Behaviour of H2O2, NH3, and black carbon in mixed-phase clouds during CIME

We investigated the partitioning of trace substances during the phase transition from supercooled to mixed-phase cloud induced by artificial seeding. Simultaneous determination of the concentrations of H₂O₂, NH₃ and black carbon (BC) in both condensed and interstitial phases with high time resolution showed that the three species undergo different behaviour in the presence of a mixture of ice crystals and supercooled droplets. Both H₂O₂ and NH₃ are efficiently scavenged by growing ice crystals, whereas BC stayed predominantly in the interstitial phase. In addition, the scavenging of H₂O₂ is driven by co-condensation with water vapour onto ice crystals while NH₃ uptake into the ice phase is more efficient than co-condensation alone. The high solubility of NH₄⁺ in the ice could explain this result. Finally, it appears that the H₂O₂–SO₂ reaction is very slow in the ice phase with respect to the liquid phase. Our results are directly applicable for clouds undergoing limited riming.     

The 1631 Vesuvius eruption. A reconstruction based on historical and stratigraphical data

The eruption of 1631 A.D. was the most violent and destructive event in the recent history of Vesuvius. More than fifty primary documents, written in either Italian or Latin, were critically examined, with preference given to the authors who eyewitnessed volcanic phenomena. The eruption started at 7 a.m. on December 16 with the formation of an eruptive column and was followed by block and lapilli fallout east and northeast of the volcano until 6 p.m. of the same day. At 10 a.m. on December 17, several nuées ardentes were observed to issue from the central crater, rapidly descending the flanks of the cone and devastating the villages at the foot of Vesuvius. In the night between the 16th and 17th and on the afternoon of the 17th, extensive lahars and floods, resulting from rainstorms, struck the radial valleys of the volcano as well as the plain north and northeast.Deposits of the eruption were identified in about 70 localities on top of an ubiquitous paleosol formed during a long preeruptive volcanic quiescence. The main tephra unit consists of a plinian fallout composed of moderately vesicular dark green lapilli, crystals and lithics. Isopachs of the fallout are elongated eastwards and permit a conservative volume calculation of 0.07 km³. The peak mass flux deduced from clast dispersal models is estimated in the range 3–6 × 10⁷ kg/s, corresponding to a column height of 17–21 km. East of the volcano the plinian fallout is overlain by ash-rich low-grade ignimbrite, surges, phreatomagmatic ashes and mud flows. Ash flows occur in paleovalleys around the cone of Vesuvius but are lacking on the Somma side, suggesting that pyroclastic flows had not enough energy to overpass the caldera wall of Mt. Somma. Deposits are generally unconsolidated, massive with virtually no ground layer and occasionally bearing sparse rests of charred vegetation. Past interpretations of the products emitted on the morning of December 17 as lava flows are inconsistent with both field observations and historical data. Features of the final phreatomagmatic ashes are suggestive of alternating episodes of wet ash fallout and rainfalls. Lahars interfingered with primary ash fallout confirm episodes of massive remobilization of loose tephra by heavy rainfalls during the final stage of the eruption.Chemical analyses of scoria clasts suggest tapping of magma from a compositionally zoned reservoir. Leucite-bearing, tephritic-phonolite (SiO₂ 51.17%) erupted in the early plinian phase was in fact followed by darker and slightly more mafic magma richer in crystals (SiO₂ 49.36%). During the nuées ardentes phase the composition returned to that of the early phase of the eruption.The reconstruction of the 1631 eruptive scenario supplies new perspectives on the hazards related to plinian eruptions of Vesuvius.     

