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Achievements and challenges in southern ocean co 2 research l.jpg
Achievements and challenges in Southern Ocean CO2 research

Dorothee Bakker, Mario Hoppema, Marta Alvarez, Leticia Barbero, Nina Bednarsek, Richard Bellerby, Jacqueline Boutin, Melissa Chierici, Bruno Delille, Judith Hauck, Oliver Huhn, Elisabeth Jones, Andrew Lenton, Nicolas Metzl, Claire Lo Monaco, Benjamin Pfeil, Aida Riós, Henk Zemmelink, ....

Funded by EU CarboOcean and / or national funding bodies

Achievements and challenges in l.jpg
Achievements and Challenges in:

The Southern Ocean CO2 sink

# Deep carbon inventories

# Air-sea CO2 fluxes

# Evolution of the Southern Ocean CO2 sink

Process studies

# Upwelling, subduction, mixing

# Iron supply

# Sea ice

# Ocean acidification

Southern ocean part of the meridional overturning circulation l.jpg
Southern Ocean: part of the Meridional Overturning Circulation

North Atlantic Southern Ocean

(Open University)

Exchange of heat, elements and momentum between the deep ocean and the atmosphere.

1 1 inventory of anthropogenic carbon l.jpg

Cant (mol m-2)

1.1) Inventory of anthropogenic carbon

Subantarctic Mode

Water (SAMW)



Water (AAIW)

  • 20 Pg C or 5% of anthropogenic carbon in SAMW and AAIW in 1994.

  • Anthropogenic carbon in AABW (Antarctic Bottom Water)?

(Hanawa and Talley, 2001; Sabine et al., 2004)

How much c ant in aaiw and aabw l.jpg
How much Cant in AAIW and AABW?




Differences in Cant (µmol/kg) from the C0 and C* methods

along 30°E

(Lo Monaco et al., JGR,


Accumulation of c ant in the weddell sea between 1992 and 2008 l.jpg
Accumulation of Cant in the Weddell Sea between 1992 and 2008

Cant accumulated in the Weddell Sea (1992 – 2008)

CT2008 fitted as a function of θ, S, O2and p

CT1992fitted as a function of θ, S , O2and p

Extended Multiple Linear Regression (eMLR)



Cant2008-1992 along 0°W (µmol/kg)

  • High Cant at the surface, especially north of 60°S and at the shelf where no sea-ice hampers the gas-exchange.

  • Low Cant in deep and bottom water - close to the error of the method.

  • (Hauck, Hoppema et al., in preparation)

1 2 air sea co 2 fluxes l.jpg

of surface water pCO2

1.2) Air-sea CO2 fluxes




Poor seasonal coverage in surface water fCO2 (Takahashi et al., 2009)

S o co 2 sink l.jpg
S.O. CO2 sink

(Pg C /yr)

Global oceans

(1990s, 2000-05)0 2.2±0.5

Surface pCO2


~40-50°S) 2, 4 0.8-1.1

PZ (SAF-PF)2 <0.1

South of 50°S 0.063-0.44

Atmospheric + ocean models

South of ~45°S5 0.3-0.6

(Takahashi et al., 2009)

  • The ’circumpolar sink zone’in the Subantarctic Zone (SAZ).

  • High pCO2 at ice edge

(Takahashi et al., 2009)

Pg = 1015 g (0 – Denman et al., 2007; 2- Metzl et al., 1999; Boutin et al., 2008; 3 - Takahashi et al., 2009; 5 – Baker et al., 2006; Gruber et al., 2003 at ICDC7; 4 -McNeil et al., 2007)

Monitoring fco 2 with carioca drifters l.jpg





oceanic sink

fCO2(water -air) (µatm)

Monitoring fCO2 with CARIOCA drifters

  • Ocean CO2 sinks of 0.8 Pg C / yr in the SAZ and <0.1 Pg C / yr in the PZ from CARIOCA data since 2001 (Boutin et al., L&O, 2008).

  • Assess the effect of SAMW formation on fCO2 in the South Pacific Ocean from CARIOCA and shipboard data (Barbero et al., in preparation, 2009).

  • Future: Quantify the effect of mesoscale activity on fCO2 and DIC from CARIOCA and satellite data.

