Variability of ozone in the marine boundary layer of the equatorial Pacific Ocean

This study examines the processes controlling the diurnal variability of ozone (O₃) in the marine boundary layer of the Kwajalein Atoll, Republic of the Marshall Islands (latitude 8° 43′ N, longitude 167° 44′ E), during July to September 1999. At the study site, situated in the equatorial Pacific Ocean, O₃ mixing ratios remained low, with an overall average of 9–10 parts per billion on a volume basis (ppbv) and a standard deviation of 2.5 ppbv. In the absence of convective storms, daily O₃ mixing ratios decreased after sunrise and reached minimum during the afternoon in response to photochemical reactions. The peak-to-peak amplitude of O₃ diurnal variation was approximately 1–3 ppbv. During the daytime, O₃ photolysis, hydroperoxyl radicals, hydroxyl radicals, and bromine atoms contributed to the destruction of O₃, which explained the observed minimum O₃ levels observed in the afternoon. The entrainment of O₃-richer air from the free troposphere to the local marine boundary layer provided a recovery mechanism of surface O₃ mixing ratio with a transport rate of 0.04 to 0.2 ppbv per hour during nighttime. In the presence of convection, downward transport of O₃-richer tropospheric air increased surface O₃ mixing ratios by 3–12 ppbv. The magnitude of O₃ increase due to moist convection was lower than that observed over the continent (as high as 20–30 ppbv). Differences were ascribed to the higher O₃ levels in the continental troposphere and weaker convection over the ocean. Present results suggest that moist convection plays a role in surface-level O₃ dynamics in the tropical marine boundary layer.     

Rječina River sediments (Croatia): from captured spring to polluted prodelta

Surface sediments (fraction <63 μm) from the source to the mouth of the Rječina, short (18.3 km) karst allogenic river in Croatia, which is an important source of drinking water, were studied to investigate their mineral (by XRD) and chemical (by ICP-MS) composition to check possible anthropogenic influence at the lower course due to paper industry and mills, and in the prodelta area from untreated municipal sewage and the large harbor of Rijeka town. In all analyzed sediment samples and in the sandstone source, rock quartz is a major mineral, while feldspar and mica group minerals are less abundant. Chlorite is a minor or trace mineral in all samples. Calcite and dolomite are abundant in the river prodelta, reflecting changes in bedrock lithology from flysch to carbonates. In river sediments, Fe is the most abundantly analyzed element, while Ca is the most abundant in prodelta sediments. Concentrations of Al, Mn, Ni, Cr, Co, La and Nd decrease downstream, while Mg, S, Na, B, Pb, Zn, As, Sn, U, Mo, Hg and Ag have relatively higher concentration in prodelta sediments. The results are compared with sediments of other rivers in the area: Raša, Rižana and Dragonja, as well as with those of the Rosandra Creek (Italy). Sediments in the Raša River showed similar behavior as those in the Rječina, as the highest concentration of metals was found in the restricted upper part of the estuary, characterized by rapid deposition of clay particles and terrestrial sedimentary organic matter. The comparison also showed that the most contaminated were the sediments from the Rižana, followed by those from the Rječina and Rosandra Creek, which had similar results. Among the studied elements, As was present in all sediment samples at concentrations >6 ppm that might have the lowest toxic effects. At the lower Rječina and in prodelta sediments, Pb was also present at slightly elevated concentrations (>31 ppm) that could cause such effects. Concentrations of Zn in the prodelta correspond to those occurring in moderately polluted sediments (90–200 ppm). In the prodelta sediments, Hg is slightly below toxicity threshold (1 ppm), while Ag is present at toxicity threshold (0.5 ppm) or close to it. Rječina River could act as a good illustrative example for behavior of toxic metals in allogenic karstic rivers, in which accumulation of anthropogenically introduced pollutants usually occurs in their estuaries, as a result of transport and deposition of fine particles.     

Quantitative multi-risk analysis for natural hazards: a framework for multi-risk modelling

This paper introduces a generic framework for multi-risk modelling developed in the project ‘Regional RiskScape’ by the Research Organizations GNS Science and the National Institute of Water and Atmospheric Research Ltd. (NIWA) in New Zealand. Our goal was to develop a generic technology for modelling risks from different natural hazards and for various elements at risk. The technical framework is not dependent on the specific nature of the individual hazard nor the vulnerability and the type of the individual assets. Based on this generic framework, a software prototype has been developed, which is capable of ‘plugging in’ various natural hazards and assets without reconfiguring or adapting the generic software framework. To achieve that, we developed a set of standards for treating the fundamental components of a risk model: hazards, assets (elements at risk) and vulnerability models (or fragility functions). Thus, the developed prototype system is able to accommodate any hazard, asset or fragility model, which is provided to the system according to that standard. The software prototype was tested by modelling earthquake, volcanic ashfall, flood, wind, and tsunami risks for several urban centres and small communities in New Zealand.     

