Anthropogenic lead isotopes in Antarctica

We report the first measurements of Pb isotopes in Antarctic snow, which show that even recent snow containing 2.3 pg/g is highly polluted with anthropogenic Pb. This follows from a comparison of isotope abundances of Pb in surface snow and terrestrial dust extracted from ancient Antarctic ice (Dome C, depth 308 m, approximate age 7,500 a BP), the latter being distinctly more radiogenic. This result is independent of geochemical arguments based on measurements of Al, Na and SO_4. South America is suggested as a likely source of this anthropogenic Pb. The presence of significantly less radiogenic Pb in the snow adjacent to two Antarctic base stations indicates that there is contamination from station emissions, although emission from Australia is an alternative explanation for a site 33 km from Dumont d'Urville

Isotopic and elemental relics of the 1815 AD Tambora eruption in ice from Law Dome, Antarctica

Lead isotopes and Pb, Ba and Bi concentrations have been recently measured at sub-annual resolution in an ice core section from Law Dome, Antarctica, corresponding to the period 1814-1819 AD and containing a SO$^{2-}_4$signal attributed to the 1815 AD eruption of Tambora volcano in Indonesia. While increasing concentrations of Pb and Bi coincide with the 1817-1818 AD volcanic SO$_4^{2-}$ peak, Pb isotope data do not confirm Tambora as the source. Barium concentrations were elevated from 1816.5 to 1818.5 AD, indicating increased atmospheric dust levels. These findings contribute to the growing body of data indicating that effusive, rather than explosive, volcanism is the most important volcanic emission process determining the flux of volcanogenic heavy metals to the polar ice sheets

Determination of bismuth down to sub PG/G level in Greenland snow by laser excited atomic fluorescence spectrometry

We present here preliminary data on the first direct determination of Bi in Greenland recent snow down to the sub pg/g level by Laser Excited Atomic Fluorescence (LEAF) spectrometry in clean room conditions. Calibration of the spectrometer was achieved using ultralow concentration Bi standards (concentration range 0.05 - 50 pg/g). The limit of detection was found to be 2.5 fg Bi. Various Greenland samples were analysed, giving Bi concentration values in good agreement with these anticipated from the available volcanic emissions data

Strontium isotope measurements in Greenland ice from the last glacial maximum to the early Holocene

Strontium isotopic composition and concentration have been measured by thermal ionisation mass spectrometry on a suite of samples from the GRIP ice core drilled at Summit, Greenland. The sample ages range from ~24 to ~7.3 ky BP extending from the last glacial maximum into the early Holocene. Less than 10 g of sample was used for each analysis. No attempt was made to separate soluble/insoluble species in the samples. Sr concentrations are between ~950 and ~1,550 pg.g$^{-1}$ over the period ~24 ky to ~14 ky BP but fall dramatically to generally less than 150 pg.g$^{-1}$ between ~14 to ~7.3 ky BP. The $^{87}$Sr/$^{86}$Sr ratio shows a general rising trend from ~0.712 to ~0.715 over the entire period however there are a number of significant deviations from this trend which are most likely due to changing source regions for aerosol dust input to Greenland. Sr isotopic composition shows a strong correlation with $\delta^{80}$O suggesting that climate plays a strong role in determining regions for dust release

Simultaneous determination of picogram per gram concentrations of Ba, Pb and Pb isotopes in Greenland ice by thermal ionisation mass spectrometry

International audienceA technique has been developed to simultaneously measure picogram per gram concentrations of Ba and Pb by isotope dilution mass spectrometry, as well as Pb isotopic ratios in polar ice by thermal ionisation mass spectrometry. and Pb+ ions were employed for these determinations. A calibrated mixture of enriched 205Pb and 137Ba was added to the samples providing an accuracy of better than approximately 2% for Pb/Ba element ratio determinations. Interference by molecular ions in the Pb mass spectrum occurred only at 204Pb and 205Pb, but these contributions were negligible in terms of precisions expected on picogram-sized Pb samples. The technique is illustrated with measurements on Greenland firn, using a drill-core section that includes the Laki volcanic eruption of 1783–1784. The data show deviations from the element concentrations indicating volatile metal enrichments, but the Pb isotopic signature of the Laki lava could not be identified

Effect of trace metal availability on coccolithophorid calcification

The deposition of atmospheric dust into the ocean has varied considerably over geological time. Because some of the trace metals contained in dust are essential plant nutrients which can limit phytoplankton growth in parts of the ocean, it has been suggested that variations in dust supply to the surface ocean might influence primary production. Whereas the role of trace metal availability in photosynthetic carbon fixation has received considerable attention, its effect on biogenic calcification is virtually unknown. The production of both particulate organic carbon and calcium carbonate (CaCO3) drives the ocean\u27s biological carbon pump. The ratio of particulate organic carbon to CaCO3 export, the so-called rain ratio, is one of the factors determining CO2 sequestration in the deep ocean. Here we investigate the influence of the essential trace metals iron and zinc on the prominent CaCO3-producing microalga Emiliania huxleyi. We show that whereas at low iron concentrations growth and calcification are equally reduced, low zinc concentrations result in a de-coupling of the two processes. Despite the reduced growth rate of zinc-limited cells, CaCO3 production rates per cell remain unaffected, thus leading to highly calcified cells. These results suggest that changes in dust deposition can affect biogenic calcification in oceanic regions characterized by trace metal limitation, with possible consequences for CO2 partitioning between the atmosphere and the ocean

An 800-Year Record of Atmospheric As, Mo, Sn, and Sb in Central Asia in High-Altitude Ice Cores from Mt. Qomolangma (Everest), Himalayas

As, Mo, Sn, and Sb have been determined by inductively coupled plasma sector field mass spectrometry (ICP-SFMS) in 143 depth intervals of high-altitude ice cores from Mt. Everest, covering an 800-year time period from 1205 to 2002 AD. The results clearly demonstrate the long-term historical record of atmospheric transport and deposition of As, Mo, Sn, and Sb that has prevailed at high altitudes in the central Himalayas. Natural contributions, mainly from mineral dust, have dominated the atmospheric cycles of As, Mo, Sn, and to some extent Sb during the 700 years prior to the 20th century. Compared to those of the pre-1900 period, pronounced increases of both concentrations and crustal enrichment factors are observed since the 1970s, with the highest increase factor for Sn and the lowest for As. Such increases are attributed to anthropogenic emissions of these elements, largely from stationary fossil fuel combustion and nonferrous metals production, particularly in India. Our central Himalayan ice core record provides an explicit recognition of rising atmospheric As, Mo, Sn, and Sb pollution in response to rapid economic growth in central Asia