Spatial and temporal evolution of lead isotope ratios in the North …boyle.mit.edu/~ed/PDFs/Weiss(2003)JGR.pdf · 2003-12-23 · Spatial and temporal evolution of lead isotope ratios

Spatial and temporal evolution of lead isotope ratios in the North

Atlantic Ocean between 1981 and 1989

Dominik Weiss,1,2 Edward A. Boyle, Jingfeng Wu,3 Valerie Chavagnac,4 Anna Michel,

and Matthew K. Reuer5

Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA

Received 11 December 2000; revised 20 May 2003; accepted 30 June 2003; published 2 October 2003.

[1] Lead concentrations and isotope ratios were measured in North Atlantic surfacewater samples collected in 1981 (29�–79�N, 6�E–49�W) and in 1989 (23�–39�N,29�–68�W). In the early 1980s, 206Pb/207Pb ratios in the North African Basinaveraged 1.193 ± 0.005 (1 s). Similar radiogenic ratios within the level of analyticalprecision (average 0.29%) were found in the Labrador and Iceland Basins (1.198 ±0.006) and in the Norwegian Sea (1.196 ± 0.008). These radiogenic mixed layersignatures along with atmospheric global lead emission patterns suggest that mostNorth Atlantic lead in the early 1980s was derived from North American leadedgasoline. Samples in the East Iberian Basin near Portugal and France showed lower206Pb/207Pb ratios, between 1.167 and 1.182, indicating a significant influence ofless radiogenic atmospheric lead transported from Europe and possibly the influenceof the Rio Tinto acid mine drainage very close to shore in the Gulf of Cadiz. [Pb]across the entire North Atlantic Basin ranged between 54 and 145 pmol/kg, with thelowest values (54–74 pmol/kg) found at high latitudes (>65�N). In the late 1980s,surface waters in the western subtropical North Atlantic (North American Basin/Sargasso Sea, >47�W) and in the eastern subtropical North Atlantic (North AfricanBasin/Central Iberian Basin, <45�W) showed very similar 206Pb/207Pb signatures withlittle zonal variation, ranging from 1.177 to 1.192. Lead concentrations rangedbetween 47 and 137 pmol/kg, increasing slightly from west to east. South of 25�N inthe equatorial North Atlantic, crossing the subtropical/tropical surface water boundary,the 206Pb/207Pb seawater signatures were significantly less radiogenic (1.170–1.175)and concentrations were lower (�51 pmol/kg). This difference suggests a relativeincrease in the atmospheric lead supply from the western Mediterranean/North Africancontinent via Trade Easterlies and illustrates the effective barrier between thesubtropical/tropical surface water exchanges. Triple-isotope plots (206Pb, 207Pb, and208Pb) suggest that most of the lead can be accounted for by wet aerosol depositionderived from the adjacent landmasses of America to the west (transported via theNorth American Westerlies) and from Europe to the east (transported via the EuropeanEasterlies) and probably by some advected surface waters from the Sargasso Sea. The1989 triple-isotope plot suggests, however, a third lead source in the subtropicalwestern North Atlantic, possibly leaded gasoline from Mexico. Gasoline lead emissionpatterns as well as atmospheric lead isotope signatures confirm that gasoline was themain pollutant source in the early 1980s but suggest that contributions from high-temperature industrial processes (coal combustion, steel manufacture, wasteincineration) have been increasing in the late 1980s. From isotopic mass balanceestimates, lead inputs to the 1980s North Atlantic were dominated by North Americansources (>53%). These elemental and isotopic results demonstrate the strongly variableisotopic and elemental signatures of North American and European lead throughoutthe North Atlantic Ocean, frequently dominated by high 206Pb/207Pb and [Pb] North

3Now at International Arctic Research Center/Frontier, University ofAlaska at Fairbanks, Fairbanks, Alaska, USA.

4Now at Southampton Oceanographic Center, University of South-ampton, Southampton, UK.

5Now at Department of Geosciences, Princeton University, Princeton,New Jersey, USA.

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 108, NO. C10, 3306, doi:10.1029/2000JC000762, 2003

1Now at Department of Earth Science and Engineering, ImperialCollege, London, UK.

2Also at Department of Mineralogy, Natural History Museum, London,UK.

Copyright 2003 by the American Geophysical Union.0148-0227/03/2000JC000762$09.00

4 - 1

American signatures throughout the subtropical North Atlantic gyre. INDEX TERMS: 4504

Oceanography: Physical: Air/sea interactions (0312); 4808 Oceanography: Biological and Chemical: Chemical

tracers; 4857 Oceanography: Biological and Chemical: Pollution; 4875 Oceanography: Biological and

Chemical: Trace elements; KEYWORDS: surface circulation, North Atlantic, Pb isotopes and concentrations,

atmospheric deposition, pollution

Citation: Weiss, D., E. A. Boyle, J. Wu, V. Chavagnac, A. Michel, and M. K. Reuer, Spatial and temporal evolution of lead isotope

ratios in the North Atlantic Ocean between 1981 and 1989, J. Geophys. Res., 108(C10), 3306, doi:10.1029/2000JC000762, 2003.

1. Introduction

[2] Anthropogenic inputs have significantly altered thebiogeochemical cycle of lead in the North Atlantic Ocean,and during the 1980s, more than 95% of lead encountered inthe surface mixed layer derived from industrial or automo-tive contamination via atmospheric deposition [Hamelin etal., 1997; Schaule and Patterson, 1983; Shen and Boyle,1987, 1988b; Veron et al., 1994]. The distribution of marinelead therefore reflects anthropogenic lead emissions to theatmosphere and its transient input to distinct water masses.During the 1970s and early 1980s, the largest single sourceof lead to the Northern Hemisphere atmosphere derivedfrom the utilization of leaded gasoline (Figure 1). Emissionsfrom the United States peaked in 1972 and have subse-quently declined, a consequence of environmental initia-tives on stricter emissions control [Wu and Boyle, 1997a].The European Community (EC) began to eliminate leadedgasoline in the mid-1980s. Monitoring of surface watersnear Bermuda and the western North Atlantic showed athreefold decline in lead concentrations from 1971 to 1987,with continuing but notably slower decline in the 1990s[Shen and Boyle, 1988b; Wu and Boyle, 1997a]. A similardecrease in lead concentrations has been detected in theMediterranean [Alleman et al., 2000; Nicolas et al., 1994].[3] Trace metals, such as lead, with atmospheric sources

and surface ocean residence times of less than a few yearsshow substantial spatial and temporal variability in thesurface mixed layer and upper thermocline due to seasonalcycles, storm, or eddy events and the changing strength ofsource emissions [Boyle et al., 1986, 1994]. This variabilitycan significantly obscure long-term trends, supported bysurface water [Pb] and [210Pb] measurements near Bermuda[Boyle et al., 1986, 1994; Veron et al., 1993]. Consequently,discrete concentration measurements at a site do not neces-sarily reflect the lead emission pattern and the varyingcontributions from different sources. While repeated obser-vations at a site over many years can overcome this noiseproblem, and sufficient spatial coverage can average out theatmospheric noise during a single period, concentrationmeasurements alone remain sparse [Boyle et al., 1994].[4] The isotopic Pb composition of a discrete sample

reflects the weighted mean of each anthropogenic source(e.g., North America, Africa, or Europe). The individualsource composition, however, reflects the relative contribu-tion of distinct anthropogenic processes emitting lead ofvariable isotopic composition (lead smelting, leaded gaso-line consumption, coal combustion). These are not affectedor altered by low-temperature environmental and biologicalprocesses after their release [Reuer and Weiss, 2002].[5] A comprehensive map of lead isotopic compositions

of aerosols collected on a hemispheric scale showed thepotential of Pb isotopes to discriminate between different

sources on a wider scale [Bollhoefer and Rosman, 2001].The isotopic composition of some regions may overlap withothers, but some are unique and the ratios span a widerange. For example, during the 1990s, the least radiogeniccompositions were found in France and Spain (206Pb/207Pbbetween 1.097 and 1.142) and the most radiogenic in theUnited States (206Pb/207Pb between 1.173 and 1.231). Withrespect to North Atlantic surface waters, the presence ofAmerican lead has been detected over the entire north andcentral North Atlantic [Veron et al., 1994] and the subtrop-ical northeastern Atlantic [Hamelin et al., 1997]. In tworecent contributions, lead isotopes were further applied toelucidate the role of oceanic circulation on contaminantdistribution in the South Atlantic [Alleman et al., 2001a,2001b].[6] As leaded petrol has been phased out on both sides of

the North Atlantic Ocean, the source strengths and contri-butions have changed, affecting the isotopic composition ofthe atmosphere [Bollhoefer and Rosman, 2001]. It wassuggested that during the 1990s, high-temperature industrialprocesses had become progressively important, as reflectedin concentration measurements of surface seawater [Wu andBoyle, 1997a] and in lake sediments [Chillrud et al., 1999].The time-dependent evolution of the lead isotope signaturein the North Atlantic atmosphere as a function of changingglobal lead emission pattern has been demonstrated usingmarine sediments [Hamelin et al., 1990; Veron et al., 1987],surface and deep waters [Alleman et al., 1999; Boyle etal., 1986; Shen and Boyle, 1988a; Veron et al., 1994, 1999],corals [Shen and Boyle, 1987; Reuer et al., 2003], marineblanket bogs [Weiss et al., 2002], and Greenland ice cores[Rosman et al., 1993; Sherrell et al., 2000]. Rosman et al.[1993] showed that the 206Pb/207Pb ratios of eolian depo-sition in Greenland shifted from 1.17–1.19 in the late1970s to 1.14–1.16 in the 1980s as the phasing out of leadadditives in North American gasoline preceded that inEuropean gasoline. Using the isotopic composition ofcorals, it was further shown that the decrease of Americaninput to the Sargasso Sea was coupled with increasingproportions of recycled European lead [Shen and Boyle,1988b].[7] With the passage of time from the 1972 maximum,

the lead tracer has been transported into intermediate anddeep water (given their greater ventilation ages) allowingstable lead isotopic compositions to be employed astracers of abyssal mixing. Vertical concentration profilesin the subarctic North Atlantic showed spatial gradients inthe isotopic signature consistent with the thermohalinecirculation pattern of the different water masses in thatregion and their discrete isotopic signatures [Veron et al.,1999]. Likewise, it was shown using Pb isotopes thatadvective transport of lead into the deep abyssal waters is

