Seasonal variation in marine C:N:P stoichiometry: can the composition of seston explain stable Redfield ratios?

Seston is suspended particulate organic matter, comprising a mixture of autotrophic, heterotrophic and detrital material. Despite variable proportions of these components, marine seston often exhibits relatively small deviations from the Redfield ratio (C:N:P = 106:16:1). Two time-series from the Norwegian shelf in Skagerrak are used to identify drivers of the seasonal variation in seston elemental ratios. An ordination identified water mass characteristics and bloom dynamics as the most important drivers for determining C:N, while changes in nutrient concentrations and biomass were most important for the C:P and N:P relationships. There is no standardized method for determining the functional composition of seston and the fractions of POC, PON and PP associated with phytoplankton, therefore any such information has to be obtained by indirect means. In this study, a generalized linear model was used to differentiate between the live autotrophic and non-autotrophic sestonic fractions, and for both stations the non-autotrophic fractions dominated with respective annual means of 76 and 55%. This regression model approach builds on assumptions (e.g. constant POC:Chl-a ratio) and the robustness of the estimates were explored with a bootstrap analysis. In addition the autotrophic percentage calculated from the statistical model was compared with estimated phytoplankton carbon, and the two independent estimates of autotrophic percentage were comparable with similar seasonal cycles. The estimated C:nutrient ratios of live autotrophs were, in general, lower than Redfield, while the non-autotrophic C:nutrient ratios were higher than the live autotrophic ratios and above, or close to, the Redfield ratio. This is due to preferential remineralization of nutrients, and the P content mainly governed the difference between the sestonic fractions. Despite the seasonal variability in seston composition and the generally low contribution of autotrophic biomass, the variation observed in the total seston ratios was low compared to the variation found in dissolved and particulate pools. Sestonic C:N:P ratios close to the Redfield ratios should not be used as an indicator of phytoplankton physiological state, but could instead reflect varying contributions of sestonic fractions that sum up to an elemental ratio close to Redfield

Variation in the seston C:N ratio of the Arctic Ocean and pan-Arctic shelves

Studying more than 3600 observations of particulate organic carbon (POC) and particulate organic nitrogen (PON), we evaluate the applicability of the classic Redfield C:N ratio (6.6) and the recently proposed Sterner ratio (8.3) for the Arctic Ocean and pan-Arctic shelves. The confidence intervals for C:N ranged from 6.43 to 8.82, while the average C:N ratio for all observations was 7.4. In general, neither the Redfield or Sterner ratios were applicable, with the Redfield ratio being too low and the Sterner ratio too high. On a regional basis, all northern high latitude regions had a C:N ratio significantly higher than the Redfield ratio, except the Arctic Ocean (6.6), Chukchi (6.4) and East Siberian (6.5) Seas. The latter two regions were influenced by nutrient-rich Pacific waters, and had a high fraction of autotrophic (i.e. algal-derived) material. The C:N ratios of the Laptev (7.9) and Kara (7.5) Seas were high, and had larger contributions of terrigenous material. The highest C:N ratios were in the North Water (8.7) and Northeast Water (8.0) polynyas, and these regions were more similar to the Sterner ratio. The C:N ratio varied between regions, and was significantly different between the Atlantic (6.7) and Arctic (7.9) influenced regions of the Barents Sea, while the Atlantic dominated regions (Norwegian, Greenland and Atlantic Barents Seas) were similar (6.7–7). All observations combined, and most individual regions, showed a pattern of decreasing C:N ratios with increasing seston concentrations. This meta-analysis has important implications for ecosystem modelling, as it demonstrated the striking temporal and spatial variability in C:N ratios and challenges the common assumption of a constant C:N ratio. The non-constant stoichiometry was believed to be caused by variable contributions of autotrophs, heterotrophs and detritus to seston, and a significant decrease in C:N ratios with increasing Chlorophyll a concentrations supports this view. This study adds support to the use of a power function model, where the exponent is system-specific, but we suggest a general Arctic relationship, where POC = 7.4 PON0.89

