Changing nutrient cycling in Lake Baikal, the world's oldest lake.

Lake Baikal, lying in a rift zone in southeastern Siberia, is the world's oldest, deepest, and most voluminous lake that began to form over 30 million years ago. Cited as the "most outstanding example of a freshwater ecosystem" and designated a World Heritage Site in 1996 due to its high level of endemicity, the lake and its ecosystem have become increasingly threatened by both climate change and anthropogenic disturbance. Here, we present a record of nutrient cycling in the lake, derived from the silicon isotope composition of diatoms, which dominate aquatic primary productivity. Using historical records from the region, we assess the extent to which natural and anthropogenic factors have altered biogeochemical cycling in the lake over the last 2,000 y. We show that rates of nutrient supply from deep waters to the photic zone have dramatically increased since the mid-19th century in response to changing wind dynamics, reduced ice cover, and their associated impact on limnological processes in the lake. With stressors linked to untreated sewage and catchment development also now impacting the near-shore region of Lake Baikal, the resilience of the lake's highly endemic ecosystem to ongoing and future disturbance is increasingly uncertain.

Combining isotope ratios for provenancing Viking Age iron artefacts in the British Isles: a pilot study.

Stable and radiogenic isotope analysis - particularly using lead isotope analysis (LIA) - has previously been shown to be a useful tool for the provenancing of ancient metal artefacts of silver and copper and its alloys, but less progress has been made in the provenancing of iron artefacts, despite their importance and frequency in the archaeological record. In this pilot study we investigate for the first time the possibilities of iron isotope analysis in combination with trace strontium isotope analysis and LIA for the provenancing of iron objects believed to be from the Viking Age in the British Isles. Previous studies have shown that analysis of each of these isotopes can contribute to provenancing iron artefacts, but they are not individually resolutory. In this proof-of-concept study, we examine the Fe, Sr and Pb isotopes of 7 artefacts believed to derive from the Viking Age: 3 from Meols - a former Viking seaport on Wirral and 4 samples from the probable location of the AD 1066 Battle of Fulford in North Yorkshire. We also examine an additional artefact of unknown antiquity from Bebington Heath - a possible location of the AD 937 Battle of Brunanburh. Although the pilot data set is too small to make definitive conclusions, it has paved the way for a fuller study involving 100 samples (including 30 from the former Viking camp of Torksey, Lincolnshire) funded by the NEIF fund of the UK National Environmental Research Council. The high range of 87Sr/86Sr values in the present data set of 8 is beyond what would be expected for bog iron (with a cut-off ∼ 0.709) and suggests that mined ore was being used, a preliminary conclusion supported by the narrow range of Fe isotope data.

The oxygen isotope relationship between the phosphate and structural carbonate fractions of human bioapatite.

RATIONALE: Oxygen isotope analysis of archaeological human dental enamel is widely used as a proxy for the drinking water composition (δ(18)O(DW)) of the individual and thus can be used as an indicator of their childhood place of origin. In this paper we demonstrate the robustness of structural carbonate oxygen isotope values (δ(18)O(C)) in bioapatite to preserve the life signal of human tooth enamel by comparing it with phosphate oxygen isotope values (δ(18)O(P)) derived from the same archaeological human tooth enamel samples. METHODS: δ(18)O(C) analysis was undertaken on 51 archaeological tooth enamel samples previously analysed for δ(18)O(P) values and strontium isotopes. δ(18)O(C) values were determined on a GV IsoPrime dual inlet mass spectrometer, following a series of methodological tests to assess: (1) The reaction time needed to ensure complete release of CO(2) from structural carbonate in the enamel; (2) The effect of an early pre-treatment with dilute acetic acid to remove diagenetic carbonate; (3) Analytical error; (4) Intra-tooth variation; and (5) Diagenetic alteration. RESULTS: This study establishes a direct relationship between δ(18)O(C) and δ(18)O(P) values from human tooth enamel (δ(18)O(P) = 1.0322 × Î´(18)O(C) - 9.6849). We have combined this equation with the drinking water equation of Daux et al. (J. Hum. Evol. 2008, 55, 1138) to allow direct calculation of δ(18)O(DW) values from human bioapatite δ(18)O(C) (δ(18)O(DW) = 1.590 × Î´(18)O(C) - 48.634). CONCLUSIONS: This is the first comprehensive study of the relationship between the ionic forms of oxygen (phosphate oxygen and structural carbonate) in archaeological human dental enamel. The new equation will allow direct comparison of data produced by the different methods and allow drinking water values to be calculated from structural carbonate data with confidence.

Applying lead (Pb) isotopes to explore mobility in humans and animals.

Lead (Pb) isotopes provide a complementary method to other provenance tools for tracking the origin and movement of humans and animals. The method is founded in the geographic distribution of Pb isotope ratios. However, unlike the Sr isotope method that is closely linked to the lithology of underlying rocks, Pb more closely reflects the tectonic regimes. This makes it particularly pertinent to use in Britain as there is major tectonic boundary (the Iapetus Suture) that runs between Berwick-upon-Tweed and the Solway Firth providing a compositional boundary in Pb isotope domains that approximates to the geographic areas of Scotland versus England and Wales. Modern pollution makes it difficult to use modern floral or faunal samples to characterize biosphere variation, and so we use geological datasets to define isoscape variation and present the first Pb isotope map of Britain. We have validated the use of these data form biosphere studies using well provenanced samples. Reference fields of diagnostic compositions, are created in µ-T space and these have been used in a test case to assess the geographic origins of Neolithic animals in Great Britain.

