Influence of sample manipulation on contaminant flux and toxicity at the sediment-water interface

Toxicities of sediments from San Diego and San Francisco Bays were compared in laboratory experiments using sea urchin (Strongylocentrotus purpuratus) embryos exposed to pore water and at the sediment-water interface (SWI). Toxicity was consistently greater to embryos exposed at the SWI to intact (unhomogenized) sediment samples relative to homogenized samples. Measurement of selected trace metals indicated considerably greater fluxes of copper, zinc, and cadmium into overlying waters of intact sediment samples. Inhibition of sea urchin embryo development was generally greater in sediment pore waters relative to SWI exposures. Pore water toxicity may have been due to elevated unionized ammonia concentrations in some samples. The results indicate that invertebrate embryos are amenable to SWI exposures, a more ecologically relevant exposure system, and that sediment homogenization may create artifacts in laboratory toxicity experiments.     

Late resonant response at Texcoco, Valley of Mexico, during distant earthquakes

Recordings of the ground motion induced by two shallow (15–25 km deep), distant (300 and 605 km) earthquakes made on deep, soft lacustrine sediments at Texcoco, Valley of Mexico, show a late monochromatic response at 0.48 Hz. Data from a strong-motion recorder array show that this late response is consistent with slow (60 m/s group velocity) Rayleigh waves generated near the 6 km distant soft/stiff soil interface of the ex-lake surface margin. It is concluded that the excitation of local Rayleigh waves in soft soil deposits by arriving earthquake ground motion provides one mechanism to explain the prolonged duration of resonant motion on soft soils, and hence the extreme damage often associated with soft soils responding to distant earthquakes.     

Historical eclipses and Earth's rotation

F Richard Stephenson took a long view of Earth's rotation history in the 2002 Harold Jeffreys Lecture in October.     

The evolution of the southern margin of the East European Craton based on seismic and potential field data

This paper presents an integrated geophysical study of the southern margin of the East European Craton (EEC) in the Karpinksy Swell-North Caucasus area. It presents new interpretations of deep refraction and wide-angle reflection “deep seismic sounding” (DSS) data as well as conventional seismic and CDP profiling and new analyses of potential field data, including three-dimensional gravity and magnetic modelling. An integrated model of the physical properties and structure of the Earth's crust and, partially, upper mantle displays distinct features that are related to tectonic history of the study area. The Voronezh Massif (VM), the Ukrainian Shield and Rostov Dome (RD) of the EEC as well as the Donbas Foldbelt (DF), Karpinsky Swell (KS), Scythian Plate (SP) and Precaspian Basin (PCB) constitute the geodynamic ensemble that developed on the southern margin of the continent Baltica. There proposed evolutionary model comprises a stage of rifting during the middle to late Devonian, post-rift extension and subsidence during Carboniferous–early Permian times (synchronous with and related to the southward displacement of the Rostov Dome and extension in a palaeo-Scythian back-arc basin), and subsequent Mesozoic and younger evolution. A pre-Ordovician, possibly Riphean (?), mafic magmatic complex is inferred on a near vertical reflection seismic cross-section through the western portion of the Astrakhan Dome in the southwest part of the Precaspian Basin. This complex combined with evidence of a subducting slab in the upper mantle imply the presence of pre-Ordovician (Riphean?) island arc, with synchronous extension in a Precaspian back-arc basin is suggested. A middle Palaeozoic back-arc basin ensemble in what is now the western Karpinsky Swell was more than 100 km to the south from its present location. The Stavropol High migrated northwards, dislocating and moving fragments of this back-arc basin sometime thereafter. Linear positive magnetic anomalies reflect the position of associated faults, which define the location of the eastern segment of the Karpinsky Swell. These faults, which dip northward, are recognised on crustal DSS profiles crossing the Donbas Foldbelt and Scythian Plate. They are interpreted in terms of compressional tectonics younger than the Hercynian stage of evolution (i.e., post-Palaeozoic).     