4 - 2 WEISS ET AL.: TEMPORAL AND SPATIAL EVOLUTION OF Pb DEPOSITION

facilitated through the formation of North Atlantic DeepWater (NADW) [Alleman et al., 1999; Reuer and Weiss,2002].[8] The anthropogenic lead transient has multiple unique

characteristics, complementing existing transient tracerstudies [e.g., Broecker and Denton, 1989; Sarmiento,1983]: (1) the depositional pathways are likely more het-erogeneous relative to other atmospherically derived tran-sient tracers, with focused deposition within the subtropicalNorth Atlantic and NADW formation sites; (2) the historicalelemental and isotopic North Atlantic variability are dis-tinct, providing independent constraints for inverse trans-port models; and (3) the historical isotopic variability issignificantly earlier relative to other transient tracers, withthe first observed North Atlantic 206Pb/207Pb reduction in1886 [Reuer et al., 2003]. However, given the difficulties ofsampling clean seawater, the high costs of cruises, and thedifficulties of precise and accurate concentration and iso-tope ratio measurements, many parts of the North Atlanticare still little studied.[9] The objective of the present study was to comple-

ment our present understanding on the spatial and tempo-ral evolution of Pb isotope ratios and concentrations in theNorth Atlantic and to discuss its implications on the use oflead as hydrographic tracer in oceanographic processes.This study builds upon results obtained from the IOCcruises in 1993 and 1996 [Alleman et al., 1999; Veron etal., 1999], the GCE/CASE/WATOX cruise in 1988 [Veronet al., 1994], the BATS station and its vicinity [Alleman etal., 1999; Shen and Boyle, 1988b; Sherrell et al., 1992;Veron et al., 1993], the Endeavor 157 cruise in 1987[Hamelin et al., 1997], and the cruises at the EUMELIsites (between 1990 and 1992) [Hamelin et al., 1997]. Thisextended data set aims to constrain our knowledge of thetemporal and spatial evolution of lead in the North

Atlantic during the 1980s, to assess how anthropogeniclead has dispersed into the surface ocean and to whatextent European and North American contributions influ-enced the oceanic lead distribution. To achieve these goals,we measured lead concentrations and isotope ratios insurface waters sampled in 1981 and 1989 from twodifferent cruises covering most of the North Atlantic anddiscuss it within the framework of the surface oceancirculation.

2. Samples and Methods

[10] Surface water samples were collected during theTTO cruise in 1981 (29.3–78.7�N, 48.6�W–5.7�E) andR/V Atlantis 123 cruise in 1989 (22.5–38.8�N, 29.5–68.4�W). The oceanographic surface sampling protocoland trace metal clean techniques used on our own cruiseR/V Atlantis 123 have been described previously [Boyle etal., 1986]. Briefly, polyethylene bottles were leached for1 day at 60�C in reagent grade 1N HCl. The bottles werethen inverted, kept at room temperature for an additionalday, and then rinsed thoroughly by high-purity distilledwater. The 1981 samples were taken by personnel from theLamont-Doherty Geological Observatory, using the long-pole sampling technique with double rinsing [Boyle et al.,1986]. Contaminated samples were observed and removedusing the following steps: (1) three independent sampleswere collected at each sampling site, (2) each of thesesamples was first analyzed for Cu, Ni, and Cd, and (3)samples were then analyzed for Pb concentration andstable lead isotopes (206Pb, 207Pb, and 208Pb). ‘‘Contami-nated’’ was defined as concentrations that greatlyexceeded the concentrations of most other samples inthe region and were unsupported by nearby samples withsimilar concentrations. The 1989 samples were taken byMIT personnel trained in trace metal procedures using theMIT underway towed fish system [Vink et al., 2000]. Allsamples were left unfiltered (to minimize contamination)and acidified using 4 ml of triple distilled 6 N HCl perliter.[11] Lead was extracted from seawater using a low blank

Mg(OH)2 preconcentration technique. The method and itsapplications for isotope ratio and concentration measure-ments have been described elsewhere [Weiss et al., 2000;Wu and Boyle, 1997b]. For concentration analyses, 1.3 mlsamples were analyzed using 204Pb isotope dilution, cor-recting for the 204Hg isobaric interference by concurrentanalyses of 202Hg. The precision of this method at 40 pmol/kg was �5%. The blank was in general �5 pmol/kg.Accuracy was assessed by analyzing selected samples byboth graphite furnace atomic absorption spectroscopy andisotope dilution plasma mass spectroscopy, and these testsindicated no analytically significant differences between themethods [Wu and Boyle, 1997b]. For isotope analyses, 13ml seawater samples were transferred into acid-leachedpolypropylene vials. Aqueous NH3 was then mixed intothe sample to precipitate Mg(OH)2. After the mixture wascentrifuged, the supernatant was discarded. This procedurewas then repeated. The resulting total precipitate wasdissolved in ca. 100 ml 5% (v/v) HNO3, and another 1300ml of sample were added. Then, NH4OH was added ina second precipitation step, centrifuged, and the super-

Figure 1. Leaded gasoline consumption in the UnitedStates and Europe, including France, UK, Germany, andItaly, which account for �70% of western Europeangasoline consumption [Wu and Boyle, 1997a]. The UnitedStates has been by far the dominant national gasoline leadconsumer of all nations surrounding the North AtlanticOcean until the early 1980s. It was only in the late 1980sthat U.S. gasoline lead consumption had decreased to lessthan 10% of its peak value.

WEISS ET AL.: TEMPORAL AND SPATIAL EVOLUTION OF Pb DEPOSITION 4 - 3

natant was discarded again. The final precipitate wasdissolved in 1000 ml of 5% (v/v) HNO3 before theanalysis. The procedural blank was determined by doingthe precipitation step on Pb-free seawater and carrying itthrough the procedure as a sample. The blanket accountedin general for less than 3% of total lead analyzed.Samples with a blank contribution above 10% werediscarded.[12] Lead isotope ratios and concentrations were mea-

sured using inductively coupled plasma mass spectrometrywith a quadrupole mass filter (VG Plasma Quad II+) and alow-flow CETAC microconcentric nebulizer. The massbias was determined using repeated measurements of NISTSRM 981, and the correction factor varied from 0.989 to1.0004 during the analyses performed in this work. Theone-sigma external precision of triplicate samples was ingeneral between 0.1 and 0.4% for 206Pb/208Pb and206Pb/207Pb at the level of �100 pmol/kg lead in seawater.Comparison between TIMS and ICP-MS on 12 samples tovalidate the ICP-MS method developed at our laboratoryshowed an average bias of 0.3% for 207Pb/206Pb and 0.4%for 208Pb/206Pb [Weiss et al., 2000]. Note that the TIMSPb sample masses were quite low (ca. 300 pg) so that veryhigh precision (50 ppm) was not attainable on thesesamples.

3. Results and Discussion

[13] In 1981 (Figure 2), surface waters of the central andeastern North Atlantic Ocean were sampled during the TTOcruise. Samples (n = 26) were taken from regions includingthe North African Basin (between the Sargasso Sea, Azores,and Canary Islands, 29.3�–34.7�N, 41.5�–18.5�W), theEast Iberian Basin (close to Portugal and France, 37.8�–46.0�N, 17.5�–10.2�W), the Labrador and Iceland Basins(between Canada, Iceland, and British Isles, 49.6�–58.5�N,48.6�–10.0�W), and the Norwegian Sea (between Green-land and Norway, 67.7�–78.7�N, 7.5�W–5.7�E).[14] In 1989 (Figure 3), surface water samples were taken

along an east-west transect within the 22�–39�N latitudeband during the R/V Atlantis 123 cruise (n = 24). Thesamples analyzed in this study included the western sub-tropical North Atlantic (North American Basin/SargassoSea, 28.3�–38.8�N, 47.4�–68.4�W), the eastern subtropicalNorth Atlantic (North African Basin/Central Iberian Basin,26.2�–33.5�N, 29.4�–44.4�W), and the equatorial NorthAtlantic (22.5�–23.2�N, 35.4�–36.6�W).[15] Tables 1 and 2 give the lead isotope ratios

206Pb/207Pb and 208Pb/206Pb, the concentrations measuredin the collected sample, and the calculated average for eachregion, sample ID, and station coordinates.

