C.C. Patterson

Chemical concentrations of pollutant lead aerosols, terrestrial dusts and sea salts in Greenland and Antarctic snow strata☆

Abstract In this study we report analyses of lead in annual ice layers from the interior of northern Greenland and in annual layers of ice from the interior of the Antarctic continent. We show that lead concentrations increase from 0.200 γPb/kg ice today in north pole ice sheets, the sharpest rise occurring after 1940, and that the levels of lead in south polar ice sheets are generally below our detection limits before 1940 and rise only to about 0.020 γPb/kg ice after 1940 (in this paper the symbol gamma, γ, means microgram, 10 −6 g). The increase of lead with time in north polar snows is ascribed mainly to lead smelteries before 1940 and to burned lead alkyls after 1940. The difference between the concentrations of lead in northern and southern polar snows is ascribed to barriers to north-south tropospheric mixing which originate from meridional circulating cells and which hinder the migration of aerosol pollutants from the northern hemisphere to the Antarctic. Our observations of the chemical concentrations of the common elements in ice from the interior of Greenland and Antarctica can be explained in terms of simple relations among sea salts and terrestrial dusts. We found about ten times more dust in Greenland interior ice (35 γ/kg) than in Antarctic interior ice (~2 γ/kg), but found twice as much sea salt in Antarctic interior ice (110 γ/kg) than in Greenland interior ice (67 γ/kg). We found that the proportions of sodium, chlorine, magnesium, calcium, and potassium adhered closely to sea salt ratios in ices that were relatively free of silicate dusts, even when the concentrations of sea salts decreased from 1100 γ/kg in NW coastal Greenland ice to 110 γ/kg in Rockefeller Plateau ice in the Antarctic interior. We also found that the amounts and chemical composition of silicate dusts in Greenland were no different in coastal and interior ices, averaging 3 γ Mg, 5.6 γCa, 2.0 γK, 0.1 γTi and 6.8 γSi per kg ice respectively in the interior. We found that there are seasonal variations in the amounts of pollutant lead, sea salts and silicate dusts in the snows, pollutant lead and sea salts being two or three times more concentrated in winter than in summer snows, while silicate dusts were three times more concentrated in spring than in winter snows. The above interpretation, which unifies all the data, is consistent with most related chemical and meteorological observations at temperate latitudes.

Age of meteorites and the earth

Within experimental error, meteorites have one age as determined by three independent radiometric methods. The most accurate method (Pb207/Pb206 gives an age of 4.55 ± 0.07 × 109 yr. Using certain assumptions which are apparently justified, one can define the isotopic evolution of lead for any meteoritic body. It is found that earth lead meets the requirements of this definition. It is therefore believed that the age for the earth is the same as for meteorites. This is the time since the earth attained its present mass

Chronological variations in concentrations and isotopic compositions of anthropogenic atmospheric lead in sediments of a remote subalpine pond

Lead concentrations decrease 4-fold in going from the surface of sediments in a mountain pond to relatively small values in layers 130 yr old. There is a corresponding change in the Pb^(206)/Pb^(207) ratio in the sediments from industrial-like values of 1.18 near the surface to natural values of 1.24 at depth. Concentrations of Ca, Sr, and Ba remain relatively constant with depth. The excess Pb is shown to be of eolian anthropogenic origin, through isotopic, chemical, and mass balance relationships with metals in aerosols, dry deposition, and precipitation. This proves that inputs of contamination Pb were nearly absent centuries ago in a remote non-domesticated subalpine canyon, but are present today in that ecosystem in amounts more than 20 times the natural inputs and are irrefutably linked with industrial sources. As a consequence of these inputs, present Pb concentrations have been elevated 5-fold in plants and 50-fold in animals above natural levels. These Pb contamination effects are being caused by present-day atmospheric concentrations of ~10 ng Pb/m^3. The ecosystem studied here characterizes the vast remote non-domesticated regions of North America, and these findings indicate that such regions are highly polluted by industrial Pb aerosols.

