WP 5: “Southern Ocean observations and processes”

Participants: UPMC: J. Boutin, L. Barbero, L. Merlivat, N. Metzl, A. Lenton,

UEA: D. BakkerAWI: M. Hoppema,

CSIC/IIM: A. Rios, X.A. Padin, F. Perez

FICARAMCoastal areas

CARIOCA driftersFrontal areas

Polarsternfrontal and seasonal sea-ice areas

OISO Frontal areas

WP5 Objectives

• To assess the air-sea CO2 flux and its space and time variability in specific sink regions of the Atlantic and Indian sectors of the Southern Ocean. – Coastal regions: seasonal variability– Frontal regions: seasonal to decadal variability

• To understand processes responsible for the observed variability of the air-sea CO2 flux– Seasonal sea-ice regions– Enhanced CO2 uptake close to islands – Net community production in frontal regions– Influence of stratospheric ozone on the observed decadal variability

• To provide inputs for estimating air-sea CO2 fluxes at regional and monthly time scales to constrain atmospheric inverse modelling.– New set of measurements incorporated in the Takahashi et al. (2009) climatology– Revised estimates of air-sea CO2 flux integrated in the SAZ

WP5 Objectives

• To assess the air-sea CO2 flux and its space and time variability in specific sink regions of the Atlantic and Indian sectors of the Southern Ocean. – Coastal regions: seasonal variability– Frontal regions: seasonal to decadal variability

• To understand processes responsible for the observed variability of the air-sea CO2 flux– Seasonal sea-ice regions– Enhanced CO2 uptake close to islands – Net community production in frontal regions– Influence of stratospheric ozone on the observed decadal variability

• To provide inputs for estimating air-sea CO2 fluxes at regional and monthly time scales to constrain atmospheric inverse modelling.– New set of measurements incorporated in the Takahashi et al. (2009) climatology– Revised estimates of air-sea CO2 flux integrated in the SAZ

FICARAM cruises: coastal region

A. Rios, X.A. Padin

See poster 7

South American Shelf South Atlantic Convergence Falkland Current

=>The majority of provinces in the Patagonian Sea behaved as an intense sink of CO2

during autumn and spring, in particular the oceanic waters of the SAC province (South Atlantic Convergence zone 40 ºS–51 ºS) :-5.4±3.6 mol m-2 yr-1

=>The Antarctic waters in the Drake Passage were found to be CO2 undersaturated during the boreal autumn

(Padin et al. 2009)

Strongest sink!

CARIOCA drifters in the frontal regions

83 months of hourly measurements (CO2 fugacity and auxiliary parameters) acquired by 7 CARIOCA drifters in the Southern Atlantic and Indian Ocean during 4 seasons.

J. Boutin, L. Merlivat, L. Barbero (UPMC)

STF

SAF

Combining part of this data set with older Carioca data in other sectors of the Southern Ocean, SAZ sink estimated to be 0.8PgC yr-1 (Boutin et al., 2008)

but large unknowns in the Pacific SAZ (the largest estimated sink: 0.5PgC yr-1)

DIC = a + b*MLD – c*SST σ = 9.7 µmol/kg

For |MLD| > 100m: DIC σ = 5.8 µmol/kg

DIC = f(SST,MLD)

AT = f(SST,SSS)

(SST and SSS from WOA)

pCO2

Fit forMLD=50m

Fit forSST=6°C

Fit forSST=10°C

0

-100

-200

-300

-400

-5002020 2060 2100 2140

MLD

(m

)

DIC (µmol/kg)

DIC vs. Climatological MLD (Dong et al. 2008) Deep MLD – Rich DIC

CARIOCA + Ship data in Pacific SAZ => air-sea CO2 source in regions of deep water formations

ΔpCO2 in July

Our study (1x1° grid):

Takahashi, 2009 (4x5° grid):

McNeil, 2007 (June, July, August) (1x1° grid):

Annual flux 2005, SAZ Pac., same k, quickscat wind speed

Barbero et al. 2009, in prep.

Barbero et al. 2009 -0.04 Pg C y-1

Takahashi et al. 2009 -0.16 Pg C y-1

McNeil et al. 2007 -0.5 Pg C y-1

Boutin et al. 2008 -0.5 Pg C y-1 BarberoTakahashiMc NeilBoutin

Trend atmosphere: + 1.7 µatm/yrTrend ocean: + 2.1 µatm/yr

Ocean sink decreases ? : -0.4 µatm/yr

trend = + 2,11 (0.07) µatm/yr

250

270

290

310

330

350

370

390

410

430

450

1990 1992 1994 1996 1998 2000 2002 2004 2006 2008

Year

fCO

2s (µ

atm

)

All 1°x1° average data in the South Indian (20°S-69°S, 30°E-90°E)

