Anthropogenic carbon in a varying ocean

Anthropogenic carbon in

a varying ocean

Fortunat Joos, Thomas Fröhlicher

Climate and Environmental Physics,

Physics Institute, University of Bern

www.climate.unibe.ch/~joos

CARBOOCEAN Meeting

Bremen, December, 2006

Thanks to C. Lo Monaco, A. Velo and co-workers

to the MPI and IPSL modelling groups

Data from the past show that anthropogenic climate change is proceeding at high speed

(IPCC, 2007, Fig. TS-2a)Time (years before present)Time (years before present)

COCO22 versus Antarctic Temperature versus Antarctic Temperature

002000020000 1000010000

The atmospheric concentration of carbon dioxide in 2005 exceeds by far the natural range over the last 650,000 years (180 to 300 ppm) as determined from ice cores (IPCC, SPM, 2007).

Nat

ura

l Ran

geN

atu

ral R

ange

What about rates of change?

(Joos and Spahni, PNAS, submitted)

The age distribution of air enclosed in ice

Greenland CH4

Antarctic (Dome C), today

Antarctic (Dome C), Last Glacial Maximum

(Joos and Spahni, PNAS, submitted)

The rate of increase

in the combined

radiative forcing

from CO2, CH4 and

N2O during the

industrial era is very

likely to have been

unprecedented in

more than 10,000

years (IPCC, SPM,

2007)

Rates of Change over the past 22,000 years

Models and system understanding: current carbon emissions will affect the climate for many millennia

Long-term CO2 and sea level

committmentin EMICs1820 -2100

2000 2500 3000

2000 2500 3000

Year

60%

60%

0

60%Atmosphere

Ocean

Land

2000 GtC

Thermal Expansion (m)

1

IPCC AR4 EMIC Intercomparison

Plattner et al., J.Clim., 2007;

Cumulative Emissions

0%

IPCC Scenario Meeting, Sep 2007

•A new set of emission mitigation andbaseline scenarios

• Four scenarios to be selected for AOGCM runs

→ use in CARBOOCEAN

Projected CO2 in 2100

Baseline Mitigation650 to 950 ppm 380 to 620 ppm

(Van Vuren et al., submitted)

-1

0

1

2

3

4

5

6

7

8 b)

Tem

pera

ture

incr

ea

se (

o C)

MESSAGEMITMiniCamIMAGEIPACAIM

0

4

8

12

16 a)

Ra

dia

tive

forc

ing

(W

/m2

)

Baseline scenarios CS + CC Bern CS + CC MAGICC CS MAGICC

Mitigation scenario CS + CC Bern CS + CC MAGICC CS MAGICC

Bern mean MAGICC mean


1900 1950 2000 2050 2100-1

0

1

2

3

4

5

6

7

8 c)

Te

mp

era

ture

incr

ea

se (

o C)

time0 500 1000 1500 2000

-1

0

1

2

3

4

5

6

7

8 d)

Uncertainty range BernUncertainty range MAGICC

Tem

pera

ture

incr

ea

se (

o C)

Cumulative CO2 emissions 2000-2100 (GtC)

Bern MAGICC


Baseline MitigationRadiative Forcing (W m-2): 6 to 10 2.4 to 5.1CO2 (ppm): 650 to 950 380 to 620

Projected Radiative Forcing in 2100

-1

0

1

2

3

4

5

6

7

8 b)

Tem

pera

ture

incr

ease

(o C

)


0

4

8

12

16 a)

Rad

iativ

e fo

rcin

g (W

/m2)

Baseline scenarios CS + CC Bern CS + CC MAGICC CS MAGICC

Mitigation scenario CS + CC Bern CS + CC MAGICC CS MAGICC

Bern mean MAGICC mean


1900 1950 2000 2050 2100-1

0

1

2

3

4

5

6

7

8 c)

Te

mpe

ratu

re in

crea

se (

o C)

time0 500 1000 1500 2000

-1

0

1

2

3

4

5

6

7

8 d)

Uncertainty range BernUncertainty range MAGICC

Tem

pera

ture

incr

ease

(o C

)

Cumulative CO2 emissions 2000-2100 (GtC)

Bern MAGICC


Baseline Mitigation2.6 to 4.6°C 1.1 to 2.4°C

Projected Temperature Change (1990 to 2100)

Are there critical thresholds ...?

.

