Modeling Ocean Biogeochemistry

Modeling Ocean Modeling Ocean BiogeochemistryBiogeochemistryModeling Ocean Modeling Ocean BiogeochemistryBiogeochemistry

Galen A. McKinleyGalen A. McKinleyUniversity of Wisconsin - MadisonUniversity of Wisconsin - Madison

ASP Summer School - Art of Climate ASP Summer School - Art of Climate ModelingModeling

June 7, 2006June 7, 2006

Galen A. McKinleyGalen A. McKinleyUniversity of Wisconsin - MadisonUniversity of Wisconsin - Madison

ASP Summer School - Art of Climate ASP Summer School - Art of Climate ModelingModeling

June 7, 2006June 7, 2006

What is Ocean What is Ocean Biogeochemistry?Biogeochemistry?

Biology - micro-scaleBiology - micro-scale Chemistry - organic and inorganicChemistry - organic and inorganic Geology - interactions with solid EarthGeology - interactions with solid Earth Physical interactions Physical interactions

Air-sea exchange; Particle settling rates; Air-sea exchange; Particle settling rates; Advection, diffusion, mixingAdvection, diffusion, mixing

Individual processes and systematics Individual processes and systematics are of key interestare of key interest

Biology - micro-scaleBiology - micro-scale Chemistry - organic and inorganicChemistry - organic and inorganic Geology - interactions with solid EarthGeology - interactions with solid Earth Physical interactions Physical interactions

Air-sea exchange; Particle settling rates; Air-sea exchange; Particle settling rates; Advection, diffusion, mixingAdvection, diffusion, mixing

Individual processes and systematics Individual processes and systematics are of key interestare of key interest

Why include Why include biogeochemistry in ocean biogeochemistry in ocean

models?models?

models?models? Carbon CycleCarbon Cycle

Ocean carbon sink - past, present, Ocean carbon sink - past, present, futurefuture

Glacial / interglacial change Glacial / interglacial change

Trace gas emissions - Atm. chemistryTrace gas emissions - Atm. chemistry e.g. Dimethyl Sulfide (DMS): CCN, e.g. Dimethyl Sulfide (DMS): CCN,

emitted by phytoplankton, theorized emitted by phytoplankton, theorized climate feedbacksclimate feedbacks

Carbon CycleCarbon Cycle Ocean carbon sink - past, present, Ocean carbon sink - past, present,

futurefuture Glacial / interglacial change Glacial / interglacial change

The ocean has absorbed 48% The ocean has absorbed 48% of anthropogenic COof anthropogenic CO22 emitted in emitted in

last 200 yrslast 200 yrs (Sabine et al., 2004)(Sabine et al., 2004)

models?models?

OutlineOutlineOutlineOutline

Carbon cycleCarbon cycle ObservationsObservations Key chemistryKey chemistry Large-scale processesLarge-scale processes

Modeling strategies and challengesModeling strategies and challenges

Selected resultsSelected results

Carbon cycleCarbon cycle ObservationsObservations Key chemistryKey chemistry Large-scale processesLarge-scale processes

Modeling strategies and challengesModeling strategies and challenges

Selected resultsSelected results

1980’s estimates from Sarmiento & Gruber (2002)

The Carbon CycleThe Carbon CycleThe Carbon CycleThe Carbon Cycle

Atlantic (A16) Atlantic (A16) Dissolved Inorganic Carbon Dissolved Inorganic Carbon

(DIC) (DIC) (umol/kg)(umol/kg)

Atlantic (A16) Atlantic (A16) Dissolved Inorganic Carbon Dissolved Inorganic Carbon

(DIC) (DIC) (umol/kg)(umol/kg)

Global sea-air COGlobal sea-air CO22 flux fluxGlobal sea-air COGlobal sea-air CO22 flux flux

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Takahashi et al. 2002Takahashi et al. 2002

