Return of naturally sourced Pb to Atlantic surface waters (original) (raw)
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Journal of Geophysical Research, 1989
Previous studies have shown that Pb can be used as a transient tracer in the atmosphere and the ocean because of strong time-variability of industrial inputs and because Pb isotopic composition can be used to identify contributions from different sources. We present Pb isotopic measurements on aerosols collected from the North Atlantic Ocean in the trade wind belt. Aerosols sampled at Barbados during the 1969-1985 period have a Pb isotopic composition different from that observed by previous investigators in Bermuda corals and Sargasso Sea waters. Barbados aerosols appear to contain significant amounts of relatively unradiogenic industrial and automotive Pb that is derived from Europe and carded to Barbados by the trade winds. In contrast, Bermuda corals and Sargasso sea waters are influenced mainly by U.S.-derived emissions, which contain more radiogenic Pb originating from Missouri-type ores. This difference generates a strong latitudinal Europe-U.S.A. isotopic gradient, thus allowing study of trans-Atlantic atmospheric transport and ocean mixing processes. 16,244 HAMELI• ET nL.: • ISOT• I• BAR•OS Tm•E Wm-• A•OSOLS Cape Verde Basin (#CV6, #CV7), all by R. Chester. We added one aerosol from the Red Sea (#R) collected in 1983 by R. Lenaz. We will also refer in the discussion to three aerosol measurements from the western Mediterranean Sea in 1981 and ISOTOP• IN BaRB•OS TP•a•E Wm'D A•OSOLS 16,249
Journal of Geophysical Research: Oceans, 1992
Decreased consumption of leaded gasoline in the United States over the past two decades has drastically altered the flux and isotopic composition of Pb entering the western North Atlantic from the atmosphere. Here we exploit the resulting temporal changes in the distribution and isotopic composition of oceanic Pb to investigate interactions between dissolved and particulate Pb in the oceanic water column. Measurements of dissolved Pb isotopic composition on samples collected in 1987 in the upper water column near Bermuda demonstrate that surface water 206Pb/207Pb decreased from ∼1.203 to ∼1.192 since 1983 and that a measurable change propagated to 300–500 m since the 1984 profile of Shen and Boyle (1988). The first accurate measurements of suspended particulate Pb in an open ocean profile show concentrations of 1–3 pmol/L, equal to 2–4% of total Pb. Vertical profiles of (1) the stable lead isotopic composition and (2) the ratio of total Pb to 210Pb in suspended particles closely tra...
Isotopic evidence of contaminant lead in the South Atlantic troposphere and surface waters
Deep-sea Research Part Ii-topical Studies in Oceanography, 2001
The third Intergovernmental Oceanographic Commission (IOC) Baseline Contaminant cruise (May–June 1996) has established the first lead isotopic compositions in the surface water and the atmosphere of the Equatorial and South Atlantic Ocean. These ratios have evidenced both anthropogenic and natural origins of lead along the cruise transect (from 33°S to 10°N). The isotopic gradients tentatively have been, attributed to aeolian as well as surface-water advective inputs from a suite of rather local and remote sources to the Southern Hemisphere. Relatively low 206Pb/207Pb ratios (x±sd) were encountered within the South Equatorial Current between 17°S and 5°S (1.156±0.003). Those were bracketed by more radiogenic ratios at higher latitudes in the Southern Hemisphere (33°S to 23°S), within the Brazil Current and the Subtropical Gyre (1.163±0.003), and in the Northern Hemisphere (0° to 10°N) (1.165±0.005). The latter were comparable to ratios of surface water in the North Atlantic Equatorial Ocean (1.169±0.006), under a combined contaminant influence of both North American westerlies (1.19–1.20) and European easterlies (1.155–1.165). That predominance of contaminant lead contrasts with the measurable presence of natural lead in surface waters of the Equatorial Ocean, which are attributed to aeolian inputs of Saharan dust. The ratios of lead in surface waters at higher latitudes in the South Atlantic are characteristic of anthropogenic lead aerosols also detected in Antarctic ice, and could substantiate as well the hypothesized aerosol recycling of lead by sea-spray emission in the far Southern Hemisphere. The atmospheric lead isotopic compositions (206Pb/207Pb) in bulk depositions (1.171±0.006), precipitation (1.171±0.006) and aerosols (1.168±0.011) were, generally, more radiogenic than the surface waters (1.162±0.005). Beside a poor representation of a short term atmospheric sampling, this difference could reflect a recent evolution in atmospheric lead emissions, which have not yet been reflected in oceanic surface waters. It may also be due, in part, to advective lead inputs from surface oceanic circulation of the South Equatorial Current.
