On the variability of the Charnock constant and the functional dependence of the drag coefficient on wind speed: Part II-Observations

An analytical expression for the 10 m drag law in terms of the 10 m wind speed at the maximum in the 10 m drag coefficient, and the Charnock constant is presented, which is based on the results obtained from a model of the air-sea interface derived in Bye et al. (2010). This drag law is almost independent of wave age and over the mid-range of wind speeds (5?17 ms^?1) is very similar to the drag law based on observed data presented in Foreman and Emeis (2010). The linear fit of the observed data which incorporates a constant into the traditional definition of the drag coefficient is shown to arise to first-order as a consequence of the momentum exchange across the air-sea boundary layer brought about by wave generation and spray production which are explicitly represented in the theoretical model.     

Actinian dominated intertidal mudflats: A new case of an extraordinary rare phenomenon from Southern Chile

Generally, estuarine intertidal mudflats constitute important nurseries for fish and foraging grounds for coastal birds by providing a plenitude of mollusks, worms, and crustaceans as prey, which in turn mostly feed on suspended and benthic microalgae, bacteria, and detritus. Despite the high productivity of such habitats, pronounced variability in both salinity and temperature results typically in low diversity. The only sea anemone reported from estuarine mud is the edwardsiid Nematostella vectensis Stephenson, 1935. It occurs widely in the northern hemisphere, and occasionally in extremely high density. Here we document another sea anemone from estuarine mud and muddy sand found in Southern Chile which has similar ecological attributes. Taxonomic confusion has impeded the reporting on this small but prominent member in a macrozoobenthic assemblage, the brooding Anthopleura hermaphroditica (Carlgren, 1899; Anthozoa: Actiniidae). It differs from N. vectensis by the presence of symbiotic algae. Average density under poly- to euhaline conditions in mud and muddy sand at around mid tide level was about 3 actinians per cm². An average abundance of 11,000 m^? 2, a biovolume of 487 cm³ m^? 2, and a biomass of 35.5 g dry organic weight m^? 2 were found in mud and muddy sand in two surveys 20 years apart. The mean fishing area of fully expanded individuals covers 42 ± 25 mm², corresponding to a circular area with a diameter of 7.3 ± 5.7 mm. Preliminary experiments indicate that associated benthos may be relegated to life below surface by the net of tentacles above the sediment. As no predators on A. hermaphroditica could be found on the mudflat, the success of this mixotrophic sea anemone may entail a trophic dead end.     

Multiple ways of producing intermediate and silicic rocks within Thingmúli and other Icelandic volcanoes

Major and trace element compositions of rocks and coexisting phenocrysts of the Thingmúli volcano suggest a revision of the existing models for the formation of intermediate and silicic melts in Iceland. The new data define two compositional tholeiitic trends with a significant gap between them. A high-iron trend (HFe) contains 6–14 wt% total FeO in silicic rocks with c. 1 wt% MgO, as well as sodic plagioclase and hedenbergite phenocrysts. A low-iron trend (LFe) contains 3–5 wt% FeO at c. 1 wt% MgO, which is typical of Iceland but higher than MORB compositions. The most evolved phenocrysts of the LFe trend do not reach iron-rich end members. The HFe trend is interpreted as a result of fractional crystallization; numerical modelling using the MELTS algorithm suggests that crystallization took place under redox conditions constrained to one-log unit below the fayalite-magnetite-quartz oxygen buffer (FMQ-1). The LFe trend is explained by a combination of mixing between rhyolite and ferrobasalt, assimilation of hydrated crust and fractional crystallization under higher redox conditions (FMQ). The two trends and the gap are best defined in a plot of Mg# versus SiO₂ that is useful to unravel petrogenetic processes. For example, intermediate and silicic rocks of the Holocene volcanic systems of spreading rifts (e.g. Krafla), propagating rifts (e.g. Hekla) and off-rifts (Öræfajökull) also fall into high- and low-iron fields and outline a gap similar to Thingmúli. The identification of two compositional trends in erupted intermediate and silicic volcanic products shows that processes in the deep roots of single volcanic systems are highly diverse and likely controlled by local variations in the thermal gradients and the extend of hydrothermal alteration. Generalizations about the relationship between the compositions of intermediate and silicic rocks and plate tectonic setting, therefore, should be avoided.     