Air-sea COAir-sea CO22 exchange exchangeAir-sea COAir-sea CO22 exchange exchange Air-sea exchange determined by air-Air-sea exchange determined by air-

water gradient of the partial pressure water gradient of the partial pressure of COof CO2 2 (pCO(pCO22): ):

pCOpCO22 = pCO = pCO22airair - pCO - pCO22

waterwater

And surface ocean turbulenceAnd surface ocean turbulence Parameterized with function of wind Parameterized with function of wind

speedspeed

pCOpCO22waterwater is determined by [H is determined by [H22COCO33

**],T,S],T,S

Air-sea exchange determined by air-Air-sea exchange determined by air-water gradient of the partial pressure water gradient of the partial pressure of COof CO2 2 (pCO(pCO22): ):

pCOpCO22 = pCO = pCO22airair - pCO - pCO22

waterwater

And surface ocean turbulenceAnd surface ocean turbulence Parameterized with function of wind Parameterized with function of wind

speedspeed

pCOpCO22waterwater is determined by [H is determined by [H22COCO33

**],T,S],T,S

Carbon Chemistry in Carbon Chemistry in SeawaterSeawater

Carbon reacts with waterCarbon reacts with water DIC = Dissolved Inorganic Carbon DIC = Dissolved Inorganic Carbon

= [CO= [CO22(aq)] + [H(aq)] + [H22COCO33] + [HCO] + [HCO33--] + [CO] + [CO33

= [H= [H22COCO33**] + [HCO] + [HCO33

--] + [CO] + [CO33==]]

At ocean pH, [HAt ocean pH, [H22COCO33**] only ~0.5% of ] only ~0.5% of

DIC. Thus, the balance of HCODIC. Thus, the balance of HCO33-- and and

COCO33== is key to setting pCO is key to setting pCO22

waterwater

Carbon reacts with waterCarbon reacts with water DIC = Dissolved Inorganic Carbon DIC = Dissolved Inorganic Carbon

= [CO= [CO22(aq)] + [H(aq)] + [H22COCO33] + [HCO] + [HCO33--] + [CO] + [CO33

= [H= [H22COCO33**] + [HCO] + [HCO33

--] + [CO] + [CO33==]]

At ocean pH, [HAt ocean pH, [H22COCO33**] only ~0.5% of ] only ~0.5% of

DIC. Thus, the balance of HCODIC. Thus, the balance of HCO33-- and and

COCO33== is key to setting pCO is key to setting pCO22

waterwater

What determines [HCOWhat determines [HCO33--] + ] +

[CO[CO33==]?]?

What determines [HCOWhat determines [HCO33--] + ] +

[CO[CO33==]?]?

Both the electronic charge and the Both the electronic charge and the carbon content of a parcelcarbon content of a parcel

Ocean charge balance = AlkalinityOcean charge balance = Alkalinity

Both the electronic charge and the Both the electronic charge and the carbon content of a parcelcarbon content of a parcel

Ocean charge balance = AlkalinityOcean charge balance = Alkalinity

AlkalinityAlkalinityAlkalinityAlkalinity Major Cations Major Cations = [Na= [Na++] + [K] + [K++] + 2[Mg] + 2[Mg++++] + 2 [Ca] + 2 [Ca++++] = ] =

+ 0.606 eq/kg+ 0.606 eq/kg Major Anions Major Anions = [Cl= [Cl--] + 2[SO4] + 2[SO4==] + [Br] + [Br--] = -0.604 eq/kg] = -0.604 eq/kg Global mean, difference is +0.002 eq/kgGlobal mean, difference is +0.002 eq/kg Carbon is one of the few elements that Carbon is one of the few elements that

can exist as ions of different charge, thus can exist as ions of different charge, thus it adjusts to balance the chargeit adjusts to balance the charge

Major Cations Major Cations = [Na= [Na++] + [K] + [K++] + 2[Mg] + 2[Mg++++] + 2 [Ca] + 2 [Ca++++] = ] =

+ 0.606 eq/kg+ 0.606 eq/kg Major Anions Major Anions = [Cl= [Cl--] + 2[SO4] + 2[SO4==] + [Br] + [Br--] = -0.604 eq/kg] = -0.604 eq/kg Global mean, difference is +0.002 eq/kgGlobal mean, difference is +0.002 eq/kg Carbon is one of the few elements that Carbon is one of the few elements that

can exist as ions of different charge, thus can exist as ions of different charge, thus it adjusts to balance the chargeit adjusts to balance the charge

AlkalinityAlkalinityAlkalinityAlkalinity

ALK = [NaALK = [Na++] + [K] + [K++] + 2[Mg] + 2[Mg++++] + 2 ] + 2 [Ca[Ca++++] - [Cl] - [Cl--] - 2[SO4] - 2[SO4==] - [Br] - [Br--] ]

≈ ≈ [HCO[HCO33--] + 2[CO] + 2[CO33

i.e. a change in alkalinity will alter i.e. a change in alkalinity will alter the distribution of the carbonate the distribution of the carbonate ionsions