Ocean Acidification and Aragonite Saturation

Observation-based

NCAR CSM1.4

su

pe

rsa

turatio

n

A

2

1

4

3

0

A2

1

4

3

0(Steinacher, 2007)

Evolution of Aragonite Saturation in the Surface

Surface pCO2 (ppm)

Lat

itu

de

90oS

90oN

300 500 700

su

pe

rsa

turatio

n

A

2

1

4

3

0

(Steinacher, 2007)

Fluxes of calcite and aragonite to depth

CaCO3 flux in PISCES (PgC/m2/y)

Aragonite

Calcite

Total CaCO3

Gangsto, in prep. CaCO3 Flux (PgC/yr)

Dep

th (

m)

0

5000

Total CaCO3

Calcite

Aragonite

Will dissolution of shallow aragonitesediments mitigate some of the ocean acidification signal? Magnitude? Time scales?

0 0.80.4

460 ppm: Arctic Ocean becomes undersaturated with respect to Aragonite

560 ppm: Antarctic surface waters become undersaturated

560 ppm: surface water that is more than 3 times oversaturated dissappears

Conclusions: Ocean Acidification

How well do different

reconstruction methods of Canth

work in the AOGCM model world?

a) Canth simulated by model

b) Canth reconstructed from simulated tracers (C, Alk, O2, ...)

Simulated and reconstructed Canth should beidentical


.

NCAR CSM1.4

Surface Temperature and CO2 for SRES A2 and B1

1900 2000 2100Year

300

500

700C

O2 (

pp

m)

0

1

2

T (

oC

)

A2

B1

A2

B1

Anthropogenic forcing- Fossil and land use CO2 emissions- CH4, N2O, CFCs- direct sulphate aerosols

Natural forcing- solar irradiance- stratospheric volcanic aerosols

1900 2000 2100Year

Instrumental

Data

.

Observation-based (GLODAP)

Anthropogenic CO2

NCAR CSM1.4

Can

th (m

ol m

-2)

0

50

100

Change in decadal-mean PO4 from 1820 to 2000 AD, Atlantic, 20 W

Dep

th (

m)

80oS 60oN

0

40

P

O4 *117 (

mo

l-C/kg

)

-40

0

4500

• No century-scale trends• decadal variability in high latitudes of NA

Modelled evolution of DIC and Canth for an individual grid cell (60 N, 20 W)

Remove natural variability in DIC by splining to get Canth

DIC

(m

mo

l/m

3)

Time

Canth

DIC

2180

21001850 20001900 1950

Canth in the Atlantic along 20 WNCAR CSM1.4, 1994

Dep

th (

m)

80oS 60oN

30

70

0

Can

th (

mo

l-C/kg

)

-10

0

5000

b) Canth reconstructed from simulated tracers (Carbon, Alk, O2, ...)

The TrOCA method as an example

The usual assumptions

- Fixed Redfield ratios to correct for remineralisation- No century-scale trends- time-invariant air-sea disequilibrium

22

1 10.5 exp( )T T TCanth C O A b c dA

a a

„Organic MatterRemineralization“

„CaCO3dissolution“

Total Carbon

„preindustrialTotal Carbon“

Canth in the Atlantic along 20 WTrOCA with NCAR output, 1994

Dep

th (

m)

0

Can

th (

mo

l-C/kg

)

80oS 60oN

0

5000

70

30

-10


b) Canth reconstructed from simulated tracers (T, S, O2, ...)

Are simulated and reconstructed Canth identical?

TrOCA-NCAR

„truth“, NCAR-Model

0

70

-10

(m

ol-C/kg)

Potential Problems

Oxygen in NCAR

TrOCA

Remineralisation of organic matter does not consumeO2 in oxygen minimum zones (OCMIP Protocoll)

Remineralisation and Canth is overestimatedin reconstruction

Anoxic remineralisation of organic

matter may bias Canth estimates

TrOCA-MPI

„truth“, MPI Model

0

70

-10

(m

ol-C/kg)

TrOCA-MPI

Century-scale Trend in PO4 in MPI Model

Negative Canthin deep ocean

Century-scale trends may bias

Canth estimates

What about interannual and

decadal variability?

Internal Variability in AOUs

dv o

f de

cal a

vera

ged

AO

U (

mo

l/kg

)

Frölicher et al., in prep.

