Arne Körtzinger IFM-GEOMAR Leibniz Institute of Marine Sciences Marine Biogeochemistry

1. Biogeochemical Observations from Profiling Floats — The Oxygen Success Story and More to Come… Arne Körtzinger IFM-GEOMAR Leibniz Institute of Marine Sciences Marine Biogeochemistry Kiel, Germany with contributions from: - Stephen C. Riser, Univ. of Washington, Seattle/USA - Denis Gilbert, Maurice-Lamontagne Institute, Mont-Joli, Québec/Canada Special thanks for letting me “piggy-back” to the German ARGO project to: - Jürgen Fischer et al., IFM-GEOMAR, Kiel /Germany - Olaf Boebel et al., AWI, Bremerhaven/Germany

2. Joos, F., G.-K. Plattner, T.F. Stocker, A. Körtzinger, and D.W.R. Wallace (2003). EOS84(21), 197-204. Joos et al., 2003

3. Oxygen Trends: What the observations tell... AOU increase: ~0.9 ± 0.5 µmol kg-1 yr-1 AOU increase: up to +5 µmol kg-1 yr-1 Ono et al., GRL28, 2001. Watanabe et al., GRL28, 2001. Time series of AOU on isopycnals 26.7, 26.8, 26.9, 27.0, and 27.2 (bottom to top) in the western subarctic Pacific (1968-1998). Annual averaged increase rate of AOU (µmol kg-1 yr-1) during the period 1985 to 1999 along 165°E (left) and 47°N (right) lines in the North Pacific.

4. Oxygen Trends: What the observations tell... ~25 µmol L-1 Kim et al., MTS Journal, 33, 2001.

5. Oxygen Trends: What the models tell... Bopp et al., GBC, . Matear et al., G3, 1, 2000. Matear et al., G3, 1, 2000.

6. Der “Mirror Image Approach“ – a flawless method to track anthropogenic CO2? the devil is in the detail.... -1.3 -1.1 Separation of terrestrial and oceanic sinks for anthropogenic CO2

7. Oxygen – a powerful biogeochemical switch in the ocean N2 N:P:Fe PFG N:P NH4+ + NO2- N2 + 2 H2O N NO3- NO2- N2O  N2 P,Fe OMZ Elemental ratios “Anammox“ Denitrification Denitrification Iron oxide reduction IFM-GEOMAR, Kiel: Proposal for large 12-year-project on control & consequences of Oxygen Minimum Zones

8. How to get oxygen on ARGO floats: Promising oxygen sensors Electrochemical sensor (Seabird SBE 43/IDO) Optode sensor (Aanderaa 3830) Principle: Clark-type polarographic membrane sensor Principle: Life time based dynamic fluorescence quenching 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) Measurement range: 120% of surface saturation Initial accuracy: 2% of saturation Response time: 6 s (e-folding time) UW floats (S. Riser)

9. The Kiel oxygen float project (since 2002)

10. The Labrador Sea pilot study: The ocean‘s breathing quasi-stationary float Körtzinger et al. (2004). The ocean takes a deep breath. Science306, 1337.

11. The Labrador Sea pilot study: The ocean‘s breathing Deep O2 inventory sealed off by low-salinity cap O2 inventory builds up with progressing convection Peak convection Decay of O2 inventory by lateral export and respiration quasi-stationary float

12. Seasonal cycle of surface oxygen saturation in the Labrador Sea Spring bloom Warming + photosynthesis Cooling + gas exchange Cooling + mixed layer deep. Peak convection

13. An example from our Weddell Sea oxygen float study 68°S, 0°W O2 disequilibrium Progressive cooling  freezing APEX float with ice detection alogorithm, O2 option (optode), and RAFOS option

14. An example from our Weddell Sea oxygen float study 62°S, 40°W Increasing O2 saturation Progressive warming APEX float with ice detection alogorithm, O2 option (optode), and RAFOS option

15. Sensor-to-sensor agreement / Accuracy of sensor batch (optode) Accuracy: Both sensors off by 17.5 ± 2.5 µmol/L Both sensors in good agreement DO2 = 1.6 µmol/L (p > 800 dbar) Körtzinger et al. (2005). J. Atm. Ocean. Techn. 22, 302-308.

16. Drift check / Long-term stability Körtzinger et al. (2005). High-quality oxygen measurements from profiling floats: A promising new technique. J. Atm. Ocean. Techn.22, 302-308. Drift check possible through air measurements O2 = 295.0 ± 0.7 µmol/L High long-term stability Tengberg et al. (2006). Evaluation of a life time based optode to measure oxygen in aquatic systems. Limnol. Oceanogr. Methods4, 7-17.

17. Results from the Canadian Oxygen Float Project (optode sensors) See poster: Denis Gilbert, Howard Freeland, Anh Tran: Canadian oxygen measurements on Argo floats High long-term stability

18. Results from the Univ. of Washington Oxygen Float Project (optode + SBE sensors) Near-surface and 1990 m time series of dissolved O2 from UW 894 float (SBE-43) near Hawaii Note the absence of any large, systematic sensor drift. See poster: Stephen C. Riser: Long-term measurements of dissolved oxygen from Argo floats The difference between O2 a measured by SBE and Optode sensors.

19. Summary, Conclusions & Outlook 2 ROLE OF OXYGEN MEASUREMENTS IN MODERN HYDROGRAPHY • Oxygen is the oldest chemical parameter in oceanography and is currently seeing a major renaissance. • Oxygen is a sensitive indicator of global change (physics & biology) in the ocean. • Oxygen is an important switch of the marine biogeochemical system. STATUS OF OXYGEN SENSORS • Float-capable oxygen sensors are now readily available (SBE 43 & Aanderaa 3830). • The SBE 43 polarographic sensor shows some tendency to drift over time. • The Aanderaa optode sensor shows no apparent drift. • The initial accuracy is an issue for improvement, especially for the optode. • The optode still has significant potential for improvement (current work: shorter response time, better temperature measurement, better optical filters, better Digital Signal Processor, individual-sensor-calibration for better accuracy) FUTURE OF OXYGEN WITHIN ARGO • “Friends of Oxygen” will write “White Paper” to make a pitch for augmentation of the ARGO project with an oxygen component. • An ARGO-O2 project might become a major component of an international carbon assessment strategy.