2. Measuring and monitoring ocean CO 2 sources and sinks Andrew Watson

3. - 180 -120 -60 0 60 120 180 90 30 -30 -90 Discrimination of sources/sinks between latitude bands is relatively easy Localising sinks in the same latitude bands is subject to wide error. Difficult to up-scale measurements of local terrestrial sinks to the continental scale. Ocean sinks are easier to constrain over large regions. Atmospheric Inversion calculations of CO 2 sources and sinks

4. How well is the global ocean sink known? Estimates of the global ocean sink 1990-1999 ReferenceSink (GtC yr -1 ) IPCC (2001) 1.7+/- 0.5 Estimate (O2/N2 ratio) OCMIP-2 Model 2.5+/- 0.4 Intercomparison (ten ocean carbon models).

5. Where does the land flux end and the ocean flux begin? Pre-industrially, a “riverine” flux of ~0.7Gt Ca -1 ran in a circuit from land to ocean to atmosphere and back to land. Today it may be larger. This flux shows up as a net land sink and ocean source, yet it is not a response to global change. Its distribution (both the land and ocean component) is very poorly known).

6. Specifying land and ocean sinks: which is easier?

7. The spatial scale of variation of CO 2 fluxes in the ocean is much larger Than the equivalent on the land surface. Land ~ 100m, Ocean > 10km

8. Direct measurement by air-side techniques –Very challenging, under development Surface pCO 2 + gas transfer equation –Need lots of data, better parameterization of gas transfer Remote sensing extension of pCO 2, gas transfer –(CASIX; eventually, direct sensing of CO 2 ) Basin-wide, full depth sections and “anthropogenic carbon” budgets. –Integrated with physical oceanography and modelling programmes –Links to global carbon observing system, Carbo-ocean. Methods for measuring ocean fluxes

9. Current state of the art: the Takahashi et al. climatology for CO 2 fluxes Data collected over > two decades, “collapsed” onto a seasonal climatology Critical assumptions used to combine the data are open to question. Equatorward of 50º, seawater pCO 2 tracks atmosphere? Poleward of 50º, no change in sea surface pCO 2 ? In fact, we expect fluxes to change with time, on seasonal, interannual and decadal time scales.

10. Remote sensing of SST, Ocean colour to enable Interpolation/ extrapolation of surface CO2 observations Approach adopted by CASIX Currently in its infancy Interesting results soon!

11. Budgeting a basin for regional, decadal uptake Measure: transport across a section or sections content of anthropogenic carbon at two different times. Then: Net air-sea exchange + net convergence into basin = Rate of change of content. Air-sea exchange Carbon transport Through section

12. Empirical Anthropogenic CO 2 Removal of large metabolic DIC and pre-industrial solubility signals -steady state assumption-O 2 surface saturation -uniform Redfield ratios-seasonal sampling bias -analogy of CFC and C anthro Sarmiento and Gruber (2002)

13. 80W 60W 40W 20W 0 E 60S 40S 20S 0 N 40N 60N AR7W (CAN) A16 (US, 2009) A13S (US, 2009) OVIDE (ES/FR, 2004) A22 (US, 2004) AMT Drake Passage repeat 24N A02 (GE, 2004) SOC, proposed 36N Extended Ellett Line 20W Programme is necessarily international, long-term. Overall umbrella: IOC ocean carbon co- ordination project. Links to: European programmes (Carbo-ocean) US & Canadian programmes

14. Carbo-Ocean – proposed European FP VI integrated project. Observing system in the Atlantic (ships of opportunity, buoys, moorings. Full-depth hydrographic programme to implement basin-budgeting. Project targeted at Southern Ocean Extensive modelling, data assimilation to provide up-to-date estimates of how sink is changing on a seasonal, inter-annual basis. ~50 EU project partners, ~10 US partners.

15. Existing and planned regular Atlantic observations

16. Existing and planned regular global observations

17. Possible effects on marine carbon uptake, next 100 years. Increased stratification, decrease in MOC, convection Iron fertilisation -- deliberate or inadvertent NO 3 fertilisation pH change mediates against calcite- precipitating organisms Reduction in MOC offset by increased efficiency of nutrient utilisation Other unforeseen ecosystem changes ProcessEffect on CO 2 uptake ?

18. Suggested marine carbon themes in a UK carbon programme Integrated with international programmes; Carbo-Ocean, US carbon cycle plan, International Ocean Carbon Co-ordination project… Integrated with terrestrial and atmospheric studies Clear aims: –Reduce (perhaps by a factor of two) current uncertainty on N. Atlantic sink –Detect change in C ant –Detect change (or lack of it) in biological pump –Detect change (or lack of it) in physical transports. –Use models and theory to understand the underlying processes.