A candidate of the Induan-Olenekian boundary stratotype in the Tethyan region

The Olenekian Stage was proposed by Kiparisova and Popov[1] based on the type section along the lower reaches of the Olenek River, Siberia. Later research showed that this section con-tains only the Olenikites spiniplicatus Zone of the Upper Olenekian Sta…     

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.     

Tracer measurements in groyne fields for the quantification of mean hydraulic residence times and of the exchange with the stream

Tracer experiments were carried out in groyne fields (GF) of the river Elbe near Havelberg (Germany) in order to estimate the hydraulic connectivity with the river channel. The characteristic times of the five groyne fields, which were estimated from the exponentially declining tracer curves in 43 runs, ranged between 15 min and 69 min and did not correlate with the water level. Methodological investigations show that single point injection and two measurements (in the outflowing water and in the dominant region) are sufficient to provide robust in‐situ tracer curves. Using simplified mathematical simulations with connected stirred tanks, the conditions are investigated for the development of breaks in tracer curves and for the occurrence of significant errors in the estimation of intrinsic residence times. It was shown that an initial uniform dye distribution is not mandatory for the estimation during steady states. In special cases, point injections are more advisable. Moreover, the mean hydraulic residence time was found to be not equivalent to the estimated characteristic time. In fact, it is mostly overestimated by tracer experiments. The degree of overestimation depends on mixing and the volumetric proportions between the different parts of the GF and can be calculated from measured dye concentration differences. For example, an overestimation of 32% was calculated for a groyne field with a commonly found circulation flow pattern.     

The GW-Fauna-Index: A first approach to a quantitative ecological assessment of groundwater habitats

Between June 2001 and December 2002, 18 hyporheic and groundwater bores were sampled for fauna and environmental data using phreatic traps. The bores were situated in three different natural geographic regions in Palatinate, Southwestern Germany.Faunal data correlated with the relative amount of detritus, bacterial abundances and the standard deviation of temperature, while very few and weak correlations were found with physical–chemical variables. Dissolved oxygen was assumed to be a limiting factor for most metazoans with a critical concentration at around 0.5–1 mg l⁻¹.To quantify the strength of the hydrological exchange with surface water and its effects on fauna, a so-called GW-Fauna-Index was developed and calculated using the relative amount of detritus, standard deviation of temperature, and oxygen concentration. From all environmental data and on all spatial scales, this index best explained the total faunal abundance and taxonomic richness.To describe the availability of organic aliments in the groundwater, the terms of “alimonic” and “alimony” [from lat. alimonium=(food) supply] were proposed.Although stygofauna was different in the geographic regions investigated, the GW-Fauna-Index was independent from these regional particularities. Using the GW-Fauna-Index, three groups of groundwater habitats could be classified according to the alimonic conditions. From oligo-alimonic group I samples, fauna was mostly absent, while meso-alimonic group II samples were prevailingly populated by stygobites, and eu-alimonic group III samples by ubiquists and stygoxenes. Total abundances and taxonomic richness increased significantly from group I to group III. Group I samples were characterized by low index values, group II samples by intermediate and group III samples by high values.The GW-Fauna-Index provides promising perspectives for application, but needs some improvement. First of all, detritus should be analysed quantitatively and qualitatively, rather than semi-quantitatively. Also, a standard protocol for sampling has to be developed.     

Climate change and North Sea storm surge extremes: an ensemble study of storm surge extremes expected in a changed climate projected by four different regional climate models

The coastal zones are facing the prospect of changing storm surge statistics due to anthropogenic climate change. In the present study, we examine these prospects for the North Sea based on numerical modelling. The main tool is the barotropic tide-surge model TRIMGEO (Tidal Residual and Intertidal Mudflat Model) to derive storm surge climate and extremes from atmospheric conditions. The analysis is carried out by using an ensemble of four 30-year atmospheric regional simulations under present-day and possible future-enhanced greenhouse gas conditions. The atmospheric regional simulations were prepared within the EU project PRUDENCE (Prediction of Regional scenarios and Uncertainties for Defining EuropeaN Climate change risks and Effects). The research strategy of PRUDENCE is to compare simulations of different regional models driven by the same global control and climate change simulations. These global conditions, representative for 1961–1990 and 2071–2100 were prepared by the Hadley Center based on the IPCC A2 SRES scenario. The results suggest that under future climatic conditions, storm surge extremes may increase along the North Sea coast towards the end of this century. Based on a comparison between the results of the different ensemble members as well as on the variability estimated from a high-resolution storm surge reconstruction of the recent decades it is found that this increase is significantly different from zero at the 95% confidence level for most of the North Sea coast. An exception represents the East coast of the UK which is not affected by this increase of storm surge extremes.     

Using paleoclimate proxy-data to select optimal realisations in an ensemble of simulations of the climate of the past millennium

We present and describe in detail the advantages and limitations of a technique that combines in an optimal way model results and proxy-data time series in order to obtain states of the climate system consistent with model physics, reconstruction of past radiative forcing and proxy records. To achieve this goal, we select among an ensemble of simulations covering the last millennium performed with a low-resolution 3-D climate model the ones that minimise a cost function. This cost function measures the misfit between model results and proxy records. In the framework of the tests performed here, an ensemble of 30 to 40 simulations appears sufficient to reach reasonable correlations between model results and reconstructions, in configurations for which a small amount of data is available as well as in data-rich areas. Preliminary applications of the technique show that it can be used to provide reconstructions of past large-scale temperature changes, complementary to the ones obtained by statistical methods. Furthermore, as model results include a representation of atmospheric and oceanic circulations, it can be used to provide insights into some amplification mechanisms responsible for past temperature changes. On the other hand, if the number of proxy records is too low, it could not be used to provide reconstructions of past changes at a regional scale.     

