1. National Environmental Research Institute Denmark Temperature sensitivity of organic matter degradation Jørgen Bendtsen National Environmental Research Institute In colaboration with: Torkel Gissel Nielsen Jørgen Hansen Karen Marie Hilligsøe

2. National Environmental Research Institute Denmark Temperature dependence of Organic matter remineralisation A simple model of the water column surface main thermocline A simple model of temperature dependence: Q 10 (T-T0)/T0

3. National Environmental Research Institute Denmark An example of potential temperature regulation of POC remineralisation Using a Q10-factor of 3 and a temperature increase of 2 °C => 25% faster remineralisation. Assuming a POC-flux of: F(z) = F(z=-100m) (z/z0)^(-b), b = -0.858 and assuming a global export of 7.2 Pg C/yr (cf. Martin et al., VERTEX, 1987) This imply that 75% of the POC is remineralised between 100 – 500 m, corresponding to a remineralisation of 5.4 Pg C/yr Increasing this by 25% => a reduced export below 500 m of 1.4 Pg C/yr!

4. National Environmental Research Institute Denmark Potential importance of temperature controlled feedback Feedback Current value (Pg C/yr) New value (Pg C/yr) Change (Pg C/yr) 1.1 1.4 -0.3 5.4 6.8 -1.4 Semilabile DOC- remineralisation z > -100 m POC- remineralisation -100 > z > - 500 m Estimates of current remineralisation rates and future values, assuming 25% faster remineralisation rates Change of export out of surface layer Change of export below 500 m

5. National Environmental Research Institute Denmark Key questions What is the future temperature change? What is the sensitivity of the remineralisation rate to temperature? How is the C/N/P ratio in the organic matter influenced?

6. National Environmental Research Institute Denmark Temperature change in 2100 SST change 2100-1860 Reference: Roeckner et al., Transient climate change simulations with a coupled atmosphere-ocean GCM including the tropospheric sulfur cycle, J. Clim., 12, 3004-3032, 1999. Ocean only climate scenario with MPI-OM1 Forcingfields from previous coupled ocean/atmosphere/sea- ice model (Roeckner et al., 1999)

7. National Environmental Research Institute Denmark Temperature changes 2100 - 1860 Atlantic vertical section Pacific vertical section

8. National Environmental Research Institute Denmark Incubation experiments Method description Water is collected in bottles and stored in incubators in 5 °C intervals Measurements of oxygen by titration or optodes Measurements of nutrients, DIC, ALK, POC/PON, TOC, TN/TP Bacteria, Chl-a

9. National Environmental Research Institute Denmark Location of incubation experiments Bergen, mesocosm TOC-experiment 100 days (bottom water, titration) Kattegat and Belt SEA TOC and POC- experiments 4 weeks (30 m, titration, optodes) Atlantic experiments: TOC-experiments 2 months (30m, optodes) POC-experiments 2 weeks (100-350 m, optodes)

10. National Environmental Research Institute Denmark Mesocosm experiment, Bergen 2005 Oxygen Incubation experiment during 100 days Oxygen (blue: 5 °C; red 15 °C)

11. National Environmental Research Institute Denmark Mesocosm experiment, Bergen 2005 Ammonification and nitrification Incubation experiment during 100 days Dissolved inorganic N (blue: 5 °C; red 15 °C) Nitrite Ammonium Nitrate

12. National Environmental Research Institute Denmark Mesocosm experiment, Bergen 2005 Bacteria, Chl-a Incubation experiment during 100 days Chl-a and bacteria (blue: 5 °C; red 15 °C)

13. National Environmental Research Institute Denmark Temperature control of pelagic respiration in the Kattegat Oxygen consumption during 4 – 5 weeks on 3 stations in Kattegat and the Belt Sea at 30 m depth

14. National Environmental Research Institute Denmark Incubation experiments on the Galathea expedition The Galathea expedition goes “round the globe” in total 39.000 nm Started august 2006 from Copenhagen and returns april 2007 Incubation experiments are done during the whole trip Funded by the Danish Expedition fund and the Danish natural science foundation (FNU) 2 2 4 POC 5 (2) (4) POC (3)

15. National Environmental Research Institute Denmark Incubation experiments of POC z=-100 m z = -200 m z = -300 m z = -400 m POC-incubation

16. National Environmental Research Institute Denmark Incubation experiment on POC POC-incubation from 100 m Station P5-1, september 2006 located south of the Azores Blue: 15 °C Green: 20 °C Red: 25 °C Duration: 16 days

17. National Environmental Research Institute Denmark Preliminary conclusions and ongoing work Incubation experiments show a significant influence from temperature on remineralisation of POC and DOC Analysis of the mesocosm measurements show that data can be explained with two pools of organic matter with different remineralisation rates Overall Q10-factor for the mesocosm experiment is 1.8

18. National Environmental Research Institute Denmark Ongoing and future work Coming TOC and POC-incubation experiments in the Southern Ocean, Pacific and the north Atlantic will be analysed New parameterisations for temperature controlled remineralisation is now made, based on results from the experiments Analysis of temperature changes in a climate change scenario will be combined with the new paramerisations to quantify the impact on the global export of organic matter Derived implications will be analysed – in particular the influence on O 2 and on feedbacks in the surface layer due to reduced export