The isotopic signature of monsoon conditions,cloud modes,and rainfall type

This work provides a comprehensive physically based framework for the interpretation of the north Australian rainfall stable isotope record (δ¹⁸O and δ²H). Until now, interpretations mainly relied on statistical relationships between rainfall amount and isotopic values on monthly timescales. Here, we use multiseason daily rainfall stable isotope and high resolution (10 min) ground‐based C‐band polarimetric radar data and show that the five weather types (monsoon regimes) that constitute the Australian wet season each have a characteristic isotope ratio. The data suggest that this is not only due to changes in regional rainfall amount during these regimes but, more importantly, is due to different rain and cloud types that are associated with the large scale circulation regimes. Negative (positive) isotope anomalies occurred when stratiform rainfall fractions were large (small) and the horizontal extent of raining areas were largest (smallest). Intense, yet isolated, convective conditions were associated with enriched isotope values whereas more depleted isotope values were observed when convection was widespread but less intense. This means that isotopic proxy records may record the frequency of which these typical wet season regimes occur. Positive anomalies in paleoclimatic records are most likely associated with periods where continental convection dominates and convection is sea‐breeze forced. Negative anomalies may be interpreted as periods when the monsoon trough is active, convection is of the oceanic type, less electric, and stratiform areas are wide spread. This connection between variability of rainfall isotope anomalies and the intrinsic properties of convection and its large‐scale environment has important implications for all fields of research that use rainfall stable isotopes.     

Sub-lethal effects of metal exposure: physiological and behavioural responses of the estuarine bivalve Macoma balthica

Variation in glycogen concentration, condition index (CI) and filtration activity were measured in the bivalve Macoma balthica buried in sediment and experimentally exposed to cadmium (Cd). The stress due to elevated but sub-lethal concentrations (300 ppb Cd) affected the overall fitness of the organism as all parameters monitored responded significantly. Lower concentrations tested (10, 30 and 100 ppb) only induced a significant decrease in filtration activity, which may play a protective role, enabling the organism to slow down its metabolic activity and preserving the integrity of its reserves (reflected by stable CI and glycogen levels). Hence, the various endpoints selected show different thresholds. Our results also demonstrate that under high exposure, small individuals loose proportionally more glycogen per unit of weight than larger ones, thus confirming the higher sensitivity of small individuals to metal contamination. Furthermore, exposure to intermediate concentration (30 ppb) seems to be beneficial to the small individuals as indicated by their high CI values compared to the control. These results showed thus that non-sigmoidal concentration-response relationship and sizes of individuals should be considered in monitoring programmes and risk assessment.     

Correlative changes in metabolism and DNA damage in turbot (Scophthalmus maximus) exposed to benzo[a]pyrene

Juvenile turbot (Scophthalmus maximus) were injected intraperitoneally with either corn oil or 5 mg/kg benzo[a]pyrene (BaP) dissolved in corn oil and sampled I and 3 days after injection. After 1 day, no elevation of 7-ethoxyresorufin O-deethylase (EROD) activity was observed, however bile metabolites (BaP-7,8 dihydrodiol representing 70% of the total metabolites) and a single hepatic DNA adduct spot (0.47 adducts/10(8) nucleotides) identified by 32P-postlabelling were formed. No BaP metabolites or DNA adducts were observed in either control or carrier control fish. Fish sampled after 3 days reported 5-fold higher (P < 0.05) levels of EROD activity, a shift in the bile metabolite profile towards BaP phenol formation (1OH and 30H BaP comprising up to 60% of total metabolites detected) and the formation of two adduct spots (0.86 and 0.71 adducts/10(8) nucleotides). These results show that BaP can be metabolised and form hydrophobic DNA adducts in turbot without EROD elevation. Following EROD elevation, a shift in the profile of both BaP metabolites and BaP metabolite-DNA interactions occurs indicative of other oxidative processes.     

Carbon-isotope composition of sediments from the Gulf of Papua

Rivers draining into the Gulf of Papua (GOP) from the Papua New Guinea mainland deliver approximately 340 × 10⁶ t yr^–1 of sediment to the marine environment. The terrestrially derived sediment contains 1.1 ± 0.2% particulate organic carbon with a carbon-isotope composition of –26.5 ± 0.2, and amounts to 3.7 ± 0.7 × 10⁶ t yr^–1. The carbon-isotope composition of sediments in the Gulf of Papua indicates that 40% of the sediment cover contains 75% or more terrestrially derived carbon. Suspended sediments that are transported beyond the delta complex of the Fly River are transported north and northwest, augmented by sediments from other rivers along the coast of the GOP. The carbon-isotope results suggest that a significant quantity of terrestrially derived sediment escapes from the GOP, either along the coastlines to east and west or into the deep ocean via the Moresby and Pandora troughs. Little sediment travels south onto the Great Barrier Reef shelf. Extrapolating the results from this study to the region of Oceania suggests a total flux of particulate organic carbon to the world's oceans from the islands of Oceania of ~ 90 × 10⁶ t yr^–1 or twice the flux of riverine POC from the major rivers of North America, South America, and Africa combined. While such a calculation must be considered illustrative only, the similar tectonic, geomorphologic, and climatic features of the islands of Oceania suggest that the calculation is unlikely to be grossly in error and that the rivers of Oceania therefore represent a major but poorly documented source of sediment and organic carbon to the global ocean.     