3.1. Lead Isotope Ratios and Concentrations inNorth Atlantic Surface Waters in 1981

[16] Two significantly different ranges of isotope ratioswere detected in the central and eastern North Atlantic in1981 (Figure 2). More radiogenic 206Pb/207Pb ratios (ingeneral >1.19, Table 1) were predominant in the NorthAfrican Basin (average: 1.193 ± 0.005 (1 s), range:1.188–1.201, n = 7), in the Labrador and Iceland Basins,north of 49�N (average: 1.198 ± 0.006, range: 1.187–1.205, n = 9), and in the Norwegian Sea north of 67�N

(average: 1.196 ± 0.008, range: 1.185–1.207, n = 5).Significantly lower 206Pb/207Pb ratios (�1.182) prevailedin the East Iberian Basin near Portugal and Francebetween 37.6� and 46.0�N (average: 1.175 ± 0.006, range:1.167–1.182, n = 5), with the lowest ratio found in theGulf of Cadiz (206Pb/207Pb ratio of 1.167, Figure 2). Theisotope ratios showed a slight east-west gradient, withsurface samples near Portugal and France having lowerratios than the rest of the North Atlantic. However, it isnoteworthy that sampling stations with similar proximityto the European continent like in the East Iberian Basin(e.g., samples taken near Africa in the North African Basinor near Norway in the Norwegian Sea) show higher206Pb/207Pb ratios (Figure 2). This might be explained bythe fact that European Easterlies are transported to thesouth from France, Spain, and Portugal, forming theIberian pattern [Church et al., 1990; Maneux et al.,1999] and showing thus a stronger influence in the EastIberian Basin compared to other basins with similarproximity to Europe. A similar spatial distribution patternwith respect to radiogenic/unradiogenic lead across NorthAtlantic surface water samples was found during the GCE/CASE/WATOX cruise in 1988 [Veron et al., 1994]. Ra-diogenic lead, expressed with respect to the 206Pb/207Pbratio, dominated the Sargasso Sea (39.3�N, 55.0�W;1.189 ± 0.002), the Labrador and Iceland Basin (45.6�–66.4�N, 20.0�–45.5�W; 1.181–1.195), and the NorthAfrican Basin (26.0�–36.0�N, 19.6�–32.4�W; 1.185–1.191). The least radiogenic lead was also found in theEast Iberian Basin (42�–46�N, 20�W; 1.1815–1.1829).Atmospheric deposition from tropospheric polar cells(North American (NA) Westerlies and European Easterlies)and advected surface waters from the Arctic were pro-posed to account for these patterns [Veron et al., 1994](see detailed discussion below).[17] [Pb] in these different regions ranged from 54 pmol/

kg (Norwegian Sea) to 140 pmol/kg (Iceland Basin). Theywere slightly higher between the Azores and CanaryIslands (118 ± 23 pmol/kg, n = 7) and lower in thesubarctic region north of 65�N (68 ± 8 pmol/kg, n = 5)compared to the Labrador and Iceland Basins (90 ±27 pmol/kg, n = 9). The higher concentrations in thecentral and eastern North Atlantic correspond to latitudeswith the most important urban emissions centers of NorthAmerica and Europe (between 35� and 60�N). Furthernorth, average [Pb] was significantly lower. Within theregions, concentrations vary around 1.5 fold. The system-atically highest lead concentrations were found in theNorth Atlantic Basin (87–145 pmol/kg), but the largeconcentration range was intersected by every North Atlan-tic region south of 65�N.

3.2. Lead Isotope Ratios and Concentrations inNorth Atlantic Surface Waters in 1989

[18] 206Pb/207Pb surface water ratios in the east to westsubtropical North Atlantic transect ranged between 1.177and 1.192 (average: 1.186 ± 0.005, n = 22). South of 25�N,crossing the subtropical/tropical surface water boundary, theisotope ratios were distinctly less radiogenic (average:1.172 ± 0.004, n = 2). The changes in the isotope ratioscorresponded to water mass boundaries as reflected inthe lower salinity and [Pb] (�51 pmol/kg). Except in the


cool continental shelf waters near Canada (�47 pmol/kg),[Pb] in the subtropical North Atlantic were elevated,ranging between 69 ± 17 pmol/kg in the western region(North American Basin/Sargasso Sea, >45�W) and 97 ±15 pmol/kg in the eastern region (North African Basin/Central Iberian Basin, <45�W). A significant increase in

[Pb] from 68�W (41 pmol/kg) to 40�W (106 pmol/kg) wasobserved. However, increased seawater [Pb] was not asso-ciated with elevated 206Pb/207Pb ratios, although diminished206Pb/207Pb (1.170–1.175) and [Pb] (41–51 pmol/kg) wereobserved in the equatorial basin. Like the 1981 sample dataset, no significant variation within regions was found.

Figure 2. Sample ID (station and bottle): [Pb] (in pmol/kg) and 206Pb/207Pb isotope ratios measured insurface waters in different regions of the North Atlantic Ocean sampled during the TTO cruise in 1981.This included the North African Basin (between Azores and Canary Islands), the East Iberian Basin(close to Portugal and France), the Labrador and Iceland Basins (between Canada and UK), and theNorwegian Sea (close to Norway). Shown are the major ocean currents: Gulf Stream, SNAG, NAD, andthe prevailing winds Trade Easterlies (between 0� and 30�N), NAWesterlies (between 30�N and 60�N),and EU Easterlies (between 60�N and 90�N) and their characteristic isotopic composition.


Average concentration was also lower in the equatorialNorth Atlantic (47 ± 7 pmol/kg) compared to North Africanand North American Basins.[19] Similar radiogenic signatures in the subtropical/

tropical North Atlantic have been found in surface watersnorth of the Canary Islands in the early 1990s [Hamelin etal., 1997]. Isotope ratios ranged between 1.177 and 1.183,suggesting a dominant North American influence even inthe early 1990s despite the considerably earlier reductionof leaded gasoline in the United States. The subtropical/tropical boundary (where surface water exchange isinhibited between the tropical and subtropical regions)on lead concentrations and isotopic ratios in the NorthAtlantic Ocean has been previously observed: Helmers

and van der Loeff [1993] found a large decrease in leadconcentrations south of the boundary and Veron et al.[1994] found that the spreading of equatorial waters by theGuyana Current between 15� and 25�N was marked by206Pb/207Pb ratios shifts from 1.17 to 1.19. Anotherexplanation for the lower signatures in the equatorial NorthAtlantic may be the increasing contributions of lessradiogenic aerosols transported from the African/Mediter-ranean region by the Trade Easterlies (206Pb/207Pb ratiosaround 1.15, Figure 3) [Hamelin et al., 1997]. The IOC-IIcruise in 1996 showed similar low 206Pb/207Pb ratioswithin surface waters in the North Atlantic equatorialoceans (0�–10�N, 1.169 ± 0.006), explained by thecombined contaminant influence of both NA Westerlies

Figure 3. Station ID (station and bottle): [Pb] (in pmol/kg) and 206Pb/207Pb isotope ratios measured insurface waters in three different regions of the North Atlantic Ocean sampled during the R/V Atlantis 123cruise in 1989: the western subtropical North Atlantic (North American Basin/Sargasso Sea), the easternsubtropical North Atlantic (North African Basin/Central Iberian Basin), and the equatorial North Atlantic.Shown are also the major oceanic currents Gulf Stream, Subtropical North Atlantic Gyre (SNAG), andCanary Current and the prevailing winds Trade Easterlies (between 0� and 30�N) and NA Westerlies(between 30�N and 60�N) and their characteristic isotopic composition.


(1.19–1.20) and European Easterlies (1.155–1.165)[Alleman et al., 2001a, 2001b].

3.3. The Temporal Evolution of Atmospheric PbIsotopic Ratios on Both Sides of the North AtlanticBasin During the 1980s

[20] Lead in the ocean is dominantly derived from atmo-spheric deposition of fine aerosols transported from theadjacent North American and European continents [Schauleand Patterson, 1983; Shen and Boyle, 1988b; Veron andChurch, 1997]. To accurately utilize the isotopic composi-tion of Pb for mixing calculations or source apportionment,one must constrain each source as precisely as possible.Table 3 shows estimated average 206Pb/207Pb ratios for theNorth American (distinguishing between Canadian and U.S.signatures in 1989), North African, and European tropo-sphere, calculated from published isotopic data for atmo-spheric lead. The data set includes mainly aerosolmeasurements from the year when surface waters weresampled and from the 2 years prior, thus taking into accountthe 2-year residence time of lead in the surface waters(although all available data from pre-1980 were taken intoaccount). The estimated 206Pb/207Pb ratio for the NA West-erlies is 1.218 ± 0.011 in 1981 and 1.206 ± 0.007 in 1989

(Table 3), assuming U.S. contributions dominating the NorthAmerican tropospheric signature [Wu and Boyle, 1997a].Our estimates in Table 3 agree well with previously pub-lished isotope ranges for the western North Atlantic tropo-sphere, e.g., 1.19–1.22 [Church et al., 1990]. Our estimated206Pb/207Pb ratios for the European troposphere are 1.110 ±0.02 in 1981 and 1.142 ± 0.006 in 1989, both agreeing wellwith previously suggested ratios (e.g., 1.130 ± 0.02 for 1988[Veron et al., 1994]). The unradiogenic signature of theEuropean troposphere was due to the use of lead fromAustralian, Moroccan, and Canadian Precambrian Pb-Znores (with 206Pb/207Pb < 1.10) for gasoline additives inEurope [Reuer and Weiss, 2002]. The significantly moreradiogenic signature of the U.S. troposphere resulted fromthe increasing use of Mississippi Valley type lead in U.S.gasoline, with 206Pb/207Pb ratios above 1.22 [Chow et al.,1975; Reuer and Weiss, 2002]. Although the lead isotopecomposition of atmospheric particulate matter was distinc-tively less radiogenic in eastern Canada during the 1980s[Sturges and Barrie, 1989], the incremental addition ofCanadian lead to North American emission had no majorconsequences at any time [Wu and Boyle, 1997a].[21] One difficulty of source apportionment is that each

region and its atmospheric signature can exhibit significant

Table 1. Lead Isotope Ratios and Concentrations in Surface Waters Collected During the TTO Cruise in 1981a

NumberSample IDSS Number

Latitude,dec.

Longitude,dec.

