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

MIT Pb concentration data (Boyle) from US GT NAT-2010 transect compared to MIT data from nearby stations from 1989 and 1999.

Background A certain amount of lead (Pb) naturally occurs in the oceans Human industry has increased the concentration of Pb in the earth’s oceans since the Industrial Revolution. Sources have different ratios of stable isotope ( 204 Pb, 206 Pb, 207 Pb, 208 Pb). 204 Pb is primordial. Back-dating Pb deposits in coral can tell us about historic Pb levels in the ocean The 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 Study Bermuda Coral atoll (North Rock, 11m; Smith’s 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 used Diploria strigosa Diploria labyrinthiformis

2 Key Questions: 1. What are the pre-anthropogenic Pb concentration and Pb I.R. (isotope ratios) of corals and seawater? 2. How has the anthropogenic Pb component evolved isotopically through time?

Fig 2: Pb/Ca ratios in coral raw data: note JSB higher than NR Range is 4 to 80 nmol Pb/mol Ca Average JSB to 1938 = 5.0 (using D p = 3.6; [Pb] = 15 pmol kg -1 )

Partition Coefficients (D p ) Ca sw = 10.3 mmol kg -1 Controls: thermodynamics and crystal chemistry but also coral species, temperature, growth rate

Fig 3: Inferred Pb Concentrations from North Rock (best record for North Atlantic) coal + ore 15 to 80 pM Leaded gasoline

Fig 4: Inferred Pb Concentrations from John Smith’s Bay 15% higher than NR

Lead Isotope Ratios (I.R.s) When the earth was formed, mineral deposits formed with different I.R.s in different places (especially 206 Pb/ 207 Pb and 208 Pb/ 206 Pb) By looking at the I.R.s present in the Bermudan corals over time, we can infer where the Pb came from

Fig 5: 206 Pb/ 207 Pb from John Smith’s Bay Ratio of 1.20 similar to NW Atlantic sediments and manganese nodules. Nature lead. Europe US UMV

Fig 6: 206 Pb/ 207 Pb from North Rock

Fig 7: 208 Pb/ 207 Pb from North Rock

Fig 8: 206 Pb/ 207 Pb from Both Sites UMV

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