Carboocean Second Annual MeetingSession on

Seasonal and Interannual Variations of Air-Sea CO2 Flux

.... in the Southern Ocean

N.Metzl, LOCEAN-IPSLthanks to A.Lenton, O. Aumont, K. Rodgers, T.Takahashi

Message 1: Seasonality and annual CO2 fluxSouthern Ocean CO2 sink is low : -0.05 to -0.2 PgC/yr(since 4 years, progress in observations and modelling)

Message 2: Interannual variabilitywhen observed, controlled by biological activitynot well simulated (limitations on co-limations ?)

Air-Sea CO2 flux climatogy Takahashi et al., (2002)

S.O. > 50°S: -0.13 PgC/yr (against -0.35 PgC/yr in T02)

New climatology, Takahashi et al. (2006, OCCC, in prep)

Annual air-sea CO2 flux in the Southern Hemisphere

Total > 50°S: -0.13 PgC/yr

New climatology(Takahashi et al., 2006, in prep; Gruber et al; 2006)

Total > 50°S: -0.06 PgC/yr

Coherent view for annual CO2 flux

Ocean Model (Aumont et al., 2004, see poster Lenton et al)

Back four years ago: Annual Flux in the Southern Ocean:OCMIP II models -0.42 Pg/yr, Climatology, –0.35 Pg/yr !!!!

Same annual flux, but opposed seasonalitybiological and mixing processes not correct in ocean models

-1,5

-0,5

0,5

0 12 24

Month

Air-

sea

CO

2 flu

x (P

gC/y

r)

OCMIP

ClimOBSnm, datasource: DivFlux.xls

Cycle annuel du flux de CO2 dans l'océan austral: observations et modèles

summer

winter winter

summer

Before discovering that rats love frogs, before ice melts in the future….

before concluding on annual fluxes, simulations need first to be seriously validated at seasonal scale

- Validate oceanic processes and forcings

- It is expected that pCO2 seasonality would changein the futur (positive, negative feedbacks ?)

pCO2 tracks, all seasons (CARBOOCEAN database, B.Pfeil

with help from A.Kozyr, CDIACand .... all contributors)

Looking for seasonal observations

Seasonality in South Indian Ocean: Large Variations in all Regions

Ocean and air fCO2 distribution in January and August 2000 eastern tracks (OISO cruises, South Indian Ocean)

280

300

320

340

360

380

400

-65 -60 -55 -50 -45 -40 -35 -30 -25 -20 -15

Latitude

fCO

2 (µ

atm

)

Wat Jan 2000

Wat Aug 2000

Air Jan 2000

Air Aug 2000

Ice

Summer Sink

Summer SourceWinter Source

Winter Sink

Metzl et al., 2001, DSR 2006

260

280

300

320

340

360

0 2 4 6 8 10 12 14 16 18 20 22 24

Month (2 years repeated)

<fC

O2>

(µat

m)

Atm. fCO2

Seasonal cycle in the Sub-Antarctic Zones (well observed)Western and Eastern Indian Ocean, Monthly Mean 1991-1995

(Sink: -0.4 PgC/yr in the Indian SAZ)

Metzl et al. 1999, Tellus

Summer sink

Winter equil

SeasonalRange

60 µatm

320

340

360

380

400

0 2 4 6 8 10 12 14Month

fCO

2 (

µa

tm)

Obs.

Atm.00

Southern Ocean > 50°S, in the POOZObservations in January and August: what is the annual cycle ???

????

Seasonality in the POOZ (western Indian sector)Observations and 1D box-model

300

320

340

360

380

400

0 2 4 6 8 10 12 14Month

fCO

2 (µ

atm

)

Obs.