Pb Concentration,pmol/kg

206Pb/207Pb(±1SD)

208Pb/206Pb(±1SD)

North African Basin (Madeira Abyssal Plane)1 44B N 33.007 W 41.488 87 1.194 ± 0.001 2.037 ± 0.0072 45B N 33.530 W 36.002 98 1.191 ± 0.002 2.040 ± 0.0023 52B N 31.977 W 26.233 103 1.195 ± 0.002 2.046 ± 0.0164 68A N 30.775 W 24.233 144 1.188 ± 0.003 2.050 ± 0.0025 80A N 29.272 W 18.518 117 1.193 ± 0.000 2.048 ± 0.0006 99B N 33.192 W 21.750 131 1.188 ± 0.002 2.074 ± 0.0067 107B N 34.767 W 23.100 145 1.201 ± 0.002 2.057 ± 0.003

Average 118 ± 23 1.193 ± 0.005 2.050 ± 0.012

East Iberian Basin8 111B N 37.877 W 17.463 81 1.178 ± 0.002 2.090 ± 0.0149 112B N 37.593 W 13.478 92 1.173 ± 0.001 2.094 ± 0.00210 113A N 37.583 W 10.192 86 1.167 ± 0.004 2.106 ± 0.00911 114B N 42.137 W 10.337 92 1.182 ± 0.001 2.075 ± 0.00912 115B N 46.028 W 11.005 118 1.173 ± 0.005 2.072 ± 0.001

Average 94 ± 15 1.175 ± 0.006 2.087 ± 0.014

Labrador and Iceland Basins13 117A N 49.550 W 16.670 76 1.195 ± 0.004 2.048 ± 0.00514 118A N 49.740 W 21.992 140 1.205 ± 0.004 2.008 ± 0.01015 120A N 51.810 W 26.793 72 1.203 ± 0.005 2.005 ± 0.01316 124C N 53.257 W 36.692 119 1.187 ± 0.004 2.056 ± 0.01317 127C N 58.493 W 29.992 69 1.194 ± 0.007 2.017 ± 0.01018 134A N 56.865 W 18.503 69 1.199 ± 0.003 2.030 ± 0.01419 135B N 56.328 W 13.827 115 1.194 ± 0.001 2.044 ± 0.00420 140B N 55.827 W 10.003 71 1.205 ± 0.002 2.105 ± 0.00321 218A, B, C N 49.740 W 48.617 77 1.204 ± 0.009 2.004 ± 0.009

Average 90 ± 27 1.198 ± 0.006 2.035 ± 0.033

Norwegian Sea22 144B N 67.687 W 3.337 74 1.207 ± 0.008 2.021 ± 0.00523 145A N 69.998 E 2.452 54 1.185 ± 0.006b 2.059 ± 0.005b

24 150A N 76.593 E 1.198 70 1.193 ± 0.006b 2.053 ± 0.005b

25 152B N 78.698 E 5.695 73 1.193 ± 0.005 2.050 ± 0.01326 158A N 71.163 W 7.490 69 1.200 ± 0.004 2.005 ± 0.009

Average 68 ± 8 1.196 ± 0.008 2.038 ± 0.023aThe isotope ratios measured with the VG Plasma Quad ICP-MS comprise measurements of three independently processed aliquots.bThe isotope ratios measured with the VG TIMS comprise measurements of one independently processed aliquot (denoted with asterisks).


isotopic variability [Church et al., 1990; Veron and Church,1997]. Indeed, precipitation scavenges lead at altitude inclouds and throughout the tropospheric column and inte-grates various isotopic information, compared to aerosolscollected close to the sea surface level. Differences in ratiosof more than 6% were found while measuring lead isotopesin aerosols and precipitation in the North Atlantic tropo-sphere [Church et al., 1990].

3.4. Source Assessment and Mixing Calculations

[22] Triple-isotope diagrams were used to assess thedominant lead sources and possible mixing end-membersfor the surface water samples collected in 1981 and 1989.Only the isotopes 206Pb, 207Pb, and 208Pb were considereddue to the analytical precision of the quadrupole ICP-MS.[23] The plots in Figures 4a and 4b show (1) measured

isotope ratios of surface seawater collected in 1981 and1989, divided into the different geographic regions shownin Figures 2 and 3, (2) the field of isotope ratios measured inU.S. (representing the NAWesterlies) and western European(representing the EU Easterlies) aerosols for the time spanmainly between 1979 and 1981 and 1987 and 1989,respectively [Flegal et al., 1989; Grousset et al., 1994;Hirao and Patterson, 1974; Hopper et al., 1991; Maring etal., 1987; Rabinowitz and Wetherill, 1972; Rosman et al.,2000; Sturges et al., 1993; Weiss et al., 1999a], and (3) thefield of isotope ratios of natural, crustal lead found inunpolluted atmospheric dust [Shotyk et al., 2001]. In addi-

tion, the plot in Figure 4b shows the field of isotope ratiospreviously (1987) measured in Sargasso Sea surface waters[Hamelin et al., 1997], the source waters of the SouthernNorth Atlantic Gyre (SNAG) [Schmitz and McCarthy, 1993;Schmitz, 1996]. The presence of a seasonal thermoclinegenerally inhibits vertical mixing from May to October andfavors transport from west (Sargasso Sea) to east (Europeanand Iberian Basins) through surface currents (North AtlanticDrift (NAD), SNAG), making the Sargasso Sea a potentialsource for lead in the eastern North Atlantic [Hamelin et al.,1997; Veron et al., 1994]. Shown in Figure 4b, only, is the

Table 2. Lead Isotope Ratios and Concentrations in Surface Waters Collected During the R/V Atlantis 123 Cruise in 1989a

NumberSample IDSS Number

Latitude,dec.

Longitude,dec.

Pb Concentration,pmol/kg

206Pb/207Pb(±1SD)

208Pb/206Pb(±1SD)

Western Subtropical North Atlantic (North American Basin/Sargasso Sea)1 1 N 38.250 W 68.360 47 1.189 ± 0.004 2.022 ± 0.0062 2 N 38.800 W 68.260 41 1.191 ± 0.001 2.050 ± 0.0053 4 N 35.800 W 66.157 46 1.181 ± 0.002 2.018 ± 0.0014 7 N 33.140 W 64.541 65 1.178 ± 0.006 2.033 ± 0.0085 9 N 31.230 W 61.178 77 1.185 ± 0.002 2.050 ± 0.0026 11 N 31.600 W 59.560 80 1.185 ± 0.003 2.046 ± 0.0097 12 N 30.500 W 58.220 77 1.187 ± 0.004 2.068 ± 0.0078 17 N 30.600 W 54.560 79 1.191 ± 0.003 2.019 ± 0.0129 18 N 29.390 W 52.600 83 1.188 ± 0.002 2.067 ± 0.00210 23 N 28.560 W 49.490 83 1.177 ± 0.002 2.083 ± 0.01611 24 N 28.300 W 47.378 83 1.184 ± 0.003 2.080 ± 0.006

Average 69 ± 17 1.185 ± 0.005 2.049 ± 0.006

Eastern Subtropical North Atlantic (North African Basin/Central Iberian Basin)12 29 N 27.480 W 44.390 87 1.182 ± 0.001 2.078 ± 0.00913 30 N 27.190 W 42.308 98 1.191 ± 0.002 2.07 ± 0.00814 33 N 26.540 W 40.350 106 1.184 ± 0.002 2.078 ± 0.00315 35 N 26.400 W 39.270 95 1.186 ± 0.005 2.048 ± 0.00716 38 N 26.280 W 37.110 87 1.181 ± 0.001 2.055 ± 0.00417 40 N 26.200 W 33.400 81 1.179 ± 0.001 2.055 ± 0.00218 47 N 28.000 W 34.000 95 1.186 ± 0.003 2.044 ± 0.00819 48 N 27.470 W 32.800 93 1.188 ± 0.002 2.044 ± 0.00420 50 N 28.460 W 29.530 137 1.188 ± 0.002 2.048 ± 0.00821 51 N 31.000 W 31.000 95 1.192 ± 0.006 2.047 ± 0.00722 52 N 33.500 W 29.360 94 1.186 ± 0.006 2.060 ± 0.008

Average 97 ± 15 1.186 ± 0.004 2.057 ± 0.013

Equatorial North Atlantic23 41 N 22.470 W 35.370 51 1.175 ± 0.009 2.048 ± 0.00224 44 N 23.170 W 36.570 41 1.170 ± 0.006 2.068 ± 0.012

Average 47 ± 7 1.172 ± 0.004 2.058 ± 0.014aThe isotope ratios measured with the VG Plasma Quad ICP-MS compromise measurements of three independently processed aliquots.

Table 3. The 206Pb/207Pb Ratios of Potential Atmospheric

(Tropospheric) Lead Sources Measured Between 1979–1981 and

1987–1989

Location Authorsa 206Pb/207Pb

1979–1981 USA 1, 2, 9, 10 1.218 ± 0.011Western Europe 1, 2, 3, 4, 11, 12 1.110 ± 0.022North Africa 5 1.156

1987–1989 USA 1, 2, 6, 7, 13 1.206 ± 0.007Canada 1, 2, 7, 13 1.146 ± 0.003Western Europe 1, 3, 6, 8, 11, 12, 13 1.142 ± 0.006North Africa 2 1.154 ± 0.005

a1: Rosman et al. [1993]; 2: Church et al. [1990]; 3: Grousset et al.[1994]; 4: Elbaz-Poulichet et al. [1984]; 5: Maring et al. [1987]; 6: Veron etal. [1994]; 7: Flegal et al. [1989]; 8: Hopper et al. [1991]; 9; Hirao andPatterson [1974]; 10: Rabinowitz and Wetherill [1972]; 11: Rosman et al.[2000]; 12: Weiss et al. [1999a]; 13: Sturges et al. [1993].