Effects of diverging coronal fields on the solar wind expansion

The expansion of the solar wind in divergent flux tubes is calculated by taking into account a magnetic acceleration of the particles, analogous to the magnetic mirror effect.The resulting force term included in the magnetohydrodynamical equations describes a conversion of thermal into kinetic energy. This causes an additional acceleration of the solar wind plasma which has never been taken into account before. The force is directed opposite to the magnetic field gradient. Consequently, in this case the solar wind velocity increases faster to its asymptotic value than it does for corresponding nonmagnetic solutions. Therefore inside and close to the solar corona markedly higher velocities are found. Compared to strictly hydrodynamical models, the critical point is shifted towards the Sun, and the radial decrease of the ratio of thermal to kinetic energy is faster.The necessary prerequisites for these calculations are (a) that the gyroperoid _g of the plasma particles is much shorter than the Coulomb collision time _c , and (b) that the collision time _c is shorter than the characteristic time _d in which an appreciable amount of thermal anisotropy is built up. Thus it is (a) insured that the particles have established magnetic moments and follow the guiding center approximation, and (b) an almost isotropic velocity distribution function is maintained which, in this first approximation of a purely radial expansion, justifies the use of isotropic pressures and temperatures.Both (a) and (b) are shown to be fulfilled in a region around the Sun out to about 20R , and thermal anisotropies developing outside of this region could explain the observed magnetically aligned anisotropies at 1 AU.     

Secondary ferrimagnetic minerals in Welsh soils: a comparison of mineral magnetic detection methods and implications for mineral formation

A study of mineral magnetic parameters was carried out on a Late Pleistocene and Holocene sedimentary sequence (of nearly 18 m) from Lake Bledowo (central Poland). Sediments of Lake Bledowo have already been analysed for bulk sediment mineralogy and biogenic materials. The mineral magnetic stratigraphy confirms the major changes in palaeo-environmental conditions that have been deduced from other methods. The most important mineral magnetic change results from the authigenetic formation of ferrimagnetic greigite, Fe₃S₄, during the beginning of lacustrine conditions (± 12 000 yr BP). Our data also indicate a detrital origin of overlying ferrimagnetic iron oxides. It is suggested that they originate from brown soils developed on the boulder clay constituting the west side of the lake shore. Variations of ferrimagnetic iron oxide size are related to the early diagenetic processes in the sediment. Larger particles are present in periods with early diagenesis of organic matter in anoxic conditions. This indicates the dissolution of fine magnetic particles by iron-oxide-reducing bacteria and results in homogeneous magnetic grain sizes, despite their origin from soils, characterized by a multimodal grain-size distribution.     

The impact of epistemic uncertainty on an earthquake loss model

Models capable of estimating losses in future earthquakes are of fundamental importance for emergency planners, for the insurance and reinsurance industries, and for code drafters. Constructing a loss model for a city, region or country involves compiling databases of earthquake activity, ground conditions, attenuation equations, building stock and infrastructure exposure, and vulnerability characteristics of the exposed inventory, all of which have large associated uncertainties. Many of these uncertainties can be classified as epistemic, implying—at least in theory—that they can be reduced by acquiring additional data or improved understanding of the physical processes. The effort and cost involved in refining the definition of each component of a loss model can be very large, for which reason it is useful to identify the relative impact on the calculated losses due to variations in these components. A mechanically sound displacement‐based approach to loss estimation is applied to a test case of buildings along the northern side of the Sea of Marmara in Turkey. Systematic variations of the parameters defining the demand (ground motion) and the capacity (vulnerability) are used to identify the relative impacts on the resulting losses, from which it is found that the influence of the epistemic uncertainty in the capacity is larger than that of the demand for a single earthquake scenario. Thus, the importance of earthquake loss models which allow the capacity parameters to be customized to the study area under consideration is highlighted. Copyright © 2005 John Wiley & Sons, Ltd.     

Geomorphological and historical changes on the Argentina delta,Ligurian coast,Italy

A preliminary investigation of the geomorphological evolution of the small delta of the Argentina river (Riviera di Ponente, Italy) shows that it has largely been affected by anthropic processes. Erosion is undermining land and structural developments not only in the delta, but also along the nearby shores and a thorough knowledge of them seems necessary prior to management applications. In fact, processes affecting the evolution of the investigated area could well be regarded as a good example of the evolution of many other deltaic areas in the Northern Mediterranean.     

Observation of a coronal mass ejection in January 1997 using radio sounding of the near-solar plasma with the GALILEO spacecraft

Measurements of frequency fluctuations in radio signals generated by the GALILEO spacecraft from January 6 to 11, 1997 are presented and analyzed. The passage of a coronal mass ejection observed by the SOHO/LASCO coronagraph on January 6, 1997 through the radio-communication path between the spacecraft and a ground station was recorded. Radio sounding was carried out at a carrier frequency of 2295 MHz at a heliocentric distance of about 32 solar radii, with the signal being received at three ground stations. As the mass ejection intersected the propagation path, the mean frequency of the signal increased and several-hour-long frequency fluctuations were enhanced. A spectral analysis of the frequency fluctuations shows that the regime and level of plasma turbulence are substantially different in different sections of the quiet solar wind and the disturbed plasmoid. A correlation between the intensity and temporal spectrum of the frequency fluctuations is found. The plasma density in the leading part of the coronal mass ejection exceeds the mean background value by more than an order of magnitude. Our correlation analysis of the frequency fluctuations recorded simultaneously at two widely separated measuring points shows that two flow components with different velocities—the quiet solar wind and a perturbed stream—crossed the communication path. The radio-sounding data are compared with observations of the coronal mass ejection by the SOHO/LASCO coronagraph and plasma measurements near the Earth’s orbit using the WIND satellite. A pronounced correlation is found between the variations in the mean frequency of the sounding signal and the plasma density in near-Earth space.