Core Theme 1: surface fluxes

1. Core Theme 1: surface fluxes • WP 4: The North Atlantic observing system • WP5: The Southern Ocean • WP6: modelling and synthesis • (WP7: mooring development; discontinued)

2. WP4: North Atlantic observing system Ongoing data collection and synthesis of fluxes

3. Data coverage in two-month intervals, 2005 Jan-Feb Mar-Apr May-Jun Jul-Aug Sep-Oct Nov-Dec

4. Constructing basin-wide fluxes • For each pCO2 measurement, assign SST, mixed layer depth, (chlorophyll, position) • Find pCO2 as a function of these variables using • multiple linear regression • Neural network • Interpolate to generate a pCO2 map for the whole area • Calculate fluxes

5. Distance (degrees lat) to Nearest data point Jan-Feb Sep-Oct

6. Jan Feb Mar Apr Jan Jan Jun Aug Jul May Nov Dec Sep Oct MLR estimates of pCO2 field for each month using independent variables SST, MLD and longitude, in 20° latitude bands

7. 0.06 0.04 Flux (Gt/ yr) 0.02 0 50 to 65 N -0.02 30 to 40 N JFM 10 to 20 N AMJ JAS OND 2005 fluxes by season and latitude band

8. CO2 fluxes into the North Atlantic – 1994/5 to 2005 (Wanninkhof 1992 gas exchange) Takahashi 1995 climatology Carbo-ocean 2005 Cavassoo – era (approx)

9. What is the uncertainty on pCO2sw? • Calculate semi-variograms of the residuals from the multiple linear regressions • Where • r are the residuals from the model • N(h) is the set of pairs of observations i, j, that are a separated by a distance h.

10. Uncertainty continued… Decorrelation length scale Variance of decorrelated data pCO2 variance (μatm2) Separation (Degrees of latitude)

11. Uncertainty continued…. • The number of degrees of freedom in the estimation problem is n ~A/x2 where A is the area of the North Atlantic and x is the decorrelation length obtained from the semi-variograms. • An upper limit on the variance, σ2,of pCO2 about the regressions is given by the sill (amplitude) of the variograms. • The 1-σ uncertainties on mean pCO2 for the region as a whole is given by = ~0.8 μatm using the summer variogram, or 1.5 μatm using the winter variogram. These represent ~6% or ~10% errors on ΔpCO2 (air-sea difference). • A more careful calculation gives overall 1-σ uncertainty of 6% on fluxes from this source.

12. N.Atlantic air-sea fluxes with unprecedented accuracy and resolution • We obtain pCO2 for the entire region (10°-65°N) by relating CO2 to SST, mixed layer depth, using regressions and/or neural nets • Fluxes are derived with ~10° spatial resolution and seasonal-to-monthly time resolution. • The precision is 6% (1-σ) for the NA annual flux – (calculated using geostats theory or data gap analysis) -- much better than for any other comparable region in the world. • In combination with atmospheric inversions should enable greatly improved estimates for adjacent land sinks.

13. WP5: Southern Ocean air-sea CO2 fluxes: From Weddel sea to open ocean areas N. Metzl, OISO10, Jan 2003

14. CARIOCA measurements • Synthesis of 65 months of CARIOCA measurements: • - SAZ strong sink (-0.8PgC yr-1) contrary to PZ (-0.1PgC yr-1) • Seasonal variation of DIC in SAZ (~30mmol kg-1) • North-South increase of DIC and fCO2 in winter between Subtropical front and Subantarctic front Boutin et al, submitted, 2007

15. Ocean pCO2 trend between 1991 and 2007 Trend atmosphere: + 1.72 µatm/yr Trend ocean: + 2.11 µatm/yr Ocean sink decreases ? Atm. trend Summer Winter (Metzl, 2007 sub.)

16. 0°W 20°E 24 December 2002 Rapid transition from ice covered CO2–rich waters to a biologically mediated sink in the eastern Weddell Gyre Ridge Ice Cover (blue=open water) (December 2002-January 2003) Antarctic ice shelf AWB (Bakker and Hoppema, in prep.)

17. Neural nets: Poster, Maciek Telszewski and colleagues

20. IFM-GEOMAR

21. CO2 Gas Exchange Rates fromInversion of Water Column Data R. Schlitzer, J. Schneider, Alfred Wegener Institute, Bremerhaven 1. Pre-industrial, annual mean CO2 Fluxes • Approach: • Use tracer calibrated model (CFC, radiocarbon, etc.; Schlitzer, 2007) • Determine CO2 fluxes by fitting to ocean interior DIC data • Results: • Outgasing in tropics, ingassing in subtropics. As in Takahashi (1999) and other studies. • Net outgasing in Southern Ocean (not seen in Takahashi, 1999 or OCMIP II models): 0.6 PgC yr-1 south of 50°S. • Near-zero pre-industrial interhemispheric C transport by ocean. Takahashi 1999 2. Seasonal CO2 Fluxes Investigation of the effect of varying strength and timing of biological production on monthly CO2 fluxes See poster of Judit Schneider.

22. Assimilation of pCO2 data into an obgc model: progress • Assimilation of pCO2 surface data into Met office FOAM model using Hadley centre OBGCM is ongoing. • Operational system assimilates SST, SSH, ARGO… • Assimilation of ocean colour with biogeochemical code • Additional nudge of DIC/ALK using ocean pCO2 data. • The system in testing phase but work delayed by other priorities in 2007. It is planned to re-start the work in the first few months of 2008.

23. Surface fluxes: progress • High precision estimates of North Atlantic flux. • Progress in characterizing the Southern Ocean using measurements and models: observations of a decreasing flux? • New techniques for constraining fluxes: neural nets, ocean inversions • Progress in assimilating carbon measurements into ocean biogeochemical models.