Description: This contribution aims to report the reflections we had with the scientific community during two international workshops on reference materials for stable isotopes in Davos (2002) and Nice (2003). After evaluating the isotopic homogeneity of some existing reference materials, based on either certificates, literature data or specific inter-laboratory rounds, we confirm these as primary reference materials or propose new ones relative to which stable isotope compositions should be reported. We propose DSM-3 for Mg, NIST SRM 915a for Ca, L-SVEC for Li and NBS28 for Si. Cadmium does not yet have a well identified delta zero material, although three commercial mono-elemental Cd solutions have yielded the same isotopic composition relative to one another. In order to scale the linearity of any mass spectrometer, some secondary reference materials are also proposed: Cambridge-1 solution for Mg, the “Münster-Cd” and JEPPIM Cd solutions for Cd and the “Big Batch” silicate for Si. The team from Nancy propose to prepare a mixed spike solution for Li isotopes. Well-characterised natural samples such as ocean or continental waters, diatoms, sponges, rocks and minerals are needed to validate the entire analytical procedure, particularly to take into account the effect of sample mineralisation and of chemical manipulations for elemental separation prior to analysis.

Description: Molybdenum (Mo) isotopic data from early Cambrian formations in southern China demonstrate the importance of non-euxinic sediments as a promising archive for coeval seawater Mo records. For the first time, in analogue to noneuxinic, nonskeletal carbonates, we report that the pristine phosphorites also can preserve the ambient fluid, which make the pristine phosphorites a new potential fingerprinting tool to record the coeval paleoseawater. Pristine phosphorite and dolomite samples of two early Cambrian formations in southern China suggest that early Cambrian seawater may have had {delta}97/95Mo values of at least 1.4{per thousand}, similar to modern oceans. Low {delta}97/95Mo (as low as -0.5{per thousand}) values were obtained from reworked phosphorite, but evidence suggests that these are reflecting Mo related to Fe oxyhydroxide minerals rather than the coeval seawater. In contrast, late Precambrian dolomite just below the transition to the Cambrian would indicate a {delta}97/95Mo of coeval seawater slightly heavier than that of the Mesoproterozoic (0.9{per thousand}-1{per thousand} versus 0.8{per thousand}), suggesting that oceanic circulation patterns may have been thoroughly reorganized by that time, and may have triggered biological diversification from the Ediacaran to the early Cambrian.

Description: Elemental and Pb isotope measurements were performed on leachates and residues from surface sediments and two 〈50 cm cores (MC04 and MC16) collected along a NE-SW transect through Fram Strait. Geochemical and isotopic properties of residues from surface sediments define three distinct spatial domains within the Strait: 1) the easternmost edge of the Strait; 2) the eastern part of the Strait off the Svalbard margins; and 3) the western part of the Strait, influenced by supplies from Svalbard, the Nordic seas with possible contributions from northwestern Siberian margins, and sea ice and water outflow from the Arctic, respectively. Core MC16, in the third domain beneath the outflowing Arctic waters, spans the Last Glacial Maximum present interval. Sediments from this core were leached to obtain detrital (residues) and exchangeable (leachates) fractions. Detrital supplies to core MC16 are believed to originate mainly from melting of the overlying sea ice and thus can be used to document changes in Arctic sedimentary sources. Detrital 206Pb/204Pb and 208Pb/206Pb ratios illustrate two mixing trends, Trends A and B, corresponding to the pre- and post-Younger Dryas (YD) intervals, respectively. These trends represent binary mixtures with a common end-member (Canadian margins) and either a Siberian (Trend A) or Greenland (Trend B) margin end-member. The YD is marked by an isotopic excursion toward the Canadian end-member, suggesting a very active Beaufort Gyre possibly triggered by massive drainage of the Laurentide ice sheet. Pb isotope compositions of leachates, thought to represent the signature of the overlying water masses, define a unique linear trend coincident with Trend A. This suggests that water masses acquired their signature through exchange with particulate fluxes along the Canadian and Siberian continental margins.

Description: Iron mining in Schefferville (1939-1977) in subarctic Quebec has left behind large numbers and quantities of tailing deposits. The impact of past mining activity on aquatic ecosystems in the Schefferville area has been studied using geochemical and isotopic (Pb, Zn and Fe) analyses of lake sediments, ore deposits, tailings and epiphytic lichens. Analysis of two sediment cores from Lakes Dauriat and Oksana reveals that the surface geochemical cycle of the Schefferville area has been profoundly disturbed by anthropogenic activity such as mining. Disturbances were particularly abrupt at the transitions from pre-mining to mining and mining to post-mining periods. Elemental and isotopic analyses of the lake sediments reveal four different end-member contributions to the lake sedimentation, with changes in terms of sources and source contribution observed throughout the sedimentation history. End-members were identified using Pb, Zn and Fe isotopes and are consistent for each element. Lead isotope ratios vary from highly radiogenic (206Pb/204Pb = 27) to less radiogenic (206Pb/204Pb = 17.7) from the bottom to the top of the sediment cores. Iron isotope compositions vary from -0.2 per mil to 1per mil, the latter value remaining constant throughout the sedimentary history of Lake Oksana. A systematic difference in the Zn isotope ratios of the two lakes is also observed, and can be explained by local differences in basin lithology. In order to identify pollution sources, samples from ores and tailings and epiphytic lichens were measured as proxies of mining activity, lithology, and atmospheric deposition, respectively. The impact of anthropogenic activity is clearly evident in the sediment records and results from mining activity, as well as local urban and industrial activities (waste water inputs). Long-range atmospheric deposition also accounts for some of the variations in isotopic composition measured in the sediments. The systematic coupling of Pb isotopes with Zn or Fe isotopes allows us to identify and constrain the metal sources that contributed to sediment contamination. This study demonstrates that disturbance due to mining activities is very effective in rapidly modifying lake sediment composition. Though the disturbances remained local in terms of geographic extent, the damage to the aquatic ecosystem has been significant and may persist for decades.