Geodynamic implications of deep mantle upwelling in the source of Tertiary volcanics from the Veneto region (South-Eastern Alps)

Major and trace element and Sr–Nd–Hf–Pb isotopic data for the most primitive Tertiary lavas from the Veneto region (South-Eastern Alps, Italy) show the typical features of HIMU hotspot volcanism, variably diluted by a depleted asthenospheric mantle component (⁸⁷Sr/⁸⁶Sr_i=0.70306–0.70378; _Ndi=+3.9 to +6.8; _Hfi=+6.4 to +8.1, ²⁰⁶Pb/²⁰⁴Pb_i=18.786–19.574). P-wave seismic tomography of the mantle below the Veneto region shows the presence of low-velocity anomalies at depth, which is consistent with possible upwellings of plume material. Between the depths of 100–250 km the velocity anomalies are approximately 2–2.5% slower than average, implying a temperature excess of about 220–280 K, in agreement with estimates for other mantle plumes in the world. In this context, the Veneto volcanics may represent the shallow expression of a mantle upflow. The presence of a HIMU-DM component in a collision environment has significant geodynamic implications. Slab detachment and ensuing rise of deep mantle material into the lithospheric gap is proposed to be a viable mechanism of hotspot magmatism in a subduction zone setting.     

Chemical Mechanism Development: Laboratory Studies and Model Applications

Within the German Tropospheric Research Programme (TFS) numerous kinetic and mechanistic studies on the tropospheric reaction/degradation of the following reactants were carried out: oxygenated VOC, aromatic VOC, biogenic VOC, short-lived intermediates, such as alkoxy and alkylperoxy radicals.At the conception of the projects these selected groups were classes of VOC or intermediates for which the atmospheric oxidation mechanisms were either poorly characterised or totally unknown. The motivation for these studies was the attainment of significant improvements in our understanding of the atmospheric chemical oxidation processes of these compounds, particularly with respect to their involvement in photooxidant formation in the troposphere. In the present paper the types of experimental investigations performed and the results obtained within the various projects are briefly summarised. The major achievements are highlighted and discussed in terms of their contribution to improving our understanding of the chemical processes controlling photosmog formation in the troposphere.     

Processing and quality control of flux data during LITFASS-2003

Different aspects of the quality assurance and quality control (QA/QC) of micrometeorological measurements were combined to create a comprehensive algorithm which was then applied to experimental data from LITFASS-2003 (Lindenberg Inhomogeneous Terrain—Fluxes between Atmosphere and Surface: a long term Study). Eddy-covariance measurements of the latent heat flux were the main focus of the QA/QC efforts. The results of a turbulence sensor intercomparison experiment showed deviations between the different eddy-covariance systems on the order of 15%, or less than 30 W m⁻², for the latent heat flux and 5%, or less than 10 W m⁻², for the sensible heat flux. In order to avoid uncertainties due to the post-processing of turbulence data, a comprehensive software package was used for the analysis of experimental data from LITFASS-2003, including all necessary procedures for corrections and quality control. An overview of the quality test results shows that for most of the days more than 80% of the available latent heat flux data are of high quality so long as there are no instrumental problems. The representativeness of a flux value for the target land-use type was analysed using a stochastic footprint model. Different methods to calculate soil heat fluxes at the surface are discussed and a sensitivity analysis is conducted to select the most robust method for LITFASS-2003. The lack of energy balance closure, which was found for LITFASS-2003, can probably be attributed to the presence of low-frequency flux contributions that cannot be resolved with an averaging time of 30 min. Though the QA/QC system has been developed for the requirements of LITFASS-2003, it can also be applied to other experiments dealing with similar objectives.     

Tidally dominated, rimmed-shelf facies of the Picún Leufú Formation (Jurassic/Cretaceous boundary) in southwest Gondwana, Neuquén Basin, Argentina

A palaeoenvironmental model for the Picún Leufú Formation (Jurassic/Cretaceous boundary), which crops out in the Neuquén Basin, Argentina, on the southwestern margin of Gondwana, is presented in this paper for the first time. Detailed stratigraphic sections exposed along National Road 40 where it crosses the Picún Leufú Creek (type locality) and in the Cerrito Caracoles area, were examined and sampled. Based on a combination of the sedimentological data obtained (facies/microfacies analysis) and the relationship between benthic macrofaunas and their taphonomic attributes, it is concluded that the formation reflects a tidally dominated, rimmed-shelf setting characterized by prograding bars dissected by channels and thick lagoonal facies with shoal developments. In the Cerrito Caracoles area, where only the basal part of the formation is exposed, it is interpreted to have been deposited in a shallow subtidal marine environment in which shelf margin facies with patch reefs have been recognized.     

