Method for analysing phosphate 18O/16O ratios for waters with high C:P ratios

In this report we outline a method to isolate phosphate as pure Ag3PO4 for waters with high C:P ratios for 18O analysis. This report details a method that can be used to minimise residual organic contamination of the final Ag3PO4, therefore significantly reducing uncertainties in the final interpretation of 18O results. This includes the use of column resins in series to (i) remove the majority of dissolved organic carbon and (ii) isolate/pre-concentrate PO4. This is followed by the use of a modified McLaughlin et al (2004) method for PO4 precipitation, with an additional final hydrogen peroxide clean-up step to remove residual organic matter following precipitation of Ag3PO4. The reagents required for this method are first listed, and then a step-by-step account of the process is outlined. Importantly, it contains adequate detail to be used by other researchers in this field or modified to suit their particular research objectives

Isotopic analysis of faunal material from South Uist, Western Isles, Scotland

This paper reports on the results from stable isotope analysis of faunal bone collagen from a number of Iron Age and later sites on the island of South Uist, in the Western Isles, Scotland. This preliminary investigation into the isotopic signatures of the fauna is part of a larger project to model the interaction between humans, animals, and the broader environment in the Western Isles. The results demonstrate that the island fauna data fall within the range of expected results for the UK, with the terrestrial herbivorous diets of cattle and sheep confi rmed. The isotopic composition for pigs suggests that some of these animals had an omnivorous diet, whilst a single red deer value might be suggestive of the consumption of marine foods, such as by grazing on seaweed. However, further analysis is needed in order to verify this anomalous isotopic ratio

Nitrate stable isotopes and major ions in snow and ice samples from four Svalbard sites

Increasing reactive nitrogen (N-r) deposition in the Arctic may adversely impact N-limited ecosystems. To investigate atmospheric transport of N-r to Svalbard, Norwegian Arctic, snow and firn samples were collected from glaciers and analysed to define spatial and temporal variations (1 10 years) in major ion concentrations and the stable isotope composition (delta N-15 and delta O-18) of nitrate (NO3-) across the archipelago. The delta N-15(NO3-) and delta O-18(NO3-) averaged -4 parts per thousand and 67 parts per thousand in seasonal snow (2010-11) and -9 parts per thousand and 74 parts per thousand in firn accumulated over the decade 2001-2011. East-west zonal gradients were observed across the archipelago for some major ions (non-sea salt sulphate and magnesium) and also for delta N-15(NO3-) and delta O-18(NO3-) in snow, which suggests a different origin for air masses arriving in different sectors of Svalbard. We propose that snowfall associated with long-distance air mass transport over the Arctic Ocean inherits relatively low delta N-15(NO3-) due to in-transport N isotope fractionation. In contrast, faster air mass transport from the north-west Atlantic or northern Europe results in snowfall with higher delta N-15(NO3-) because in-transport fractionation of N is then time-limited

The preservation and interpretation of δ34 S values in charred archaeobotanical remains

The measurement of sulphur isotope (δ34S) values in charred plant remains has the potential to inform understanding of the spatial configuration and ecology of crop production. We investigated the effects of charring, manuring, oxidation and anaerobic soil conditions on modern cereal grain/pulse seed δ34S values, and assessed the effect of chemical pre‐treatment on charred modern and archaeobotanical grain/seed δ34S values. We used these results to interpret δ34S values in archaeobotanical material from Neolithic Çatalhöyük. Our results suggest that δ34S values can be reliably preserved in charred grain/seeds but are subject to influence by anaerobic soil conditions, the effect depending on the timing of flooding in relation to S assimilation

Variations in the 13C/12C ratios of modern wheat grain, and implications for interpretating data from Bronze Age Assiros Toumba, Greece

Variations in the 13C/12C ratios of wheat grain at different spatial and temporal scales are examined by analysis of modern samples, including harvests of einkorn and durum wheat from Greece, and serve as a guide to interpreting data for Bronze Age grains from Assiros Toumba. The normal distribution and low variability of δ13C values of einkorn from 24 containers in the Assiros storerooms are consistent with pooling of local harvests, but less likely to represent the harvest of several years or include grain imported from further afield. Correlation between emmer and spelt δ13C values provides strong support for other evidence that these were grown together as a maslin crop. 13C discrimination (Δ) for the Bronze Age samples is estimated to be 2.5‰ larger than at present, and would be consistent with an intensive, horticultural regime of cereal cultivation, possibly involving some watering