Vertical concentration profiles of lead in the Central Pacific at 15°N and 20°S

Concentrations of lead were measured in a surface transect and at two vertical profile stations (15°N and 20°S) in the Central Pacific. These measurements complement similar measurements made earlier in the North Pacific at 33°N and in the Northwest Atlantic at 34°N, as well as recent measurements of eolian lead input fluxes near each of these locations. The new transect of surface water concentrations of lead corroborates previous measurements, which decrease from 13 ng/kg at 30°N to 4 ng/kg at 17°S in the Central Pacific. This transect gradient is shown to overlie a similar geographic gradient of subsurface maximum concentrations of lead in the three Pacific vertical profile stations, decreasing from 14 ng/kg at 33°N to 11 ng/kg at 14°N to 2.5 ng/kg at 20°S. Lead concentrations at each of those locations exhibit maxima at 400 m, decreasing concentrations to 2500 m and approximately concentrations of 0.8–1.1 ng/kg below that depth. The subsurface maximum at the northwest Atlantic profile station (36 ng/kg at 34°N) is also congruent with surface water lead concentrations which decrease from 806 ng/kg to 32 ng/kg in an offshore transect from Rhode Island to 34°N, 66°W, and the shape of the Atlantic profile is congruent with those in the Pacific. There is a positive correlation between the magnitudes of eolian lead input fluxes and the magnitudes of the upper water maxima in lead concentration profiles at corresponding locations as follows: South Pacific easterlies 3 ng/cm^2 yr vs. 2.5 ng/kg; North Pacific easterlies 6 ng/cm^2 yr vs. 11 ng/kg; North Pacific westerlies 50 ng/cm^2 yr vs. 14 ng/kg; and North Atlantic westerlies 170 ng/cm^2 yr vs. 36 ng/kg. This relationship enables one to view the anthropogenic perturbations of the marine lead cycle on a global scale, since the industrial origin of eolian and seawater lead has been established by correlations between geographic patterns of industrial lead emissions to the atmosphere and isotopic ratios of industrial leads and by geographic patterns of Pb/silicate-dust ratios and lead isotopic ratios in ocean surface waters. These new data coupled with earlier biogeochemical data indicate that surface water concentrations of lead in the North Pacific and North Atlantic are now conservatively estimated to be 8 to 20-fold greater and those in the South Pacific are 2-fold greater than natural concentrations because of industrial emissions of lead to the atmosphere.

The significance of lead isotopes in detrital feldspar with respect to chemical differentiation within the earth's mantle

On a continental scale, leads in K-feldspars from North America were found to deviate from closed system evolution such that there is an excess of Pb206 and, in lesser extent, Pb208 which increases as the age of the feldspar decreases. This effect can be shown to result from the transport of uranium and thorium, over long periods in the past, from the interior of the earth to an outer mantle layer which functioned as a source of segments of continental crust that were formed and isolated at different times and locations. The effect is decisive in defining, as a function of time, the rates of transport of uranium, thorium and lead from the inner mantle to the outer mantle : there was a sharp decrease in the rates of transport of these three elements during the first one hundred m.y. after the earth was formed; during the remaining aeons, lead transport became essentially zero while uranium and thorium transport remained appreciable. The effect also suggests that the bulk of the North American continent was formed during the interval 3500-2500 m.y. ago.

The Pb207/Pb206 ages of some stone meteorites

Abstract The isotopic compositions have been determined for the leads isolated from three stone meteorites. Based upon certain assumptions, Pb 207 /Pb 206 ages of about 4.5 × 10 9 years are calculated for the meteorites. The lead data indicate that the concentrations of uranium should be about 0.1 p.p.m. and the concentrations of thorium should be about 0.5 p.p.m. in stone meteorites.

USE OF STABLE LEAD ISOTOPES TO CHARACTERIZE THE SOURCES OF ANTHROPOGENIC LEAD IN NORTH ATLANTIC SURFACE WATERS

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.

Natural levels of lead and cadmium in a remote mountain stream

Lead and cadmium concentrations in marine and terrestrial ecosystems, on surfaces of soil particles, and in the atmosphere have been highly elevated on a global scale because of industrial pollution. In order to ascertain the natural (rock-derived) levels of lead and cadmium in streams, a pristine mountain watershed in the Sierra Nevada, California, was studied in respect to its lead and cadmium contents. The transport of lead and cadmium was compared to iron since it shares similar transport patterns with lead and cadmium, and is relatively uninfluenced by pollution. The concentrations of lead and cadmium in a late-summer mountain drainage water are shown to be close to natural levels that are controlled by the weathering of bedrock and soil. This is demonstrated by (1) measurements of lead isotopic composition, and Fe/Pb ratios in stream water, ground water, soil and bedrock, and (2) the rapid removal rate of excess atmospheric lead and cadmium from the water as it flows downstream. Lead is taken up by particles (mostly hydrous iron oxides) in the studied stream during the autumn at a relatively constant rate. On the other hand, cadmium behavior in the stream water is erratic and cannot be explained by the same adsorption mechanism as lead. The Fe/Pb ratio is constant within an order of magnitude in the bedrock, the soil, soil and rock leachates, unfiltered and filtered ground water, and in filtered and unfiltered stream water. Therefore, the Fe/Pb ratio may provide a first-order estimate for the concentration of natural lead in streams draining through granitoid bedrocks.

LEAD ISOTOPES IN MANGANESE NODULES

Abstract The isotopic compositions of leads which were isolated from manganese nodules of the Atlantic and the Pacific Oceans were determined. The Atlantic leads were more radiogenic than those of the Pacific. The Pacific samples showed a trend of increasing radiogenic leads from the north-west toward the south-east Pacific. The relationship between the collecting sites and the isotopic compositions of leads can be used to trace the circulation patterns of deep-water masses. The oceanic leads originated from rock systems whose uranium and lead contents have differentiated at various times appreciably later than 4·5 × 109 years.