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Lead Concentrations and Isotopes in Corals and Water near Bermuda, 1780-2000

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Lead Concentrations and Isotopes in Corals and Water near Bermuda, 1780-2000. Amy E. Kelly, Matthew K. Reuer , Nathalie F. Goodkin , Edward A. Boyle (2009) Earth and Planetary Science Letters 283, 93-100. - PowerPoint PPT Presentation

Text of Lead Concentrations and Isotopes in Corals and Water near Bermuda, 1780-2000

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Lead Concentrations and Isotopes in Corals and Water near Bermuda, 1780-2000Amy E. Kelly, Matthew K. Reuer, Nathalie F. Goodkin, Edward A. Boyle (2009) Earth and Planetary Science Letters 283, 93-100

MIT Pb concentration data (Boyle) from US GT NAT-2010 transect compared to MIT data from nearby stations from 1989 and 1999.BackgroundA certain amount of lead (Pb) naturally occurs in the oceansHuman industry has increased the concentration of Pb in the earths oceans since the Industrial Revolution. Sources have different ratios of stable isotope (204Pb, 206Pb, 207Pb, 208Pb). 204Pb is primordial.Back-dating Pb deposits in coral can tell us about historic Pb levels in the oceanThe amount of Pb that corals incorporate into their calcium (Ca) structures is proportional to the Pb concentration in the water where they live. First order removal process!

Fig 1: Location of StudyBermudaCoral atoll (North Rock, 11m; Smiths Bay, 15m)Atlantic Ocean (BATS)Westerly winds carry aerosols with Pb from the US.(some) European Pb aerosols are carried there as well.Residence time in surface SW ~ 2 years

Types of Coral usedDiploria strigosaDiploria labyrinthiformishttp://www.reefcolors.de/Galleries/2006_Varadero/index.html

http://www.dcbiodata.net/explorer/results/detail/52582 Key Questions:What are the pre-anthropogenic Pb concentration and Pb I.R. (isotope ratios) of corals and seawater?How has the anthropogenic Pb component evolved isotopically through time?Fig 2: Pb/Ca ratios in coralraw data: note JSB higher than NR

Range is 4 to 80 nmol Pb/mol CaAverage JSB to 1938 = 5.0 (using Dp = 3.6; [Pb] = 15 pmol kg-1)Partition Coefficients (Dp)

Casw = 10.3 mmol kg-1Controls: thermodynamics and crystal chemistry but also coral species, temperature, growth rateFig 3: Inferred Pb Concentrations from North Rock (best record for North Atlantic)

coal + ore15 to 80 pMLeadedgasolineFig 4: Inferred Pb Concentrations from John Smiths Bay

15% higher than NRLead Isotope Ratios (I.R.s)When the earth was formed, mineral deposits formed with different I.R.s in different places (especially 206Pb/207Pb and 208Pb/206Pb)By looking at the I.R.s present in the Bermudan corals over time, we can infer where the Pb came fromFig 5: 206Pb/207Pb from John Smiths Bay

Ratio of 1.20 similar to NW Atlantic sediments and manganese nodules.Nature lead.EuropeUSUMVFig 6: 206Pb/207Pb from North Rock

Fig 7: 208Pb/207Pb from North Rock

Fig 8: 206Pb/207Pb from Both Sites

UMV208Pb/206Pb vs. 206Pb/207Pb Over Time

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