A groundwater tracing investigation as an aid of locating groundwater monitoring stations on the Mitchell Plain of southern Indiana

. A groundwater tracing study was conducted on the Mitchell Plain of southern Indiana to aid in the design of a karst groundwater monitoring program for a proposed landfill facility. Fluorescein and rhodamine WT dyes were introduced into sinkholes at the project site. On-site fluorometric analyses and concentration-dependent sampling were utilized at springs and a local stream for data resolution while minimizing delays between tracing events. As a result of this investigation, springs including a submerged spring that drain groundwater from the site have been identified and two groundwater monitoring stations have been established. The submerged spring was discovered in the streambed at intersections between prominent joints and solution-enlarged bedding-plane partings. It could not have been identified readily during a typical karst hydrogeologic inventory, nor would it have been detected by analyzing charcoal dye receptors with a spectrofluorophotometer.     

Lunar magnetic field palaeointensities determined by an anhysteretic remanent magnetization method

Anhysteretic remanent magnetization (ARM) is used as a means of estimating lunar magnetic field palaeointensities from several Apollo 11 and 16 samples. A value of 1.4 Oe was obtained by this method for an Apollo 16 sample of age 3.9 AE and this value is in close agreement with the value obtained by the conventional Thellier method (1.2 Oe) carried out on the same sample. A further sample which was of age 4.0 AE and which had been reheated at 3.84 AE also showed evidence of a primary magnetization acquired in a field of this magnitude. Determinations on two younger samples (about 3.6 AE) gave palaeofields of about one quarter of this value (0.33 and 0.38 Oe respectively). These estimates of field strengths are considerably higher than previously reported.     

Mn and Ca enriched olivines from nepheline syenites of the South Qôroq Centre,south Greenland

Electron microprobe analyses of olivines from augite syenites and foyaites of the South Qôroq Centre, Igaliko Complex, show a range from hortonolite (Fo₃₆Fa₆₂Te₂) to manganiferous fayalite (Fo₂Fa₈₂Te₁₆). The trend is continuous except for a gap between compositions from augite syenite mafic bands and normal augite syenite. Mn increases with Fe³⁺ and in the more fractionated compositions becomes the principal fractionating element. High Ca contents may be a result of a high level of emplacement. Fayalite instability appears to be related to oxygen fugacity during late stages of crystallization or recrystallization.     

Implications of tectonic subsidence models for crustal structure beneath the Mid-Polish Trough

Summary Tectonic subsidence analysis of the preserved and reconstructed stratigraphy of the Polish Basin indicates an initial Late Permian-Early Triassic (255-241 Ma) syn-rift phase of development with a subsequent extensional rejuvenation during the Late Jurassic (ca. 157-152 Ma). Forward modelling of the subsidence data, in view of existing geophysical interpretations which show the presence of a deep Moho and a very high seismic velocity lower crustal layer beneath the Mid-Polish Trough (MPT), suggest that Permo-Mesozoic basin development may be related at least in part to the intrusion of mantle material into and densification of the lower crust rather than exclusively to crustal extension and thinning.     

Numerical Modeling and Observations of Tsunami Waves in Alberni Inlet and Barkley Sound, British Columbia

Alberni Inlet is a long and narrow fjord adjacent to Barkley Sound on the Pacific Coast of Vancouver Island, Canada. Port Alberni, at the head of the inlet, was affected in 1964 by the largest Pacific tsunami waves in Canadian history. We use observations and results from two numerical models to investigate the resonant characteristics of the region and amplification of tsunami waves in Barkley Sound and Alberni Inlet. The first model (A) was forced at its open boundary with a stationary autoregressive signal, similar to the observed background noise. The second model (B) used an initial sea-level deformation from a potential earthquake off California in the southern segment of the Cascadia Subduction Zone, producing transient tsunami waves. Spectral, cross-spectral and frequency-time (f-t) analyses of the observations were used to examine the resonant properties and topographic response of the local area. The respective results show large admittance functions over a wide 0.5–0.9 cph frequency band, implying a low Q factor but high amplification of arriving waves. This unusual behavior is a result of two effects: A quarter-wave resonance of the system for its fundamental Helmholtz mode and amplification due to the narrowing of the channel cross section from Barkley Sound to Alberni Inlet. The model A numerical results agree favorably with the observations, indicating an energetic resonant mode at frequency of ~0.53 cph (112 min), with its nodal line located near the entrance to Barkley Sound and amplification factor value close to 12. The results from the tsunami propagation model (B) yield spectral characteristics similar to those from the model A and from the observations. The maximum tsunami current speed for this scenario is 2.4 ms^?1 in Sproat Narrows, which divides Alberni Inlet into two parts, while the largest computed wave height is 1.6 m in the northern Alberni Inlet, in the area of Port Alberni.