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

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 earth’s 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 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

http://www.reefcolors.de/Galleries/2006_Varadero/index.html

http://www.dcbiodata.net/explorer/results/detail/5258

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 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-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 + ore15 to 80 pM

Leadedgasoline

Fig 4: Inferred Pb Concentrations from John

Smith’s Bay15% 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 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 from

Fig 5: 206Pb/207Pb from John Smith’s Bay

Ratio of 1.20 similar to NW Atlantic sediments and manganese nodules.Nature lead.

Europe

US

UMV

Fig 6: 206Pb/207Pb from North Rock

Fig 7: 208Pb/207Pb from North Rock

Fig 8: 206Pb/207Pb from Both SitesUMV

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