Evolving Pb isotope signatures of London airborne particulate matter (PM 10)-constraints from on-filter and solution-mode MC-ICP-MS.

Pb isotope compositions of biologically significant PM(10) atmospheric particulates from a busy roadside location in London UK were measured using solution- and laser ablation-mode MC-ICP-MS. The solution-mode data for PM(10) sampled between 1998-2001 document a dramatic shift to increasingly radiogenic compositions as leaded petrol was phased out. LA-MC-ICP-MS isotope analysis, piloted on a subset of the available samples, is shown to be a potential reconnaissance analytical technique. PM(10) particles trapped on quartz filters were liberated from the filter surface, without ablating the filter substrate, using a 266 nm UV laser and a dynamic, large diameter, low-fluence ablation protocol. The Pb isotope evolution noted in the London data set obtained by both analytical protocols is similar to that observed elsewhere in Western Europe following leaded petrol elimination. The data therefore provide important baseline isotope composition information useful for continued UK atmospheric monitoring through the early 21(st) century.

Tracking natural and anthropogenic Pb exposure to its geological source.

Human Pb exposure comes from two sources: (i) natural uptake through ingestion of soils and typified by populations that predate mining activity and (ii) anthropogenic exposure caused by the exposure to Pb derived from ore deposits. Currently, the measured concentration of Pb within a sample is used to discriminate between these two exposure routes, with the upper limit for natural exposure in skeletal studies given as 0.5 or 0.7 mg/kg in enamel and 0.5/0.7 µg/dL in blood. This threshold approach to categorising Pb exposure does not distinguish between the geological origins of the exposure types. However, Pb isotopes potentially provide a more definitive means of discriminating between sources. Whereas Pb from soil displays a crustal average 238U/204Pb (µ) value of c 9.7, Pb from ore displays a much wider range of evolution pathways. These characteristics are transferred into tooth enamel, making it possible to characterize human Pb exposure in terms of the primary source of ingested Pb and to relate mining activity to geotectonic domains. We surmise that this ability to discriminate between silicate and sulphide Pb exposure will lead to a better understanding of the evolution of early human mining activity and development of exposure models through the Anthropocene.

Geogenic lead isotope signatures from meat products in Great Britain: Potential for use in food authentication and supply chain traceability.

This paper presents lead (Pb) isotope data from samples of farm livestock raised in three areas of Britain that have elevated natural Pb levels: Central Wales, the Mendips and the Derbyshire Peak District. This study highlights three important observations; that the Pb found in modern British meat from these three areas is geogenic and shows no clear evidence of modern tetraethyl anthropogenic Pb contribution; that the generally excellent match between the biological samples and the ore field data, particularly for the Mendip and Welsh data, suggests that this technique might be used to provenance biological products to specific ore sites, under favourable conditions; and that modern systems reflect the same process of biosphere averaging that is analogous to cultural focusing in human archaeological studies that is the process of biological averaging leading to an homogenised isotope signature with increasing Pb concentration.

Regional lead isotope study of a polluted river catchment: River Wear, Northern England, UK.

High precision, lead isotope analyses of archived stream sediments from the River Wear catchment, northeast England (1986-88), provide evidence for three main sources of anthropogenic lead pollution; lead mining, industrial lead emissions and leaded petrol. In the upper catchment, pollution is totally controlled and dominated by large lead discharges from historic mining centres in the North Pennine Orefield ((208)Pb/(206)Pb, (207)Pb/(206)Pb ratios range from 2.0744-2.0954 and 0.8413-0.8554 respectively). In the lower catchment, co-extensive with the Durham Coalfield and areas of high population density, pollution levels are lower and regionally more uniform. Isotope ratios are systematically higher than in the upper catchment ((208)Pb/(206)Pb, (207)Pb/(206)Pb ratios range from 2.0856-2.1397 and 0.8554-0.8896 respectively) and far exceed values determined for the geogenic regional background. Here, the pollution is characterised by the atmospheric deposition of industrial lead and petrol lead. Lead derived from the combustion of coal, although present, is masked by the other two sources. Recent sediments from the main channel of the River Wear are isotopically indistinguishable from older, low order stream sediments of the North Pennine Orefield, indicating that contamination of the river by lead mining waste (up to several 1000 mg/kg Pb at some locations) continues to pose an environmental problem; a pattern that can be traced all the way to the tidal reach. Using within-catchment isotope variation and sediment lead concentrations, estimates can be made of the discharges from discrete mines or groups of mines to the overall level of lead pollution in the River Wear. As well as providing information pertinent to source apportionment and on-going catchment remediation measures, the database is a valuable resource for epidemiologists concerned with the health risks posed by environmental lead.