Core theme 1

WP4: North Atlantic observing system

WP 5: Southern Ocean

WP6: Data synthesis and modelling

Sea-surface CO2 fugacity in the subpolar North AtlanticA. Olsen, K. R. Brown, M. Chierici, T. Johannessen, and C. Neill

ΔpCO2

SOM estimates of annual cycles, 2004, 2005, 2006.(Telszewski et al, submitted)

Rates of increase (uatm per year) of pCO2 in the North Atlantic, linear fit 1990-2006

Schuster et al., in press, DSR II

•Rapid increases in the subpolar gyre

•slightly above atmospheric increase in the subtropical gyre

Accurate Air-sea fluxes of CO2 in the North Atlantic in 2005 from an in – situ observing system

Watson et al., about to be submitted (promise!)

Monitoring of fCO2 in the Southern Ocean using CARIOCA drifters: Results

Since 2006, in the frame of CarboOcean, 6 CARIOCA recording fCO2:

-Exploration of the polar zone and of the subantarctic zone-Combination with CARIOCA measurements since 2001 in the Pacific and Indian Oceans

=> SAZ sink ~0.8PgC/yr ; PF sink <0.1PgC/yr (Boutin et al., Limnol. Ocean., 2008)

-Combination with ship measurements =>Influence of SAMW formation in the Southern Pacific Ocean (Barbero et al., in preparation, 2008)

-Evidence of a strong diurnal cycle => methodology to estimate in situ net biological community production from CARIOCA measurements (Boutin and Merlivat, in revision, GRL,2008)

PF

SAF

Monitoring of fCO2 in the Southern Ocean using CARIOCA drifters: Perspectives

2-New in situ estimates of biological net community production from biological activity signature on fCO2 and on DIC for all CARIOCA drifters (at present, study limited to 2006 drifter in the polar zone) => improve spatio-temporal distribution of NCP

CARIOCA - 29/11/06 to 8/12/06

365

370

375

380

385

390

395

400

405

410

29/11 30/11 1/12 2/12 3/12 4/12 5/12 6/12 7/12 8/12

local time

fCO

2 (m

icro

atm

)

2110

2112

2114

2116

2118

2120

2122

2124

DIC

(m

icro

mo

l/kg

)

fCO2

fCO2_atm

DICSunset

~ <Net community production>~ 0. 3mol/kg/day

9 days (Nov-Dec06) in polar zone; high fluorescence

~Gross Community Production-Respiration

fCO

2 (

atm

)

1-Influence of mesoscale activity on fCO2 and DIC; combination of satellite/in situ measurements

DIC

(m

ol/k

g)

Process studies at local scale

Simulated interannual variability (from LSCE) 4th year progress on sensitivity to 3 factors :

1. Effect of model resolution ? – Mercator-vert collaboration

• ORCA/PISCES model simulations (2º, ½ º, & ¼º) completed• Mercator ocean reanalysis fields: 2001 to 2005 completed

– DRAKKAR collaboration• Global: Forced NEMO (OPA9) global ocean-model dynamic simulations (2º, ½ º, & ¼º)

over last 50 years completed (started - coupling with BGC model)• Southern Ocean, high-res (1/12º) regional simulations with NEMO/PISCES in

preparation (started - thesis study of Carolina Dufour) Does explictly resolving eddies change estimated ongoing slowdown in Southern-

Ocean CO2 uptake?

2. Effect of forcing fields ? NEMO/PISCES simulations over last ~50 years Coding and tests underway (started, Jennifer Simeon)

• at 3 resolutions (2º, ½ º, & ¼º) & different sets of forcing fields • with different sets of forcing fields (NCEP, ERA40, CORE, DFS3, DFS4)

• Effect of physical data assimilation (SST, altimetry, …)?– Ongoing study within the Mercator-vert project (Moulin et al., 2008)

this studythis study

COCO22 Gas Exchange Rates from Gas Exchange Rates from

Inversion of Water Column DataInversion of Water Column DataR. Schlitzer, Alfred Wegener Institute, Bremerhaven

Pre-industrial (“natural”) annual-mean COPre-industrial (“natural”) annual-mean CO22 Fluxes from Fluxes from

inversion of ocean interior DIC datainversion of ocean interior DIC data

• broad agreement with Mikaloff Fletcher, 2007 and other modelsMikaloff Fletcher, 2007 and other models

• net outgasing in Southern Ocean 0.6 PgC yrnet outgasing in Southern Ocean 0.6 PgC yr-1 -1 south of 50°Ssouth of 50°S

• near-zero interhemispheric oceanic C transportnear-zero interhemispheric oceanic C transport

Seasonal mean RMSE for ARGO-based pCO2 estimates

ARGO-based

Position+SST+Chl

MLD+SST+Chl

Annual cycle of basinwide RMS-error for remote-sensing and ARGO-based pCO2 estimates

Friedrich, T., and A. Oschlies 2008, Neural-network based estimates of North Atlantic

surface pCO2 from satellite data - a methodological study, submitted

Friedrich, T., and A. Oschlies 2008, How to estimate North Atlantic surface pCO2

from ARGO float data, submitted

Assimilation of pCO2 data into an obgc model: rationale and progress

• The Met Office uses the Forecast Ocean Assimilation Model (FOAM) for its operational ocean forecasts. FOAM assimilates SST (and SSH) data to adjust the T and S fields (and so indirectly also the velocity fields).

• As part of the UK CASIX project, a scheme was developed to assimilate ocean colour data into a simple obgc model (the HadOCC model) embedded in FOAM. As well as altering the plankton, compensating adjustments are made to nutrients, DIC and alkalinity. However this does not affect errors in the background DIC and alkalinity fields.

•, This work aims to adjust those background fields by assimilating pCO2 data from SOO and from surveys (method explained on the next slide).

• Unfortunately, this project has not progressed this year due to personnel being required for development of the operational model (now completed). Work should restart in the new year.

Assimilation of pCO2 data into an obgc model: the scheme

pCO2

Model pCO2

Effect of ocean colour assimilation

Option A: orthogonal to pCO2 isobar

DIC

Alk

alin

ity T

arg

et p

CO

2

Option B: orthogonal to ocean colour

The model pCO2 is adjusted when the ocean colour is assimilated (compensating increments in DIC and Alk).

We will test two options for adjusting towards the target pCO2 (we assume pCO2 data are available but not DIC or Alkalinity).

Option A: the shift is orthogonal to the lines of constant pCO2

Option B: the shift is orthogonal to the adjustment due to ocean colour assimilation.