Seasonal variability of CO2 air-sea fluxes and DICin the Southern Pacific Ocean

Leticia Barbero, Jacqueline Boutin, Liliane Merlivat

4th CarboOcean meeting, Dourdan, France8-12 December 2008

Buoy and ship trajectories in the Southern Pacific Ocean

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

STF

SAF

SAZ

•STF: Climatoligical (Orsi)•SAF: Altimetry data (J.B. Sallée)

Buoy trajectories colour-coded for month

STF

SAF

Palmer Ships: April-May/2004 March/2005 September/2005 September/2006

SAZ

fCO2 (µatm) measured by CARIOCA and ships

AT computed from SST,SSS (Lee et al., 2006)DIC computed from fCO2 and AT (Mehrbach et al. (1973) after Dickson and Millero (1987) )

• ARGO floats co-located in time and space used to compute mixed layer depth (MLD)

DIC (µmol/kg) computed along trajectories

220 data points (0.5% of total)No data for November

Late winter: deep MLD, rich DIC values

In order to increase data: Dong et al. (2008) MLD climatology for Southern Ocean

100% 46000 data points

Deep MLD-rich DIC

Buoy and ship DIC data vs. Dong et al.’s (2008) climatological MLD (m)

Sep.

Oct.

Aug.

Jan.

DIC hyperbolic f(MLD) σ = 19 µmol/kg

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

Similar algorithm for fCO2:

fCO2 = a’ + b’*MLD + c’*SST σ = 16 µatm

For |MLD| > 100m: fCO2 = a’’ + b’’*MLD + c’’*SST σ = 8 µatm

August 2005

Dong et al. (2008),Density difference criteria,Δρ = 0.03 kg m-3

MLD (m)

SST (ºC)

SST, WOA 2005 :Objective analyzed mean

Estimation results for August 2005ΔpCO2Exchange coefficient, Kw (Sweeney et al., 2007)

0.04 0.08 0.12µatm

Sea-air flux

(mmol m-2 d-

1)

Mol m-2 yr-1 µatmWeekly Quickscat winds from Ifremer

Takahashi et al. (2009)

Air-sea CO2 flux for August 2005Our study

Flux estimates (Pg C/year), Kw Sweeney et al., 2007:

•McNeil et al. (2007), 40-50ºS: 0.92•Takahashi et al. (2009), Pacific Oc., 14-50ºS: 0.4•Boutin et al. (2008), SAZ: 0.67•This study, SAZ Pacific Oc (72% of total): 0.81

ΔpCO2Exchange coefficient, Kw (Sweeney et al., 2007)

0.04 0.08 0.12µatmMol m-2 yr-1 µatm

(mmol m-2 d-

1)

Estimation of biological production

DIC and AT vs. time DIC and SST vs. time

Aug.

Jan.

Sunrise

Sunset

Time # Days NCP(µmol/kgd)

Chl-a(mg m-3)

30/11-1/12 2 0.48 ± 0.53 0.27

16-20/12 3 1.22 ± 0.59 0.31

18-21/1 3 0.49 ± 0.66 0.14

29-30/1 2 1.17 ± 0.25 0.14

Method described in detail by Merlivat et al. (2008)

hF

tCNCP

1

Net Community Production:

F = air-sea fluxh = MLD

No direct relationship between satellite Chl-a and NCP

Chl-a from MODISA-SEAWIFS weekly average

Estimates of air-sea CO2 flux in SAZ in the Pacific Ocean: 0.81 Pg C yr-1.

Lack of buoy and ship data in big area on the North-eastern Pacific SAZ.

Large variability in DIC during the summer months estimates of NCP (0.5-1.22 µmol kg-1 day-1). Questions remain concerning how representative these values are. Is this an intermittent event or can we extract a mean value?

No direct correlation between NCP and satellite products for low chlorophyll-a concentrations.

Still a work in progress!

In summary:

THANK YOUFOR YOUR ATTENTION

Time # DaysCM-Cm

(µmol/kg)ΔC/Δt

(µmol/kg) q pFair-sea

(mmol/m2d)

h(m)

NCP(µmol/kgd)

NCPint(mmol/

m2d)

Chl-a(mg m-3)

30/11-1/12 2 2.79 ± 0.78 0.52 ± 0.54 0.66 0.63 -2.17 50 0.48 ± 0.53 23.81 0.27

16-20/12 3 3.83 ± 0.50 1.29 ± 0.61 0.68 0.58 -4.34 60 1.22 ± 0.59 73.37 0.31

18-21/1 3 2.21 ± 0.59 0.63 ± 0.65 0.64 0.61 -6.48 45 0.49 ± 0.66 22.07 0.14

29-30/1 2 4.03 ± 0.92 1.34 ± 0.33 0.63 0.61 -7.71 45 1.17 ± 0.25 52.69 0.14