Isotope and dissolved gas evidence for nitrogen attenuation in landfill leachate dispersing into a chalk aquifer

The authors present data for the chemical, stable isotope (13C/12C, 15N/14N and 34S/32S), and dissolved gas (N2, Ar, O2 and CH4) composition of groundwaters sampled in and around a landfill site in Cambridgeshire, England. Decomposition of 3 × 106 m3 of largely domestic waste, placed in unlined quarries, has given rise to the formation of an NH4-rich leachate dispersing as a plume into the surrounding Middle Chalk aquifer. In addition to identifying zones of methanogenesis and SO4 reduction, the data indicate processes of NH4 transformation by either assimilation or oxidation, and losses by formation of N2. Depending on the mixing ratio between leachate and background water, it may be possible to account for all NH4 loss by combined nitrification + denitrification in a system where there are abrupt temporal and spatial changes in redox conditions

Effects of pre-treatment on ostracod valve chemistry

The stable-isotope and trace-element analysis of ostracod calcite are commonly used in palaeoenvironmental reconstruction. We tested the effects on shell composition of a number of methods for the pre-treatment of ostracod valves, including roasting in a vacuum; plasma ashing; and soaking in reagents including hydrogen peroxide, sodium hypochlorite, hydroxylamine hydrochloride solution and sodium dithionite complexing reagent. We found large differences in the geochemical effects of these methods and showed that all have the potential to alter the trace element and stable isotope composition of ostracod valves. We recommend that valves only be cleaned manually, with fine brushes, needles and deionised water whenever possible. However, we recognise that there will be occasions where manual cleaning will be insufficient to remove inorganic or organic contamination. In such cases, we recommend hydrogen peroxide and plasma ashing as good methods for oxygen isotope analysis, if no other analyses are to be performed. For carbon isotope analysis, only plasma ashing should be used. Hydroxylamine hydrochloride is a suitable method for the removal of aluminosilicate material, and sodium hypochlorite is a suitably non-invasive method for the removal of organic material, if subsequent trace element analysis is to be carried out

Isotopic evidence for the occurrence of biological nitrification and nitrogen deposition processing in forest canopies

This study examines the role of tree canopies in processing atmospheric nitrogen (N-dep) for four forests in the United Kingdom subjected to different N-dep: Scots pine and beech stands under high N-dep (HN, 13-19kgNha(-1)yr(-1)), compared to Scots pine and beech stands under low N-dep (LN, 9kgNha(-1)yr(-1)). Changes of NO3-N and NH4-N concentrations in rainfall (RF) and throughfall (TF) together with a quadruple isotope approach, which combines delta O-18, Delta O-17 and delta N-15 in NO3- and delta N-15 in NH4+, were used to assess N transformations by the canopies. Generally, HN sites showed higher NH4-N and NO3-N concentrations in RF compared to the LN sites. Similar values of delta N-15-NO3- and delta O-18 in RF suggested similar source of atmospheric NO3- (i.e. local traffic), while more positive values for delta N-15-NH4+ at HN compared to LN likely reflected the contribution of dry NHx deposition from intensive local farming. The isotopic signatures of the N-forms changed after interacting with tree canopies. Indeed, delta N-15-enriched NH4+ in TF compared to RF at all sites suggested that canopies played an important role in buffering dry N-dep also at the low N-dep site. Using two independent methods, based on delta O-18 and Delta O-17, we quantified for the first time the proportion of NO3- in TF, which derived from nitrification occurring in tree canopies at the HN site. Specifically, for Scots pine, all the considered isotope approaches detected biological nitrification. By contrast for the beech, only using the mixing model with Delta O-17, we were able to depict the occurrence of nitrification within canopies. Our study suggests that tree canopies play an active role in the N cycling within forest ecosystems. Processing of N-dep within canopies should not be neglected and needs further exploration, with the combination of multiple isotope tracers, with particular reference to Delta O-17