1. The vulnerable ocean: Decadal changes in the ocean carbon and oxygen cycles Holger Brix 1, Curtis Deutsch 2, Scott C. Doney 3, Arne Koertzinger 4, Doug W. R. Wallace 4, and Rik Wanninkhof 5 Nicolas Gruber Environmental Physics, Institute of Biogeochemistry and Pollutant Dynamics, ETH Zürich, Switzerland (1) IGPP, UCLA, Los Angeles, USA; (2) Univ. of Washington, Seattle, USA; (3) WHOI, Woods Hole, USA; (4) Leibniz Inst. for Marine Sciences, GER; (5) NOAA AOML, Miami, USA.

2. 1955-1998: Rate of 3.3x10 21 J yr -1 = 0.2 W m -2 = 0.1 PW

5. APPARENT OXYGEN UTILIZATION AAIW MED LAB AAIW NADW MED STMW NADW LAB SPMW AOU = [O 2 sat ] - [O 2 ]

6. AOU CHANGES 2003-1993

7. AOU AND DIC CHANGES 2003-1993 Expected change from anthropogenic CO 2: max 0-8  mol/kg

10. IMBER-SOLAS CO 2 /CLIVAR Repeat Hydrography Program status ~2005

11. ARGO: The next generation observing system A global array of profiling floats that measure the temperature and salinity of the upper 2000 m on a ~10 day repeat cycle.

13. How to get oxygen on ARGO floats: Promising oxygen sensors Electrochemical sensor (Seabird SBE 43/IDO) Optode sensor (Aanderaa 3830) Measurement range: 120% of surface saturation Initial accuracy: 2% of saturation Response time: 6 s (e-folding time) Measurement range: 0-120% of surface saturation (0-500 µM) Precision: <1 µM (0.4%) Initial accuracy: 8 µM or 5% (whichever is greater) Response time: 25 s (63% e-folding time) Principle: Life time based dynamic fluorescence quenching Principle: Clark-type polarographic membrane sensor UW floats (S. Riser)

14. Summary & Outlook Oxygen concentrations in the thermocline of the North Atlantic have decreased substantially over the last decade, accompanied by a faster than expected increase in DIC. The records are too short to attribute these changes to anthropogenic climate change or to natural variability. Oxygen is a very sensitive tracer for studying and understanding the response of ocean biogeochemistry to climate variability and global climate change. Most of these changes are likely due to a reduction in the circulation rate of thermocline waters, possibly related to the predominantly positive phase of NAO during the 1990s.

16. The End.

19. Apparent Oxygen Utilization AOU = O 2 sat -O 2 ΔO 2 = ΔO 2 sat - ΔAOU Fundamentals (σ θ ) σ θ 26.8 σ θ 26.4 (σ θ )

20. DIC CHANGES 2003-1993