Journal of Geophysical Research, 2003
Lead concentrations and isotope ratios were measured in North Atlantic surface water 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 Basin averaged 1.193 +/- 0.005 (1 sigma). Similar radiogenic ratios within the level of analytical precision (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 layer signatures along with atmospheric global lead emission patterns suggest that most North Atlantic lead in the early 1980s was derived from North American leaded gasoline. Samples in the East Iberian Basin near Portugal and France showed lower 206Pb/207Pb ratios, between 1.167 and 1.182, indicating a significant influence of less radiogenic atmospheric lead transported from Europe and possibly the influence of the Rio Tinto acid mine drainage very close to shore in the Gulf of Cadiz. [Pb] across the entire...
Lead isotopes in marine surface sediments reveal historical use of leaded fuel
Analyses of lead (Pb) isotopes have been performed in terrestrial and fresh water environments to estimate historical uses of leaded fuel, but so far this method has not been employed in studies of worldwide marine surface sediments. We analyzed Pb and its isotopes in 23 surface sediments from four continents collected during the Galathea 3 expedition in 2006–2007. To enhance the anthropogenic signal, a partial digestion using nitric acid was performed. The concentrations of Pb, Th, U and Al were determined with an ICP-Quadrupole MS, and Pb-isotope ratios with an ICP-multi-collector MS. The samples could be divided into three groups: Harbor areas in larger cities with concentrations of 150 to 265 mg kg À1 dry weight, smaller towns with concentrations between 20 and 40 mg kg À1 dry weight, and remotely located sites with concentrations below 15 mg kg À1 dry weight. Pb-isotope ratios were compared to literature values for gasoline and local or geological background values, and the contribution of leaded-gasoline to total concentrations was calculated for contaminated sites using both a one-dimensional and a novel two-dimensional (vector) method. The North American sites had Pb-isotope ratios corresponding to the US leaded gasoline, with 24–88% of the Pb from leaded gasoline. Samples from Oceania showed Pb-isotope ratios corresponding to Australian gasoline, with 60% attributed to leaded gasoline in Sydney and 21% in Christchurch. Outside Cape Town, 15 to 46% of Pb in sediments was from leaded gasoline.
Journal of Geophysical Research. D. Atmospheres, 1997
Stable lead isotopes (2ø4pb, 2ø6pb, 2ø7pb, 2ø8pb) and trace metals (Mn, A1, Fe, Ni, Cu, Cd, Zn, Pb) have been analyzed in aerosol collected during the Atlantic Stratocumulus Transition Experiment-Marine Aerosol and Gas Exchange (ASTEX-MAGE) cruise that transited between Miami and the Azores from May to July 1992. Our goal was to define the continental signatures of the air masses encountered between the Azores and the subtropical regions. The combination of air mass trajectories, trace metal concentrations and stable lead isotopes allowed us to characterize the anthropogenic character of encountered air masses. The average 2ø6pb/2ø7pb ratio was 1.148+_0.021 and corresponded to a mixing between well defined European (such as Great Britain with 1.115 < 2ø6pb/2ø7pb < 1.125 and France with 206Pb/2ø7pb = 1.141 _+ 0.000) and North American sources (with 2ø6pb/2ø7pb = 1.184 +_ 0.000). On the basis of air mass trajectories and trace metal concentrations, the background isotopic signature associated with the trade winds (2ø6pb/2ø7pb= 1.161 _+0.004) is consistent with previous reports by Church et al. [1990] such as 2ø6pb/2ø7pb = 1.154 +_ 0.004 in 1988, (V•ron et al., 1993), 2ø6pb/2ø7pb= 1.155+_0.004 in 1989, and Hamelin et al. [1996] (2ø6pb/2ø7pb = 1.158_+ 0.006) in 1991. Short-term variations of continental air mass sources was particularly investigated by considering the anthropogenic character of aerosols collected during two Lagrangian experiments conducted as part of the ASTEX-MAGE cruise. We demonstrated the utility of stable lead isotopes to assign a "continental source signature" (or mixture thereof) to air masses beyond that normally possible by conventional air mass trajectory analysis in remote oceanic regions. Introduction Trace metal sources in the remote ocean include continemally derived anthropogenic (metal refining and fuel combustion) and natural (volcanoes, soil erosion, vegetation) origins [Duce et al., 1975; Goldberg, 1976; Patterson and Settle, 1987; Lambert, 1988; Nriagu and Pacyna, 1988] as well as marine derived trace metals resuspended from surface seawater [Blanchard, 1983; Weisel et al., 1984]. Due to the extensive urbanized and industrialized areas in the North Atlantic, most of the trace metals are greatly