Metzl, DSR, 2009

All data 1991-2008 in SOCAT and CDIAC

(OISO Cruises)

Observations suggest a recent stabilization of the CO2 uptake in the Southern Ocean

Decadal variations of fCO2 in the Southern OceanNicolas Metzl and Andrew Lenton (UPMC)

Cruises: 1991-1995 (MINERVE) and 1998-2007 (OISO)

Exploring fCO2 trends in four selected regions and for summer and winter

0,0

0,5

1,0

1,5

2,0

2,5

3,0

Ann

ual R

ate

fCO

2s (µ

atm

/yr)

20-35°S 35-40°S 40-42°S 50-55°S

Summer and winter ocean fCO2 trends (µatm/yr)in four regions in the Southern Indian Ocean (1991-2007)

Almost always above the atmospheric CO2 rateMainly explained by import of DIC from subsurface

linked to positive phase of the SAM.

Metzl, DSR 2009

Average:2.1 (+0.3) µatm/yr

(same as moon view)Summer Winter

Atm.

O3 clim: ocean CO2 sink increases, Ocean pCO2: +1.1 uatm/yr

O3 hole: ocean CO2 sink stabilizedOcean pCO2: +2.0 µatm/yr

Air-sea CO2 fluxes in the Southern OceanResults from a coupled climate/carbon model

(IPSL/LOOP with and without O3 hole)

(Lenton et al, GRL, 2009)

WP5 Objectives

• To assess the air-sea CO2 flux and its space and time variability in specific sink regions of the Atlantic and Indian sectors of the Southern Ocean. – Coastal regions: seasonal variability– Frontal regions: seasonal to decadal variability

• To understand processes responsible for the observed variability of the air-sea CO2 flux– Seasonal sea-ice regions– Enhanced CO2 uptake close to islands – Net community production in frontal regions– Influence of stratospheric ozone on the observed decadal variability

• To provide inputs for estimating air-sea CO2 fluxes at regional and monthly time scales to constrain atmospheric inverse modelling.– New set of measurements incorporated in the Takahashi et al. (2009) climatology– Revised estimates of air-sea CO2 flux integrated in the SAZ

Seasonal sea-ice region:High fCO2 and DIC below sea ice, low values upon ice melt.

Ice concentration (fraction)fCO2(w-a) (µatm)

Oceanic CO2 source

potential

Oceanic CO2 sink potential

03/12

07/12 21/12

30/12

14/01

15/12

07/01

fCO2(w-a) (µatm)

Why?FS Polarstern, ANT 20-2,

03/12/2002-14/01/2003

Below ice: fCO2(w-a) 0 to 40 µatmUpon melt: fCO2(w-a) -50 to 0 µatm Bakker et al., Biogeosciences, 2008

High fCO2 and DIC below sea ice by entrainment of ‘old’ CO2-rich Warm Deep Water

Below sea ice: fCO2(w-a) of 0 - 40 µatm.

The ice mostly (?) stops outgassing of CO2

(Bakker et al., 2008).

N.B. Air-sea ice CO2 fluxes are important (Delille et al., Nomura et al. @ ICDC8).

Dissolved inorganic carbon (µmol/kg)

High DIC at 50 m depth

Rapid reduction of surface fCO2 during and upon ice melt

Brown ice, 17-20/12/02

Below ice: fCO2(w-a) 0 to 40 µatmUpon melt: fCO2(w-a) -50 to 0 µatm

Biological carbon uptake rapidly creates a CO2 sink during and upon ice melt.

08-10/12/2004

20/12/2004

0°W Surface fCO2 decrease during ice melt

17/12/2004

(%)

Sea ice cover

The Weddell Gyre may well 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).

DIC deficit in the upper 100 m

SOUTH: HNLC, upstream of the plateau

Little air-sea CO2 transfer;DIC deficit 1 mol/m2

Are HNLC waters more productive than we think?

NORTH: Crozet bloom, downstream of the plateau

Sink for atmospheric CO2;DIC deficit 2-3 mol/m2;How important are such blooms for Southern Ocean carbon export?

(Bakker et al., 2007, DSR II)

The island mass effect and biological carbon uptake for the Crozet Plateau

During some periods (with no salinity or temperature variations (except diurnal variation)), diurnal variation of DIC (max. at sunrise, min. at sunset) and high fluorescence indicate large biological activity. The day-to-day decrease of the

DIC maximum at the end of the night provides an estimate of the net community production in the mixed layer

DIC~Net community production in the mixed layer – air-sea flux

SunriseSunset

Net community production derived from CARIOCA hourly measurements

See poster 5(Boutin & Merlivat, GRL, 2009)

March April November-December

PF

SAF

Estimating biological carbon production rates by an in situ non-intrusive method using CARIOCA measurements (Boutin & Merlivat, GRL, 2009).