Mod-W92

Mod-WM99

Atm.00

summer sink, bio >> warming

winter source, MIX >> cooling

Metzl et al., 2001, DSR, 2006

Extrapolation S.O. >50°S: = -0.17 PgC/yr, POOZ: -0.05 PgC/yr + SIZ: -0.12 PgC/yr

SeasonalRange

40 µatm

Monthly Air-sea CO2 fluxes (Ocean model, PISCES-NOCES)20 years of seasonality at latitude >50°S

-1.5

-1

-0.5

0

0.5

1

1.5

79 81 83 85 87 89 91 93 95 97 99 01 03 05

Year

Sea

-to

-Air

CO

2 fl

ux

(Pg

C/y

r)

PISCES, NOCES, monthly flux, PgC/yr summer sink

winter source

Seasonal Cycle: Regional observations and ocean modelsgood phasing, encouraging

Seasonal Sea-to-Air CO2 fluxes in the Southern Ocean

-12

0

12

0 3 6 9 12 15 18 21 24

Month (2 years rep.)

Flu

x (m

mo

l/m

2/d

)

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

Flu

x (P

gC

/yr)

Obs-OISO-00

ORCA-P-95winter source

summer sink

Seasonal Sea-to-Air CO2 fluxes in the Southern Ocean

-12

0

12

0 3 6 9 12 15 18 21 24

Month (2 years rep.)

Flu

x (m

mo

l/m

2/d

)

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

Flu

x (P

gC

/yr)

Obs-OISO-00

Obs-Clim-95

ORCA-P-95

AIM 88-97

winter source

summer sink

Seasonal cycle: observations, ocean models, climatology, atm. inversionsnot bad: summer sink/ winter source or equilibrium

IPSL, ORCA-PISCES, run NOCES

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

78 80 82 84 86 88 90 92 94 96 98 00 02 04 06

Year

Se

a-A

ir C

O2

flu

x (

Pg

C/y

r) Average: -0.06 PgC/yr

Interannual CO2 flux in the Southern Ocean >50°S:A view from an ocean model(between -0.1 and 0.1 PgC/yr)

OISO

Kerguelen

Amsterdam

Crozet

La Réunion

OISO cruises onboard R.V. Marion-DufresneWestern Indian - Antarctic Sector

Interannual Variability Observed in the Southern Indian Ocean(6 OISO cruises conducted in the same region during January)

320

330

340

350

360

370

380

390

400

-64 -62 -60 -58 -56 -54 -52 -50 -48

Latitude

fCO

2 (

µa

tm)

oiso1-98

oiso3-99

oiso4-00

oiso6-01

oiso8-02

oiso11-04

Air 2004

Air 1998

SIZ POOZ

Metzl, IGBPnews 2005, and unp. res.

InterannualRange

50 µatm

-6

-5

-4

-3

-2

-1

0

1Jan-98 Jan-99 Jan-00 Jan-01 Jan-02 Jan-03 Jan-04

Air-

Sea

CO

2 flu

x (m

mol

/m2/

d)

Interannual variability of air-sea CO2 fluxesin the S.O. (sector POOZ Indian Ocean)

(observed pCO2 water and air, Wind Quickscat + Wanninkhof 92)

These variations are not captured in physical-biological models (e.g. see poster Lenton et al.)

0.0

0.1

0.2

0.3

0.4

0.5

Jan-97 Jan-98 Jan-99 Jan-00 Dec-00 Dec-01 Dec-02 Dec-03 Dec-04

Year

Ch

la (

mg

/m3 )

330

340

350

360

370

380

fCO

2@3C

(µ

atm

)

chl-a

fCO2@3C

High Chl-a event, low fCO2 axis reversed

Interannual variability of Chla in the POOZ, Indian sectorgood candidate to explain the decrease of the CO2 sink since 1998

Carboocean Second Annual MeetingSession on

Seasonal and Interannual Variations of Air-Sea CO2 Flux

.... in the Southern Ocean

Message 1: Seasonality and annual CO2 fluxSouthern Ocean CO2 sink is low : -0.05 to -0.2 PgC/yr(since 4 years, progress in observations and modelling)

Message 2: Interannual variabilitywhen observed, controlled by biological activitynot well simulated (limitations on co-limations ?)

Message 3: If seasonality is well reproduced (happy), but not interannual variability (maybe not dramatic ?) what analysis need to be performed in priority (1-3 years) to better understand future scenarios and feedbacks.