Simulating coseismic deformation of quartz in the middle crust and fabric evolution during postseismic stress relaxation — An experimental study

Non-steady state deformation and annealing experiments on vein quartz are designed to simulate earthquake-driven episodic deformation in the middle crust. Three types of experiments were carried out using a modified Griggs-type solid medium deformation apparatus. All three start with high stress deformation at a temperature of 400 °C and a constant strain rate of 10^− 4 s^− 1 (type A), some are followed by annealing in the stability field of α-quartz for 14–15 h at zero nominal differential stress and temperatures of 800–1000 °C (type A + B), or by annealing for 15 h at 900 °C and at a residual stress (type A + C).The quartz samples reveal a very high strength > 2 GPa at a few percent of permanent strain. The microstructures after short-term high stress deformation (type A) record localized brittle and plastic deformation. Statisc annealing (type A + B) results in recrystallisation restricted to the highly damaged zones. The new grains aligned in strings and without crystallographic preferred orientation, indicate nucleation and growth. Annealing at non-hydrostatic conditions (type A + C) results in shear zones that also develop from deformation bands or cracks that formed during the preceding high stress deformation. In this case, however, the recrystallised zone is several grain diameters wide, the grains are elongate, and a marked crystallographic preferred orientation indicates flow by dislocation creep with dynamic recrystallisation. Quartz microstructures identical to those produced in type A + B experiments are observed in cores recovered from Long Valley Exploratory Well in the Quaternary Long Valley Caldera, California, with considerable seismic activity.The experiments demonstrate the behaviour of quartz at coseismic loading (type A) and subsequent static annealing (type A + B) or creep at decaying stress (type A + C) in the middle crust. The experimentally produced microfabrics allow to identify similar processes and conditions in exhumed rocks.     

Magmatic History of Somma-Vesuvius on the Basis of New Geochemical and Isotopic Data from a Deep Borehole (Camaldoli della Torre)

A continuous-coring borehole recently drilled at Camaldoli dellaTorre on the southern slopes of Somma–Vesuvius providesconstraints on the volcanic and magmatic history of the Vesuvianvolcanic area since c. 126 ka BP. The cored sequence includesvolcanic units, defined on stratigraphical, sedimentological,petrological and geochemical grounds, emitted from both localand distal vents. Some of these units are of known age, suchas one Phlegraean pre-Campanian Ignimbrite, Campanian Ignimbrite(39 ka), Neapolitan Yellow Tuff (14· 9 ka) and VesuvianPlinian deposits, which helps to constrain the relative ageof the other units. The main rock types encountered are shoshonite,phonotephrite, latite, trachyte and phonolite. The sequenceincludes, from the base upwards: a thick succession of pyroclasticunits emplaced between 126 and 39 ka, most of them attributedto eruptions that occurred in the Phlegraean area; the CampanianIgnimbrite; the products of a local tuff cone formed between39 ka and the deposition of the products of the earliest activityof the Mt. Somma volcano; the products of the Somma–Vesuviusvolcano, which include from the base upwards a thick sequenceof lavas, pyroclastic rocks and the products of a local spattercone dated between 3· 7 ka and AD 79. The data obtainedfrom the study of the borehole show that, before the CampanianIgnimbrite eruption, low-energy explosive volcanism took placein the Vesuvian area, whereas mostly high-energy explosive eruptionscharacterized the Campi Flegrei activity. In the Vesuvian area,Campanian Ignimbrite deposition was followed by the eruptionof a local tuff cone and a long repose time, which predatedthe formation of the Mt. Somma edifice. Since 18· 3 ka(Pomici di Base eruption) the activity of Somma–Vesuviusbecame mostly explosive with rare lava effusions. The shallowestcored deposits belong to the Camaldoli della Torre cone, formedbetween the Pomici di Avellino and Pomici di Pompei eruptions(3· 7 ka–AD 79). New geochemical and Sr–Nd–Pb–B-isotopicdata on samples from the drilled core, together with those availablefrom the literature, allow us to further distinguish the volcanicrocks as a function of both their provenance (i.e. Phlegraeanor Vesuvian areas) and age, and to identify different magmaticprocesses acting through time in the Vesuvian mantle source(s)and during magma ascent towards the surface. Isotopically distinctmagmas, rising from a mantle source variably contaminated byslab-derived components, stagnated at mid-crustal depths (8–10km below sea level) where magmas differentiated and were probablycontaminated. Contamination occurred either with Hercynian continentalcrust, mostly during the oldest stages of Vesuvian activity(from 39 to 16 ka), or with Mesozoic limestone, mostly duringrecent Vesuvian activity. Energy constrained assimilation andfractional crystallization (EC-AFC) modelling results show thatcontamination with Hercynian crust probably occurred duringdifferentiation from shoshonite to latite. Contamination withlimestone, which is not well constrained with the availabledata, might have occurred only during the transition from shoshoniteto tephrite. From the ‘deep’ reservoir, magmas rosetowards a series of shallow reservoirs, in which they differentiatedfurther, mixed, and fed volcanic activity. KEY WORDS: Somma–Vesuvius; crustal contamination; source heterogeneity; radiogenic and stable isotopes; magmatic system     