Main avantages of the method:

- non-intrusive method,

- compared to in situ O2/Argon method, the contribution of air-sea flux is small with respect to biological contribution

- provides an estimate of NCP averaged over a few days in the mixed layer

In march-april, close to polar front in western Atlantic: 1.4< NCP < 2.9 mol kg-1 d-1

In nov-dec., in SAZ of eastern Atlantic, 0.3<NCP<0.6 mol kg-1 d-1

Main results• Increased number of surface CO2 measurements in the Southern Atlantic

and Indian Oceans (open and coastal regions) from ships and CARIOCA drifters.

• With respect to Takahashi et al. (2009) climatology, SAZ sink in the Southern Ocean could be reduced by 0,1 Pg C yr-1 when taking into account outgassing in regions of deep water formation.

• On a decadal scale, surface ocean CO2 fugacity increases at a rate almost always above the atmospheric rate in the Southern Indian Ocean (1991-2007). In agreement with simulations of a coupled model including stratospheric ozone depletion.

• Large phytoplankton blooms downstream of the Crozet and Kerguelen islands and in coastal areas create a strong sink for atmospheric CO2.

• Large variability of air-sea CO2 flux close to sea ice

• New methodology developped to estimate in situ carbon biological production from CARIOCA drifters

Future needs/ Remaining questions

• Maintain repetitive tracks to monitor long term trends: is the southern ocean sink decreasing or not?

• Deepen process studies based on Carboocean acquired measurements:

among others:

– New in situ estimates of carbon biological production from all CARIOCA drifters:

– Impact of mesoscale variability on fCO2 measurements– CO2 variability in seasonal sea ice regions– .....

Thanks to :

-WP5 participants for fruitful and constructive work

-Benjamin for helping in data synthesis

-Andrea for helping in the workshops organisation

-Andy and Christoph for coordination

Figure 5: Temporal variation of the averaged SST, SSS, chl-a, WS, fCO2 and FCO2 cruise (error bars stand for the respective standard deviation) in SAS (South American Shelf 31ºS S–40ºS), SAC (South Atlantic Convergence zone 40 ºS–51 ºS), and FC (Falkland Current 51 ºS–56 ºS). Spring and autumn values are shown as squares and circles, respectively. Significant regression lines (p<0.05) and regression slopes including the standard error are also given. Solid lines stand for spring results and dashed lines for autumn.

South American Shelf South Atlantic Convergence Falkland Current

=>The majority of provinces in the Patagonian Sea behaved as an intense sink of CO2

during autumn and spring, in particular the oceanic waters of the SAC province (South Atlantic Convergence zone 40 ºS–51 ºS) :-5.4±3.6 mol m-2 yr-1

=>The Antarctic waters in the Drake Passage were found to be CO2 undersaturated during the boreal autumn (Padin et al. 2009)

Strongest sink!

Buoy and ship trajectories in the South Pacific

CARIOCA 01110 April/2004-April/2005CARIOCA 03740 April/2004-June/2005Palmer cruises April-May/2004 March/2005 September/2005 September/2006

STF

SAF

SAZ

•Subtropical Front (STF): Climatological (Orsi et al.,1995, Deep Sea Res.)•Subantarctic Front (SAF): Altimetry data (Sallée et al., 2008, J. Climate)

Method for the estimation of air-sea CO2 fluxes from MLD, SST and SSS in the SAZ of the Southern Pacific Ocean.

Large variability in DIC during the summer months due to biological production.

No direct correlation between NCP and SEAWIFS-MODIS colour images for weak Chl concentrations.

Method validated against independent measurements (1979-2008)

The Pacific SAZ is a weaker sink than estimated by other methods.

Conclusions:

For more info:

Leticia.Barbero@locean-ipsl.upmc.fr

Diagram showing depth zones in a typical mixed layer cycle (Brainerd and Gregg, DSR 1,1995)

Schematic principle of NCP estimation from observed diurnal variation of DIC:a DIC minimum at sunset and a DIC maximum at sunrise together with significant fluorescence and no change in salinity (also alkalinity). a warm diurnal layer is formed during the daylight period during the second part of the day, nocturnal convection mixes the warm layer within the mixed layer

(surface buoyancy flux)

From ice covered CO2–rich waters to a biologically mediated CO2 sink upon ice

melt in the eastern Weddell Gyre

Dorothee Bakker, Mario Hoppema, Mike Schröder, Walter Geibert, Hein de Baar

School of Environmental Sciences, University of East Anglia, Norwich, U.K.Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany

Earth Science, School of Geosciences, University of Edinburgh, U.K.Royal Netherlands Institute for Sea Research, Texel, The Netherlands

Funding from EU CarboOcean, the Royal Society and NERC CASIX