Hyperpycnal plumes and plume fronts over the Huanghe (Yellow River) delta front

The Huanghe (Yellow River) discharges extremely high suspended sediment concentrations (25 to 220 g/l) which favor sustained hyperpycnal plumes (underflows). Observations of weakly hyperpycnal unchannelized plumes and indirect evidence of strongly hyperpycnal channelized underflows over the delta front indicate the importance of these modes of sediment dispersal. The weakly hyperpycnal plumes occupy the entire water column over the shallow (<5 m) delta top. From a pronounced front near the break in slope at about 5 m depth, they descend over the delta-front slope as wide-spread underflows. Evidence of strongly hyperpycnal underflows was shown from subaqueous valleys partly filled with low-density mud.     

现行黄河口水下三角洲海底形貌及不稳定性

高分辨力的声学仪器调查表明,现行黄河口水下三角洲海底的形貌十分复杂,由于高浓度巨量黄河泥沙快速沉积的结果,使河口底坡出现了大量的不稳定性现象,如塌陷冲沟,高密度沉积物重力流,切割—充填结构海底,V形水下河谷、滑塌等。根据海底扰动程度作了分区,划分了地形单元,并对不同的海底形态的成因作了分析。比较了1985和1986年两个航次考查结果的变动,分析了原因。     

A study on combining global and regional climate model results for generating climate scenarios of temperature and precipitation for the Netherlands

Climate scenarios for the Netherlands are constructed by combining information from global and regional climate models employing a simplified, conceptual framework of three sources (levels) of uncertainty impacting on predictions of the local climate. In this framework, the first level of uncertainty is determined by the global radiation balance, resulting in a range of the projected changes in the global mean temperature. On the regional (1,000–5,000 km) scale, the response of the atmospheric circulation determines the second important level of uncertainty. The third level of uncertainty, acting mainly on a local scale of 10 (and less) to 1,000 km, is related to the small-scale processes, like for example those acting in atmospheric convection, clouds and atmospheric meso-scale circulations—processes that play an important role in extreme events which are highly relevant for society. Global climate models (GCMs) are the main tools to quantify the first two levels of uncertainty, while high resolution regional climate models (RCMs) are more suitable to quantify the third level. Along these lines, results of an ensemble of RCMs, driven by only two GCM boundaries and therefore spanning only a rather narrow range in future climate predictions, are rescaled to obtain a broader uncertainty range. The rescaling is done by first disentangling the climate change response in the RCM simulations into a part related to the circulation, and a residual part which is related to the global temperature rise. Second, these responses are rescaled using the range of the predictions of global temperature change and circulation change from five GCMs. These GCMs have been selected on their ability to simulate the present-day circulation, in particular over Europe. For the seasonal means, the rescaled RCM results obey the range in the GCM ensemble using a high and low emission scenario. Thus, the rescaled RCM results are consistent with the GCM results for the means, while adding information on the small scales and the extremes. The method can be interpreted as a combined statistical–dynamical downscaling approach, with the statistical relations based on regional model output.     

Semi-empirical solar line blanketing

Statistical data for line blanketing in the solar atmosphere have been extracted from the Revised Rowland Table. The data are corrected for apparent observational incompleteness due to line crowding and blending and are placed in a convenient form for calculations. An attempt is made to interpret the data in terms of schematic representations of the energy levels and distribution of gf-values for the important absorbers. The analysis leads to predictions in good agreement with the forms of the statistical data and substantiates the assumption of observational incompleteness in the original data. The analysis suggests that the solar data may provide useful guidance in the blanketing of stellar atmospheres sufficiently close to solar type.A blanketing method is presented which makes use of a uniformly-smeared-line (single picket) procedure and which assumes LTE and a weak-line curve of growth. The blanketing coefficient is obtained in a simple manner from the corrected statistical data and is both depth and wavelength dependent. An alternative method utilizing a four-picket scheme and average absorption coefficient profiles is suggested. Comparison of solar models computed by the two methods shows good agreement and gives support for the smeared-line procedure. Comparison of the solar model with a non-LTE blanketed model of Athay also shows reasonable agreement.Publications of the Goethe Link Observatory, Indiana University, No. 110.     

