d 18 O records Ice Volume
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Transcript of d 18 O records Ice Volume
18O records Ice Volume Every 10-m change in sea level produces an Every 10-m change in sea level produces an
~0.1~0.1‰‰ change in change in 1818O of benthic foraminiferO of benthic foraminifer The age of most prominent The age of most prominent 1818O minimaO minima Correspond with ages of most prominent Correspond with ages of most prominent
reef recording sea level high standsreef recording sea level high standsAbsolute sea levels estimates from reefsAbsolute sea levels estimates from reefs
•Correspond to shifts in Correspond to shifts in 1818OO Reef sea level record agreement with Reef sea level record agreement with
assumption of orbital forcingassumption of orbital forcing125K, 104K and 82K events forced by 125K, 104K and 82K events forced by precessionprecession
Astronomical 18O as a Chronometer
Relationship between orbital forcing and Relationship between orbital forcing and 1818O so strongO so strong 1818O values can orbitally tune sediment O values can orbitally tune sediment
ageageConstant relationship in time between Constant relationship in time between insolation and ice volumeinsolation and ice volume
Constant lag between insolation Constant lag between insolation change and ice volume changechange and ice volume change
Date climate records in ocean sedimentsDate climate records in ocean sedimentsIn relation to the known timing of In relation to the known timing of orbital changesorbital changes
Orbital Tuning 41,000 and 23,000 41,000 and 23,000
year cycles from year cycles from astronomically dated astronomically dated insolation curvesinsolation curves Provide tuning Provide tuning
targetstargets Similar cycles Similar cycles
embedded in the embedded in the 1818O ice volume O ice volume curves are curves are matched and datedmatched and dated
Now most accurate Now most accurate way to date marine way to date marine sedimentssediments
Orbital-Scale Change in CH4 & CO2 Important climate records from last 400 kyaImportant climate records from last 400 kya
Direct sampling of greenhouse gases in iceDirect sampling of greenhouse gases in ice Critical questions must be addressedCritical questions must be addressed
Before scale of variability in records Before scale of variability in records determineddeterminedReliability of age dating of ice core?Reliability of age dating of ice core?Mechanisms and timing of gas trapping?Mechanisms and timing of gas trapping?Accuracy of the record?Accuracy of the record?
•How well gases can be measured?How well gases can be measured?•How well do they represent How well do they represent
atmospheric compositions and atmospheric compositions and concentrations?concentrations?
Vostok Climate Records Illustrates strong correlation Illustrates strong correlation
between paleotemperature between paleotemperature and the concentration of and the concentration of atmospheric greenhouse atmospheric greenhouse gasesgases
Concentrations of COConcentrations of CO22 and CH and CH44
moved in tandem with moved in tandem with paleotemperatures derived paleotemperatures derived from stable isotope recordsfrom stable isotope records
Mechanisms of relationships Mechanisms of relationships poorly understoodpoorly understood
To what extent did higher To what extent did higher greenhouse gases cause greenhouse gases cause greater radiative warming of greater radiative warming of the Earth's atmosphere?the Earth's atmosphere?
Dating Ice Core Records Ice sheets thickest in centerIce sheets thickest in center
Ice flow slowly downwardIce flow slowly downward Then flows laterally outwardThen flows laterally outward
Annual layers may be preserved and countedAnnual layers may be preserved and counted Deposition of dust during winterDeposition of dust during winter
Blurred at depth due to ice deformationBlurred at depth due to ice deformation
Reliability of Dating Dust layer countingDust layer counting
Best when ice deposition rapidBest when ice deposition rapidGreenland ice accumulates at 0.5 m yGreenland ice accumulates at 0.5 m y-1-1
•Layer counting good to 10,000 yearsLayer counting good to 10,000 yearsAntarctica ice accumulates at 0.05 m yAntarctica ice accumulates at 0.05 m y-1-1
•Layering unreliable due to slow Layering unreliable due to slow depositiondeposition
Where unreliable, ice flow models usedWhere unreliable, ice flow models usedPhysical properties of icePhysical properties of iceAssumes smooth steady flowAssumes smooth steady flow
•Produces “fairly good estimates” of Produces “fairly good estimates” of ageage
Dust Layers Greenland has two primary sources for dustGreenland has two primary sources for dust