Thecamoebians in Lake Winnipeg: a tool for Holocene paleolimnology

Holocene sediments in Lake Winnipeg are expressed in the lower Lake Agassiz sequence which is unconformably overlain by the Lake Winnipeg sequence. Nine sites, covering the North and South basins and the connecting Narrows, were selected for analysis of Holocene changes in thecamoebian faunae. Only the Lake Winnipeg sequence contains thecamoebians. This study indicates that biologic productivity and consequently the type of organic material in the sediments is the main control on thecamoebian taxa in Lake Winnipeg. Other factors controlling the distribution of thecamoebians are water chemistry and turbidity. Inorganic sediment geochemistry and water temperature do not appear to significantly influence the thecamoebian fauna of Lake Winnipeg. Variations in the abundance of key thecamoebian species along a north-south transect divide Lake Winnipeg into three distinct areas. The North Basin has remained relatively unchanged since the retreat of Lake Agassiz as indicated by the domination of Difflugia manicata throughout its history. This species appears to prefer Cyanophyta and diatoms as its food source. In the Narrows harsh conditions created by turbid waters and lack of algal food taxa result in Centropyxis aculeata replacing Difflugia manicata as the dominant species. In the South Basin three thecamoebian assemblages are recognized. Cucurbitella tricuspis, indicative of eutrophic conditions, dominates the most recent sediments of the South Basin. The underlying sediments are characterized by Difflugia globulus. In Lake Winnipeg this species is not a cold climate (arctic) indicator as suggested elsewhere but instead seems to prefer sediments containing green and yellow-green algal material. A Centropyxis-Arcella Assemblage occurs only at the base of the southernmost core where it is indicative of an early phase of hyposaline conditions as developed in shallow pools during the southward transgression of Lake Winnipeg. This study illustrates the usefulness of thecamoebians as paleolimnological indicators. Environmental changes are more significant in the restricted South Basin resulting in distinct thecamoebian assemblages. In contrast, the North Basin provided a stable environment throughout the late Holocene reflected in only subtle faunal changes.     

Sedimentary processes and trace metal contaminants in the buccaneer oil/gas field,northwestern gulf of Mexico

Sediments are the ultimate sink for contaminants in the marine environment, and physical processes of sedimentation influence the distribution and accumulation of these contaminants. Evaluation of contaminant levels in sediments is one approach to assessing environmental impact; data interpretation depends on consideration of sediment texture and mineralogy, however, which profoundly influence chemical composition. In this study, comparison of potentially contaminated sediments from the production field with control populations was done only within the context of similar (as to texture and organic carbon and carbonate content) sample groups as determined by cluster analysis. Ba, Cd, and Sr are identified as contaminants. Supported by the identification of a well-crystallized expandable clay—possibly bentonite—drilling fluids are a potential source of Ba. Ba and Sr may be unnaturally high because of their abundance in discharged produced formation waters, but may also be naturally controlled by the unique faunal assemblage associated with the structures. Cd is probably derived from corrosion of the structures and assorted debris on the seafloor. In general, contamination is limited to an area within 100 m of the platforms. Furthermore, substantial erosion around platforms has probably effectively removed and dispersed the bulk of the contaminants introduced into the marine environment by the offshore exploration/production operations.