1. Climate Change Forcing of Intense Oceanic O 2 Minimum Zones n Existence dependent on interplay of ocean physics and biogeochemistry - focus on ETP n Paleo-evidence for climate forcing on Ma to decadal scales n Prospects for model simulation and experimentation

2. Modern Open-Ocean Suboxic zones High surface productivity and downward OM flux Poor subsurface water mass ventilation -closed regional circulation (shadow zone) -remote surface (outcrop) ventilation zone A B C DEF

3. 3 Lothar Stramma, et al. Science 320, 655 (2008); DOI: 10.1126/science.1153847

4. 4 Hydrography Along P18

5. Contours are CFC-12 ages SAMW & AAIW Ventilation Remote Subpolar Ventilation NPIW Ventilation

6. Contours are CFC-12 ages Property Relationships along σ θ 26.3 to 26.5 Slope ~ 8 Slope ~ 1.3

7. Locations of Paleo-records ODP 1012

8. 8 Important Locations for Denitrification

9. 100 kyr 40 kyr Pliocene ‘hothouse’

10. ENSO, Walker Circulation, and Eq. Pacific Thermocline Structure Cool, Nut rich, low O2 Warm, Nut poor, high O2

11. Consistent with shoaling thermocline theory?

12. Eastern Pacific Productivity Productivity max ~3-1.5 Ma (Cortese et al., 2004);

13. Peru ETNP Arabian Sea Regional comparison last glacial cycle

14. Relationship to southern polar climate

15. Late Holocene Variations Linked to Productivity?

16. 16 GCM’s can simulate the major low O 2 zones, but are too coarse for getting the detailed circulation right!

17. 17

18. 18

19. 19 A 50-year modern simulation using the Pacific ROMS-CoSine

20. 20 Comparison at the P18 Section

21. 21 Simulated variability over the last 60 years

22. Summary n Oceanic low O 2 zones are sensitive to climate forcing on a large range on time scales including those relevant to future global warming n Forcing may be through either remote subpolar ventilation and/or regional productivity depending on time scale and nature of forcing n Feedbacks through ocean biogeochemistry likely as well as impacts on regional living marine resources n Advances are needed in understanding the interplay of hydrography, ventilation, and productivity n Numerical models will be an important experimental approach given resolution of key circulation features

23. Last 1.5 Myr; denitrification (suboxia) variability strongly correlated with orbital-scale climate oscillation and transition from 40 kyr to 100 kyr dominance. Obliquity signal (40 kyr) also consistent with polar forcing. Wavelet Analysis

24. 24 NO 3 - ➡ NO 2 - ➡ N 2

25. Locations of denitrification records ODP 1012

26. 26

27. Preservation of  15 N Signal in Marine Sediments 0 1 2 3 4 5 6 7 8 9 10 11 12 0123456789101112 Black Sea+ Cariaco Basin Gulf of California San Pedro Basin Monterey Bay Arabian Sea 1:1 line Framhaven Fjord+ Peru Margin  15 N Surface Sediment (‰)  15 N Sub-euphotic zone NO 3 - Oceanic Average Sedimentary diagenesis Northern N. Atlantic Bermuda

29. 29 Hydrography of σ θ = 26.5

30. Composite Denitrification Record