5

3

0

2

1

4

The impact of volcanic forcing on global mean AOU and O2


100

1500

Dep

th (

m)

-AOU O2

1960 2000 1960 2000Year

Optical Depth

The impact of volcanic forcing on global meanO2 and AOU


100

1500

Dep

th (

m)

-AOU O2

1960 2000 1960 2000Year

.

Internal Variability in DIC and in C* from a control run in top 2000 m

dep

th

(m

ol-

C/k

g)

-4

4

Levine et al., in press

60oS 80oN

1, DIC C*

0

60oS 80oN -15

15

0

.

Difference between modeled and reconstructed Canth for the C* method

0

-15

15

Levine et al., in press

Modelled increase over 10 year

Difference (model-reconstruction)

60oS 80oN (mol-C/kg)

Both externally-forced and

internal variability may bias

Canth estimates

Other potential problems?

• Parameters of reconstruction method have not been determined with model output

• Fixed Redfield ratios assumed in model – correct?

How do results from different

methods compare with modeled

Canth?

Reconstruction methods:

• TrOCA (Touratier et al.)

• CT0 (Vazquez-Rodriguez;

adjusted C* method)

• CT0 IPSL: (Lo Monaco; back-calculation method,

uses different preformed relationships for southern and northern water)

TrOCA

„Truth“: NCAR Model

CT0

IPSL0

70

-10

(m

ol-C/kg)

Difference between simulated and reconstructed Canth, 20 W,1994

(m

ol-C

/kg)

50

0

-50

Dep

th (

m)

0

5000

60oN80oS

TrOCA


(m

ol-C

/kg)

50

0

-50

Dep

th (

m)

0

5000

60oN80oS

CT0


(m

ol-C

/kg)

50

0

-50

Dep

th (

m)

0

5000

60oN80oS

IPSL

Conclusions

• Significant deviations between predicted and reconstructed Canth are found for all methods

• Potential biases: - externally-forced and internal variability- anoxic remineralisation- century-scale trends in watermasses/tracers- deviations from fixed Redfield ratios

- parameters not determined with model output (IPSL Reconstruction Method)

What ist the impact of

1. temperature distribution2. organic matter export3. CaCO3 export

on DIC and atm. CO2?

Apply a model to discriminate themechanisms

Dead ocean with T=18oC(present day carbon inventory in ocean-atmosphere system)

Uniform distribution of DICpCO2(atm) = 560 ppm

Atlantic Southern Ocean Pacific

Dep

thD

IC (m

mol/m

3)

Temperatures in the World Ocean

1. Solubility and carbon chemistry: cold water holds more DIC than warm water

→ DIC concentration in the (warm) surface are on average depleted with respect to the

(cold) deep ocean

→ atmospheric CO2 is lower compared to an ocean with a uniform temperature of T=18oC

Dead ocean with present temperature distribution(present-day carbon inventory in ocean-atmosphere system)

Surface water somewhat depleted in DICpCO2(atm) = 439 ppm

Dep

th


DIC

(mm

ol/m3)

2. Marine biota removes carbon from surface waters and this carbon is exported to the deep

→ DIC and nutrient concentrations in the surface are on average depleted with respect to the deep ocean

→ atmospheric CO2 is lower compared to a dead ocean

The marine organic carbon cycle

Vertical distribution of tracers in the North Pacific

Redfield ratio:P:N:C:O2 = 1:16:120:-170

Observed distribution of phosphate

Surface water in the Atlantic and Pacific are depleted in nutrients by biological activities

Dep

th


(mm

ol/m3)

Ocean with organic matter production and temperature distribution (but no calcite production)

Surface water depleted in DICpCO2(atm) = 229 ppm

Dep

th


DIC

(mm

ol/m3)

3. Production and export of CaCO3 increases the partial pressure of CO2 in surface waters

→ A range of marine organisms form shells made of CaCO3

Ca++ + 2 HCO3- → CaCO3 + CO2 + H2O

→ Decrease in DIC, but shift in the ratio between different carbonate species → Alkalinity ~ [HCO3

-]+2 [CO3--] is decreasing

→ [H2CO3*] in the surface and atmospheric CO2 is increased compared to an ocean without calcifying organisms

Observed distribution of potential Alkalinity

Surface water is depleted in alkalinity

Dep

thP

ot. Alk

(mm

ol/m3)


Observed distribution of DIC

Surface water depleted in DIC and in alkalinitypCO2(atm) = 278 ppm

Dep

thD

IC (m

mol/m

3)


Regulation of atmospheric CO2

Dead ocean with uniform T of 18oC: 560 ppm

Realistic temperature distribution: 439 ppm+ organic matter export 229 ppm+ CaCO3 export 278 ppm

Greenland and Antarctic temperature, CO2 and CH4 over the last

transition

Stauffer, Monnin, Blunier and co-workers, 2003

Past changes indicate the magnitude of potential future feedbacks

„Surprises in the Climate System“?