isotope field from the West African Trade winds [Hamelinet al., 1997] and finally for comparison, surface water ratiosmeasured in the western and central North Atlantic [Veron etal., 1994].[24] In 1981 (Figure 4a), the observed 206Pb/207Pb

surface water ratios (1.167–1.207) span the isotope rangeof the proposed atmospheric sources from European andNorth American aerosols (EU Easterlies, NA Westerlies).Plotted on a 208Pb/206Pb versus 206Pb/207Pb graph, theratios of most surface water samples spread along amixing line linking these two end-members (within theachieved analytical precision of the quadrupole ICP-MSmeasurements). However, there are a few important out-liers. The four samples from the East Iberian Basin locatedclosest to the European continent (samples 111B, 112B,113A, 114B) lie slightly above the binary mixing line ofthe European and American aerosols and form a straightmixing line with natural background dust. This mayindicate important contributions from Saharan dust. Sam-ple 115B, taken furthest north of all the samples in thisregion in the East Iberian Basin (46.028�N) is significantlybelow the natural dust/European aerosol mixing line andfits within the European and American aerosols mixingline. Saharan dust is less important at greater distances andfurther north from mainland Europe. However, one has toconsider that the U.S. aerosol field for 1981 is ratherpoorly constrained, with few measurements giving both206Pb/207Pb and 208Pb/206Pb ratios. Nevertheless, a triple-isotope plot assessing the sources of air masses betweenthe Azores and the subtropical North Atlantic regionsshowed a very similar pattern [Veron and Church, 1997],supporting the possible importance of Saharan dust and/orother natural sources as additional lead source to the EastIberian Basin. Similarly, within the North African Basin,the samples 99B and 107B suggest a higher natural dustcomponent (higher 208Pb/206Pb ratios) than the rest of thesamples within that region (Figure 4). The other surfacesamples in the North African Basin as well as thesignatures in the other investigated regions (NorwegianSea, Labrador, and Iceland Basin) are clearly derived fromthe mixing of European and American lead. Only sample140B in the Iceland Basin, taken just offshore of Ireland,is significantly different with high 208Pb/206Pb. To assessthe Sargasso Sea as an additional source for the leadencountered in the eastern North Atlantic, we need iso-topic measurements of lead prior to 1981, but these are notavailable at present. However, assuming that samples 44Band 45B represent Sargasso Surface water (33�–34�N,36�–41�W), then samples 144B and 158A in the Norwe-gian Sea and most samples of the Labrador and IcelandBasin could be derived from binary mixing betweenEuropean Easterlies and/or Sargasso Sea surface waterPb as one end-member and NA Westerlies as the otherend-member (Figure 4a). In the same way, the samplesfrom the East Iberian Basin could represent a binarymixing of European Easterlies as one end-member andSargasso Sea surface water and/or NA Westerlies as theother end-member. It has been suggested before that theeastern Atlantic contains contributions from surface waterscoming from the Sargasso Sea via the Gulf Stream andNorth Atlantic Drift (NAD) [Hamelin et al., 1997; Veron etal., 1994].

[25] In 1989 (Figure 4b), the observed 206Pb/207Pb ratiosof the surface waters in the western and the easternsubtropical as well as in equatorial North Atlantic (1.170–1.192) show a significantly smaller spread than in 1981,possibly due to the smaller geographical coverage of thecruise (latitude only between 23� and 39�N). As in 1981,most of the samples can be explained by the binary Pbmixing from NA Westerlies (eastern United States) andEuropean Easterlies. However, four samples from the west-ern North Atlantic (samples 1, 4, 7, and 17, Table 2) havesignificantly lower 208Pb/206Pb ratios, and it appears that athird mixing component needs to be taken into account withlower 208Pb/206Pb ratios. In addition, the two samples fromthe equatorial North Atlantic appear to include a thirdcomponent, possibly recycled lead from the western NorthAtlantic, as proposed by Veron et al. [1994].[26] The isotope composition of most of the surface water

samples in 1981 and 1989 can presumably be approximatedby binary mixing between eastern United States and westernEuropean atmospheric Pb. It is impossible to calculate thecontribution of each component precisely, given the rangeof isotope signatures of the sources and the possibleinfluence of a third end-member. However, we attempteda rough estimate of the relative contributions of easternUnited States and European lead contribution using con-ventional two-component mixing. The 206Pb/207Pb ratios ofthe different end-members used for the mixing calculationswere 1.218 (1981) and 1.206 (1989) for eastern UnitedStates lead and 1.110 (1981) and 1.142 (1989) for Europeanlead, derived from Table 3. Table 4 shows the calculatedrange of U.S. lead contributions for the different regions ofthe North Atlantic Basin for both years.[27] In 1981, U.S. lead contributions were lowest in the

East Iberian Basin (between 53 and 65%) and higher in theother regions (between 69 and 94%). In 1989, NorthAmerican lead contributions were still dominant in theNorth American and North Africa Basins; however, theywere significantly lower compared to 1981 (57–79%). Inthe equatorial North Atlantic, they were even lower, fallingbetween 43 and 52%. Comparable contributions to leaddeposition from NAWesterlies along the Irish coast in 1988(58%) have been calculated using wind direction rosette[Veron et al., 1994]. Peat bog archives in Norway, Ireland,and Scotland [Dunlap et al., 1999; Schell et al., 1997; Weisset al., 2002] as well as eolian particulate measurements inOslo [Aberg et al., 1999] suggest similar mixing ratios forwestern European maritime locations.[28] Although North American lead emissions from gas-

oline decreased during the 1980s, the relative contributionfrom eastern American sources dominated in the early andlate 1980s. This result may indicate that emissions fromhigh-temperature industrial processes in North Americaincreased again in importance in the late 1980s. Mexicanleaded gasoline emissions have been small compared toAmerican leaded gasoline usage, and it was suggested itshould not overwhelm emissions from American high-temperature industrial activities [Wu and Boyle, 1997a].However, some studies have suggested that Mexican leadis becoming increasingly important in the total inventory,especially in southern United States [Bollhoefer and Rosman,2001; Dunlap et al., 2000]. Also, this might explain thethird lead component identified in 1989 in the western



subtropical North Atlantic which would also agree with theradiogenic lead isotope ratios found in lead ores fromMexico and Peru [see Graney et al., 1995, and referencestherein]. A more careful source assessment, however, isclearly warranted.

3.5. Temporal Variations of Isotopic Signature andConcentrations Within the North Atlantic Basin

[29] Table 5 shows a compilation of reported 206Pb/207Pbisotopic compositions of dissolved lead measured in NorthAtlantic surface waters and NADW collected during differ-ent cruises in the 1980s and 1990s (EN 157 in 1987, GCE/CASE/WATOX in 1988, EUMELI between 1990 and 1992,IOC-II and IOC-III in 1993 and 1996, respectively, andMED II in 1989) and from the Bermuda OFP-BATS stationin 1997 [Alleman et al., 2001b, 2000, 1999; Hamelin et al.,1997; Veron et al., 1994, 1999]. This compilation allows usto discuss the data set of this study within the larger contextof temporal and spatial variability.3.5.1. North American Basin/Sargasso Sea[30] The Sargasso Sea in the North American Basin has

been sampled during the TTO cruise in 1981 (33�–34�N,36�–42�W, this study), during the EN157 cruise in 1987(31�–42�N, 47�–71�W, [Hamelin et al., 1997]), during theGCE/CASE/WATOX cruise in 1988 (39�N, 55�W, [Veronet al., 1994]), and the R/V Atlantis 123 cruise in 1989(28�–38�N, 47�–68�W, this study). In addition to thesesurface water surveys, 206Pb/207Pb isotopic data have beenobtained for water column profiles near Bermuda in 1984[Shen and Boyle, 1987], 1987 [Sherrell et al., 1992], and1989 [Veron et al., 1993]. In 1981, the 206Pb/207Pb ratiosare radiogenic and average 1.192 (Table 1). They remainradiogenic ranging between 1.186 and 1.197 in 1987[Hamelin et al., 1997]), �1.1889 in 1988 [Veron et al.,1994] and decline slightly only in 1989 between 1.177and 1.191 (Table 2). The constant radiogenic signaturein the North American Basin/Sargasso Sea surface watersand U.S. atmosphere (Table 3), despite the strong declinein gasoline Pb emissions from the United States duringthe 1980s (Figure 1), confirms that another radiogenicPb source from the North American continent hasbecome increasingly important. This suggestion agrees

with Pb concentration measurements in the sedimentsof Central Park, New York City [Chillrud et al., 1999].The 206Pb/207Pb signature in the surface seawater of theSargasso Sea is below the NA Westerlies (1.218 in 1981and 1.206 in 1989, Table 3), likely because of the additionof European and/or North African lead into the western andcentral North Atlantic by Trade Easterlies [Hamelin et al.,1989; Schaule and Patterson, 1983; Veron et al., 1993].The small decrease in 206Pb/207Pb ratios between 1981 and1989 is correlated with a small decrease in [Pb] (from 93 ±6 pmol/kg in samples 44B and 45B in 1981 to 69 ±17 pmol/kg in samples 1–24 in 1989), which agrees withthe decrease in lead concentration by a factor of two tothree evidenced in the Sargasso Sea surface water [Wu andBoyle, 1997a].3.5.2. The Subarctic North Atlantic Region[31] The subarctic region has been sampled during the

TTO cruise in 1981, during the GCE/CASE/WATOXcruise in 1988 [Veron et al., 1994], and in great detailduring the OCI-II cruise in 1993 [Veron et al., 1999], thelatter also including intermediate and deep water samples.The OCI-II cruise showed that different water masses(thermohaline and surface waters) in the subarctic NorthAtlantic have distinct 206Pb/207Pb ratios, e.g., Iceland-Scotland overflow waters with signatures between 1.173and 1.176, Denmark Straits Overflow Waters between1.179 and 1.182, or the North East Atlantic deep waterbetween 1.181 and 1.187. Comparing the surface waterdata from the Labrador Basin and the Iceland Basin fromthe three different cruises, we find different temporaltrends. The Iceland Basin had 206Pb/207Pb ratios between1.194 and 1.205 in 1981 (49�–61�N, 10�–26�W), 1.181in 1988 (60�N, 20�W, [Veron et al., 1994]), and between1.179 and 1.187 in 1993 (56�–59�N, 26�–28�W, [Veron etal., 1999]), showing a decreasing trend. The LabradorBasin, however, had ratios between 1.187 and 1.204 in1981 (49�–53�N, 37�–49�W), between 1.188 and 1.192in 1988 (46�–55�N, 39�–45�W, [Veron et al., 1994]), and1.209 in 1993 (55�N, 49�W, [Veron et al., 1999]), showinga consistently high radiogenic ratio. These differingtrends suggest that the Iceland Basin is more affected byEuropean aerosol emissions, and the changing gasolineemission pattern is consequently reflected in the surfacewaters of that basin. The Labrador Basin, in contrast,seems dominated by North American emissions as the206Pb/207Pb isotopic signatures are not changing with time,and in fact, the ratio of 1993 (1.209) agrees with estimatesof the NA Westerlies (1.206 ± 0.007).3.5.3. North African Basin[32] In the North African Basin, the 206Pb/207Pb ratios

range between 1.188 and 1.201 (29�–35�N, 19�–41�W) in1981, between 1.1898 and 1.1913 (26�–35�N, 28�–32�W,[Veron et al., 1994]) in 1988, and decrease slightly in 1989to ratios ranging between 1.179 and 1.192 (26�–33�N,

Figure 4. (opposite) Lead isotopic signatures of seawater surface samples of (a) 1981 TTO cruise and (b) 1989 R/VAtlantis 123 cruise, plotted using three isotope graphs including 206Pb, 207Pb, and 208Pb. The different geographical regionshave different symbols. Also shown are the lead isotope fields of natural dust, NAWesterlies, and European aerosols (EUEasterlies). Figure 4b includes in addition published Sargasso Sea surface water ratios (Sargasso Sea), West Africanaerosols (WATrade winds) and central/western North Atlantic surface waters (wc-NA). See text for detailed discussion ofthe isotopic fields and the references used.

