The 231 Pa/ 230 Th Paleoproxy: How should we interpret the growing observational dataset?

1. The 231Pa/230Th Paleoproxy: How should we interpret the growing observational dataset? Gideon Henderson Alex Thomas Mark Siddall James Rae Ben Hickey University of Oxford

2. A proxy for past rates of ocean circulation Lynch Stieglitz et al. 2007

3. Oceanic behaviour of U-series nuclides

4. Oceanic behaviour of U-series nuclides

5. Fluxes of 231Pa and 230Th Scavenging of nuclide Downward transport Continued equilibration

6. Fluxes of 231Pa and 230Th

7. Fluxes of 231Pa and 230Th

8. Residence time of waters in North Atlantic Rhien et al. 2001

9. Some real 230Th data South Atlantic Labrador Sea

10. Fluxes of 231Pa and 230Th

11. Fluxes of 231Pa and 230Th

12. 231Pa/230Th in the oceans

13. Glacial NADW formation rates Suggests similar rates of NADW flow in glacial and Holocene Yu et al. 1996

14. Sensitivity of the proxy Marchal 2000

15. Millennial changes in NADW flow McManus et al. 2004

16. So that’s how it’s supposed to work. but… 1. Which depth water-mass is it telling us about? 2. Doesn’t it have a big particle flux effect as well? 3. How about preferential scavenging by opal? 4. Do other things reset Pa/Th except for ventilation? 5. Does it look as though it works in other settings? 6. Do we really understand it?

17. 1. Which depth of water mass? `

18. ` Southern Indian Ocean Thomas et al. 2006

19. ` Indian Ocean seawater profiles 230Th 231Pa 232Th Thomas et al. 2006

20. ` Where does the proxy signal come from? Is sedimentary 231Pa/230Th representative of whole water column?

21. 2. The role of particle flux? Chase et al. 2003

22. 3. Preferential opal scavenging Chase et al. 2003

23. Modelling the behaviour of Pa and Th Distribution coefficients after Luo and Ku (Pa with strong preference for lithogenic particles) Distribution coefficients after Chase et al (Pa with preference for opal, Th for carbonate) Siddall, Henderson, et al. (2005)

24. ` 4. What else resets it?

25. ` Indian Ocean seawater profiles 230Th 231Pa 232Th Thomas et al. 2006

26. ` Southern Indian Ocean

27. ` Benthic d18O Reconstruction of deep inflow to Indian Ocean Down core record from East of Madagascar indicates little or no change in ABW flow into Indian Ocean during full climate cycle (231Pa/230Th)xs Authigenic U Thomas et al. 2007

28. 5. Does it work in other settings? Present day model - 14Sv MOC Siddall et al. 2007

29. Modelling ocean Pa/Th - MOC shutdown Shut down model - 2Sv MOC Siddall et al. 2007

30. Effect of MOC shutdown on Pa/Th Difference between full and shutdown MOC Siddall et al. 2007

31. Effect of MOC shutdown on Pa/Th Difference between full and shutdown MOC Siddall et al. 2007

32. Preliminary data from the Argentine Basin

33. Ice core 18O Benthic 18O McManus Pa/Th Fast New Pa/Th Slow Fe/Ca Sea level Rae et al

34. NADW AIW/NADW AIW And some other cores… Different water masses? Or different sediment composition?

35. Effect of MOC shutdown on Pa/Th Difference between full and shutdown MOC Siddall et al. 2007

36. Preliminary Cape Basin results Difference between full and shutdown MOC Negre et al. 2007

37. Preliminary Cape Basin results Negre et al. 2007

38. Upstream silica scavenging?

39. 6. Do we really understand it? Model of sediment Pa/Th compared to water-columnobservations Siddall, Henderson, et al. (2005)

40. Interpretation of data by 3D modeling Model of sediment Pa/Th compared to sediment observations Siddall, Henderson, et al. (2005)

42. U-Series Geochemistry

43. Don’t get fooled by models