Projected strenght of the North Atlantic overturning

Cubasch et al., 2001

From the past to the future

Indermühle et al, 1999

NADW collapse: limited impact on atmospheric CO2 and ocean uptake

CO2 varies by up to 20 ppmduring D/O events

WRE1000

Joos et al, 1999; Plattner et al., 2001

How well can ocean carbon cycle

model simulate the present state?

Selected Results from NCAR CSM1.4-carbon

Thanks to S. Doney, I. Fung, K. Lindsay

.

Ocean Acidification and Aragonite Saturation

Observation-based

NCAR CSM1.4

su

pe

rsa

turatio

n

A

2

1

4

3

0

A2

1

4

3

0

.

Observation-based

Aragonite Saturation in the Atlantic

NCAR CSM1.4

sup

ersaturatio

n

0

10

20

-10

CO3— [mol/m3]

1000

4000

0

dep

th [

m]

90oS 90oN

Export Production of POC

Laws et al. (2000)

Global: 9.2 Pg C

0

100

200

Exp

ort (g

-C m

-2)

CSM1.4

11.1 Pg C

0

100

200

.

NCAR CSM1.4

Surface Temperature and CO2 for SRES A2 and B1

1900 2000 2100Year

300

500

700C

O2 (

pp

m)

0

1

2

T (

oC

)

A2

B1

A2

B1

Anthropogenic forcing- Fossil and land use CO2 emissions- CH4, N2O, CFCs- direct sulphate aerosols

Natural forcing- solar irradiance- stratospheric volcanic aerosols

1900 2000 2100Year

Instrumental

Difference 2100 - 1820

Decrease in Export of DOM

1820 -2100

∆ ~ 8 %

1820 2100

Year

Variability and a decreasing trend in meridional overturning circulation

80oN

Lat

itu

de

40oN

0o

40oS

1820 2000 2100Year

-10

0

10

20

30

Overtu

rnin

g (S

v)

1900

Long-term CO2 and sea level

committmentin EMICs1820 -2100

2000 2500 3000

2000 2500 3000

Year

60%

60%

0

60%Atmosphere

Ocean

Land

2000 GtC

Thermal Expansion (m)

1

IPCC AR4 EMIC Intercomparison

Plattner et al., 2006;

Cumulative Emissions

0%

1. Inverse methods such as Ensemble Kalman filtering provide powerful tools for improved estimates of biogeochemical quantities.

It is time to include CARBOOCEAN measurements.

2. Bomb radiocarbon data suggest that the OCMIP air-sea transfer velocity field must be downscaled by ~26%;global mean: 16 cm/hr (Müller et al., 2006, Sweeney, 2006, Ho et al., 2006, Nägler et al., 2006)

It is time to use a downscaled transfer velocity

3. Simulations with forced and internal variability available

It is time to analyse internal and externally-forced variability

Conclusions

CSM1.4-carbonFossil only

Sabine et al. (2003)

CO2 [mol/m2]

Column Inventory of anth. CO2

1994

http://www.climate.unibe.ch/logo_explain.html

A Historical Perspective

Siegenthaler and Oeschger, Science, 1978:

“With climate models becoming more and more realistic, a maximum permissible atmospheric CO2 level might be found which should not be exceeded if the atmospheric radiation balance is not to be disturbed in a dangerous way. … This scenario clearly does not allow us to go on burning fossil fuel at the present growth rate for a long time … Around the turn of the century new technologies would have to take over a substantial part of global energy production.”

Atmospheric Increase and Fossil Emissions

IPCC, Chap 7, 2007

Fraction of Fossil Emissions Staying Airborne

IPCC, Chap 7, 2007

Evaluating the overall impact in a probabilistic way

SRES B1

Knutti et al, 2003

Higher CO2 under global warming leads toan increased probability for high warming

Documents

Anthropogenic carbon in a varying ocean