ALK = [NaALK = [Na++] + [K] + [K++] + 2[Mg] + 2[Mg++++] + 2 ] + 2 [Ca[Ca++++] - [Cl] - [Cl--] - 2[SO4] - 2[SO4==] - [Br] - [Br--] ]

≈ ≈ [HCO[HCO33--] + 2[CO] + 2[CO33

i.e. a change in alkalinity will alter i.e. a change in alkalinity will alter the distribution of the carbonate the distribution of the carbonate ionsions

Simplified balance Simplified balance equationsequations

ALK ≈ [HCOALK ≈ [HCO33--] + 2[CO] + 2[CO33

DIC ≈ [HCODIC ≈ [HCO33--] + [CO] + [CO33

i.e. a parcel must both conserve i.e. a parcel must both conserve both its charge and its carbon both its charge and its carbon contentcontent

ALK ≈ [HCOALK ≈ [HCO33--] + 2[CO] + 2[CO33

DIC ≈ [HCODIC ≈ [HCO33--] + [CO] + [CO33

i.e. a parcel must both conserve i.e. a parcel must both conserve both its charge and its carbon both its charge and its carbon contentcontent

Rearranging and solvingRearranging and solvingRearranging and solvingRearranging and solving

[CO[CO33==] ≈ ALK - DIC ] ≈ ALK - DIC

[HCO[HCO33--] ≈ 2DIC - ALK] ≈ 2DIC - ALK

e.g. for constant DIC:e.g. for constant DIC:

if ALKif ALK, [CO, [CO33==]] and and

[HCO[HCO33--]]

[CO[CO33==] ≈ ALK - DIC ] ≈ ALK - DIC

[HCO[HCO33--] ≈ 2DIC - ALK] ≈ 2DIC - ALK

e.g. for constant DIC:e.g. for constant DIC:

if ALKif ALK, [CO, [CO33==]] and and

[HCO[HCO33--]]

What happens to [HWhat happens to [H22COCO33**] and ] and

pCOpCO22 as [CO as [CO33==]] and and

[HCO[HCO33--]]??

What happens to [HWhat happens to [H22COCO33**] and ] and

pCOpCO22 as [CO as [CO33==]] and and

[HCO[HCO33--]]?? Full equationFull equation

DIC = [HDIC = [H22COCO33**] + [HCO] + [HCO33

--] + [CO] + [CO33==]]

As balance shifts away from [COAs balance shifts away from [CO33==], [H], [H22COCO33

**] and ] and pCOpCO22

waterwater are increased are increased

Full equationFull equation

DIC = [HDIC = [H22COCO33**] + [HCO] + [HCO33

--] + [CO] + [CO33==]]

As balance shifts away from [COAs balance shifts away from [CO33==], [H], [H22COCO33

**] and ] and pCOpCO22

waterwater are increased are increased

Carbon chemistry: Carbon chemistry: SummarySummary

pCOpCO22 key for air-sea exchange key for air-sea exchange

pCOpCO22waterwater a function of [H a function of [H22COCO33

**], T, S], T, S

[H[H22COCO33**] is a small part of total DIC, ] is a small part of total DIC,

determined by balance with other determined by balance with other ionsions

[HCO[HCO33--], [CO], [CO33

==] set by alkalinity, or ] set by alkalinity, or charge balancecharge balance

pCOpCO22 key for air-sea exchange key for air-sea exchange

pCOpCO22waterwater a function of [H a function of [H22COCO33

**], T, S], T, S

[H[H22COCO33**] is a small part of total DIC, ] is a small part of total DIC,

determined by balance with other determined by balance with other ionsions

[HCO[HCO33--], [CO], [CO33

==] set by alkalinity, or ] set by alkalinity, or charge balancecharge balance

Solubility PumpSolubility PumpSolubility PumpSolubility Pump

Temperature influenceTemperature influenceTemperature influenceTemperature influenceMean sea-air COMean sea-air CO22 flux flux

pCO2 pCO2

UpwellingUpwellingUpwellingUpwelling

Atlantic DIC Atlantic DIC

Biological ProcessesBiological ProcessesBiological ProcessesBiological Processes

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

SeaWiFS - NASA

Organic Carbon PumpOrganic Carbon PumpOrganic Carbon PumpOrganic Carbon Pump

Carbonate pumpCarbonate pumpCarbonate pumpCarbonate pump

Removes DIC to Removes DIC to depth, but also depth, but also reduces ALKreduces ALK

