Phase-resolved Faraday rotation in pulsars

We have detected significant rotation measure (RM) variations for nine bright pulsars, as a function of pulse longitude. An additional sample of 10 pulsars showed a rather constant RM with phase, yet a small degree of RM fluctuation is visible in at least three of those cases. In all cases, we have found that the rotation of the polarization position angle across our 1.4 GHz observing band is consistent with the  λ²  law of interstellar Faraday rotation. We provide for the first time convincing evidence that RM variations across the pulse are largely due to interstellar scattering, although we cannot exclude that magnetospheric Faraday rotation may still have a minor contribution; alternative explanations of this phenomenon, like erroneous de-dispersion and the presence of non-orthogonal polarization modes, are excluded. If the observed, phase-resolved RM variations are common amongst pulsars, then many of the previously measured pulsar RMs may be in error by as much as a few tens of rad m⁻².     

The stable isotopic composition (Cl/Cl) of dissolved chloride in rainwater

The stable isotopic composition of dissolved Cl^-${\text{Cl}}^{-}$ in rainwater was measured from a coastal and an interior location in eastern Canada. At the interior Bonner Lake, Ontario, site the δ³⁷Cl values of dissolved Cl^-${\text{Cl}}^{-}$ in precipitation ranged from −3.5‰ to −1.2‰ (SMOC) with an amount-weighted annual average of −2.3‰. At the coastal site, Bay D’Espoir, Newfoundland, δ³⁷Cl values of dissolved Cl^-${\text{Cl}}^{-}$ values ranged from −3.1‰ to 0.0‰ with an amount-weighted annual average of −1.3‰. These negative δ³⁷Cl values provide evidence that atmospheric HCl is ³⁷Cl depleted, presumably from acidification of sea-salt aerosols. Accordingly, dissolved Cl^-${\text{Cl}}^{-}$ in the headwaters of two montane rivers in Western Canada had similarly depleted δ³⁷Cl values. These results have implications to the interpretation of the isotopic compositions of dissolved Cl^-${\text{Cl}}^{-}$ in surface waters, formation fluids, and groundwaters.     

Late glacial vegetation and climate oscillations on the southeastern Tibetan Plateau inferred from the Lake Naleng pollen profile

We present a late glacial pollen record (17,700 to 8500 cal yr BP) from a Lake Naleng sediment core. Lake Naleng is located on the southeastern Tibetan Plateau (31.10°N 99.75°E, 4200 m) along the upper tree-line. Variations in the summer monsoon are evident from shifts in vegetation that correspond to late glacial climate trends from other monsoon-sensitive regions. Alpine steppe was recorded between 17,700 and 14,800 cal yr BP, indicating low effective moisture at the study site. Expansion of alpine meadows followed by advances in the position of tree-line around Lake Naleng suggest that climate became warmer and wetter between ∼ 14,800 and 12,500 cal yr BP, probably representing an enhancement of the Asian monsoon. Climatic cooling and reduced effective moisture are inferred from multivariate analysis and the upward retreat of tree-line between ∼ 12,500 and 11,700 cal yr BP. The timing and nature of these shifts to warm, wet and then cold, dry climatic conditions suggest that they correspond to the Bølling/Allerød and Younger Dryas intervals. Abies-Betula forests, representing warm and moist conditions, spread during the early Holocene.     

Social networks in spatial data infrastructures

Data sharing over the internet is increasingly efficient and increasingly anonymous. This growing anonymity makes it difficult for data users to exchange feedback: interesting ideas, innovations, ancillary data, concerns about data quality, etcetera. For data producers not knowing the end-users makes it more difficult to collect end-user feedback and tailor the production process to users needs. Feedback can be exchanged through social networks, in other words contacts with other users. Very little is known about such social networks in the case of data sharing. In this paper we present an analysis of the social networks associated with two land cover datasets. We found that most users have zero to two links to other users and virtually no links to users in other her organisations. Without these links, it seems almost impossible to identify users of a particular dataset. Internet technology can help but is currently not used to enhance exchange of feedback within the user community.     

Upper-ocean heat budget and ocean eddy transport in the south-east Pacific in a high-resolution coupled model

We present an analysis of the oceanic heat advection and its variability in the upper 500 m in the southeastern tropical Pacific (100W–75W, 25S–10S) as simulated by the global coupled model HiGEM, which has one of the highest resolutions currently used in long-term integrations. The simulated climatology represents a temperature advection field arising from transient small-scale (<450 km) features, with structures and transport that appear consistent with estimates based on available observational data for the mooring at 20S, 85W. The transient structures are very persistent (>4 months), and in specific locations they generate an important contribution to the local upper-ocean heat budget, characterised by scales of a few hundred kilometres, and periods of over a year. The contribution from such structures to the local, long-term oceanic heat budget however can be of either sign, or vanishing, depending on the location; and, although there appears some organisation in preferential areas of activity, the average over the entire region is small. While several different mechanisms may be responsible for the temperature advection by transients, we find that a significant, and possibly dominant, component is associated with vortices embedded in the large-scale, climatological salinity gradient associated with the fresh intrusion of mid-latitude intermediate water which penetrates north-westward beneath the tropical thermocline.     