enriched in the troposphere relative to crustal sources [Duce et al., 1976]. Anthropogenic trace metals are generally associated with submicron aerosols which can be transported far from their sources, into the remote oceanic troposphere, and before their deposition by wet or dry removal processes [Slinn and Slinn, 1981; Slinn, 1983; Arimoto et al., 1985; Arimoto and Duce, 1986]. Sea-salt spray and natural crustal contributions to airborne lead were found not to be Lead anthropogenic perturbation has been monitored using stable isotopes of lead measured in ice cores [Rosman et al,, 1993], corals [Shen and Boyle, 1987], surface seawater [Vdron et al., 1993] and pelagic sedimems [Vdron et al., 1987; Hamelin et al., 1990]. Indeed, these isotopes display specific anthropogenic signatures from the different countries surrounding the North Atlantic owing to the variety of lead ores used in the industry or to produce alkyl lead additives for gasoline [Chow et al., 1975; Church et al., 1990;
Role of oceanic circulation on contaminant lead distribution in the South Atlantic
Deep-sea Research Part Ii-topical Studies in Oceanography, 2001
Both the relatively high lead concentrations and their characteristic anthropogenic isotopic compositions attest to the widespread contamination of industrial lead in the western Equatorial and South Atlantic Ocean. Spatial gradients in those isotopic signatures evidence the conservative lateral transport of lead in oceanic water masses, while the discrete isotopic signatures in deep oceanic waters substantiate the complementary hypothesis that the release of lead from settling particles is relatively small on a decadal time-scale. Specifically, the relatively low radiogenic lead (e.g., 206Pb/207Pb=1.148±0.009) in the Lower-North Atlantic Deep Water (l-NADW) south of 10° North is primarily attributed to US industrial lead emitted in the Northern Hemisphere prior to 1965, and the more radiogenic lead (e.g., 206Pb/207Pb=1.180±0.006) in the Upper-North Atlantic Deep Water (u-NADW) is primarily attributed to subsequent industrial lead emissions in that hemisphere. In contrast, the relatively radiogenic lead (e.g., 206Pb/207Pb=1.186±0.007) in the Antarctic Bottom Water (AABW) seemingly reflects a mixture of natural and anthropogenic lead sources within the Southern Hemisphere; and its isotopic dissimilarity with that (e.g., 206Pb/207Pb=1.159±0.002) of Antarctic Intermediate Water (AAIW) and the AABW may be due to differences in either their aeolian or water-mass inputs.
Journal of Geophysical Research, 1993
Lead and aluminum were measured with a 40-100 km resolution in surface water on two transects across the Ariantic Ocean, one in May 1990 from Cape Town to the North Sea, the other in November 1990 from the North Sea to the Strait of Magellan. Samples were drawn 14 m below surface at normal speed from a 2-m-long snorkel system mounted on the bottom of the ship directly into a clean-room area. In the tropics, both Pb and A1 show maximum concentrations in the Intertropical Convergence Zone (rrcz) correlated with each other and with minimum salinities, indicating wet deposition as their common source. Even in this area characterized by large inputs of mineral aerosols, the Pb/AI ratio shows that the major source of soluble lead (>95%) is anthropogenic. At higher latitudes, AI is low throughout (10-20 nmol/kg), whereas enhanced Pb values show the anthropogenic inputs off south Africa, northern Argentina and especially western Europe. Very low Pb and especially A1 concentrations in the upwelling areas associated with the Canary and Benguela currents show that the enhanced biogenic particle fluxes cause an efficient scavenging of both lithogenic particles known to arrive here by dry deposition, and of the adhering reactive trace metals.
Geochimica Et Cosmochimica Acta, 1994
Stable lead isotopes are used to illustrate the impact of surface water circulation on dissolved lead distribution in North Atlantic surface waters during oligotrophic conditions. Using stable lead isotopic signatures from (1) the Sargasso Sea and (2) direct tropospheric deposition to the North Atlantic, we estimate that 10–40% of the lead accumulated in surface waters of the European Basin is transported from the western North Atlantic by the North Atlantic Current. South of 50°N, lead appears to be primarily distributed by the Subtropical North Atlantic Gyre that extends well beyond the western basins to 30°W in the North African Basin (at 30–40°N). There are different lead isotopic signatures between the subtropical gyre to the Guiana and western Guinea Basins, which suggests that the Inter Tropical Convergence Zone acts as an efficient barrier limiting chemical exchanges between the gyre and the equatorial currents.