ALKALK, [CO, [CO33==]] and and

[HCO[HCO33--]]

pCOpCO22waterwater increased increased

Removes DIC to Removes DIC to depth, but also depth, but also reduces ALKreduces ALK

ALKALK, [CO, [CO33==]] and and

[HCO[HCO33--]]

pCOpCO22waterwater increased increased

Ecosystem ComplexityEcosystem ComplexityEcosystem ComplexityEcosystem Complexity There are ~20,000 of identified species of There are ~20,000 of identified species of

phytoplankton in 4 major groupsphytoplankton in 4 major groups PicoplanktonPicoplankton Diatoms (silicate shells)Diatoms (silicate shells) Coccolithophorids (carbonate shells)Coccolithophorids (carbonate shells) DinoflagellitesDinoflagellites

Zooplankton - also great varietyZooplankton - also great variety Much variability in key aspectsMuch variability in key aspects

Carbon to Nutrient, Carbon to Chlorophyll ratiosCarbon to Nutrient, Carbon to Chlorophyll ratios Sinking velocities Sinking velocities Growth rates, mortality rates, etc.Growth rates, mortality rates, etc.

There are ~20,000 of identified species of There are ~20,000 of identified species of phytoplankton in 4 major groupsphytoplankton in 4 major groups PicoplanktonPicoplankton Diatoms (silicate shells)Diatoms (silicate shells) Coccolithophorids (carbonate shells)Coccolithophorids (carbonate shells) DinoflagellitesDinoflagellites

Zooplankton - also great varietyZooplankton - also great variety Much variability in key aspectsMuch variability in key aspects

Carbon to Nutrient, Carbon to Chlorophyll ratiosCarbon to Nutrient, Carbon to Chlorophyll ratios Sinking velocities Sinking velocities Growth rates, mortality rates, etc.Growth rates, mortality rates, etc.

Best Modeling Strategy?Best Modeling Strategy?Best Modeling Strategy?Best Modeling Strategy?

Simple vs. Complex ?Simple vs. Complex ?

Simple EquationsSimple EquationsSimple EquationsSimple Equations

dt= −α

N + No

I + Io+ remin

vs. Complex vs. Complex EquationsEquations

Simple Simple EcosystemEcosystem

PROSPROS Reduced Reduced

computational computational costcost

More direct More direct understanding of understanding of resultsresults

PROSPROS Reduced Reduced

computational computational costcost

More direct More direct understanding of understanding of resultsresults

CONSCONS No species shiftsNo species shifts

Will it work for Will it work for past or future past or future climate? climate?

More difficult to More difficult to compare to compare to observationsobservations

CONSCONS No species shiftsNo species shifts

Will it work for Will it work for past or future past or future climate? climate?

More difficult to More difficult to compare to compare to observationsobservations

Modeling global COModeling global CO22 flux flux (mol/m(mol/m22/yr)/yr)

McKinley et al. 2004

MITgcm Data

Complex Complex EcosystemEcosystemComplex Complex

EcosystemEcosystem

PROSPROS More realisticMore realistic Allows species Allows species

shifts with climateshifts with climate More direct More direct

comparison to datacomparison to data Enhanced process Enhanced process

understandingunderstanding

PROSPROS More realisticMore realistic Allows species Allows species

shifts with climateshifts with climate More direct More direct

comparison to datacomparison to data Enhanced process Enhanced process

understandingunderstanding

CONSCONS Computational Computational

costs increase by costs increase by 10x’s10x’s

Many unconstrained Many unconstrained parametersparameters

More difficult to More difficult to interpretinterpret

CONSCONS Computational Computational

costs increase by costs increase by 10x’s10x’s

Many unconstrained Many unconstrained parametersparameters

More difficult to More difficult to interpretinterpret

Surface Surface ChlorophyllChlorophyll

Lima & Doney, 2004Lima & Doney, 2004

Biogeochemical model Biogeochemical model intercomparison: North intercomparison: North

Pacific Pacific

Biogeochemical model Biogeochemical model intercomparison: North intercomparison: North