Evidence of carcinogenicity in humans of water-soluble nickel salts

<p>Abstract</p> <p>Background</p> <p>Increased risks of nasal cancer and lung cancer in nickel refiners have been investigated scientifically and discussed since they were detected in the 1930s. Nickel compounds are considered to be the main cause of the cancer excess. Parts of the nickel producing industry and their consultants oppose the classification of water-soluble nickel salts as human carcinogens, and argue that the risk in exposed workers should be ascribed to other occupational exposures and smoking.</p> <p>Discussion</p> <p>Respiratory cancer risks in Welsh, Finnish, and Norwegian nickel refiners add to the evidence of carcinogenicity of water-soluble nickel. In Norwegian refiners, the first epidemiological study in 1973 identified high risks of lung cancer and nasal cancer among long-term electrolysis workers. Risk analyses based on exposure estimates developed in the 1980s supported the view that water-soluble nickel compounds were central in the development of cancer. Recently, new exposure estimates were worked out for the same cohort based on personal monitoring of total nickel and chemical determination of four forms of nickel. Additional data have been collected on life-time smoking habits, and on exposure to arsenic, asbestos, sulphuric acid mists, cobalt, and occupational lung carcinogens outside the refinery. After adjustment for these potential confounding exposures in case-control analyses, the risk pattern added to the evidence of an important role of water-soluble nickel compounds as causes of lung cancer. These Norwegian cancer studies rely on national Cancer Registry data, considered close to complete from 1953 onwards; and on National Population Register data continuously updated with mortality and emigration. Canadian mortality studies--perceived to offer the strongest support to the industry position not to recognise carcinogenicity of water-soluble nickel--appear to suffer from limitations in follow-up time, loss to follow-up, absence of risk analysis with individual exposure estimates, no confounder control, and a likely underestimation of cancer mortality.</p> <p>Conclusions</p> <p>Rejection to recognise water-soluble nickel as a human carcinogen seems to contradict material epidemiological evidence that demonstrates a strong association between water-soluble nickel compounds and risks of lung cancer and nasal cancer. Independent international scientific bodies have classified nickel compounds as carcinogenic to humans, inclusive of water-soluble nickel.</p

Preliminary Results on Waypoint Tracking for Spacecraft with Actuator Constraints

This paper presents preliminary results on how to perform waypoint tracking with spacecraft with actuator constraints. It considers a simplified spacecraft model and can be considered a deep space model, and shows how to perform waypoint tracking with only one main thruster together with full attitude control. As the spacecraft reaches close to the waypoint during a deceleration phase that makes the speed go towards zero, reaction control thrusters are used to make the remaining velocity error go to zero achieving the control objective

Dehydration Melting and Proterozoic Granite Petrogenesis in a Collisional Orogen-A Case from the Svecofennian of Southern Finland

Dehydration melting of metasupracrustal rocks at mid- to deep-crustal levels can generate water undersaturated granitic melt. In this study, we evaluate the potential of similar to 1.89-1.88 Ga metasupracrustal rocks of the Precambrian of southern Finland as source rocks for the 1.86-1.79 Ga late-orogenic leucogranites in the region, using the Rhyolite-MELTS approach. Melt close in composition to leucogranite is produced over a range of realistic pressures (5 to 8 kbar) and temperatures (800 to 850 degrees C), at 20%-30% of partial melting, allowing separation of melt from unmelted residue. The solid residue is a dry, enderbitic to charnoenderbitic ganulite depleted in incompatible components, and will only yield further melt above 1 000-1 050 degrees C, when rapidly increasing fractions of increasingly calcic (granodioritic to tonalitic) melts are formed. The solid residue after melt extraction is incapable of producing syenogranitic magmas similar to the Mid-Proterozoic, A-type rapakivi granites on further heating. The granitic fraction of the syenogranitic rapakivi complexes must thus have been formed by a different chain of processes, involving mantle-derived mafic melts and melts from crustal rock types not conditioned by the preceding late-orogenic Svecofennian anatexisPeer reviewe

Imaging hydrogen interactions with materials at the nanoscale: SIMS-based correlative microscopy

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Extracting risk neutral probability densities by fitting implied volatility smiles: some methodological points and an application to the 3M Euribor futures option prices

Following Shimko (1993), a large amount of research has evolved around the problem of extracting risk neutral densities from options prices by interpolating the Balck-Scholes implied volatility smile. Some of the methods recently proposed use variants of the cubic spline. Thesee methods have the property of producing non-differentiable probability densities. We argue that this is an undesirable feature and suggest circumventing the problem by fitting a smoothing spline of higher order polynomials with a relatively low number of knot points. In the estimations we opt for a measure of roughness penalty, which is more appropriate than the plain second partial derivative often used. We apply this technique to the LIFFE three-month Euribor future option proces. Constant horizon risk neutral densities are calculated and summary statistics from these densities are used to assess market uncertainty on a day-by-day basis. Finally, we analyse the impact of the 11 September attacks on the expectation of future Euribor interest rates. JEL Classification: C14, F33, G15