Particulates from Arctic Canada and coastal Particulates from Arctic Canada and coastal GreenlandGreenland
Large volcanic eruptions anywhere on the globeLarge volcanic eruptions anywhere on the globe
Gas Trapping in Ice Gases trapped during ice Gases trapped during ice
sinteringsintering When gas flow to When gas flow to
surface shut downsurface shut down Crystallization of iceCrystallization of ice Depths of about 50 to Depths of about 50 to
100 m below surface100 m below surface Gases younger than Gases younger than
host icehost ice Fast accumulation Fast accumulation
minimizes age difference minimizes age difference (100 years)(100 years)
Slow deposition Slow deposition maximizes age difference maximizes age difference (1000-2000 years)(1000-2000 years)
Implication of Age Difference If change in greenhouse gas If change in greenhouse gas
concentrationsconcentrations Force changes in ice volumeForce changes in ice volume
Gas concentration should lead ice Gas concentration should lead ice volumevolume
Gas age is younger than ice ageGas age is younger than ice ageTherefore offset between changes in Therefore offset between changes in atmospheric gas concentrationsatmospheric gas concentrations•Which should be relatively rapidWhich should be relatively rapid
Closer to change in ice volumeCloser to change in ice volume•Which should be relatively slowWhich should be relatively slow
Reliability and Accuracy of Records
Can be evaluated by comparing instrumental recordCan be evaluated by comparing instrumental record With records from rapidly accumulating ice sheetsWith records from rapidly accumulating ice sheets
Instrumental records date to 1958 for COInstrumental records date to 1958 for CO22 and and 1983 for CH1983 for CH44
• Mauna Loa Observatory (David Keeling)Mauna Loa Observatory (David Keeling)
NOAA/CMDL Air Sampling Network
35 Sampling stations or about half world-wide stations35 Sampling stations or about half world-wide stations
CSIRO CH4 Sampling Network
Carbon Dioxide Measurements of COMeasurements of CO22 concentration concentration
Core from rapidly accumulating iceCore from rapidly accumulating ice Merge well with instrumental dataMerge well with instrumental data
Methane Measurements of CHMeasurements of CH44 concentration concentration
Core from rapidly accumulating iceCore from rapidly accumulating ice Merge well with instrumental dataMerge well with instrumental data
CH4 and CO2 in Ice Cores Given agreement between records from Given agreement between records from
rapidly accumulating icerapidly accumulating ice Instrumental dataInstrumental data
Accuracy and variability about the Accuracy and variability about the trendstrends
Assume that longer-term records Assume that longer-term records collected from ice corescollected from ice coresReliable for determining the scale of Reliable for determining the scale of variabilityvariability
Orbital-Scale Changes in CH4 CHCH44 variability variability
Interglacial maxima Interglacial maxima 550-700 ppb550-700 ppb
Glacial minima 350-450 Glacial minima 350-450 ppbppb
Five cycles apparent in Five cycles apparent in recordrecord 23,000 precession 23,000 precession
periodperiod Dominates low-Dominates low-
latitude insolationlatitude insolation Resemble monsoon Resemble monsoon
signalsignal•Magnitude of Magnitude of
signals matchsignals match
Monsoon forcing of CH4
Match of high CHMatch of high CH44 with strong monsoon with strong monsoon Strongly suggests connectionStrongly suggests connection
Monsoon fluctuations in SE AsiaMonsoon fluctuations in SE Asia Produce heavy rainfall, saturate groundProduce heavy rainfall, saturate ground
Builds up bogsBuilds up bogs•Organic matter deposition and Organic matter deposition and anaerobic respiration likelyanaerobic respiration likely–Bogs expand during strong Bogs expand during strong summer monsoonsummer monsoon
–Shrink during weak summer Shrink during weak summer monsoonmonsoon
Alternative Explanation High-latitude soils and continental margins High-latitude soils and continental margins
source of atmospheric methanesource of atmospheric methane CHCH44 stored in frozen soils (permafrost) stored in frozen soils (permafrost) Continental margin sediments (hydrates)Continental margin sediments (hydrates)
Released during exceptionally warm Released during exceptionally warm summerssummers Precessional changes in summer Precessional changes in summer
insolation affects high latitudesinsolation affects high latitudes Cycles of summer warming should also Cycles of summer warming should also
occur on 41,000 year cyclesoccur on 41,000 year cycles Lack of 41,000 cycle in record argues Lack of 41,000 cycle in record argues
against high latitude sourceagainst high latitude source
Orbital-Scale Changes in CO2
