemisphere ice sheets

Seasonal Changes in Precession

Although insolation Although insolation changes due to axial tilt in changes due to axial tilt in N and S Hemispheres in N and S Hemispheres in phasephase Precession changes are Precession changes are

out of phaseout of phaseWhen one hemisphere When one hemisphere

is warm (close to Sun)is warm (close to Sun)Other Hemisphere is Other Hemisphere is

coldcold Patterns of insolation Patterns of insolation

changes look differentchanges look different Phase of the precession Phase of the precession

cycle is reversed cycle is reversed between hemispheresbetween hemispheres

Phasing of Insolation and Ice Volume

41,000 and 23,000 year 41,000 and 23,000 year components of ice volumecomponents of ice volume Lag behind N. Lag behind N.

Hemisphere insolation Hemisphere insolation by physically by physically reasonable amountreasonable amount

41,000 year S. 41,000 year S. Hemisphere cycles has Hemisphere cycles has same lagsame lag 23,000 year ice volume 23,000 year ice volume

leads S. Hemisphere leads S. Hemisphere summer insolation summer insolation forcingforcing

Unreasonable Unreasonable relationshiprelationship

Global Transfer of Signals Changes in sea levelChanges in sea level

Creating more temperate maritime or harsh Creating more temperate maritime or harsh continental climate regionscontinental climate regions

Change in deep water circulationChange in deep water circulation Relatively warm and salty water directed away Relatively warm and salty water directed away

from Southern Hemisphere in Atlanticfrom Southern Hemisphere in Atlantic Atmospheric COAtmospheric CO22 levels levels

Lower glacial COLower glacial CO22 levels can cool entire planet levels can cool entire planet Reduce the amount of water vapor in Reduce the amount of water vapor in

atmosphereatmosphereMost reasonable explanation for widespread Most reasonable explanation for widespread

changeschanges•Which came first COWhich came first CO22 change or change or

glaciations?glaciations?

CO2 and Ice Volume Records of CORecords of CO22 and ice volume well correlated and ice volume well correlated

Both must be related ultimately to orbital changesBoth must be related ultimately to orbital changes Strong correlation also indicatesStrong correlation also indicates

Two records are linkedTwo records are linked

CO2 Drives Ice Sheets Sensible conclusion since COSensible conclusion since CO22 affects affects

temperature temperature Therefore ice sheet mass balanceTherefore ice sheet mass balance

However, COHowever, CO22 should lead ice volume should lead ice volume Pattern in records are not consistent Pattern in records are not consistent

with premisewith premiseNo persistent lag in signalsNo persistent lag in signals

Correlation between COCorrelation between CO22 and and temperature excellenttemperature excellent

COCO22 does not lead ice volume does not lead ice volume

Ice Sheets Drive CO2

COCO22 signal tracks closely ice volume signal tracks closely ice volume Similar to other ice-driven climate Similar to other ice-driven climate

signalssignals COCO22 record connected to changes in record connected to changes in

ocean circulation and carbon storageocean circulation and carbon storageOcean circulation responds quickly to Ocean circulation responds quickly to changes in climate forcingchanges in climate forcing

Timing of changes in COTiming of changes in CO22 and ice and ice volume match this expectationvolume match this expectation

CO2 Feedbacks COCO22 levels provide positive feedbacks to levels provide positive feedbacks to

climate systemclimate system Ice sheet growth caused COIce sheet growth caused CO22 decrease decrease

Lower COLower CO22 levels further cool climate levels further cool climate

•Increase ice sheet growthIncrease ice sheet growth COCO22 levels should also carry ice volume levels should also carry ice volume

signalsignalOther parts of climate systemOther parts of climate system

•Changes in temperature or Changes in temperature or moisturemoisture

Complete Story Unknown Text points to mismatches in COText points to mismatches in CO22 and ice and ice

volume/temperature recordsvolume/temperature records Mismatch with temperature is not as Mismatch with temperature is not as

great as believed only 2-3 years agogreat as believed only 2-3 years ago Mismatch with ice volume real?Mismatch with ice volume real?

However, records still insufficiently However, records still insufficiently refinedrefined•To answer clearly chicken and egg To answer clearly chicken and egg dilemmadilemma

Part of the uncertainty lies in poorly Part of the uncertainty lies in poorly dated ice coresdated ice cores