Effects of storm-induced salinity changes on submersed aquatic vegetation in Kings Bay, Florida

Hurricanes and other major storms cause acute changes in salinity within Florida's streams and rivers. Winddriven tidal surges that increase salinities may have long-lasting effects on submersed aquatic vegetation (SAV) and the associated fauna. We investigated potential effects of salinity pulses on SAV in Kings Bay, Florida, by subjecting the three most common macrophytes,Vallisneria americana, Myriophyllum spicatum., andHydrilla verticillata, to simulated salinity pulses. In Kings Bay, we documented changes in salinity during three storms in September 2004 and measured biomass and percent cover before and after these storms. During experiments, macrophytes were exposed to salinities of 5‰, 15‰, or 25‰ for 1, 2, or 7 d, with a 28-d recovery period in freshwater. Relative to controls, plants subjected to salinities of 5‰ exhibited few significant decreases in growth and no increase in mortality. All three species exhibited decreased growth in salinities of 15‰ or 25‰.H. verticillata, exhibited 100% mortality at 15‰ and 25‰, irrespective of the duration of exposure.M. spicatum andV. american exhibited increased mortality after 7-d exposures to 15‰ or any exposure to 25‰ Maximum daily salinities in Kings Bay approached or exceeded 15‰ after each of the three storms, with pulses generally lasting less than 2 d. Total aboveground biomass and percent cover of vascular plants, were reduced following the storms.M. spicatum exhibited an 83% decrease in aboveground biomass and an 80% decrease in percent cover.H. verticillata exhibited a 47% and 15% decline in biomass and percent cover, respectively.V. americana, exhibited an 18% increase in aboveground biomass and a 37% increase in percent cover, which suggests greater tolerance of salinity pulses and release from competition with the invasiveH. verticillata andM. spicatum. Our results indicate that rapid, storm-induced pulses of high salinity can have important consequences for submersed aquatic vegetation, restoration efforts, and management of invasive species.     

From basalt to dacite: origin and evolution of the calc-alkaline series of Salina, Aeolian Arc, Italy

The island of Salina comprises one of the most distinct calc-alkaline series of the Aeolian arc (Italy), in which calc-alkaline, high-K calc-alkaline, shoshonitic and leucite-shoshonitic magma series are developed. Detailed petrological, geochemical and isotopic (Sr, Nd, Pb, O) data are reported for a stratigraphically well-established sequence of lavas and pyroclastic rocks from the Middle Pleistocene volcanic cycle (430–127 ka) of Salina, which is characterized by an early period of basaltic volcanism (Corvo; Capo; Rivi; Fossa delle Felci, group 1) and a sequence of basaltic andesites, and andesites and dacites in the final stages of activity (Fossa delle Felci, groups 2–8). Major and trace element compositional trends, rare earth element (REE) abundances and mineralogy reveal the importance of crystal fractionation of plagioclase + clinopyroxene + olivine/ orthopyroxene ± titanomagnetite ± amphibole ± apatite in generating the more evolved magma types from parental basaltic magmas, and plagioclase accumulation in producing the high Al₂O₃ contents of some of the more evolved basalts. Sr isotope ratios range from 0.70410 to 0.70463 throughout the suite and show a well-defined negative correlation with ¹⁴³Nd/¹⁴⁴Nd (0.51275–0.51279). Pb isotope compositions are distinctly radiogenic with relatively large variations in ²⁰⁶Pb/²⁰⁴Pb (19.30–19.66), fairly constant ²⁰⁷Pb/²⁰⁴Pb (15.68–15.76) and minor variations in ²⁰⁸Pb/²⁰⁴Pb ratios (39.15–39.51). Whole-rock δ¹⁸O values range from +6.4 to +8.5‰ and correlate positively with Sr isotope ratios. Overall, the isotopic variations are correlated with the degree of differentiation of the rocks, indicating that only small degrees of crustal assimilation are overprinting the dominant evolution by crystal–liquid fractionation (AFC-type processes). The radiogenic and oxygen isotope composition of the Salina basalts suggests derivation from primary magmas from a depleted mantle source contaminated by slab-derived fluids and subducted sediments with an isotopic signature of typical upper continental crust. These magmas then evolved further to andesitic and dacitic compositions through the prevailing process of low-pressure fractional crystallization in a shallow magma reservoir, accompanied by minor assimilation of crustal lithologies similar to those of the Calabrian lower crust. Received: 29 November 1999 / Accepted: 16 April 2000     

