Carbon isotope analyses of n-alkanes in dust from the lower atmosphere over the central eastern Atlantic

Atmospheric dust samples collected along a transect off the West African coast have been investigated for their lipid content and compound-specific stable carbon isotope compositions. The saturated hydrocarbon fractions of the organic solvent extracts consist mainly of long-chain n-alkanes derived from epicuticular wax coatings of terrestrial plants. Backward trajectories for each sampling day and location were calculated using a global atmospheric circulation model. The main atmospheric transport took place in the low-level trade-wind layer, except in the southern region, where long-range transport in the mid-troposphere occurred. Changes in the chain length distributions of the n-alkane homologous series are probably related to aridity, rather than temperature or vegetation type. The carbon preference of the leaf-wax n-alkanes shows significant variation, attributed to a variable contribution of fossil fuel- or marine-derived lipids. The effect of this nonwax contribution on the δ¹³C values of the two dominant n-alkanes in the aerosols, n-C₂₉ and n-C₃₁ alkane, is, however, insignificant. Their δ¹³C values were translated into a percentage of C₄ vs. C₃ plant type contribution, using a two-component mixing equation with isotopic end-member values from the literature. The data indicate that only regions with a predominant C₄ type vegetation, i.e. the Sahara, the Sahel, and Gabon, supply C₄ plant-derived lipids to dust organic matter. The stable carbon isotopic compositions of leaf-wax lipids in aerosols mainly reflect the modern vegetation type along their transport pathway. Wind abrasion of wax particles from leaf surfaces, enhanced by a sandblasting effect, is most probably the dominant process of terrigenous lipid contribution to aerosols.     

The nitrogen distribution in soils formed under widely differing climatic conditions

Amino acids, amino sugars and ammonia were determined in 6N HCl hydrolyzates of soils formed under arctic, cool temperate, subtropical and tropical climates. Soils from warmer climates yielded relatively more amino acids and amino sugars but less NH₃ than did those from colder regions. The amino acid composition of all soils, however, was remarkably similar, resembled that of lake sediments and was somewhat similar to that of bacteria, suggesting the importance of microorganisms in their formation. Climate appears to have little effect on the amino acid composition of soils.     

Potassium-argon ages from the Ceneri Zone,Southern Swiss Alps

The Ceneri Zone is a unit of the crystalline basement of the Southern Alps. Its northern boundary is the Tonale Line segment of the Periadriatic Line, an important tectonic lineament separating the Oligocene and younger features of the Central Alps from the older metamorphic and structural trends of the Southern Alps. Unmetamorphosed Permian and younger sedimentary units lap onto the Southern Alpine basement from the south.Potassium-argon results from the Ceneri Zone define a Hercynian age pattern typical for the basement of continental Europe. This pattern extends to within at least 100 meters of the Tonale Line. Thus, amphibolite facies metamorphism in this region occurred around 325 m.y. ago. The geochronologic similarity of the Southern Alps to many other European regions must be taken into account in megatectonic theories.In detail, the Hercynian age pattern of the Ceneri Zone is complicated. Some hornblendes have apparent ages between the Hercynian and a Caledonian value (430 m.y.). They probably retained some radiogenic argon during the Hercynian upper amphibolite facies metamorphism. In addition, mica results between 200 and 300 m.y. have a strong geographic correlation. Apparently, the northwestern portion of the Ceneri Zone was reheated or mildly metamorphosed during the Upper Triassic to Lower Jurassic. A relationship between these ages and 170–180 m.y. ages from the neighboring Ivrea-Verbano Zone seems likely. No geologic evidence for any post-Hercynian event has been noted as yet in the Ceneri Zone.     

Fractionation of sulfur isotopes during laboratory synthesis of pyrite at low temperatures

The reaction products and the accompanying sulfur isotope fractionations during the reaction of H₂S with goethite in aqueous media at 22–24°C for periods from 0.5 hr to 65 days were studied. Fine-grained pyrite formed within two days and was isotopically 0.8‰ lighter than the H₂S source. After 65 days reaction time the pyrite had nearly the same isotopic value as the H₂S. Aqueous precipitation of pyrite from H₂S and goethite at room temperature involved three major steps, namely: (1) the rapid oxidation of H₂S and reduction of Fe³⁺ during which elemental S is formed; (2) the formation of acid-volatile sulfides and the disappearance of elemental S; and (3) the formation of pyrite at the expense of acid-volatile sulfides.     