Table 4. Estimated Contribution of United States Derived Lead to

the Total Lead Concentration in North Atlantic Surface Waters

Date Cruise RegionPercent

U.S. Lead

1981 TTO East Iberian Basin 53–65North African Basin 72–84Labrador and Iceland Basins 71–88Norwegian Sea 69–94

1989 R/V Atlantis 123 North African and NorthAmerican Basins

57–79

Equatorial North Atlantic 43–52


29�–44�W). Similar to the Sargasso Sea and LabradorBasin, isotope ratios in the North African Basin remainradiogenic throughout the 1980s. They are apparentlyuninfluenced by the decline in American Pb gasolineemissions relative to European during the 1980s (Figure 1)and agree with the trends of the estimated U.S. troposphericsignature, which becomes only slightly less radiogenic in1989 (Table 3). The continuingly large contribution ofNorth American lead to the North African Basin in the late1980s suggests elevated industrial contribution from theeastern United States to the North African Basin, either dueto advective transport from the Sargasso Sea and/or atmo-spheric transport. Figure 4a shows two samples that repre-sent Sargasso Sea surface water signature (45B and 44B).However, they lie on the atmospheric mixing line, and it istherefore not possible to distinguish between the SargassoSea and the atmosphere as different end-members. Contri-bution of U.S. lead transported by advective surface cur-rents from the Sargasso Sea to the eastern North Atlanticwas estimated to account up to 40% of total Pb. Thequalitative assumptions regarding possible transport of Pbfrom the western North Atlantic and Sargasso Seas to thesubtropical eastern North Atlantic via the SNAG can beevaluated by semiquantitative calculations using surfacecurrent velocities. A smoothed map of averaged surfacecurrents for the North Atlantic, based on ship drift data forthe summer is given by Schmitz [1996]. Currents haveaverage velocities of �1.7 km/h (�47 cm/s) between theSargasso Sea and the central North Atlantic (at ca. 45�N).In the European basin, the velocities are lower by half. Atthis speed, water may travel from the western edge of theNorth Atlantic Basin to the eastern edge in a year or less.This transit time is shorter than the residence time oflead in surface waters (2 years) as estimated from 210Pb[Bacon et al., 1976]. However, ship drift velocities arecontaminated by the effect of wind on the superstructures of

the ship, so that in the Westerlies there will be a bias ofcurrent speed toward higher velocities. Recent work byFratantoni [2001] based on drogued drifters showed thatapart from the NAD and the Azores current, velocities inthe central North Atlantic Gyre are generally 10 cm/s orless. Hence okay advective zonal lead transport can besignificant in boundary currents, such transport might beless significant relative to atmospheric deposition in thecentral gyres.3.5.4. East Iberian Basin[33] The East Iberian Basin surface waters in 1981 show

the least radiogenic lead measured in this study. The206Pb/207Pb ratios range from 1.173 to 1.182 with one verylow value of 1.167. An exceptional source for this low leadisotope value (station sample 113A, Table 1) may be seen inthe Gulf of Cadiz acid mine drainage by the rivers Rio Tintoand Odiel, which drain the Iberian Pyrite Belt (IPB). In theestuary of the Rio Tinto, the Pb concentration is 420,000pmol/kg at 31% salinity. This water could be diluted byfour orders of magnitude (barely detectable by salinitymeasurement) and still affect the [Pb] and its isotopecomposition. This would agree with findings of previouswork on trace element concentrations in sediments andsurface water of the Gulf of Cadiz [van Geen et al., 1997]and with average reported 206Pb/207Pb ratios of �1.165 forthe IPB.[34] In 1988, surface water isotope ratios became slightly

more radiogenic and ranged between 1.1815 and 1.1850(36�–46�N, 20�W, [Veron et al., 1994]). No decline inisotope ratios similar to the other basins at the end of1980 was seen. This might be due to the fact that (1)in Europe, in 1989, gasoline Pb emissions had stronglydecreased and lead isotope ratios became again more radio-genic, e.g., 1.151 for 206Pb/207Pb in 1989 as derived frompeat bogs archives [Weiss et al., 1999b], (2) the decreasinginput from acid mine drainage, or (3) the simply increasing

Table 5. The 206Pb/207Pb Isotopic Composition of Dissolved Lead in Bulk Seawater (Surface Waters and NADW) in the North Atlantic

Ocean During 1980s and 1990s

Region Date Cruise Surface Waters Author NADW Author

Labrador Basin 1993 IOC-II 1.209 Veron et al. [1999] 1.191 Alleman et al. [1999]1988 GCE/CASE/WATOX 1.1879–1.1992 Veron et al. [1994]1981 TTO 1.187–1.204 this study

Iceland Basin 1993 IOC-II 1.179–1.187 Veron et al. [1999]1988 GCE/CASE/WATOX 1.181 Veron et al. [1994]1981 TTO 1.194–1.205 this study

Iceland-Scotland Ridge 1993 IOC-II 1.169, 1.179 Veron et al. [1999] 1.174 Alleman et al. [1999]Denmark Straits 1993 IOC-II 1.183, 1.181 Veron et al. [1999] 1.183, 1.182 Alleman et al. [1999]

1993 IOC-II 1.165 Veron et al. [1999] 1.178 Alleman et al. [1999]North American Basin 1997 OFP-BATS 1.187 Alleman et al. [1999]

1989 R/V Atlantis 123 1.178–1.191 this study1988 GCE/CASE/WATOX 1.1889 Veron et al. [1994]1987 EN 157 1.186–1.197 Hamelin [1997]1981 TTO 1.192–1.194 this study

North African Basin 1991 EUMELI 1.156 Alleman et al. [1999]1992 MED II 1.162 Alleman et al. [1999]1989 R/V Atlantis 123 1.179–1.192 this study1988 GCE/CASE/WATOX 1.1895–1.1913 Veron et al. [1994]1981 TTO 1.188–1.201 this study

East Iberian Basin 1988 GCE/CASE/WATOX 1.1815–1.185 Veron et al. [1994]1981 TTO 1.167–1.182 this study

Equatorial Basin <10 �N 1996 IOC-III 1.158–1.171 Alleman et al. [2001a] 1.154 Alleman et al. [1999]<10 �N 1996 IOC-III 1.165 ± 0.005 Alleman et al. [2001b]<25 �N 1989 R/V Atlantis 123 1.170–1.175 this study<20 �N 1988 GCE/CASE/WATOX 1.166–1.170 Veron et al. [1994]


North American industrial lead contribution to the total leadconcentration via the Sargasso sea surface waters and/oratmospheric deposition.3.5.5. NADW and Ventilation Rates[35] Table 5 shows the 206Pb/207Pb signatures of NADW

from the far North Atlantic measured in 1993 (LabradorBasin, Iceland-Scotland Ridge, and Denmark Straits,1.174–1.191), from the Sargasso Sea measured in 1997(1.187), from the North African Basin measured in 1991and 1989 (1.156–1.162), and from the equatorial basinmeasured in 1996 (1.154) [Alleman et al., 1999].[36] Newly formed NADW in the far North Atlantic

shows 206Pb/207Pb ratios between 1.175 and 1.191 in1993. These ratios are significantly different from contem-porary American signatures, reflecting the mixing ofradiogenic North American lead with less radiogenicwestern European lead [Alleman et al., 1999]. The inter-mediate and deep waters formed in the Labrador Seainclude the intermediate water mass of Labrador Seawater(LSW) and Upper NADW (UNADW). Both water massesare formed by winter convection, and LSW crosses theNorth Atlantic in approximately 11 years [Sy et al., 1998].The isotopic compositions of the surface waters of theLabrador Sea, the NAD, and North American Basin, allcontributing source waters for the NADW in the Arctic[Schmitz and McCarthy, 1993] ranged between 1.187 and1.205 (Tables 1 and 5) in 1981. Thus they representpossible radiogenic end-members of the NADW mixingline in the far North Atlantic measured in 1993 [Allemanet al., 1999] and the UNADW in the Labrador Basin.Similarly, the radiogenic ratio of the NADW measured inthe Sargasso Sea in 1997 (206Pb/207Pb = 1.187) wouldagree with radiogenic source waters from 1981 in the farNorth Atlantic and estimated abyssal ventilation rates ofthe western North Atlantic Basin of 10–40 years, based on3H [Doney and Jenkins, 1994].[37] The isotope ratios measured in surface water samples

in the early 1980s (this study) and in NADW samplesduring the mid-1990s [Alleman et al., 1999; Veron et al.,1999] confirm the role of oceanic circulation on contami-nant lead distribution in the North Atlantic and its advectivetransport into deep basin waters through the thermohalineformation of NADW and along isopycnals [Schmitz andMcCarthy, 1993]. Of note is the homogeneity of the isotoperatios in the surface waters in the western and easternsubtropical North Atlantic (North American and NorthAfrican Basins) during the late 1980s but the significantvariations are between the abyssal waters measured in 1997in the North American Basin (206Pb/207Pb = 1.187 at OFP-BATS station) and in 1991 in the North African Basin(206Pb/207Pb = 1.156 at EUMELI stations). However, as theNADW ventilates the deep Sargasso Sea in 80–160 yearsand the deep eastern basin in 160–240 years, it takes manydecades for the NADW to ventilate the North Atlantic. Onlya small component gets there quickly [Broecker et al.,1991], and this spatial variation is therefore not unexpected[Schmitz and McCarthy, 1993].