Estimating ncp with carioca drifters l.jpg

9 days (Nov-Dec 2006) in the Polar Zone; high fluorescence

~<Net community production>

~ 0. 3 mmol/kg/day

~Gross Community Production-Respiration

fCO2 (matm)



Estimating NCP with CARIOCA drifters

Strong diurnal cycle allows estimation of net community production (NCP) from CARIOCA data.

Future: Provide estimates of NCP from the diurnal cycle in fCO2 and DIC for all CARIOCA drifters.

(Boutin, Merlivat et al., in revision, GRL, 2008)

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1.3) Evolution of the Southern Ocean CO2 sink

Sea-air CO2 flux anomaly (Pg C/yr)

Less upta-ke

+ pulse model

More upta-ke

Atmospheric CO2 data

and an ocean model

suggest a reduction in the efficiency of the Southern Ocean

CO2 sink since 1980.

Changes have been ascribed to an increase in wind speed.

Model, observed winds

Model, constant winds

Le Quéré et al., Science, 2007

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A decrease of the S.O. sink?

Trend atmosphere: + 1.7 µatm/yr

Trend ocean: + 2.1 µatm/yr

Decrease of ocean sink? -0.4 µatm/yr

All data 1991-2008 in SOCAT and CDIAC

(Metzl, 2009, DSR SOCOVV, in press)

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Decadal changes of

natural and anthropogenic carbon

Anthropogenic carbon

at 500m in the late 1990’s

Section around 70E: Comparing 2000-1985

Total Carbon change (µmol/kg)

Anthropogenic Carbon change (µmol/kg)

DDIC < 0, DCant > 0

Decrease in ”natural” carbon

(Lo Monaco et al., sub., 2008)

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What drives the observed variability

of the carbon cycle in the Southern Ocean ?

(Lenton et al., sub., 2008)

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Oceanic CO2 sink - ongoing

  • Data synthesis in CARINA and SOCAT (Surface Ocean CO2 Atlas)

  • NEW surface pCO2 VOS on RRS James Clark Ross (Hardman-Mountford, Jones, et al.) and FS Polarstern (Hoppema, Neil et al.)

  • Hydrographic sections with carbon and tracers

Falkland Islands

South Georgia


Cruises in Scotia Sea

on JCR since 2006

(Poster Jones et al.)


SOCAT version 1,

d.d. 21/11/2008,

@Benjamin Pfeil

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2) Process studies on interactions between physics, biology and the CO2 sink

Diffusivity (log (m2/s))

Scotia Sea (Naveira-

Garabato et al., 200x)

  • Enhanced mixing and upwelling over steep topography, iron supply, and occurrence of blooms.

  • Mesoscale dynamics and eddies;

  • Entrainment of CDW below ice;

  • Preconditioning of CO2 before subduction;

  • Sea ice dynamics.

  • (Naveira-Garabato et al., 2007; Solokov and Rintoul, 2007; Blain et al., 2007; Bakker et al., 2007, 2008; Boutin et al., 2008)

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Marine productivity and sea ice







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Natural iron fertilisation

at the Kerguelen Plateau,


January 2005

fCO2 (µatm)

(Blain et al., 2007; Jouandet et al., 2008)

Natural iron fertilisation at crozet l.jpg









Natural iron fertilisation at Crozet

14 - 18 November 2004

8 November – 8 December 2004

Chlorophyll (mg/m3)

fCO2(w-a) (µatm)

Upstream (South): Little effect of marine biota on surface water fCO2.

Downstream (North): Large phytoplankton blooms lower fCO2 by 70 µatm.

(Bakker et al., 2007)

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Island blooms vs HNLC


HNLC stations

Blooms are 2-3 times as productive as HNLC waters and are large CO2 sinks.

bloom stations

(Jones et al., see poster)

1 M-P. Jouandet et al., Deep-Sea Res. II, 2008, 55, 856 2 D. Bakker et al., Deep-Sea Res. II, 2007, 54, 2174

Entrainment creates high fco 2 and dic below sea ice in the weddell gyre l.jpg

Dissolved inorganic carbon (µmol/kg), 17-23°E


Entrainment creates high fCO2 and DIC below sea ice in the Weddell Gyre

  • Below sea ice: fCO2(w-a) 0 to +40 µatm in December 2002.

