1. Ideas about Pb NERC Standard Grant Proposal
Target: January 2015 or July 2015
Involved: Tina van de Flierdt, Mark Rehkampfer, Samar Khatiwala, Yves Plancherel
Meeting at Imperial College, UK, 4 Dec 2014

2. Generalities about Pb
Pb concentrations are today dominated by anthropogenic sources
Pb is one of few “global geophysical experiments”:
Similar to CO2, CFC, Bomb 14C
Some advantages of Pb:
One can reconstruct evolution of Pb concentration and isotopic composition in time from analysis of Pb in corals (Kelly et al. 2009). This is not possible for CO2 or CFC.
Would adding analysis of Pb to the “climate change” toolbox become valuable? What could we learn?
Better constraint on models than CO2 as we have time series data available going a long time back, but less spatial coverage.
Source function for Pb is time dependent and space dependent
Strongest source in Northern Hemisphere (industrialized world)
There is a lag in terms of peak discharge due to the phasing out of leaded-fuels happening at different times in different countries
South East Asia is currently one of the largest emitter (Echegoyen et al. 2014, PNAS, Indian Ocean study)

3. Pb cycle Natural Pb + anthropogenic Pb
Isotopes of Pb (total 38 known isotopes):
Stable: Pb204, Pb206, Pb207, Pb208
Pb204 is primordial (not at all radiogenic)
Pb206: primordial + final step of U238 series
Pb207: primordial + final step of U235 series
Pb208: primordial + final step of Th232 series
Analyzing excess Pb204/Pb20X is basis for Pb206-Pb204 vs Pb207-Pb203 dating or Pb206/U238 and Pb207/U235 dating
The Pb206/Pb207/Pb208 content depends on “mineralogy” and different sources of coal/gasoline have different ratios depending on where the coal/gasoline comes from
The burning of coal/gasoline of different 206/207 biases the natural ratio towards the coal/gasoline ratio
Since Pb emissions are tied to industrialization, can an argument be made that knowledge about fate of Pb will help identity polluting countries? Some form of accountability with regards to CO2 remediation (i.e. cap and trade schemes, etc)
Pb isotope reconstruction possible from corals (i.e. Kelly et el 2009)
Pb isotope pioneers: Patterson and coworkers

4. Time series of Pb isotopes in seawater can be inferred from Pb in corals
- From Kelly et al. 2009, using coral from Bermuda. - This is a reconstruction for the North West Atlantic surface water.
- Can the same be done elsewhere? At different depths?
Also: any lag between source/input and record is not clear, this can be looked at in a model
Penetration of Pb in ocean not well understood, also we don’t know the mixture of different 206/207/208 sources

5. Pb cycle Pb-210: natural Pb cycle
Pb210 has shortest half-life of naturally occuring Pb isotopes (22.2 yrs)
Pb210 modeled in ocean by Henderson & Maier-Reimer (2002)
In seawater: U238 – Th230 (scavenged-profile + sediment enrichment) – 226Ra (nutrient-like profile??) – 222Rn (t1/2=3.8d, negligible for transport in ocean) …– 210Pb
In atmosphere: U238 - … - 222Rn (gas escapes from soil, in spite of short half-life)- … – 210Pb
In the ocean, Pb210 profiles are affected by both atmospheric dry+wet deposition and in-situ production from 226Ra.
Interesting quantity: 226Ra/210Pb ratio to establish excess 210Pb or removal relative to in situ secular equilibrium
To model ocean Pb210, one needs:
A model of 226Ra to calculate in-situ decay source
Atmospheric deposition fluxes, this requires a model of Rn222

6. Atmospheric fluxes Rn222 – Pb210 Models:
MOZART; Brasseur et al. (1998)
Jacob et al. (1997)
Anything more recent?
Any possible like with Met Office – this could be useful on the long-term (Be deposition, etc)

7. Data coverage: Pb-210

8. Data coverage: Pb concentration

9. Interesting signals: Zonal North Atlantic section GA03
Subsurface Pb maximum vs CFC shallow max
The Pb maximum is clearly separated from the surface
The CFC maximum is at the surface.
There is a secondary CFC maximum at the same depth as the dominating Pb maximum
The CFC high extends to the bottom on the Western Boundary. The distribution of Pb does not show strong zonal gradients

10. GA03: Compare Pb with CFC11

11. Interesting signals: Meridional Atlantic section GA02
AAIW (GA02): the salinity minimum is not equal to Pb minimum. The Pb minimum is below 1000m, while the salinity minimum is at or above 1000m
Can that be used to study AAIW sources/formation mechanism?
Contribution of mode waters to AAIW formation?
Any link to anthropogenic CO2?
The equatorial particle curtain (GA02):
seems to remove Pb very efficiently, limiting the southward penetration of Pb through the Atlantic
Effect of curtain strong in Pb, can be seen with Nitrate, not clear with DIC
Repeated meridional Pb sections in the North Atlantic that aross the equator needed to study fate of Pb and influence of equatorial curtain.
eMLR-like study of repeated Pb section
Clear and strong re-emergence at 10oN (GA02).
Very different subtropical cell signature than DIC
high DIC vs strong hemispheric asymetry in Pb)

12. GA02: Compare Pb with Salinity

13. GA02: Compare Pb with Temperature

14. GA02: Compare Pb with DIC

15. GA02: Compare Pb with Nitrate

16. GA02: Compare Pb with Oxygen

17. GA02: Compare Pb with Silicate

18. GA02: Compare Pb with Alkalinity

19. Interesting signals: Pb vs other metals
Pb seems to have a unique distribution

20. GA02: Compare Pb with Aluminium

21. GA02: Compare Pb with Cadmium

22. GA02: Compare Pb with Iron

23. GA02: Compare Pb with Manganese

24. GA02: Compare Pb with Nikel

25. GA02: Compare Pb with Zinc

26. Interesting signals: Southern Ocean GIPY4
Pb shows strong minimum, full water column, over ridge, at 55S.
Why is the whole water colum free of Pb when other tracers show stratification?
Can Pb distribution have some memory of open-ocean convection events?
Is that minimum a tracer of old Pacific-type deep water?
Pb concentration increases towards the South/Antarctica
This Pb distribution seems to show a strong “barotropic” circulation component, more than a “ meridional overturning” type distribution
This distribution pattern for Pb in the Southern Ocean seems unique, also relative to other metals (based on the few data available)

27. GIPY4: Compare Pb with Temperature

28. GIPY4: Compare Pb with Salinity

29. GIPY4: Compare Pb with Nitrate

30. GIPY4: Compare Pb with Oxygen

31. GIPY4: Compare Pb with Phosphate

32. GIPY4: Compare Pb with Silicate

33. GIPY4: Compare Pb with DIC (GIPY5)

34. Large spatial gradients, inter-basin differences
The distribution of Pb is quite heterogenous
The southern Ocean looks like nothing else
Neither other metals, hydrographic or biogeochemical tracers
What bout combined (star-like) tracer?
Distribution affected by shape of source function and rate of input vs. ventilation, but also by scavenging sink. This is unique with regards to other “great geophysical experiment” tracers

35. Pb concentration - Atlantic: GA03_e

36. Pb concentration - Indian: GI04

37. U238 decay series – Pb206

38. U235 decay series – Pb 207

39. Th232 decay series – Pb208

40. CFC source function
Laube et al. 2014, Nature Geoscience, Newly detected ozone-depleting substances in the atmosphere