COCO22 record from Vostok record from Vostok Interglacial maxima 280-Interglacial maxima 280-
300 ppm300 ppm Glacial minima 180-190 Glacial minima 180-190
ppmppm 100,000 year cycle dominant100,000 year cycle dominant Match ice volume recordMatch ice volume record
Timing Timing AsymmetryAsymmetry
Abrupt increases in COAbrupt increases in CO22 match rapid ice meltingmatch rapid ice melting
Slow decreases in COSlow decreases in CO22 match slow build-up of match slow build-up of iceice
Orbital-Scale Changes in CO2 Vostok 150,000 recordVostok 150,000 record
23,000 and 41,000 23,000 and 41,000 cyclescycles
Match similar cycles Match similar cycles in ice volumein ice volume
Agreement suggests Agreement suggests cause and effect cause and effect relationshiprelationship Relationship Relationship
unknownunknowne.g., does COe.g., does CO22 lead lead
ice volume?ice volume? Correlations not Correlations not
sufficient to provide sufficient to provide definite evaluationdefinite evaluation
Problems with Records Ice cores poorly datedIce cores poorly dated
COCO22 older than ice by variable amount older than ice by variable amount Greenland ice core well-dated (dust layers)Greenland ice core well-dated (dust layers)
Dust is CaCODust is CaCO33-rich-richDissolution of CaCODissolution of CaCO33 releases CO releases CO22
Precise timing between changes in COPrecise timing between changes in CO22 and and ice volume uncertainice volume uncertain New data provide better correlationNew data provide better correlation
Data do show that signals correlateData do show that signals correlate Some causal link must existSome causal link must exist
Big question – how did COBig question – how did CO22 vary by 30%? vary by 30%?
Covariation Between CO2 and D
Substantial mismatch in Vostok records (Substantial mismatch in Vostok records (rr22 = = 0.64 over the last 150 kya)0.64 over the last 150 kya)
Values shown Values shown normalizednormalizedto their mean valuesto their mean valuesduring the mid-Holoceneduring the mid-Holocene(5–7 kya BP) and the(5–7 kya BP) and thelast glacial (18–last glacial (18–60 kya BP)60 kya BP)
Clearly visible are theClearly visible are thedisproportionately lowdisproportionately lowdeuterium values duringdeuterium values duringthe mid-glacial (60–80the mid-glacial (60–80Kya BP), the glacialKya BP), the glacialinception (95–125 Kyainception (95–125 KyaBP), and the BP), and the penultimatepenultimateglacial maximum (140–glacial maximum (140–150 Kya BP)150 Kya BP)
If the If the D change reflects a D change reflects a proportional T drop, then proportional T drop, then more than ½ of the more than ½ of the interglacial-to-glacial change interglacial-to-glacial change occurred before significant occurred before significant removal of atmospheric COremoval of atmospheric CO22
Temperature from Ice Cores Snow falling on ice sheets under colder Snow falling on ice sheets under colder
temperatures is more negativetemperatures is more negative A plot of the A plot of the 1818O of snow versus temperature O of snow versus temperature
shows an excellent correlationshows an excellent correlation Thus Thus 1818O serves as a paleothermometerO serves as a paleothermometer
18O in Ice Cores Several factors in addition to temperature of Several factors in addition to temperature of
precipitationprecipitation Affect the Affect the 1818O of snow and ice on glaciersO of snow and ice on glaciers
Meteoric Water Line D and D and 1818O in precipitation correlatedO in precipitation correlated
Determined by evaporation/precipitation and rainoutDetermined by evaporation/precipitation and rainout Mixture of equilibrium and non-equilibrium processesMixture of equilibrium and non-equilibrium processes Deuterium excess Deuterium excess ((dd = = D – 8D – 81818O)O) quantifies intercept quantifies intercept
and disequilibriaand disequilibria
Deuterium Excess in Marine Rain
Deuterium-excess value in marine environmentsDeuterium-excess value in marine environments Established at the site of the air-sea interactionEstablished at the site of the air-sea interaction
The offset from equilibrium conditionsThe offset from equilibrium conditions•Determined by the humidity deficit above Determined by the humidity deficit above
the sea surfacethe sea surfaceThis deuterium-excess value is conserved This deuterium-excess value is conserved
during the rainout over the continentsduring the rainout over the continents If humidity deficit is known or can be modeledIf humidity deficit is known or can be modeled
Can be used to correct Can be used to correct D/D/1818O of precipitationO of precipitationDetermine more precisely ambient Determine more precisely ambient
temperature during precipitationtemperature during precipitation