Pacific Pacific

Seven independent Seven independent modelsmodels

ROMSROMS MITMIT UMDUMD NCOMNCOM ECCO-ECCO-CCSM*CCSM*

MPIMPI PISCES-TPISCES-T

ResolutioResolutionn

0.5 x 0.5 x

0.50.51.0 x1.0 x

0.3-1.00.3-1.01.0 x 1.0 x

0.3-0.70.3-0.72.0 x2.0 x

0.50.53.0 x3.0 x

0.6-1.60.6-1.6VariesVaries

0.3x0.3 0.3x0.3 in in tropicstropics

2.0 x 2.0 x

0.5-1.50.5-1.5

EcosysteEcosystem m complexitcomplexityy

HighHigh LowLow HighHigh HighHigh HighHigh HighHigh HighHigh

YearsYears 1990-1990-20042004

1980-1980-19981998

1979-1979-20032003

1951-1951-19991999

1958-1958-20042004

1948-1948-20032003

1948-1948-20042004

AuthorsAuthors Chai, Shi,Chai, Shi,

JiiangJiiangMcKinley, McKinley, Follows, Follows, MarshallMarshall

Christian, Christian, MurtuguddMurtuguddee

Chai, Chai, Shi,Shi,

JiiangJiiang

Doney, Doney, Moore, Moore, LindsayLindsay

WetzelWetzel LeQuereLeQuere* Preindustrial* Preindustrial

Subtropical cycle: Station Subtropical cycle: Station ALOHAALOHA

Data, Takahashi et al. 2005, submittedData, Takahashi et al. 2005, submitted

Station ALOHA pCOStation ALOHA pCO2 2

variabilityvariabilityStation ALOHA pCOStation ALOHA pCO2 2

variabilityvariability

High-latitude seasonal High-latitude seasonal cycle: Kuril region cycle: Kuril region

Modeling ChallengesModeling ChallengesModeling ChallengesModeling Challenges Lack of data constraintsLack of data constraints

Ecosystem parametersEcosystem parameters Variability at large-scaleVariability at large-scale High latitudesHigh latitudes

Alkalinity / Freshwater fluxesAlkalinity / Freshwater fluxes Remineralization controls Remineralization controls Gas exchange Gas exchange

Lack of data constraintsLack of data constraints Ecosystem parametersEcosystem parameters Variability at large-scaleVariability at large-scale High latitudesHigh latitudes

Alkalinity / Freshwater fluxesAlkalinity / Freshwater fluxes Remineralization controls Remineralization controls Gas exchange Gas exchange

SummarySummarySummarySummary

Biogeochemistry of the carbon cycle Biogeochemistry of the carbon cycle is infinitely complexis infinitely complex

How much complexity must be How much complexity must be modeled?modeled? Ongoing debateOngoing debate Depends on timescales and questions Depends on timescales and questions

of interestof interest

Biogeochemistry of the carbon cycle Biogeochemistry of the carbon cycle is infinitely complexis infinitely complex

How much complexity must be How much complexity must be modeled?modeled? Ongoing debateOngoing debate Depends on timescales and questions Depends on timescales and questions

of interestof interest

Suggested readingSuggested readingSuggested readingSuggested reading Text: Sarmiento and Gruber (2006) Text: Sarmiento and Gruber (2006)

Ocean Biogeochemical DynamicsOcean Biogeochemical Dynamics Complex ecosystem modelsComplex ecosystem models

Fasham et al. 1993Fasham et al. 1993 Moore et al. 2002a,b; Lima and Doney 2004Moore et al. 2002a,b; Lima and Doney 2004 Dutkiewicz et al. 2005Dutkiewicz et al. 2005

SimpleSimple ecosystem modelsecosystem models Najjar et al. 1992Najjar et al. 1992 McKinley et al. 2004McKinley et al. 2004 Dunne et al. 2005Dunne et al. 2005

Text: Sarmiento and Gruber (2006) Text: Sarmiento and Gruber (2006) Ocean Biogeochemical DynamicsOcean Biogeochemical Dynamics

Complex ecosystem modelsComplex ecosystem models Fasham et al. 1993Fasham et al. 1993 Moore et al. 2002a,b; Lima and Doney 2004Moore et al. 2002a,b; Lima and Doney 2004 Dutkiewicz et al. 2005Dutkiewicz et al. 2005

SimpleSimple ecosystem modelsecosystem models Najjar et al. 1992Najjar et al. 1992 McKinley et al. 2004McKinley et al. 2004 Dunne et al. 2005Dunne et al. 2005

Modeling Ocean Biogeochemistry

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