4. Conclusions

[38] Surface water samples collected across most regionsof the North Atlantic Ocean during two cruises in 1981 and

1989 were analyzed for lead isotope ratios including 206Pb,207Pb, and 208Pb, and for [Pb] using a newly developed ICP-MS technique for small seawater samples. In the early1980s, the 206Pb/207Pb ratios found in the Labrador andIceland Basins and in the Norwegian Sea ranged between1.185 and 1.207, reflecting mixing between the isotopicrange of the two main atmospheric lead sources, namely NAWesterlies and western European Easterlies, to theseregions. The concentrations ranged between 54 and140 pmol/kg, with lowest values at high latitudes >65�N.Radiogenic ratios and/or elevated [Pb] in those regions aswell as triple-isotope plots suggest that the pollutant leadderived dominantly from North America (between 71 and94%, calculated using a simple two-component mixingmodel). Ratios in surface waters near Portugal were lessradiogenic (�1.182), indicating an important contribution(between 35 and 47%) of European lead and possibly theinfluence of the Rio Tinto acid mine drainage from the IPBvery close to shore. In the late 1980s, surface waters of thewestern and eastern subtropical North Atlantic showed stillradiogenic 206Pb/207Pb signatures (1.177–1.192), indicatinga prevalent impact of North American lead despite strongdecreases in gasoline Pb emissions from the United Statesby the end of the 1980s. This suggests an increasingcontribution from high-temperature industrial processes inthe United States. The isotopic signatures of the surfacewaters were less radiogenic (between 1.170 and 1.175)south of the subtropical/tropical surface water boundary in1989, suggesting a relative increase in the atmosphericimprint of lead from the western Mediterranean/AfricanEasterlies. Lead in the North Atlantic during the 1980scould mostly be explained by lead deposition from theadjacent landmasses of North America and Europe, as tripleisotope plots revealed. However, surface water samplesfrom 1989 taken close to the southern North Americancontinent suggest a third source. This is at present uniden-tified but may be attributable to Mexican leaded gasoline.

[39] Acknowledgments. We are especially grateful to the Lamont-Doherty Geological Observatory scientists who collected samples for usduring the 1981 TTO expedition, as well as the officers and crew of the R/VKnorr. We thank Debra Colodner, Rob Sherrell, and the officers and crewof the R/V Atlantis 123 for their assistance during the 1989 expedition. Wethank Rick Kayser and Barry Grant for expert help and support in the MITanalytical laboratory. Thomas Stocker, Jan Kramers, Tom Church, AlainVeron, Kerry Gallagher, and Friedhelm von Blanckenburg are thanked fortheir interest in this study and helpful comments and discussions. D.W.acknowledges the financial support of the Swiss National Science Foun-dation, The Natural History Museum and Imperial College London. E.B.acknowledges support from the U.S. National Science Foundation andOffice of Naval Research. We thank Bruno Hamelin, Malin Kylander, andone anonymous reviewer for comments on an earlier version and Dicksonand Klink for the editorial handling. Their comments were very helpful andimproved the manuscript. D.W. wishes to dedicate this paper to Meret,Peter, and Ingrid for their continuing support.

ReferencesAberg, G., J. M. Pacyna, H. Stray, and B. L. Skjelkvale, The origin ofatmospheric lead in Oslo, Norway, studied with the use of isotopic ratios,Atmos. Environ., 33, 3335–3344, 1999.

Alleman, L. Y., A. J. Veron, T. M. Church, A. R. Flegal, and B. Hamelin,Invasion of the abyssal North Atlantic by modern anthropogenic lead,Geophys. Res. Lett., 26, 1477–1480, 1999.

Alleman, L. Y., B. Hamelin, A. J. Veron, J.-C. Miquel, and S. Heussner,Lead sources and transfer in the coastal Mediterranean: Evidence fromstable lead isotopes in marine particles, Deep Sea Res., Part II, 47,2257–2279, 2000.


Alleman, L. Y., T. M. Church, P. Ganguli, A. J. Veron, B. Hamelin, andA. R. Flegal, Role of oceanic circulation on contaminant lead distributionin the South Atlantic, Deep Sea Res., Part II, 48, 2855–2876, 2001a.

Alleman, L. Y., T. M. Church, A. J. Veron, G. Kim, B. Hamelin, and A. R.Flegal, Isotopic evidence of contaminant lead in the South Atlantic tropo-sphere and surface waters, Deep Sea Res., Part II, 48, 2811–2827,2001b.

Bacon, M. P., D. W. Spencer, and P. G. Brewer, 210Pb/226Ra and210Po/210Pb disequilibria in seawater and suspended particulate matter,Earth Planet. Sci. Lett., 32, 277–296, 1976.

Bollhoefer, A., and K. J. R. Rosman, Isotopic source signatures for atmo-spheric lead: The Northern Hemisphere, Geochim. Cosmochim. Acta, 65,1727–1740, 2001.

Boyle, E. A., S. D. Chapnick, G. T. Shen, and M. P. Bacon, Temporalvariability of lead in the western North Atlantic, J. Geophys. Res., 91,8573–8593, 1986.

Boyle, E. A., R. M. Sherrell, and M. P. Bacon, Lead variability in thewestern North Atlantic Ocean and central Greenland: Implications forthe search for decadal trends in anthropogenic emissions, Geochim. Cos-mochim. Acta, 58, 3227–3238, 1994.

Broecker, W. S., and G. H. Denton, The role of ocean-atmosphere re-orga-nizations in glacial cycles, Geochim. Cosmochim. Acta, 53, 2465–2501,1989.

Broecker, W. S., et al., Radiocarbon decay and oxygen utilization in thedeep Atlantic Ocean, Global Biogeochem. Cycles, 5, 87–117, 1991.

Chillrud, S. N., R. F. Bopp, H. J. Simpson, J. M. Ross, E. L. Shuster, D. A.Chaky, D. C. Walsh, C. C. Choy, and A. Yarme, Twentieth century atmo-spheric metal fluxes into Central Park Lake, New York City, Environ. Sci.Technol., 33, 657–662, 1999.

Chow, T. J., C. B. Snyder, and J. L. Earl, Isotope ratios of lead as pollutantsource indicators, in UN, FAO and IAEA Symposium, IAEA-SM-191/4,pp. 95–105, Int. At. Energy Agency, Vienna, 1975.

Church, T. M., A. J. Veron, C. C. Patterson, D. Settle, Y. Erel, H. R. Maring,and A. R. Flegal, Trace elements in the North Atlantic troposphere: Ship-board results of precipitation and aerosols, Global Biogeochem. Cycles,4, 431–443, 1990.

Doney, S. C., and W. J. Jenkins, Ventilation of the deep western boundarycurrent and abyssal western North Atlantic: Estimates from tritium and3He distribution, J. Phys. Oceanogr., 24, 638–659, 1994.

Dunlap, C. E., E. Steinnes, and A. R. Flegal, A synthesis of lead isotopes intwo millennia of European air, Earth Planet. Sci. Lett., 167, 81–88,1999.

Dunlap, C. E., R. N. Bouse, and A. R. Flegal, Past leaded gasoline emis-sions as non-point source tracer in riparian systems: A study of riverinputs to San Francisco Bay, Environ. Sci. Technol., 34, 1211–1215,2000.

Elbaz-Poulichet, F., P. Holliger, W. W. Huang, and J. M. Martin, Leadcycling in estuaries, illustrated by the Gironde estuary, France, Nature,308, 409–414, 1984.

Flegal, A. R., J. O. Nriagu, S. Niemeyer, and K. H. Coale, Isotopic tracersof lead contamination in the Great Lakes, Nature, 339, 455–458, 1989.

Fratantoni, D. M., North African surface circulation during the 1990sobserved with satellite tracked drifters, J. Geophys. Res., 106, 22,067–22,093, 2001.

Graney, J. P., A. N. Halliday, G. J. Keeler, J. O. Nriagu, J. A. Robbins, andS. A. Norton, Isotopic record of lead pollution in lake sediments fromnortheastern United States, Geochim. Cosmochim. Acta, 59, 1715–1728,1995.

Grousset, F. E., C. R. Quetel, B. Thomas, P. Buat-Menard, O. F. X. Donard,and A. Bucher, Transient Pb isotopic signatures in the western Europeanatmosphere, Environ. Sci. Technol., 28, 1605–1608, 1994.

Hamelin, B., F. E. Grousset, P. E. Biscaye, and A. Zindler, Lead isotopes inTrade wind aerosols at Barbados: The influence of European emissionsover the North Atlantic, J. Geophys. Res., 94, 16,243–16,250, 1989.

Hamelin, B., F. E. Grousset, and E. R. Sholkovitz, Pb isotopes in surficialpelagic sediments from North Atlantic, Geochim. Cosmochim. Acta, 54,37–47, 1990.

Hamelin, B., J. L. Ferrand, L. Alleman, and E. Nicolas, Isotopic evidence ofpollutant lead transport from North America to the subtropical NorthAtlantic gyre, Geochim. Cosmochim. Acta, 61, 4423–4428, 1997.