D on Antarctica Determine by the temperature, humidity Determine by the temperature, humidity
and and D of the vapor source regionD of the vapor source region Cuffy and Vimeux (2001, Cuffy and Vimeux (2001, NatureNature, ,
415:523-527) showed using deuterium 415:523-527) showed using deuterium excessexcessMismatch is an artifact caused by Mismatch is an artifact caused by variations in climate of the vapor variations in climate of the vapor source regionsource region
Used a climate model and measured Used a climate model and measured deuterium excessdeuterium excess•Calculate Southern Hemisphere Calculate Southern Hemisphere temperature variationstemperature variations
Vostok Temperature and CO2 Deuterium excess corrected Southern Deuterium excess corrected Southern
Hemisphere temperature correlate remarkably Hemisphere temperature correlate remarkably well with COwell with CO22 variations variations
Covariation of COCovariation of CO22 and andtemperature havetemperature haverr22 = 0.89 for last 150 = 0.89 for last 150kya and kya and rr22 = 0.84 for = 0.84 forlast 350-400 kyalast 350-400 kya
Implications of Results COCO22 is an important climate forcing on the Modern is an important climate forcing on the Modern
EarthEarth Long-term synchrony of glacial-interglacial cyclingLong-term synchrony of glacial-interglacial cycling
Between Northern and Southern HemispheresBetween Northern and Southern HemispheresDue to greenhouse gas variations and Due to greenhouse gas variations and
feedbacks associated with variationsfeedbacks associated with variations Southern Hemisphere Southern Hemisphere T explained byT explained by
COCO22 variations variationsWithout considering changes in N. Hemisphere Without considering changes in N. Hemisphere
insolationinsolation Delay between CODelay between CO22 decrease and decrease and TT
During last glacial inception only ~5,000 yearsDuring last glacial inception only ~5,000 years
Unresolved Issues Cuffy and Vimeux (2001) show thatCuffy and Vimeux (2001) show that
90% of 90% of T can be explained by T can be explained by variations in COvariations in CO22 and CH and CH44
Reasonably firm grasp on causes of CHReasonably firm grasp on causes of CH44 variations (Monsoon forcing)variations (Monsoon forcing) What produced COWhat produced CO22 variations? variations?
Variations are large – 30%Variations are large – 30%Show rapid changes – drop of 90 ppm Show rapid changes – drop of 90 ppm from interglacial to glacialfrom interglacial to glacial
Physical Oceanographic Changes in CO2
During glaciations physical properties changeDuring glaciations physical properties change Temperature and salinityTemperature and salinity Affect solubility of COAffect solubility of CO22(aq) and thus pCO(aq) and thus pCO22
90% of the CO90% of the CO22
decrease unexplaineddecrease unexplainedby physical processesby physical processes
Exchange of Carbon Carbon in rock reservoir exchanges slowlyCarbon in rock reservoir exchanges slowly
Cannot account for 90 ppm change in 10Cannot account for 90 ppm change in 1033 y y Rapid exchange of carbon must involve near-Rapid exchange of carbon must involve near-
surface reservoirssurface reservoirs
Changes in Soil Carbon Expansion of ice sheets Expansion of ice sheets
Covered or displaced forestsCovered or displaced forestsConiferous and deciduous treesConiferous and deciduous trees
•Displaced forests replaced by steppes Displaced forests replaced by steppes and grasslandsand grasslands– Have lower carbon biomassHave lower carbon biomass
Pollen records in lakesPollen records in lakes Indicate glacial times were dryer and less Indicate glacial times were dryer and less
vegetated than interglacialvegetated than interglacialEstimates of total vegetation reduced by Estimates of total vegetation reduced by
25% (15-30%) during glacial maxima25% (15-30%) during glacial maxima•COCO22 removed from atmosphere did not removed from atmosphere did not
go into vegetation on land!go into vegetation on land!
Where is the Missing Carbon? Carbon from reduced COCarbon from reduced CO22 during glacial times during glacial times
Not explained by physical properties of Not explained by physical properties of surface oceansurface ocean
Did not go into biomass on landDid not go into biomass on land Must have gone into oceansMust have gone into oceans
Surface ocean not likelySurface ocean not likely•Exchanges carbon with atmosphere too Exchanges carbon with atmosphere too
rapidlyrapidly•Most areas of ocean within 30 ppm of Most areas of ocean within 30 ppm of
atmosphereatmosphere– Glacial surface ocean must also have Glacial surface ocean must also have
been lower, like atmospherebeen lower, like atmosphereDeep ocean only likely remaining reservoirDeep ocean only likely remaining reservoir