Rock magnetic properties and palaeomagnetic results of sediments from a stone implement layer in the Bose Basin,Guangxi

Directional samples were taken to study rock magnetism and palaeomagnetic records from the Dong- sheng profile, which is 5 m thick and on the northwest edge of the Bose Basin. Mineralogy and rock magnetism of typical samples indicate that coarse granular titanomagnetite, and fine-grained hematite, superparamagnetic maghemite formed by pedogenesis are in the sediment, which has undergone many transformative processes during different stages of pedogenesis. Parallel samples were taken for thermal demagnetization (TH) (0 to 680℃) and alternating field (AF) demagnetization (0 to 80 mT) respectively. Experimental results of these two kinds of demagnetization illustrate that there are two or more magnetic components in the samples. Intensity of NRM decreases by almost 60% to 90% rapidly when the temperature ranges from 100℃ to 350℃, with a steady magnetic component. It is impossible to analyze the magnetic components at high temperature because those fluctuate widely when the temperature is higher than 400℃. Steady magnetic components from 100℃ to 350℃ indicate that the remanence was mainly carried by fine-grained hematite formed by pedogenesis, reflecting a change in the geomagnetic field while the magnetite was being oxidized into hematite by chemical weathering after deposition. The formative age of the sediments cannot be obtained by magnetic methods in this profile.     

Analysis of Russian Hydroacoustic Data for CTBT Monitoring

—?As part of a collaborative research program for the purpose of monitoring the Comprehensive Nuclear-Test-Ban Treaty (CTBT), we are in the process of examining and analyzing hydroacoustic data from underwater explosions conducted in the former Soviet Union. We are using these data as constraints on modeling the hydroacoustic source as a function of depth below the water surface. This is of interest to the CTBT because although even small explosions at depth generate signals easily observable at large distances, the hydroacoustic source amplitude decreases as the source approaches the surface. Consequently, explosions in the ocean will be more difficult to identify if they are on or near the ocean surface. We are particularly interested in records featuring various combinations of depths of explosion, and distances and depths of recording.¶Unique historical Russian data sets have now become available from test explosions of 100-kg TNT cast spherical charges in a shallow reservoir (87?m length, 25?m to 55?m width, and 3?m depth) with a low-velocity air-saturated layer of sand on the bottom. A number of tests were conducted with varying water level and charge depths. Pressure measurements were taken at varying depths and horizontal distances in the water. The available data include measurements of peak pressures from all explosions and digitized pressure-time histories from some of them. A reduction of peak pressure by about 60–70% is observed in these measurements for half-immersed charges as compared with deeper explosions. In addition, several peak-pressure measurements are also available from a 1957 underwater nuclear explosion (yield <10?kt and depth 30?m) in the Bay of Chernaya (Novaya Zemlya).¶The 100-kg TNT data were compared with model predictions. Shockwave modeling is based on spherical wave propagation and finite element calculations, constrained by empirical data from US underwater chemical and nuclear tests. Modeling was performed for digitized pressure-time histories from two fully-immersed explosions and one explosion of a half-immersed charge, as well as for the peak-pressure measurements from all explosions carried out in the reservoir with water level at its maximum (3?m). We found that the model predictions match the Russian data well.¶Peak-pressure measurements and pressure-time histories were simulated at 10?km distance from hypothetical 1-kt and 10-kt nuclear explosions conducted at various depths in the ocean. The ocean water was characterized by a realistic sound velocity profile featuring a velocity minimum at 700?m depth. Simulated measurements at that same depth predict at least a tenfold increase in peak pressures from explosions in the SOFAR channel as compared with very shallow explosions (e.g., ～3?m depth).¶ The observations and the modeling results were also compared with predictions calculated at the Lawrence Livermore National Laboratory using a different modeling approach. All results suggest that although the coupling is reduced for very shallow explosions, a shallow 1-kt explosion should be detectable by the IMS hydroacoustic network.     

Influence of oxygen fugacity on the solubility of nitrogen, carbon, and hydrogen in FeO-Na2O-SiO2-Al2O3 melts in equilibrium with metallic iron at 1.5 GPa and 1400°C

It is assumed in the theories of Earth formation that the composition of gases extracted by primary planetary magmas is formed by the large-scale melting of the early mantle, which occurred in the presence of a metallic Fe phase. The molten Fe metal and silicate materials underwent gravitational migration, which affected the fractionation of siderophile elements. Volatile compounds had to form simultaneously in the zones of large-scale melting of the early Earth; their compositions were controlled by interaction with silicate and metallic melts. This process remains poorly understood.     

Pitfalls in Nonlinear Inversion

— We discuss and illustrate graphically with simple 2-D problems, four common pitfalls in geophysical nonlinear inversion. The first one establishes that the Lagrange multiplier, used to incorporate a priori information in the geophysical inverse problem, should be the largest value still compatible with a reasonable data fitting. This procedure should be used only when the interpreter is sure about the importance of the a priori information used to stabilize the inverse problem relative to the geophysical observations. Because this is rarely the case, the user should use the smallest Lagrange multiplier still producing stable solutions. The second pitfall is an attempt to automatically estimate the Lagrange multiplier by decreasing it along the iterative process used to solve the nonlinear optimization problem. Consequently, at the last iteration, the Lagrange multiplier may be so small that the problem may become ill-posed and any computed solution in this case is meaningless. The third pitfall is related to the incorporation of a priori information by a technique known as “Jumping.” This formulation, from the viewpoint of the class of Acceptable Gradient Methods, is incomplete and may lead to a premature halt in the iteration, and, consequently, to solutions far from the true one. Finally, the fourth pitfall is an inadequate convergence criterion which stops the iteration when the data misfit drops just below the noise level, irrespective of the fact that the functional to be minimized may not have attained its minimum. This means that the a priori information has not been completely incorporated, so that this stopping criterion partially neutralizes the effect of the stabilizing functional, and opens the possibility of obtaining unstable, meaningless estimates.