Helmers, E., and M. M. R. van der Loeff, Lead and aluminum in Atlanticsurface waters (50�N to 50�S) reflecting anthropogenic and naturalsources in the eolian transport, J. Geophys. Res., 98, 20,261–20,273,1993.

Hirao, Y., and C. C. Patterson, Lead aerosol pollution in the High Sierraoverrides natural mechanism which exclude lead from a food chain,Science, 184, 989–992, 1974.

Hopper, J. F., H. B. Ross, W. T. Sturges, and L. A. Barrie, Regional sourcesdiscrimination of atmospheric aerosols in Europe using the isotopic com-position of lead, Tellus, Ser. B, 43, 45–60, 1991.

Maneux, E., F. E. Grousset, P. Buat-Menard, G. Lavaux, P. Rimmelin, andY. Lapaquellerie, Temporal patterns of the wet deposition of Zn, Cu, Ni,Cd and Pb: The Arcachoon lagoon (France), Water Air Soil Pollut., 114,95–120, 1999.

Maring, H., C. C. Patterson, D. Settle, P. Buat-Menard, and F. Dulac, Stablelead isotope tracers of air mass trajectories in the Mediterranean region,Nature, 330, 154–159, 1987.

Nicolas, E., D. Ruiz Pino, P. Buat-Menard, and J. P. Bethoux, Abruptdecrease of lead concentrations in the Mediterranean: A response to antipollution policy, Geophys. Res. Lett., 21, 2119–2122, 1994.

Rabinowitz, M. B., and G. Wetherill, Identifying sources of lead contam-ination by stable isotope techniques, Environ. Sci. Technol., 6, 705–709,1972.

Reuer, M. K., and D. J. Weiss, Anthropogenic lead dynamics in the terres-trial and marine environment, Philos. Trans. R. Soc. London, Ser. A, 360,2889–2904, 2002.

Reuer, M. K., E. A. Boyle, and B. C. Grant, Lead isotope analysis of marinecarbonates and seawater by multiple collector ICP-MS, Chem. Geol., inpress, 2003.

Rosman, K. J. R., W. Chisholm, C. F. Boutron, J. P. Candelone, andU. Gorlach, Isotopic evidence for the source of lead in Greenland snowssince the late 1960s, Nature, 362, 333–334, 1993.

Rosman, K. J. R., C. Ly, K. Van der Velde, and C. F. Boutron, A twocentury record of lead isotopes in high altitude Alpine snow and ice,Earth Planet. Sci. Lett., 176, 413–424, 2000.

Sarmiento, J. L., A tritium box model of the North Atlantic thermocline,J. Phys. Oceanogr., 13, 1269–1274, 1983.

Schaule, B. K., and C. C. Patterson, Perturbations of the natural lead profilein the Sargasso Sea by industrial lead, in Trace Metals in Sea Water,edited by C. S. Wong et al., pp. 487–504, Plenum, New York, 1983.

Schell, W. R., M. J. Tobin, M. J. V. Novak, R. K. Wieder, and P. I. Mitchell,Deposition history of trace metals and fallout radionuclides in wetlandecosystems using Pb-210 chronology, Water Air Soil Pollut., 100, 233–239, 1997.

Schmitz, W. J., On the world ocean circulation: vol. I, WHOI-96-03, WoodsHole Oceanogr. Inst., Woods Hole, Mass., 1996.

Schmitz, W. J., and M. S. McCarthy, On the North Atlantic circulation, Rev.Geophys., 31, 29–49, 1993.

Shen, G. T., and E. A. Boyle, Lead in corals: Reconstruction of historicalindustrial fluxes to the surface ocean, Earth Planet. Sci. Lett., 82, 289–304, 1987.

Shen, G. T., and E. A. Boyle, Determination of lead, cadmium and othertrace elements in annually-banded corals, Chem. Geol., 67, 47–62,1988a.

Shen, G. T., and E. A. Boyle, Thermocline ventilation of anthropogenic Pbin the western North Atlantic, J. Geophys. Res., 93, 15,715–15,732,1988b.

Sherrell, R. M., E. A. Boyle, and B. Hamelin, Isotopic equilibrationbetween dissolved and suspended particulate lead in the Atlantic Ocean:Evidence from Pb-210 and stable Pb isotopes, J. Geophys. Res., 97,11,257–11,268, 1992.

Sherrell, R. M., E. A. Boyle, K. K. Falkner, and N. R. Harris, Temporalvariability of Cd, Pb, and Pb isotope deposition in central Greenlandsnow, Geochem. Geophys. Geosyst., 1, paper number 1999GC00000,2000. (Available at http//gcubed.magnet.fsu.edu/main.html)

Shotyk, W., D. Weiss, J. D. Kramers, R. Frei, A. K. Cheburkin, M. Gloor,and S. Reese, Geochemistry of the peat bog at Etang de la Gruere, JuraMountains, Switzerland, and its record of Pb and lithogenic trace ele-ments (Sc, Ti, Y, Zr, Hf, and REE) since 12,370 C-14 yr BP, Geochim.Cosmochim. Acta, 65, 2337–2360, 2001.

Sturges, W., and L. Barrie, The use of stable lead 206/207 isotope ratiosand elemental composition to discriminate the origins of lead in aero-sols at a rural site in eastern Canada, Atmos. Environ., 23, 1645–1657,1989.

Sturges, W. T., J. F. Hopper, L. A. Barrie, and R. C. Schnell, Stable leadisotope in Alaskan Arctic aerosols, Atmos. Environ., Part A, 27, 2865–2871, 1993.

Sy, A., M. Rhein, J. R. N. Lazier, K. P. Koltermann, J. Meinecke,A. Putzka, and M. Bersch, Surprisingly rapid spreading of newly formedintermediate waters across the North Atlantic Ocean, Nature, 386, 675–679, 1998.

van Geen, A., J. F. Adkins, E. A. Boyle, C. H. Nelson, and A. Palanques, A129 yr record of widespread contamination from mining of the Iberianpyrite belt, Geology, 25, 291–294, 1997.

Veron, A. J., and T. M. Church, Use of stable lead isotopes and trace metalsto characterize air mass sources into the eastern Atlantic, J. Geophys.Res., 102, 28,049–28,058, 1997.

Veron, A. J., C. E. Lambert, A. Isley, P. Linet, and F. E. Grousset, Evidenceof recent lead pollution in deep north-east Atlantic sediments, Nature,326, 278–281, 1987.


Veron, A. J., T. M. Church, A. R. Flegal, C. C. Patterson, and Y. Erel,Response of lead cycling in the surface Sargasso Sea to changes in tropo-spheric input, J. Geophys. Res., 98, 18,269–18,276, 1993.

Veron, A. J., T. M. Church, C. C. Patterson, and A. R. Flegal, Use of stableisotopes to characterise the sources of anthropogenic lead in North Atlan-tic surface waters, Geochim. Cosmochim. Acta, 58, 3199–3206, 1994.

Veron, A. J., T. M. Church, I. Rivera-Duarte, and A. R. Flegal, Stable leadisotopic ratios trace thermohaline circulation in the subarctic North Atlan-tic, Deep Sea Res., Part II, 46, 919–935, 1999.

Vink, S., E. A. Boyle, and C. I. Measures, Automated high resolutiondetermination of the trace elements aluminum and iron in the surfacewaters using a towed fish coupled to flow injection analyses, Deep SeaRes., Part II, 47, 1141–1156, 2000.

Weiss, D., W. Shotyk, P. G. Appleby, J. D. Kramers, and A. K. Cheburkin,Atmospheric Pb deposition since the Industrial Revolution recorded byfive Swiss peat profiles: Enrichment factors, fluxes, isotopic composition,and sources, Environ. Sci. Technol., 33, 1340–1352, 1999a.

Weiss, D., W. Shotyk, and O. Kempf, Archives of atmospheric lead pollu-tion, Naturwissenschaften, 86, 262–275, 1999b.

Weiss, D., V. Chavagnac, E. A. Boyle, J. F. Wu, and M. Herwegh, Deter-mination of lead isotope ratios in seawater by quadrupole inductivelycoupled plasma mass spectrometry after Mg(OH)2 co-precipitation,Spectrochim. Acta, Part B, 55, 363–374, 2000.

Weiss, D., E. A. Boyle, W. Shotyk, J. D. Kramers, and P. G. Appleby,Comparative study of the temporal evolution of atmospheric lead deposi-tion in Scotland and eastern Canada using blanket peat bogs, Sci. TotalEnviron., 292, 7–18, 2002.

Wu, J., and E. A. Boyle, Lead in the western North Atlantic Ocean: Com-pleted response to leaded gasoline phase out, Geochim. Cosmochim.Acta, 61, 3279–3283, 1997a.

Wu, J., and E. A. Boyle, Low blank pre-concentration technique for thedetermination of lead, copper and cadmium in small-volume samples byisotope dilution ICP-MS, Anal. Chem., 69, 2464–2470, 1997b.

��E. A. Boyle and A. Michel, Earth, Atmospheric, and Planetary Sciences,

Massachusetts Institute of Technology, Cambridge, MA 02139, USA.V. Chavagnac, Southampton Oceanographic Center, University of

Southampton, Southampton SO14 32H, UK.M. K. Reuer, Department of Geosciences, Princeton University, 152

Guyot Hall, Princeton, NJ 08544, USA.D. Weiss, Department of Earth Science and Engineering, Imperial

College, London SW7 2BP, UK. ([email protected])J. Wu, International Arctic Research Center/Frontier, University of

Alaska at Fairbanks, P.O. Box 757335, Fairbanks, AK 99775-7335, USA.


Documents

Spatial and temporal evolution of lead isotope ratios in the North …boyle.mit.edu/~ed/PDFs/Weiss(2003)JGR.pdf · 2003-12-23 · Spatial and temporal evolution of lead isotope ratios