1. Methane related microbial activity in sediments of the Beaufort Sea (Arctic Ocean) Stefan Krause 1, Johanna Schweers 1, Leila Hamdan 2 & Tina Treude 1 1 Leibniz Institute of Marine Sciences (IFM-GEOMAR), Cluster of Excellence: "The Future Ocean", Junior Research Group "Marine Geobiology", Kiel, Germany 2 Naval Research Laboratory (NRL), Washington, USA

2. Methane hydrates Methane clathrate, also called methane hydrate or methane ice. Formation and stability of methane hydrates depend on the temperature-pressure regime. Global amount : +/- 10.000 Gt C Arctic amount: unknown Source: Wikipedia Source: IFM-GEOMAR

3. Sulfate reduction (SR) 2 CH 2 O + SO 4 2-  2 HCO 3 - + H 2 S Methanogenesis (MG) 4 H 2 + CO 2  CH 4 + 2 H 2 O 4 CH 3 COOH  CH 4 + 3 CO 2 + 2 H 2 O AOM and SR within the methane-sulfate transition zone CH 4 + SO 4 2-  HCO 3 - + HS - + H 2 O Kattegat and Skagerrak sediments (Denmark), (Iversen & Jørgensen 1985) Sulfate reduction, methanogenesis and methane oxidation in organic-rich, diffusive sediments

4. Microbial and biogeochemical reactions at methane seeps Microbial methane filter in marine systems water column oxygenated sediment reduced sediment Anaerobic oxidation of methane (AOM) CH 4 + SO 4 2-  HCO 3 - + HS - + H 2 O SO 4 2- H2SH2S Sulfide oxidation H 2 S + 2O 2  SO 4 2- + 2 H + 5H 2 S + 8NO 3 -  5SO 4 2- + 4N 2 + 4H 2 O + 2H + Aerobic oxidation of methane CH 4 + 2O 2  CO 2 + 2H 2 O atmosphere NO 3 - O2O2 CH 4 hydrate CH 4 CaCO 3

5. Influence of temperature increase on microbial activity Microbial methane filter in marine systems GroupRangeOptimum Psychrophiles -10 – 20°C10 – 15°C Mesophiles10 – 50°C25 – 38°C Thermophiles40 – 70°C55 – 65°C Hyperthermophiles 65 – 110°C85 – 100°C Source: www.bmb.leeds.ac.uk/.../temperature.jpg

6. Field study Barrow Survey: Three Transects (20 to 2000 m) Piston corer + Multicorer Source: Google Earth Source: J. Greinert PC12 PC13

7. Central Questions Objectives of the cruise: What controls methane emissions to the atmosphere? How will degradation and emission rates vary in response to climate change? Our Tasks: Characterization of methane related microbiological and biogeochemical processes in sediments of the Beaufort Sea (Arctic Ocean) Response of microbial methanogenesis on temperature increases

8. Characterization of methane related microbiological and biogeochemical processes in sediments of the Beaufort Sea (Arctic Ocean) Results

9. sediment depth (cmbsf) Piston Core 12, water depth 342 m SR Zone AOM Zone MG Zone SR – Sulfate reduction AOM – Anaerobic oxidation of methane MG- Methanogenesis

10. sediment depth (cmbsf) Results In vitro Methanogenesis SR Zone MG Zone AOM Zone

11. sediment depth (cmbsf) Results In vitro Methanogenesis SR Zone AOM Zone MG Zone

12. Methanogenesis and sulfate reduction Methanogenesis (MG) 4 H 2 + CO 2  CH 4 + 2 H 2 O Reverse methanogenesis (AOM) CH 4 + 3 H 2 O  HCO 3 - + H + + 4 H 2 Anaerobic oxidation of methane (AOM) with sulfate reduction (SR) CH 4 + SO 4 2-  HCO 3 - + HS - + H 2 O Molybdate (Mo) – inhibitor of sulfate reduction 2-bromoethanesulfonate (BES) - inhibitor of MG and AOM

