The evolution of Cenozoic explosive volcanism: The Iceland Plume

This paper reviews original and published data on the abundance and composition of pyroclastics due to explosive discharges by volcanoes on the Iceland Plume. The pyroclastics were deposited in the Cenozoic sediments in the North Atlantic Ocean and in the Norwegian-Greenland basin. The DSDP and ODP initial reports (70 deep wells), 100 geologic columns sampled during cruises of the R/Vs Akademik Kurchatov and Mikhail Lomonosov furnished the database from which we constructed stratigraphic and areal-maps of pyroclastics abundance and computed the distribution of the volumes and amounts of pyroclastic layers over the stratigraphic intervals of the Cenozoic sedimentary sequence. The distribution of these layers was found to be cyclic; the highest frequency occurred during the Quaternary. Basaltoid pyroclastics prevailed in the late Paleocene and Early Eocene. The Oligocene has typically subalkaline ankaramite pyroclastics. From the Miocene until the Quaternary the pyroclastics became bimodal (basalt-rhyolite) and high potassium rhyolite pyroclastics appeared. This evolution seems to have been caused by crystallization differentiation of basaltoid magmas in magma chambers that came into being in prespreading grabens where a thick (> 20 km) sequence of volcanic rocks accumulated to produce a dipping reflector.     

Multidimensional statistical technique for detection of low contrast geochemical anomalies

In this article we propose an advanced technique for detecting low contrast geochemical anomalies using a set of features. There are three principal elements in this technique: (1) a statistical measure of the contrast of the anomaly, denoted as τ; (2) selection of a background population; and (3) reduction of the dimensionality of the feature space. In the frame of the model, which describes the statistical distribution of geochemical background as a multidimensional normal distribution of logarithms of concentrations, the index, τ, is a powerful test statistic for the hypothesis of abnormality of an observation. Maps of τ anomalies can be rigorously interpreted on the basis of statistical inferences. Under all equal conditions this technique allows the detection of geochemical anomalies with at least the same contrast (if the chemical elements in a background population are correlated, then even the better) as using selective extractions of metals from soil or other techniques for data processing. The advantages of the proposed technique are demonstrated both theoretically and on examples of rare-metal and copper–nickel mineral deposits.     

A cyclicity in the early brigantian (D2) limestones east of the clwydian range,north wales and its use in correlation

For the first time, minor cyclicity is described from some limestones in the lower part of the Brigantian (D2) succession of the Mold district North Wales which can be traced throughout the area enabling a detailed correlation to be established. The minor cyclicity may have been caused by eustatic sea-level fluctuations. Periods of emergence associated with each regressive phase are demonstrated by the presence of subaerial features and terrestrial deposits. The lateral persistence of the cycles is confirmed by comparison with established faunal and lithological horizons. Correlation with other cyclic Brigantian strata in Yorkshire, Derbyshire and Bristol is briefly discussed. The Asbian/Brigantian (D1/D2) boundary in North Wales is described and distinctive faunal and lithological changes similar to those in the area of the stratotype in north England have been recorded.     

Bildung bromhaltiger Desinfektionsnebenprodukte nach Chlorung von Bodenseewasser in Abhängigkeit von Aufbereitungsschritten und der Bromidkonzentration

Formation of Brominated Disinfection By-products after Chlorination of Water from Lake Constance Depending on Treatment Steps and Bromide Concentration The formation of halogenated disinfection by-products (DNP) (trihalomethanes (THM), haloacetic acids (HES), haloacetonitriles (HAN), haloketones (HKE) and chloropicrin (TCNM)) was studied after chlorination (0.5 mg/L) of raw water and drinking water from Lake Constance. The objectives of this study were to investigate the effect of bromide ion on the distribution of DNP-species resulting from chlorination and to draw up a bromide mass-balance. The treatment of water from Lake Constance with ozone decreased the formation of DNP about 35% and of total organic halogens (AOX) about 45%. This decline in DNP-formation is mainly due to the formation of chloroform, dichloro- and trichloroacetic acid. Though there is only a small amount of bromide (6.2 μg/L) in water from Lake Constance, about 32% of THM, 16% of HES, and 30% of HAN contained bromine after chlorination of treated water. The addition of bromide ion (up to 1 mg/L) shifted the DNP-composition to more brominated species. The distribution of the DNP-species depends on the initial molar bromide-to-chlorine ratio. A mathematic model showed the same pattern of DNP-species depending on the initial molar bromide-to-chlorine ratio that was observed experimentally in microstrained raw water and drinking water from Lake Constance. After chlorination of microstrained raw water, 27% of the bromide were incorporated in known DNP, 34% in unknown substances, and about 39% of bromide were not converted to organic bromine. After chlorination of treated water, only 16% of the bromide were incorporated in unknown substances, whereas 34% were found in known DNP. About 50% were found as bromide again. After addition of bromide (up to 25 μg/L) to ozonated and treated water from Lake Constance, between 60 and 72% of the bromide that had reacted after chlorination were found in analyzed low-molecular DNP.     

