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

Interglacial-Glacial Change in Carbon

At LGM, reduction of carbon occurred in atmosphere, At LGM, reduction of carbon occurred in atmosphere, vegetation and soils on land and in surface oceanvegetation and soils on land and in surface ocean

This carbon (1010 gigatons) must have been moved to This carbon (1010 gigatons) must have been moved to deep oceandeep ocean

Ice core data indicateIce core data indicateatmospheric COatmospheric CO22 30% lower 30% lower

Ocean mixed layer inOcean mixed layer inequilibrium with atmosphere equilibrium with atmosphere so it too was lower by 30%so it too was lower by 30%

Terrestrial vegetation 25% lowerTerrestrial vegetation 25% lower

Mass balance indicatesMass balance indicates2.7% increase in deep ocean2.7% increase in deep ocean

Tracking Carbon 1313C values can be used to determine how carbon C values can be used to determine how carbon

moved from surface reservoirs to deep oceanmoved from surface reservoirs to deep ocean Major carbon reservoirs have different amounts of Major carbon reservoirs have different amounts of

organic and inorganic carbonorganic and inorganic carbon Each with characteristic Each with characteristic 1313C valuesC values

13C Changes During Photosynthesis Large KIE during carbon fixation by plantsLarge KIE during carbon fixation by plants

Magnitude depends on C-fixation pathwayMagnitude depends on C-fixation pathway

13C Tracks Carbon Transfer Isotope mass balance Isotope mass balance

quantifies transfer of quantifies transfer of terrestrial Cterrestrial Corgorg to deep to deep oceanocean CCinorginorg**1313CCinorginorg + C + Corgorg**1313CCorgorg

= C= Ctottot**1313CC (38,000*0(38,000*0‰‰) + (530*-) + (530*-

2525‰‰) ) = (38530*x)= (38530*x)Solving for x = -0.34Solving for x = -0.34‰‰

Just this transfer predicts Just this transfer predicts a shift in deep ocean DIC a shift in deep ocean DIC of –0.34of –0.34‰‰ Isotopic change Isotopic change

recorded in benthic recorded in benthic foraminiferaforaminifera

Change in Benthic 13C Oscillations in benthic Oscillations in benthic

1313C correspond to C correspond to benthic benthic 1818OO 100,000 and 41,000 100,000 and 41,000

year cyclesyear cycles Confirm transfer of Confirm transfer of

organic carbon to organic carbon to deep ocean during deep ocean during ice sheet expansionice sheet expansion

1313C shifts greater than C shifts greater than ~0.4~0.4‰‰ Suggesting Suggesting

additional factors additional factors have affected have affected oceanic oceanic 1313C valuesC values

Increase the Ocean Carbon Pump

If biological productivity and CIf biological productivity and Corgorg export were export were higher in surface waters during glacial intervalshigher in surface waters during glacial intervals Atmospheric COAtmospheric CO22 could be fixed in shallow could be fixed in shallow

ocean by phytoplanktonocean by phytoplanktonSinking dead organic matter transfers that Sinking dead organic matter transfers that

carbon to the deep oceancarbon to the deep ocean Biological productivity and export can only Biological productivity and export can only

increase if essential nutrients increase in surface increase if essential nutrients increase in surface oceanocean Increases in wind-driven upwelling of deep, Increases in wind-driven upwelling of deep,

nutrient-rich waternutrient-rich water Increases in the nutrient concentration of deep Increases in the nutrient concentration of deep

water that is already upwellingwater that is already upwelling

The Iron Hypothesis In the 1980s, the late John Martin suggested thatIn the 1980s, the late John Martin suggested that

Carbon uptake during plankton growth in many Carbon uptake during plankton growth in many regions of the world's surface oceanregions of the world's surface ocean

Was limited not by light or the nutrients N and P Was limited not by light or the nutrients N and P • But by the lack of the trace metal ironBut by the lack of the trace metal iron

Iron is typically added to the open ocean as a Iron is typically added to the open ocean as a component of dust particlescomponent of dust particles

The Iron Hypothesis Correlations between dust and atmospheric carbon dioxide levels in Correlations between dust and atmospheric carbon dioxide levels in

ancient ice core recordsancient ice core records Suggest that the ocean would respond to natural changes in iron inputsSuggest that the ocean would respond to natural changes in iron inputs Higher glacial winds would increase the amount of windblown dust Higher glacial winds would increase the amount of windblown dust

containing Fe to oceanscontaining Fe to oceansStimulate phytoplankton growthStimulate phytoplankton growth

•Increasing carbon uptake and decrease atmospheric COIncreasing carbon uptake and decrease atmospheric CO22

•Alter the greenhouse gas balance and climate of the earthAlter the greenhouse gas balance and climate of the earth

Evidence for Iron hypothesis Some areas of the ocean contain high amounts of essential Some areas of the ocean contain high amounts of essential

nutrients (N, P)nutrients (N, P) Yet low amounts of chlorophyll (HNLC)Yet low amounts of chlorophyll (HNLC)