A data exploration framework for validation and setup of hydrological models

Over the course of hydrological research projects often a large number of heterogeneous data sets are acquired from sources as diverse as boreholes, gauging stations or satellite imagery. This data then need to be integrated into models for the simulation of hydrological processes. We propose a framework for exploration of geoscientific data and visually guided preparation of such models. Data sets from a large number of sources can be imported, combined and validated to avoid potential problems due to artefacts or inconsistencies between data sets in a subsequent simulation. Boundary conditions and domain discretisations for surface and subsurface models can be created and tested regarding criteria indicating possible numerical instabilities. All data sets including simulation results can be integrated into a user-controlled 3D scene and aspects of the data can be enhanced using a number of established visualisation techniques including thresholding and user-defined transfer functions. We present the application of this framework for the preparation of a model for simulation of groundwater flow in a river catchment in southwest Germany investigated in the scope of the WESS project.     

Hydrodynamics and sediment dynamics in the German Bight. A focus on observations and numerical modelling in the East Frisian Wadden Sea

This work deals with analysis of hydrographic observations and results of numerical simulations. The data base includes acoustic Doppler current profilers (ADCP) observations, continuous measurements on data stations and satellite data originating from the medium resolution imaging spectrometer (MERIS) onboard the European Space Agency (ESA) satellite ENVISAT with a spatial resolution of 300 m. Numerical simulations use nested models with horizontal resolutions ranging from 1 km in the German Bight to 200 m in the East Frisian Wadden Sea coupled with a suspended matter transport model. Modern satellite observations have now a comparable horizontal resolution with high-resolution numerical model of the entire area of the East Frisian Wadden Sea allowing to describe and validate new and so far unknown patterns of sediment distribution. The two data sets are consistent and reveal an oscillatory behaviour of sediment pools to the north of the back-barrier basins and clear propagation patterns of tidally driven suspended particulate matter outflow into the North Sea. The good agreement between observations and simulations is convincing evidence that the model simulates the basic dynamics and sediment transport processes, which motivates its further use in hindcasting, as well as in the initial steps towards forecasting circulation and sediment dynamics in the coastal zone.     

蒙古古生代地层研究的新进展

蒙古国古生代地层的研究以往主要侧重底栖大化石的研究, 很多地层的时代划分、归属问题不能得到很好的解决,底栖化石的地方性很强,不能与国际直接对比。 牙形刺是古生代地层的主导化石, 很多古生代地层问题都可以用牙形刺解决并进行可靠的洲际间对比。2001年笔者在蒙古南戈壁采集了158个样品, 经分析发现了大量牙形刺标本, 解决了很多蒙古的重大地层问题。Arynshand组应当归入下石炭统, 泥盆-石炭系界线在Arynshand组之下, 而不是在此组的内部。Mushgai地区Bayan-Khoshuu Ruins剖面的Mandalovoo组Gavuu 段的上部应属早泥盆世早期, 而不是以前所确定的早志留世, 称为奥咯诺伍德组（Olonovoot Formation）;Gavuu段的下部仍归早志留世。Mandalovoo组应提升为Mandalovoo群;Gavuu段应提升为Gavuu组。南戈壁Shine Jinst地区Tsakhir剖面Tsagaanbulag组的时代是早泥盆世洛霍考夫期, 而不是中晚志留世,Ulaan-Shand剖面Tsagaanbulag组的时代也是早泥盆世洛霍考夫期。Chuluun组的时代为早泥盆世晚埃姆斯期。Tsagaankhaalga组的时代为早艾菲尔期。Indert组为早石炭世。蒙古古生代海相地层大部分是浅水相地层, 并可能存在5个间断：志留系的文洛克统和罗德洛统的下部,下泥盆统布拉格阶的一部分,中泥盆统艾菲尔阶上部,泥盆-石炭系界线地层。蒙古国南部和中部很可能缺失上二叠统的海相沉积。     

Investigating hydrological drivers of nitrate export dynamics in two agricultural catchments in Germany using high-frequency data series

