Enhanced climate instability in the North Atlantic and southern Europe during the Last Interglacial.

Considerable ambiguity remains over the extent and nature of millennial/centennial-scale climate instability during the Last Interglacial (LIG). Here we analyse marine and terrestrial proxies from a deep-sea sediment sequence on the Portuguese Margin and combine results with an intensively dated Italian speleothem record and climate-model experiments. The strongest expression of climate variability occurred during the transitions into and out of the LIG. Our records also document a series of multi-centennial intra-interglacial arid events in southern Europe, coherent with cold water-mass expansions in the North Atlantic. The spatial and temporal fingerprints of these changes indicate a reorganization of ocean surface circulation, consistent with low-intensity disruptions of the Atlantic meridional overturning circulation (AMOC). The amplitude of this LIG variability is greater than that observed in Holocene records. Episodic Greenland ice melt and runoff as a result of excess warmth may have contributed to AMOC weakening and increased climate instability throughout the LIG.

Testing the use of septum-capped vials for 13C-isotope abundance analysis of carbon dioxide.

Studying ecosystem processes in the context of carbon cycling and climate change has never been more important. Stable carbon isotope studies of gas exchange within terrestrial ecosystems are commonly undertaken to determine sources and rates of carbon cycling. To this end, septum-capped vials ('Exetainers') are often used to store samples of CO(2) prior to mass spectrometric analysis. To evaluate the performance of such vials for preserving the isotopic integrity (delta(13)C) and concentration of stored CO(2) we performed a rigorous suite of tests. Septum-capped vials were filled with standard gases of varying CO(2) concentrations (approximately 700 to 4000 ppm), delta(13)C values (approx. -26.5 to +1.8 per thousand(V-PDB)) and pressures (33 and 67% above ambient), and analysed after a storage period of between 7 and 28 days. The vials performed well, with the vast majority of both isotope and CO(2) concentration results falling within the analytical uncertainty of chamber standard gas values. Although the study supports the use of septum-capped vials for storing samples prior to mass spectrometric analysis, it does highlight the need to ensure that sampling chamber construction is robust (air-tight).

Evidence for obliquity forcing of glacial Termination II.

Variations in the intensity of high-latitude Northern Hemisphere summer insolation, driven largely by precession of the equinoxes, are widely thought to control the timing of Late Pleistocene glacial terminations. However, recently it has been suggested that changes in Earth's obliquity may be a more important mechanism. We present a new speleothem-based North Atlantic marine chronology that shows that the penultimate glacial termination (Termination II) commenced 141,000 +/- 2500 years before the present, too early to be explained by Northern Hemisphere summer insolation but consistent with changes in Earth's obliquity. Our record reveals that Terminations I and II are separated by three obliquity cycles and that they started at near-identical obliquity phases.

Investigation of extraction and clean-up procedures used in the quantification and stable isotopic characterisation of PAHs in contaminated urban soils.

Four different extraction methods, soxhlet, soxtherm, sonication and accelerated solvent extraction (ASE), were used to isolate the 16 priority pollutant PAHs from a certified reference soil (LGC 6140) and from a contaminated soil (BG CLR 17). Based on SIM-GC-MS results, all methods were found to give accurate and highly reproducible concentration data. There was, however, significant between-method and sometimes within-method variability in the stable carbon isotope signatures obtained for individual PAHs from the contaminated soil (BG CLR 17) using GC-C-IRMS. When two clean-up procedures, silica/dichloromethane and alumina/hexane/toluene, were used to remove co-extracted material, however, it was found that ASE gave the more consistent and reproducible stable carbon isotope data. These findings are likely to be of importance for the characterisation of natural and anthropogenic organic matter and, in particular, in source identification and apportionment studies.

Denitrification and phenol degradation in a contaminated aquifer.

A natural groundwater system modified by pollutant phenols and agricultural nitrate has been modelled in the laboratory by a series of sacrificial microcosm experiments. Samples of aquifer sediment and groundwater from the margin of the phenol plume were used to inoculate anaerobic microcosms enriched in nitrate and pollutant phenols. Rapid degradation of phenol and p-cresol was observed over a 35-day period leading to the generation of inorganic carbon and a number of transient intermediates. O-cresol proved to be recalcitrant on the experimental time-scale. A mass balance calculation shows that, during degradation, carbon was conserved in the aqueous phase. Groundwater-sediment interactions were monitored using carbon stable isotope data. A mass balance for solution TIC indicates thatp-cresol degradation stimulated the dissolution of sedimentary carbonate phases due to the formation of carbonic acid. Compound-specific carbon isotope analysis (GC-IRMS) was used to search for 13C enrichment in residual p-cresol. A slight enrichment trend (epsilon = -2.5/1000) was tentatively identified. The potential of this fractionation effect for obtaining in situ degradation rates is discussed. Results from the microcosm experiments help to explain the observed distribution of nitrate and phenols within the polluted aquifer.

Stable-carbon-isotope composition of Fatty acids in hydrothermal vent mussels containing methanotrophic and thiotrophic bacterial endosymbionts.

Fatty acid biomarker analysis coupled with gas chromatography-isotope ratio mass spectrometry was used to confirm the presence of methanotrophic and thiotrophic bacterial endosymbionts in the tissues of a hydrothermal vent mussel (Bathymodiolus sp.), collected from the Menez Gwen vent field on the mid-Atlantic ridge. Monounsaturated (n-8) fatty acids, which are diagnostic of methanotrophic bacteria, were detected in all three types of tissues examined (gill, posterior adductor, and mantle), although levels were highest in gill tissues where the bacteria were found. Stable-carbon-isotope compositions (delta-C per mille relative to that of Peedee belemnite) of fatty acids for all three tissues ranged from -24.9 to -34.9 per thousand, which encompasses the range predicted for both thiotroph- and methanotroph-based nutrition. The data suggest that these thio- and methanotrophic bacterial endosymbionts are equally important in the nutrition of the vent mussel at this particular vent site.

Characterisation of refractory wastes at hydrocarbon-contaminated sites-II. Screening of reference oils by stable carbon isotope fingerprinting.

The preliminary evaluation of stable carbon-isotope ratio mass spectrometry (IRMS) as a novel, alternative method for screening residual heavy or weathered petroleum wastes is presented. Seven well-characterised middle-to high-boiling range oils (predominant boiling range: 150-600 degrees C) and their isolated class fractions were analysed by IRMS. Whole oil delta13C values (which express the ratio of (13)C to (12)C within each sample) showed a small but significant decrease with decreasing oil asphaltene content, from -26.8% for heavier oils to -28.8% for lighter, predominantly paraffinic oils. In agreement with the conventionally observed trend, delta13C values of isolated class fractions were found to increase in the following order: delta13Csat (congruent with delta13Coil) < delta13Caro < delta13Cpol < delta13Casp, delta13Csat up to 2.5% more negative than delta13Cpol and delta13Casp. However, this variation was much less pronounced for the heavier oil samples. As a result, isotope type curves exhibited a clear distinction between heavier oils, which produced much flatter type curves, and lighter oils, for which type curves were characteristically sloping. From these preliminary results, IRMS would appear to have application as a potential method for identifying a predominance of asphaltene class fractions in residual hydrocarbon wastes and for distinguishing between heavy and light oily contaminants.