Silver in the subarctic northeast Pacific Ocean: Explaining the basin scale distribution of silver

Five vertical profiles of silver (Ag) in the subarctic northeast Pacific are presented. Dissolved (< 0.2 μm) Ag concentrations within the surface mixed layer range from 6–25 pM, with the highest observed values at the most coastal site. Elevated Ag concentrations at this station are most likely attributable to the estuarine circulation in the Juan de Fuca Strait. One open-ocean station (P20) exhibited a strong surface Ag maximum. The station was located at the edge of a Haida eddy which raises the possibility that such eddies transport Ag seaward from the coastal zone. Ag concentrations in the deep waters ranged from 60–80 pM. These measurements are consistent with other recent Ag data collected in the Pacific. Ag profiles throughout the Pacific Ocean yield a strong positive correlation between Ag concentration and dissolved silicic acid concentration. However, Ag is depleted relative to silicic acid at intermediate depths where dissolved O₂ concentrations are low, implying a possible removal of Ag from oxygen-depleted waters by scavenging and/or precipitation.     

On the Classification of Meteorites

The classification of meteorites as a whole is briefly presented and discussed; in particular, it is pointed out that the intermediate or transitional group, now universally known as the siderolites (symbol, So), consists of 2 main subdivisions, namely the “irony stones,” hereinafter termed sideraerolites (Sa), and the “stony irons” or so-called lithosiderites (Li).     

Groundwater transport of crater-lake brine at Poa´s Volcano, Costa Rica

Poa´s Volcano is an active stratovolcano in Costa Rica that has a lake in its active crater. The crater lake has high temperatures (50–90 °C), high acidity (pH ≈ 0.0), and a high dissolved-solids content (100 g/kg). The volcano has numerous freshwater springs on its flanks, but a few on the northwestern flank are highly acidic (pH = 1.6–2.5) and have high dissolved-solids concentrations (2–22 g/kg). This study analyzes the regional groundwater system at Poa´s and demonstrates the likelihood that the water discharging from the acidic springs in the Rio Agrio watershed originates at the acidic crater lake. Both heat and solute transport are analyzed on a regional scale through numerical simulations using the HST3D finite-difference model, which solves the coupled equations for fluid flow, heat transport, and solute transport. The code allows fluid viscosity and density to be functions of both temperature and solute concentration. The simulations use estimates for recharge to the mountain and a range of values and various distributions of permeability and porosity. Several sensitivity analyses are performed to test how the uncertainty in many of the model parameters affects the simulation results. These uncertainties yield an estimated range of travel times from the crater lake to the Rio Agrio springs of 1–30 years, which is in close agreement with the results of tritium analyses of the springs. Calculated groundwater fluxes into and out of the crater lake are both about several hundred kg/s. These fluxes must be accounted for in water budgets of the crater lake.     

Case history of one of the few successful Superfund remediation sites: A site at Salinas, California, USA

In 1985, a former tire manufacturing plant surrounded by agricultural fields in the Salinas Valley was designated a Superfund Site by the US Environmental Protection Agency. The plant had been operating for seventeen years, from 1963 until 1980. When dismantling of the plant was started, it was determined that toxic hydrocarbon solvents and oils from the plant had contaminated soil and groundwater in alluvial deposits alongside the plant. It was determined later that the groundwater contamination also lay beneath the agricultural fields in a narrow groundwater plume that extends about 4.3 km downgradient from the plant. Because of the complex architecture of the aquifer system, the gradient, and extensive pumping of agricultural wells, the contaminants migrated northwestward and downward to deeper levels away from the plant.

The agricultural fields are underlain by an unconfined shallow aquifer and by a system of confined aquifers that extend to more than 180 m below surface. Aquifers are discontinuous beds of channel sand and gravel; confining beds are overbank clay and silt, and estuarine clay.

Geophysical data, logs of existing agricultural and other wells, and careful consideration of the stratigraphic architecture of the depositional environment provided the basis for a conceptual hydrogeologic model and for locating characterization wells for detailed visual and geophysical logging and hydrologic testing. Successive refinements of the characterization by sequential installation of wells indicated optimal locations for installation of extraction and monitoring wells. Validity of the concept of the hydrogeologic regime was verified by close match of predictions made by modeling with the later results of pumping from the extraction wells in a pump-and-treat system.

Successful remediation was accomplished by analyzing data from 110 agricultural wells, the few domestic water wells, nearly 200 sequentially installed stratigraphic-characterization and monitoring wells, 25 extraction wells, and by close cooperation among federal, state and local agencies, and the ranchers and growers.

Total contaminants recovered from activated-charcoal strippers of the treatment system totalled < 230 kg. Large quantities were harmlessly volatilized and dispersed into the atmosphere by air strippers and by agricultural sprinkling systems spraying water onto the fields. Crop testing showed no contamination of food crops. The activity has taken seven years and has cost more than US$22 million.