Probing the wind–wind collision in γ2 Velorum with high-resolution Chandra X-ray spectroscopy: evidence for sudden radiative braking and non-equilibrium ionization

We present a new analysis of an archived Chandra HETGS X-ray spectrum of the WR+O colliding wind binary γ² Velorum. The spectrum is dominated by emission lines from astrophysically abundant elements: Ne, Mg, Si, S and Fe. From a combination of broad-band spectral analysis and an analysis of line flux ratios we infer a wide range of temperatures in the X-ray-emitting plasma (∼4–40 MK). As in the previously published analysis, we find the X-ray emission lines are essentially unshifted, with a mean FWHM of  1240 ± 30 km s⁻¹  . Calculations of line profiles based on hydrodynamical simulations of the wind–wind collision predict lines that are blueshifted by a few hundred  km s⁻¹  . The lack of any observed shift in the lines may be evidence of a large shock-cone opening half-angle (>85°), and we suggest this may be evidence of sudden radiative braking. From the R and G ratios measured from He-like forbidden-intercombination-resonance triplets we find evidence that the Mg  xi emission originates from hotter gas closer to the O star than the Si  xiii emission, which suggests that non-equilibrium ionization may be present.     

Air–sea CO2 fluxes in the north-eastern shelf of the Gulf of Cádiz (southwest Iberian Peninsula)

An intra-annual investigation of the fugacity of CO₂ (fCO₂) has been conducted in surface waters of the north-eastern shelf of the Gulf of Cádiz (SW Iberian Peninsula) in four cruises made in 2006 and 2007. Intra-annual variability of fCO₂ was assessed and is discussed in terms of mixing, temperature and biology. In the study area of the shelf, thermodynamic control over fCO₂ predominates from early May to late November, and this is opposite and similar in magnitude to the net biological effect. However, biological control over fCO₂ predominates during winter. The results suggest that surface waters in the coastal area are under-saturated with respect to atmospheric CO₂ during most of the year; therefore they represent a sink for atmospheric CO₂ between November and May (? 1.0 mmol m^? 2 day^? 1), but a weak source in June (1.3 mmol m^? 2 day^? 1). In contrast, the coastal ecosystems studied (the lower estuary of Guadalquivir Estuary and Bay of Cádiz) acted as a weak sink for atmospheric CO₂ during February (? 1.3 mmol m^? 2 day^? 1) and as a source between May and November (2.6 mmol m^? 2 day^? 1). The resulting mean annual CO₂ flux in the north-eastern shelf of the Gulf of Cádiz was ? 0.07 mol m^? 2 year^? 1 (? 0.2 mmol m^? 2 day^? 1), indicating that the area acts as a net sink on an annual basis.     

A regional model for studies of atmosphere-ice-ocean interaction in the western Arctic

Summary Asa step in the development of a fully coupled regional model of the atmosphere-ice-ocean system, atmospheric and sea ice models have been adapted to a western Arctic domain centered on the Bering Strait. Lateral boundary conditions derived from operational analyses drive the models through simulations on grids having horizontal resolutions of 21 km and 7 km. Sensitivities to the presence of sea ice are large after only 48 hours, by which time the surface temperatures in the Bering and Chukchi Seas are 10–15°C higher without sea ice than with sea ice. The temperatures, in turn, modify the fields of sea level pressure, surface wind and precipitation. By influencing the surface wind stress through the static static stability, the surface state feeds back to the surface momentum exchange, ice/ocean transport, and the rate of formation of new ice. The results also show a resolution-dependence of the surface winds, precipitation rates and new ice formation rates, particularly in areas in which the coastal configuration and topography are spatially complex. The experiments will be augmented by the implementation of an ocean model on the same grids.With 12 Figures     