Atmospheric trace metals: global cycles and assessment of man's impact

Global data are presented for sources of atmospheric input for 20 trace metals, and the relative importance of natural and anthropogenic sources is assessed. Interference factors are calculated as (total anthropogenic emissions/total natural emissions) × 100. For lithophile metals such as Fe and Mn, interference factors are small. In contrast, the atmophile metals, such as As, Se and Hg, exhibit large interference factors. A significant degree of correlation exists between interference factors and enrichment factors, where enrichment factor is defined as the metal/Al ratio in atmospheric particulates divided by the metal/Al ratio in soils. For many of the trace metals, enrichment factors are of the same order of magnitude at high latitudes in both the Northern and Southern Hemispheres, and are larger at high latitude than at mid latitude.A simple mathematical model is used to calculate present-day enrichment factors in both hemispheres based on natural and anthropogenic influxes, effluxes, and transfer between hemispheres. The calculated enrichment factors are in good agreement with the observed enrichment factors for lithophile metals at both mid and high latitude, and for atmophile metals at mid latitude. However, calculated enrichment factors for atmophile metals are lower than observed enrichment factors at high latitude. To explain these results, we propose that for Hg, As and Se, and perhaps for other atmophile metals, there are significant fluxes from the sea surface to the atmosphere. If the estimated low-temperature fluxes of As, Se and Hg from the land and sea surfaces are included in the interference factor calculations for these metals, the factors are reduced to less than 100%.     

Regional landslide risk to the Cairns community

A GIS-based regional reconnaissance-level assessment of landslide risk to the Cairns community has been carried out to provide information to the Cairns City Council for planning and emergency management purposes. Magnitude recurrence relations were tentatively established for the two main slope processes: landslides on the hill slopes; and large debris flows extending out from the gully systems on to the plains. From the recurrence relations, landslide hazard (H) was estimated as the annual probability of a point being impacted by a landslide. The nature, number (E) and geographic distribution of the elements at risk were obtained by interrogating the GIS, and their vulnerabilities (V) to destruction by the two main landslide slope processes were assessed. From this information, specific risk (= H × V) and total risk (= H × V× E) maps were produced.Although total landslide risk is relatively low at present, it will increase as development extends further into the hill slopes, unless adequate mitigation measures are taken. Large debris flows, while considerably less frequent than landslides on cut slopes, could impact on subdivisions at the base of the slopes. Blockage by landslides of roads and railways providing access to Cairns can cause isolation of the community. Flash flooding in Freshwater Creek, or debris flows, have the potential to disrupt the Cairns water supply by blocking the intake or destroying sections of the pipeline.     

Century-scale nitrogen and phosphorus controls of the carbon cycle

In recent decades, humans have become a very important force in the Earth system, demonstrating that emissions (gaseous, liquid, and solid) are the cause of many of our environmental issues. These emissions are responsible for major global reorganizations of the biogeochemical cycles. The oceans are now a net sink of atmospheric CO₂, whereas in their preindustrial state they were a source; the trophic state of the coastal oceans is progressively moving toward increased heterotrophy; and the terrestrial realm is now vacillating between trophic states, whereas in preindustrial times it was autotrophic. In this paper, we present model calculations that underscore the role of human-induced perturbations in changing Earth's climate, specifically the role of anthropogenic nitrogen and phosphorus in controlling processes in the global carbon cycle since the year 1850 with projections to the year 2035. Our studies show that since the late 1940's emissions of nitrogen and phosphorus have been sequestered in the terrestrial living phytomass and groundwater. This nutrient-enhanced fertilization of terrestrial biota, coupled with rising atmospheric CO₂ and global temperature, has induced a sink of anthropogenic CO₂ that roughly balances the emission of CO₂ owing to land use change. In the year 2000, for example, the model-calculated terrestrial biotic sink was 1730 Mtons C/year, while the emission of CO₂ from changes in land use was 1820 Mtons C/year, a net flux of 90 Mtons C/year emitted to the atmosphere. In the global aquatic environment, enhanced terrestrial inputs of biotically reactive phosphorus (about 8.5 Mtons P/year) and inorganic nitrogen (about 54 Mtons N/year), have induced increased new production and burial of organic carbon in marine sediments, which is a small sink of anthropogenic CO₂. It is predicted that the response of the global land reservoirs of C, N, and P to sustained anthropogenic perturbations will be maintained in the same direction of change over the range of projected scenarios of global population increase and temperature change for the next 35 years. The magnitude of change is significantly larger when the global temperature increase is maximum, especially with respect to the processes of remobilization of the biotically important nutrients nitrogen and phosphorus.