Phytoplankton require Fe in small amounts for growthPhytoplankton require Fe in small amounts for growth ““Bottle experiments” demonstrate conclusively that addition Bottle experiments” demonstrate conclusively that addition

of Fe stimulates phytoplankton growthof Fe stimulates phytoplankton growth COCO22 uptake uptake

If Iron HypothesisIf Iron Hypothesisincreased biologicalincreased biologicalpump, iron additionpump, iron additionmust increasemust increaseproduction and production and exportexport

Open-Ocean Iron Enrichment "Give me half a tanker full of iron and I'll give you an "Give me half a tanker full of iron and I'll give you an

ice age“ice age“ (John Martin) (John Martin) Results of “fertilizing” large patches of the ocean Results of “fertilizing” large patches of the ocean

with ironwith iron Showed strong biological response and chemical Showed strong biological response and chemical

draw-down of COdraw-down of CO22 in the water column in the water column But what was the fate of this carbon?But what was the fate of this carbon?

Plant uptake of carbon in the ocean is generally Plant uptake of carbon in the ocean is generally followed by zooplankton bloomfollowed by zooplankton bloom

•Grazers respond to the increased food supplyGrazers respond to the increased food supply– Producing a blizzard of fecal pellets that Producing a blizzard of fecal pellets that

descend through the water columndescend through the water column– Exporting the carbon to the deep seaExporting the carbon to the deep sea

Quantifying Carbon Export Thorium is a naturally Thorium is a naturally

occurring element that by its occurring element that by its chemical nature is "sticky" chemical nature is "sticky" Due to its natural Due to its natural

radioactive properties, radioactive properties, relatively easy to measure. relatively easy to measure.

Analysis of a series of Analysis of a series of samples collected during the samples collected during the 1995 FeEx II1995 FeEx II Indicated that as iron was Indicated that as iron was

addedadded Plant biomass increasedPlant biomass increased Total thorium levels Total thorium levels

decreased indicating decreased indicating carbon exportcarbon export

Quantifying Carbon Export After some delayAfter some delay

Particulate organic Particulate organic carbon export increased carbon export increased in the equatorial Pacificin the equatorial Pacific

Relationship between Relationship between uptake and export not 1:1uptake and export not 1:1 The iron-stimulated The iron-stimulated

biological community biological community showed showed

Very high ratios of Very high ratios of export relative to export relative to carbon uptakecarbon uptake

Thus the efficiency of Thus the efficiency of the biological pump had the biological pump had increased dramaticallyincreased dramatically

Quantifying Carbon Export Results of similar iron Results of similar iron

fertilization of Southern fertilization of Southern OceanOcean Slower biological Slower biological

responseresponse Total thorium levels Total thorium levels

never respondednever responded The biological pump The biological pump

was not activatedwas not activated Speculate that differenceSpeculate that difference

Slowness of the Slowness of the biological community's biological community's response to stimulation response to stimulation in colder watersin colder waters

Biological pump may Biological pump may have turned on laterhave turned on later

Persistence of Patch Sea surface color satellite image taken 32 days Sea surface color satellite image taken 32 days

after the addition of Feafter the addition of Fe Colored ring indicates area of high chlorophyllColored ring indicates area of high chlorophyll

Believed to be a result of the increased FeBelieved to be a result of the increased Fe

Iron Fertilization is Hot Topic Iron fertilization of the ocean captured attention of Iron fertilization of the ocean captured attention of

entrepreneurs and venture capitalistsentrepreneurs and venture capitalists See potential for enhancing fisheries and gaining “C See potential for enhancing fisheries and gaining “C

credits” through large-scale ocean manipulationscredits” through large-scale ocean manipulations

Marshall Islands Territorial waters of the Marshall IslandsTerritorial waters of the Marshall Islands

Leased to conduct an iron fertilization experimentLeased to conduct an iron fertilization experiment The new businesses involved suggest thatThe new businesses involved suggest that

Iron fertilization process will reduce atmospheric Iron fertilization process will reduce atmospheric COCO22 levels levels

Allowing Marshall Islands to profit by trading Allowing Marshall Islands to profit by trading carbon credits with more industrialized nationscarbon credits with more industrialized nations

Increased fisheries as a consequence of Increased fisheries as a consequence of enhanced phytoplankton productionenhanced phytoplankton production

Iron additions could alter the ocean in unforeseen Iron additions could alter the ocean in unforeseen waysways Creating a polluted ocean with new opportunistic Creating a polluted ocean with new opportunistic

species that do not support enhanced fisheriesspecies that do not support enhanced fisheries

13CDIC Tracks Productivity Photosynthesis removes Photosynthesis removes 1212C from surface ocean C from surface ocean

and exports it to deep oceanand exports it to deep ocean Close correlations between Close correlations between 1313CCDICDIC and nutrients and nutrients

Measuring Changes in the Carbon Pump

Greater productivity during glaciations pumps Greater productivity during glaciations pumps more Cmore Corgorg to deep sea, reduces atmospheric CO to deep sea, reduces atmospheric CO22