  • Upward movement of Warm Deep Water in the Weddell Gyre creates high fCO2 and DIC below the winter ice. The ice prevents outgassing of CO2 (Bakker et al., 2008, Biogeosciences).

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Rapid reduction of surface water fCO2 during and upon ice melt

0°W Surface fCO2 decrease during ice melt



Sea ice cover

Brown ice, 17-20/12/02


Below ice: fCO2(w-a) 0 to 40 µatm

Upon melt: fCO2(w-a) -50 to 0 µatm

Biological carbon uptake rapidly creates a CO2 sink during and upon ice melt. The importance of ice-related

CaCO3 processes is not clear. The Weddell Gyre may be an annual CO2 sink. (Bakker et al., 2008)

This supports the role of Antarctic sea ice on glacial-interglacial CO2 variations (Stephens and Keeling, 2000).

(Bakker et al., 2008,



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Role of ikaite in sea ice

Ikaite CaCO3.6H2O in sea ice (Dieckman et al., 2008)

Ikaite precipitates along brine channels during ice formation, thus increasing fCO2. Ikaite dissolves during/upon ice melt, thus reducing fCO2.

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CO2 uptake by multi-year sea ice

in the western Weddell Sea

Turbulent CO2 fluxes (g CO2 m-2 d-1) by eddy correlation in December 2004.

Total carbon uptake by the multi-year ice zone of the western Weddell Sea could have been 6.6 Tg C y-1 in December 2004 (Zemmelink, 2005).

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Sea ice: Ikaite and biological carbon uptake

Semiletov et al. 2004, 2007

Zemmelink et al. 2006



-8°C < T° < -5°C

T° < -5°C

-8°C > T°

CO2 uptake by biology

at both top and bottom of sea ice

CaCO3 + H2O + CO2


Papadimitriou et al. 2004

Dieckmann et al.2008

2 HCO3- + Ca22+

2 HCO3- + Ca22+

Zemmelink et al.


Delille et al. 2007

CaCO3 + H2O

+ CO2

Graphics by

Bruno Delille

Brine sinking entrain produced

CO2 below the pycnocline while

CaCO3 remain trapped within sea ice

Rysgaard et al. 2007

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Future studies of the role of

sea ice in CO2 chemistry

1) Measurement of air-ice CO2 fluxes by micro-meterological methods


2) Sea ice processes should be addressed by ice-coring and related analysis

2 HCO3- + Ca22+

CaCO3 + H2O

+ CO2

3) Impact of precipitation of CaCO3 to the water column can be addressed by TA profiles and specific reanalysis of TA/DIC profiles

Slide by Bruno Delille

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Effect of ocean acidification on the CO2 sink?

  • A more acid ocean reduces the carbonate concentration and calcification.

  • Models predict that the Southern Ocean will become undersaturated for aragonite by 2050 in the IS92a scenario (Orr et al., 2005).

  • The importance of calcifying organisms for the Southern Ocean carbon cycle is poorly known.

Abundance of the pteropod Limacina helicina in the Scotia Sea (Nina Bednarsek et al., 2008; poster)

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  • Achievements

  • Significant progress has been made on quantifying Southern Ocean CO2 uptake in the CarboOcean era. New topics have emerged, notably the evolution of the Southern Ocean CO2 sink and the role of sea ice.

  • Challenges:

  • I) Quantify the evolution of the Southern Oceanic CO2 sink

  • Sustained observations of surface fCO2, deep carbon transport and atmospheric CO2

  • Identify the best method(s) for quantification of anthropogenic carbon

  • Quantify Cant in Antarctic Bottom and Intermediate Water

  • II) Assess the processes driving (changes in) oceanic CO2 uptake:

  • Iron supply,

  • Sea ice,

  • Entrainment, mixing, subduction, pre-conditioning,

  • Marine productivity,

  • Ocean acidification.

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(more wind)

Higher pCO2w

DpCO2 --

Less uptake

CO2uptake --

Evolution of the oceanic CO2 sink

with / without an O3 hole

in a coupled carbon climate model

(Lenton et al., sub., 2008)


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Vertical CO2 gradients in snow on top of

sea ice in the western Weddell Sea

Over slush

Over solid ice


In snow

  • CO2 concentrations (ppmv)

  • in the atmosphere at 0.85 m from the ice and

  • in snow, as a function of distance from the ice surface.

  • (Zemmelink)