The Cretaceous–Palaeogene boundary at Gorgonilla Island,Colombia, South America

The discovery of a new Cretaceous/Palaeogene (K/Pg) bathyal marine sequence on Gorgonilla Island, SW Colombia, extends the presence of Chicxulub impact spherule deposits to the Pacific region of northern South America and to the Eastern Pacific Ocean. The Gorgonilla spherule layer is approximately 20 mm thick and consists of extraordinarily well‐preserved glass spherules up to 1.1 mm in diameter. About 70–90% of the spherules are vitrified, and their chemical composition is consistent with Haiti (Beloc) impact glass spherules. Normal size‐grading, delicate spherule textures, welded melt components and an absence of bioturbation or traction transport suggest that the Gorgonilla spherule layer represents an almost undisturbed settling deposit.     

Representation of planar integral-transformations by 4-D wavelet decomposition

In one way or the other, numerical methods for the evaluation of integral operators can often be related to the solution of the so-called Galerkin equations. For convolution operators and exponentials with purely imaginary exponents as base functions the Galerkin matrix becomes diagonal and this fact is the core of the FFT techniques, used in Physical Geodesy. For non-convolution operators the FFT technique is not applicable. This paper aims at the development of a technique, which can also be applied for non-convolution operators. This technique is based on the use of wavelets as base functions. In this case the Galerkin matrix is not diagonal but (after thresholding) very sparse and this leads to methods, which are similarly efficient as FFT in the convolution case. The paper starts with the theoretical background for n-dimensional wavelet analysis and the representation of integral operators with respect to those wavelet bases. The resulting algorithm is tested for convolution and non-convolution operators.     

The economics (or lack thereof) of aerosol geoengineering

Anthropogenic greenhouse gas emissions are changing the Earth’s climate and impose substantial risks for current and future generations. What are scientifically sound, economically viable, and ethically defendable strategies to manage these climate risks? Ratified international agreements call for a reduction of greenhouse gas emissions to avoid dangerous anthropogenic interference with the climate system. Recent proposals, however, call for a different approach: to geoengineer climate by injecting aerosol precursors into the stratosphere. Published economic studies typically neglect the risks of aerosol geoengineering due to (i) the potential for a failure to sustain the aerosol forcing and (ii) the negative impacts associated with the aerosol forcing. Here we use a simple integrated assessment model of climate change to analyze potential economic impacts of aerosol geoengineering strategies over a wide range of uncertain parameters such as climate sensitivity, the economic damages due to climate change, and the economic damages due to aerosol geoengineering forcing. The simplicity of the model provides the advantages of parsimony and transparency, but it also imposes severe caveats on the interpretation of the results. For example, the analysis is based on a globally aggregated model and is hence silent on intragenerational distribution of costs and benefits. In addition, the analysis neglects the effects of learning and has a very simplistic representation of climate change impacts. Our analysis suggests three main conclusions. First, substituting aerosol geoengineering for CO₂ abatement can be an economically ineffective strategy. One key to this finding is that a failure to sustain the aerosol forcing can lead to sizeable and abrupt climatic changes. The monetary damages due to such a discontinuous aerosol geoengineering can dominate the cost-benefit analysis because the monetary damages of climate change are expected to increase with the rate of change. Second, the relative contribution of aerosol geoengineering to an economically optimal portfolio hinges critically on, thus far, deeply uncertain estimates of the damages due to aerosol forcing. Even if we assume that aerosol forcing could be deployed continuously, the aerosol geoengineering does not considerably displace CO₂ abatement in the simple economic optimal growth model until the damages due to the aerosol forcing are rather low. Third, substituting aerosol geoengineering for greenhouse gas emission abatement can fail an ethical test regarding intergenerational justice. Substituting aerosol geoengineering for greenhouse gas emissions abatements constitutes a conscious risk transfer to future generations, in violation of principles of intergenerational justice which demands that present generations should not create benefits for themselves in exchange for burdens on future generations.