Past changes in strength of carbon pumpPast changes in strength of carbon pump Recorded in planktic and benthic foraminiferRecorded in planktic and benthic foraminifer

Past Changes in the Ocean Carbon Pump

1313C planktic-benthic C planktic-benthic are tantalizingly large are tantalizingly large when COwhen CO22 is low and is low and small when COsmall when CO22 is high is high Correlation not perfectCorrelation not perfect

May explain as May explain as much as 25 ppm much as 25 ppm COCO22 lowering lowering

Best documented in Best documented in equatorial regionsequatorial regions Worse in Southern Worse in Southern

OceanOcean Even HNLC regionsEven HNLC regions Detailed records Detailed records

lackinglacking

Changes in Deep Water Circulation

1313C can be used to trace carbon transferC can be used to trace carbon transfer Photosynthetic ratePhotosynthetic rate

Sets Sets 1313C and nutrient levels in C and nutrient levels in surface waterssurface waters•Water gets down-welled and carry Water gets down-welled and carry the signalsthe signals

These factors can produce regional These factors can produce regional differences in the differences in the 1313CCDICDIC

•Deep waters in different ocean Deep waters in different ocean basinsbasins

•Monitors changes in deep water Monitors changes in deep water circulation with timecirculation with time

Modern Deep Ocean Circulation High High 1313C values in N. C values in N.

Atlantic results fromAtlantic results from High production in High production in

surface waters in surface waters in subtropical latitudessubtropical latitudes

Transported north and Transported north and sinkssinks

In contrast, intermediate In contrast, intermediate waters originate in waters originate in AntarcticaAntarctica Seasonal production Seasonal production

produces lower produces lower 1313C C enrichmentenrichment

These contrasts allows These contrasts allows water masses to be trackedwater masses to be tracked

Atlantic Deep Water 13C Deep water formed in N. Atlantic have high Deep water formed in N. Atlantic have high 1313C values C values

and low nutrient concentrationsand low nutrient concentrations Intermediate waters formed in the Southern Ocean Intermediate waters formed in the Southern Ocean

have low have low 1313C values and high nutrient concentrationsC values and high nutrient concentrations

13C Aging As the CAs the Corgorg in deep water is gradually oxidized in deep water is gradually oxidized

1212C-rich COC-rich CO22 released lowering released lowering 1313CCDICDIC

Particularly evident in deep Pacific watersParticularly evident in deep Pacific waters

Past Changes in 13CDIC 1313C of benthic C of benthic

foraminifera indicate foraminifera indicate changes in Atlantic deep changes in Atlantic deep water flow at the LGMwater flow at the LGM Northern water did not Northern water did not

sink as deeply, not as sink as deeply, not as densedense

Relative increase in Relative increase in water flowing from water flowing from AntarcticaAntarctica

Knowing the Knowing the 1313C of the C of the source region (planktic source region (planktic foraminifera)foraminifera) Percent contribution Percent contribution

from each region can from each region can be determinedbe determined

Changing Sources of Atlantic Deep Water

Long records of Long records of 1313C C indicate cyclic changes in indicate cyclic changes in deep water sourcesdeep water sources North sources dominate North sources dominate

during interglacialduring interglacial Southern sources Southern sources

dominate during glacialdominate during glacial 100,000 year cycle100,000 year cycle

During glacialDuring glacial Low Low 1313C water from C water from

AntarcticaAntarctica Increase flux of Increase flux of 1212C C

carbon from continentscarbon from continents Additive effects Additive effects

explains large shifts explains large shifts noted earliernoted earlier

Summary 1313C results indicate an important linkC results indicate an important link

Size of N. Hemisphere ice sheetsSize of N. Hemisphere ice sheetsFormation of deep water in N. AtlanticFormation of deep water in N. Atlantic

Less deep water formed in the N. AtlanticLess deep water formed in the N. Atlantic Every time ice sheets grew at a Every time ice sheets grew at a

100,000 year cycle100,000 year cycleMust have affected atmospheric COMust have affected atmospheric CO22 concentrationsconcentrations•But how?But how?

Changes in Ocean Chemistry COCO22 levels in surface waters sensitive to carbonate levels in surface waters sensitive to carbonate

ion concentrationion concentration COCO33

2-2- produced when corrosive bottom waters produced when corrosive bottom waters dissolve CaCOdissolve CaCO33

When COWhen CO332-2- returned to surface waters returned to surface waters

•Combine with COCombine with CO22 to form HCO to form HCO33--

•Thus reducing COThus reducing CO22 content of surface ocean content of surface ocean The corrosiveness of deep water determined by The corrosiveness of deep water determined by

the weight of foraminifer shellsthe weight of foraminifer shells Depth of the CCDDepth of the CCD

Southern Ocean particularly vulnerable to changes Southern Ocean particularly vulnerable to changes in carbon ion concentrationin carbon ion concentration

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