Ideas about Pb

NERC Standard Grant ProposalTarget: January 2015 or July 2015

Involved: Tina van de Flierdt, Mark Rehkampfer, Samar Khatiwala, Yves Plancherel

Meeting at Imperial College, UK, 4 Dec 2014

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)

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

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

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

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)

Data coverage: Pb-210

Data coverage: Pb concentration

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

GA03: Compare Pb with CFC11

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)

GA02: Compare Pb with Salinity

GA02: Compare Pb with Temperature

GA02: Compare Pb with DIC

GA02: Compare Pb with Nitrate

GA02: Compare Pb with Oxygen

GA02: Compare Pb with Silicate

GA02: Compare Pb with Alkalinity

Interesting signals: Pb vs other metals

• Pb seems to have a unique distribution

GA02: Compare Pb with Aluminium

GA02: Compare Pb with Cadmium

GA02: Compare Pb with Iron

GA02: Compare Pb with Manganese

GA02: Compare Pb with Nikel

GA02: Compare Pb with Zinc

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)

GIPY4: Compare Pb with Temperature

GIPY4: Compare Pb with Salinity

GIPY4: Compare Pb with Nitrate

GIPY4: Compare Pb with Oxygen

GIPY4: Compare Pb with Phosphate

GIPY4: Compare Pb with Silicate

GIPY4: Compare Pb with DIC (GIPY5)

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

Pb concentration - Atlantic: GA03_e

Pb concentration - Indian: GI04

U238 decay series – Pb206

U235 decay series – Pb 207

Th232 decay series – Pb208

CFC source function

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