Newly available gas analyzers based on off-axis integrated cavity output spectroscopy (OA-ICOS) lasers have been advocated as an alternative to conventional isotope-ratio mass spectrometers (IRMS) for the stable isotopic analysis of water samples. In the case of H2O, OA-ICOS is attractive because it has comparatively low capital and maintenance costs, the instrument is small and field laboratory portable, and provides simultaneous D/H and 16O/18O ratio measurements directly on H2O molecules with no conversion of H2O to H2, CO, or H2/CO2-water equilibration required. Here we present a detailed assessment of the performance of a liquid-water isotope analyzer, including instrument precision, estimates of sample memory and sample mass effects, and instrumental drift. We provide a recommended analysis procedure to achieve optimum results using OA-ICOS. Our results show that, by using a systematic sample analysis and data normalization procedure routine, measurement accuracies of +/-0.8 per thousand for deltaD and +/-0.1 per thousand delta18O are achievable on nanoliter water samples. This is equivalent or better than current IRMS-based methods and at a comparable sample throughput rate.

Peer reviewe

A new H2O(liquid)-H2O(vapor) pore water equilibration and laser spectroscopy method provides a fast way to obtain accurate high resolution deltaD and delta18O profiles from single core samples from saturated and unsaturated geologic media. The precision and accuracy of the H2O(liquid)-H2O(vapor) equilibration method was comparable to or better than conventional IRMS-based methods, and it can be conducted on geologic cores that contain volumetric water contents as low as 5%. Significant advantages of the H2O(liquid)-H2O(vapor) pore water equilibration method and laser isotopic analysis method include dual hydrogen- and oxygen-isotope assays on single small core samples, low consumable and instrumentation costs, and the potential for field-based hydrogeologic profiling. A single core is sufficient to obtain detailed vertical isotopic depth profiles in geologic, soil, and lacustrine pore water, dramatically reducing the cost of obtaining pore water by conventional wells or physical water extraction methods. In addition, other inherent problems like contamination of wells by leakage and drilling fluids can be eliminated.

[1] The influence of meltwater on the dynamics and geomorphic impact of the Greenland Ice Sheet is strongly controlled by the morphology of the ice sheet's drainage system. However, this system and its evolution through the melt season remain poorly understood. Here we present the results of an intensive programme of dye tracing experiments undertaken along the lower 14km of a land-terminating Greenlandic outlet glacier over a period of four months during the 2010 melt season. These data are interpreted in conjunction with observations of proglacial discharge, englacial water storage, surface melt rates and ice velocity to produce a detailed picture of the changing hydrology of the glacier. Following the onset of melt in the spring, inputs to the drainage system regularly exceed outputs, causing the englacial water level to rise to the ice sheet surface. During this time there is a rapid transition from distributed to channelized drainage in those parts of the drainage system closed by ice deformation over winter. As the melt season progresses, channel efficiency increases and englacial storage and ice velocity decrease. High-velocity events continue to be observed following the channelization of the drainage system however, indicating that hydrological forcing of ice velocity occurs despite the existence of channels during periods when meltwater inputs exceed the capacity of the subglacial drainage system. Citation: Cowton, T

Abstract. Runoff from small glacier systems contains dissolved organic carbon (DOC) rich in protein-like, low molecular weight (LMW) compounds, designating glaciers as an important source of bioavailable carbon for downstream heterotrophic activity. Fluxes of DOC and particulate organic carbon (POC) exported from large Greenland catchments, however, remain unquantified, despite the Greenland Ice Sheet (GrIS) being the largest source of global glacial runoff (ca. 400 km3 yr−1). We report high and episodic fluxes of POC and DOC from a large (>600 km2) GrIS catchment during contrasting melt seasons. POC dominates organic carbon (OC) export (70–89% on average), is sourced from the ice sheet bed, and contains a significant bioreactive component (9% carbohydrates). A major source of the "bioavailable" (free carbohydrate) LMW–DOC fraction is microbial activity on the ice sheet surface, with some further addition of LMW–DOC to meltwaters by biogeochemical processes at the ice sheet bed. The bioavailability of the exported DOC (26–53%) to downstream marine microorganisms is similar to that reported from other glacial watersheds. Annual fluxes of DOC and free carbohydrates during two melt seasons were similar, despite the approximately two-fold difference in runoff fluxes, suggesting production-limited DOC sources. POC fluxes were also insensitive to an increase in seasonal runoff volumes, indicating a supply limitation in suspended sediment in runoff. Scaled to the GrIS, the combined DOC (0.13–0.17 Tg C yr−1 (±13%)) and POC fluxes (mean = 0.36–1.52 Tg C yr−1 (±14%)) are of a similar order of magnitude to a large Arctic river system, and hence may represent an important OC source to the near-coastal North Atlantic, Greenland and Labrador seas.

Once thought to be devoid of life, the ice-covered parts of Antarctica are now known to be a reservoir of metabolically active microbial cells and organic carbon. The potential for methanogenic archaea to support the degradation of organic carbon to methane beneath the ice, however, has not yet been evaluated. Large sedimentary basins containing marine sequences up to 14 kilometres thick and an estimated 21,000 petagrams (1 Pg equals 10(15) g) of organic carbon are buried beneath the Antarctic Ice Sheet. No data exist for rates of methanogenesis in sub-Antarctic marine sediments. Here we present experimental data from other subglacial environments that demonstrate the potential for overridden organic matter beneath glacial systems to produce methane. We also numerically simulate the accumulation of methane in Antarctic sedimentary basins using an established one-dimensional hydrate model and show that pressure/temperature conditions favour methane hydrate formation down to sediment depths of about 300 metres in West Antarctica and 700 metres in East Antarctica. Our results demonstrate the potential for methane hydrate accumulation in Antarctic sedimentary basins, where the total inventory depends on rates of organic carbon degradation and conditions at the ice-sheet bed. We calculate that the sub-Antarctic hydrate inventory could be of the same order of magnitude as that of recent estimates made for Arctic permafrost. Our findings suggest that the Antarctic Ice Sheet may be a neglected but important component of the global methane budget, with the potential to act as a positive feedback on climate warming during ice-sheet wastage.

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There is evidence that the prevalence of allergies and asthma differs between populations in western and eastern Europe. This study investigated the prevalence of wheezing, rhinitis and eczema among schoolchildren in urban and rural areas of Scandinavia and the formerly socialist countries of Eastern Europe. A total of 79,000 children from two age groups (13-14 yrs and 6-7 yrs) in 18 study centres responded to a questionnaire within the International Study of Asthma and Allergy in Children (ISAAC). The 12 month period prevalence of symptoms of asthma, allergic rhinoconjunctivitis and atopic eczema was calculated. The prevalence of wheezing among the 13-14 yr old children was 11.2-19.7% in Finland and Sweden, 7.6-8.5% in Estonia, Latvia and Poland and 2.6-5.9% in Albania, Romania, Russia, Georgia and Uzbekistan (except Samarkand). The prevalence of itching eyes and flexural dermatitis varied in a similar manner between the three regions. The regional differences were less pronounced among the 6-7 yr old children in the seven participating centres. The highest prevalence of rhinitis was recorded in April-July in Scandinavia and during the winter months in the other countries. The prevalence of atopy-related disorders was higher in Scandinavia than in Estonia, Latvia and Poland, which in turn had a higher prevalence than five other countries of eastern Europe with a culture less similar to western Europe. This supports the hypothesis that "Western life style" is associated with a high prevalence of childhood allergy.