In this study near-continuous time series of nitrate, electrical conductivity, and discharge were used to identify the dominating hydrological mechanisms that control nitrate export dynamics in two agricultural catchments. The main goal was to assess relationships between contrasting event based as well as long-term nitrate transport behaviour and catchment hydrology. Data records were obtained from online probes that allow field based high-frequency analyses over long time periods. The catchments of the Ammer River (southwestern Germany) and the Weida River (eastern Germany) are similar with respect to size (~100 km²), morphology, and climate and are dominated by agricultural use. Main differences are the stronger urbanization and the occurrence of karstic rocks in the Ammer catchment. Nitrate concentrations are high in water of both streams and range mostly between 20 and 50 mg l^?1. Nitrate export in the Ammer catchment is dominated by baseflow and a minor second, diluting runoff component generated in urbanized areas. In contrast, nitrate dynamics of the Weida catchment is governed by the interplay of at least three runoff components, while the largest amount of nitrate is mobilized intermittently by a delayed fast component generated in the catchment’s soils during wet conditions. These interpretations, derived with one online probe at the outlet of each catchment, are well in line with the former modeling results. This study shows that high-resolution data obtained by online techniques offers a large potential to improve the conceptualization of dominating flow and transport processes at catchment scales at relatively low costs and effort.     

The evolution of the Arabian lower crust and lithospheric mantle — Geochemical constraints from southern Syrian mafic and ultramafic xenoliths

Geochemical compositions of lower crustal and lithospheric mantle xenoliths found in alkali basaltic lavas from the Harrat Ash Shamah volcanic field in southern Syria place constraints on the formation of the Arabian–Nubian Shield in northern Arabia. Compositions of lower crustal granulites are compatible with a cumulate formation from mafic melts and indicate that they are not genetically related to their host rocks. Instead, their depletion in Nb relative to other incompatible elements points to an origin in a Neoproterozoic subduction zone as recorded by an average depleted mantle Sm–Nd model age of 630 Ma.Lithospheric spinel peridotites typically represent relatively low degree (< 10%) partial melting residues of spinel lherzolite with primitive mantle compositions as indicated by major and trace element modelling of clinopyroxene and spinel. The primary compositions of the xenoliths were subsequently altered by metasomatic reactions with low degree silicate melts and possibly carbonatites. Because host lavas lack these signatures any recent reaction of the lherzolites with their host magma can be ruled out. Sm–Nd data of clinopyroxene from Arabian lithospheric mantle lherzolites yield an average age of 640 Ma suggesting that the lithosphere was not replaced since its formation and supporting a common origin of the Arabian lower crustal and lithospheric mantle sections.The new data along with published Arabian mantle xenolith compositions are consistent with a model in which the lithospheric precursor was depleted oceanic lithosphere that was overprinted by metasomatic processes related to subduction and arc accretion during the generation of the Arabian–Nubian Shield. The less refractory nature of the northern Arabian lithosphere as indicated by higher Al, Na and lower Si and Mg contents of clinopyroxenes compared to the more depleted nature of the south Arabian lithospheric mantle, and the comparable low extent of melt extraction suggest that the northern Arabian lithosphere formed in a continental arc system, whereas the lithosphere in the southern part of Arabia appears to be of oceanic arc origin.     

Microfabrics of calcite ultramylonites as records of coaxial and non-coaxial deformation kinematics: Examples from the Rocher de l'Yret shear zone (Western Alps)

Microfabrics were analysed in calcite mylonites from the rim of the Pelvoux massif (Western Alps, France). WNW-directed emplacement of the internal Penninic units onto the Dauphinois domain produced intense deformation of an Eocene-age nummulitic limestone under lower anchizone metamorphic conditions (slightly below 300 °C). Two types of microfabrics developed primarily by dislocation creep accompanied by dynamic recrystallisation in the absence of twinning. Coaxial kinematics are inferred for samples exhibiting grain shape fabrics and textures with orthorhombic symmetry. Their texture (crystallographic preferred orientation, CPO) is characterised by two c-axis maxima, symmetrically oriented at 15° from the normal to the macroscopic foliation. Non-coaxial deformation is evident in samples with monoclinic shape fabrics and textures characterised by a single oblique c-axis maximum tilted with the sense of shear by about 15°. From the analysis of suitably oriented slip systems for the main texture components under given kinematics it is inferred that the orthorhombic textures, which developed in coaxial kinematics, favour activity of <10–11> and <02–21> slip along the f and r planes, respectively, with minor contributions of basal-<a> slip. In contrast, the monoclinic textures, which developed during simple shear, are most suited for duplex <a> slip along the basal plane. The transition between the dominating slip systems for the orthorhombic and monoclinic microfabrics is interpreted to be due to the effects of dynamic recrystallisation upon texture development. Since oblique c-axis maxima documented in the literature are most often rotated not with but against the shear sense, calcite textures alone should not be used as unequivocal shear sense indicators, but need to be complemented by microstructural criteria such as shape preferred orientations, grain size estimates and amount of twinning.