A high-resolution reconstruction of Storglaciären mass balance back to 1780/81 using tree-ring data and circulation indices

Storglaciären in northernmost Sweden has the world's longest ongoing continuous mass-balance record, starting in 1946. To extend this mass-balance record, we have reconstructed summer (b_S) and winter (b_W) mass balances separately back to the mass balance year 1780/81 with annual resolution. We used tree-ring data for b_S and a set of circulation indices, based on the sea-level pressure, for b_W. Both proxies have correlation coefficients with respective mass balance components of ca. 0.7. The reconstructed net balance (b_N) of Storglaciären was well correlated to the observations during 1946-1980 (r = 0.8, p < 0.05). Our reconstruction agrees well with previously obtained results of northern Sweden glacier variability, where the predominantly positive b_N years between 1890 and 1910 correspond to the well documented post-Little Ice Age advance of Storglaciären. Furthermore, the results suggest that b_S, as a function of summer temperatures, is more important than b_W in determining the b_N, which is contrary to glaciers in the maritime parts of western Scandinavia. In general, b_N has been negative over the last 220 yr, suggesting a predomination of continental conditions over northern Sweden. However, the influence of b_W increased in the late twentieth century, indicating a shift to a more oceanic climate regime.     

Geometry and chronology of growth and drowning of Middle Triassic carbonate platforms (Cernera and Bivera/Clapsavon) in the Southern Alps (northern Italy)

The depositional architecture and the geometric relationships between platform-slope deposits and basinal sediments along with paleontological evidence indicate the time interval of the younger Anisian Reitziites reitzi ammonoid zone to largely represent the main stage of platform aggradation at the Cernera and Bivera/Clapsavon carbonate platforms. Published and new U-Pb age data of zircons from volcaniclastic layers bracketing the stratigraphic interval of platform growth constrain the duration of platform evolution to a time span shorter than 1.8±0.7m.y., probably in the order of 0.5-1m.y., reflecting fast rates of vertical platform aggradation exceeding 500 m/m.y. In the range of growth potentials for shallow-water carbonate systems estimated in relation to the time span of observation, this high rate is in agreement with values for short intervals of 10⁵-10⁶yrs (e.g., Schlager 1999). After drowning, the platforms at Cernera and Bivera/Clapsavon were blanketed by thin pelagic carbonates. On the former platform flanks the draping sediments in places comprise red nodular pelagic limestones (Clapsavon Limestone) similar in facies to the Han Bulog Limestones occurring elsewhere in Middle Triassic successions of the Mediterranean Tethys. The drowning of vast areas of former carbonate platforms possibly triggered the onset of bottom-water circulation in adjacent basins as suggested by the abrupt transition from laminated to bioturbated pelagic nodular limestones in the Buchenstein Formation which occurred close to the time of initial platform submergence. During the Late Ladinian the topographic features of the drowned platforms were onlapped by rapidly deposited, predominantly clastic successions including coarse breccias and volcanic rocks sealing and preserving the peculiar stratigraphic setting.     

陕西关中及周边地区近500a来初夏旱涝事件初步分析

基于华山树轮宽度差值年表重建的陕西关中及周边地区近500a来的初夏干燥指数序列,对该地区初夏极端旱涝事件及其连续旱涝变化特征进行了初步分析.区域干燥指数与Palmer指数在变化上极为相似,可用于反映该地区的旱涝变化.结果表明:该地区近500a来初夏共发生18次极端干旱事件和11次极端洪涝事件,除公元1521年与历史文献记录的旱涝事件相反,公元1513年、1574年、1675年和1945年未发现历史记录外,其余年份均能找到相应记录;近500a来初夏存在9个显著的连续偏旱期和10个显著的连续偏涝期,并以16和19世纪发生的连续旱涝事件最为频繁,而17和18世纪发生的旱涝事件相对较少,20世纪发生的干旱事件明显多于洪涝事件.     

The clustering of K∼20 galaxies in 17 radio galaxy fields

We investigate the angular correlation function, ο(θ), of the galaxies detected in the 2.1-μm K ' band in 17 fields (101.5 arcmin² in total), each containing a z ∼1.1 radio galaxy. There is a significant detection of galaxy clustering at a limit of K ∼20, with a ο(θ) amplitude similar to that estimated by Carlberg et al. at K =21.5. The ο(θ) amplitudes of these K -limited samples are higher than expected from the faint galaxy clustering in the blue and red passbands, but consistent with a pure luminosity evolution model if clustering is stable (ε=0) and the correlation function of early-type galaxies is steeper than that of spirals.
We do not detect a significant cross-correlation between the radio galaxies and the other galaxies in these fields. The upper limits on the cross-correlation are consistent with a mean clustering environment of Abell class 0 for z ∼1.1 radio galaxies, similar to that observed for radio galaxies at z ∼0.5, but would argue against an Abell class 1 or richer environment. As Abell 0 clustering around the radio galaxies would not significantly increase the ο(θ) amplitude of galaxies in these fields, stable clustering with a steep ξ( r ) for E/S0 galaxies appears to remain the most likely interpretation of the ο(θ) amplitude.
At K ≤20, the number of galaxy–galaxy pairs of 2–3 arcsec separation exceeds the random expectation by a factor of 2.15±0.26. The excess of close pairs is comparable to that previously reported for R -band data, and consistent with a ∼(1+ z )² evolution of the galaxy merger rate.