Decorrelated GRACE time-variable gravity solutions by GFZ,and their validation using a hydrological model

We have analyzed recent gravity recovery and climate experiment (GRACE) RL04 monthly gravity solutions, using a new decorrelating post-processing approach. We find very good agreement with mass anomalies derived from a global hydrological model. The post-processed GRACE solutions exhibit only little amplitude damping and an almost negligible phase shift and period distortion for relevant hydrological basins. Furthermore, these post-processed GRACE solutions have been inspected in terms of data fit with respect to the original inter-satellite ranging and to SLR and GPS observations. This kind of comparison is new. We find variations of the data fit due to solution post-processing only within very narrow limits. This confirms our suspicion that GRACE data do not firmly ‘pinpoint’ the standard unconstrained solutions. Regarding the original Kusche (J Geod 81:733–749, 2007) decorrelation and smoothing method, a simplified (order-convolution) approach has been developed. This simplified approach allows to realize a higher resolution—as necessary, e.g., for generating computed GRACE observations—and needs far less coefficients to be stored.     

High-resolution spectroscopy of ROSAT-discovered weak-line T Tauri stars near Lupus

We present high-resolution optical echelle spectroscopy for a large fraction of the Li-rich late-type stars recently discovered in the vicinity of the Lupus dark clouds. Our results confirm the high Li  i   λ 6708 equivalent widths previously estimated from medium-resolution spectra, thus adding strength to the conclusion that the large majority of these stars are still in the pre-main-sequence phase of their evolution, contrary to claims from other authors that many of them might be zero-age main-sequence stars. We present a statistical approach to derive a mean distance for the sample, and find that it is consistent with, or slightly lower than, the Hipparcos distance of the Lupus star-forming region. The radial velocities measured for part of these stars are consistent with those observed for the Lupus star-forming region, while stars outside the dark clouds show a mean difference of the order of 3 km s⁻¹. The projected rotational velocities show a lack of slow rotators, which is interpreted as a consequence of the X-ray selection of the sample. The Li-rich stars in Lupus studied in this work yield a fairly 'clean' sample of very young stars, while in other star-forming regions a larger fraction of older zero-age main-sequence stars has been found among ROSAT -discovered Li-rich stars. We argue that this fact reflects the relation of these stars with the Gould Belt.     

Interpretation of Mars southern highlands high amplitude magnetic field with total gradient and fractal source modeling: New insights into the magnetic mystery of Mars

Using model studies, the total gradient (TG) of the Z-component magnetic field is shown to be a useful quantity for delineating sources of satellite-altitude magnetic anomalies; this field is used to constrain the location and lateral boundaries of sources of high amplitude magnetic anomalies of southern highlands of Mars. The TG field suggests two parallel linear and oppositely magnetized sources of 1000 and 1800 km length separated by 1000 km of region of intervening non-parallel sources. The simplest interpretation of the long, linear features is that they are zones of multitudinous crustal scale dikes formed in separate episodes of rifting, and not features associated with the mechanism of seafloor spreading. Forward modeling with uniformly magnetized sources suggests that magnetizations of the order of 10-50 A/m (40 km thickness) over ∼100 km width in the case of the southern source and of 12.5-27.5 A/m (40 km thickness) and ∼200 km width for the northern source are necessary to explain the Z-component amplitudes and features of the TG field. If the crustal magnetization on Mars were to be distributed fractally as on Earth, magnetizations matching the largest amplitude features on Mars may be spatially correlated from a 50-100 km distance range (β ∼ 3) to approaching nearly uniform magnetization (β ∼ 5) values. To keep magnetization intensity as small as possible, the higher end of β values are preferred, whereas, small amplitude anomaly features could be generated from sources with β ∼ 3. Many of the Mars anomaly features could be coalescence effects similar to the coalescence of anomaly features observed on http://icarus.cornell.edu/information/keywords.html.Earth.