13. Incubation in methanogen medium [SO 4 2- ]: 500 µM [CH 4 ]: saturated (~1.3 mM) Temperature: 13°C sediment depth (cmbsf) Results Sulfate reduction activity in sediments from the methanogenic zone – inhibition experiments with molybdate SR Zone AOM Zone MG Zone

14. sediment depth (cmbsf) Results Incubation in methanogen medium [SO 4 2- ]: 500 µM [CH 4 ]: saturated (~1.3 mM) Temperature: 13°C Sulfate reduction activity in sediments from the methanogenic zone – inhibition experiments with molybdate SR Zone AOM Zone MG Zone

15. sediment depth (cmbsf) Results SR Zone MG Zone AOM Zone AOM activity in sediments from the methanogenic zone – inhibition experiments with molybdate Incubation in methanogen medium [SO 4 2- ]: 500 µM [CH 4 ]: saturated (~1.3 mM) Temperature: 13°C

16. sediment depth (cmbsf) Results SR Zone AOM Zone MG Zone AOM activity in sediments from the methanogenic zone – inhibition experiments with molybdate Incubation in methanogen medium [SO 4 2- ]: 500 µM [CH 4 ]: saturated (~1.3 mM) Temperature: 13°C

17. sediment depth (cmbsf) Results SR Zone MG Zone AOM Zone Sulfate reduction activity in sediments from the methanogenic Zone – inhibition experiments with BES (methanogen/AOM inhibitor) Incubation in methanogen medium [SO 4 2- ]: 500 µM [CH 4 ]: saturated (~1.3 mM) Temperature: 13°C

18. sediment depth (cmbsf) Results SR Zone AOM Zone MG Zone Incubation in methanogen medium [SO 4 2- ]: 500 µM [CH 4 ]: saturated (~1.3 mM) Temperature: 13°C Sulfate reduction activity in sediments from the methanogenic Zone – inhibition experiments with BES (methanogen/AOM inhibitor)

19. Active sulfate reduction in the MG-zone Where does the sulfate come from? Possible explanation: Barite Results BaSO 4 Ba 2+ + SO 4 2-

20. Barium First indications of barite/AOM coupling from Benguela Upwelling Region: Riedinger et al. 2006, EPSL, 241 BaSO 4  Ba 2+ + SO 4 2-

21. Average seawater concentration of Ba in Arctic Ocean (shelf regions): 20-170 nM (Guay & Falkner 1996) Piston Core 12, water depth 342 m Results sediment depth (cmbsf)

22. Piston Core 13, water depth 280 m Results

23. Response of microbial methanogenesis on temperature increases Results

24. In vitro methanogenesis rates

25. Results In vitro methanogenesis rates

26. Results In vitro methanogenesis rates

27. Conclusions We confirmed the activity of AOM in Arctic methane-rich sediments. The process will most likely play a key role in controlling methane fluxes from the seafloor into the water column in Global Warming scenarios. Barite may represent an additional sulfate source in Arctic sediments (or generally below productive water columns) enabling SR (and possibly AOM) in the predominantly methanogenic zone, i.e., below the penetration depth of seawater sulfate. Methanogenesis generally increased with temperature rise revealing a physiology behaviour (optimum around 25°C). In case of a temperature increase of 1-2°C we expect an increase in methane production of 50-120% in sediment types sampled here.

28. Beaufort Sea Expedition: On-board sampling: Rick Coffin (NRL, US) Scientific Party Crew of USCGC Polar Sea Microbial turnover rates (lab of Tina Treude): Geochemical analyzes: Geochemical Lab Hamdan/Coffin (NRL, US) Regina Suhrberg (IFM-GEOMAR) Funding of Tina Treude‘s research group was provided by: German Research Foundation (DFG) via the Cluster of Excellence "The Future Ocean" Acknowledgements:

29. Thank you for your attention