Geochemical processes in the Onyx River, Wright Valley, Antarctica: Major ions, nutrients, trace metals

We present data on major ions, nutrients and trace metals in an Antarctic stream. The Onyx River is located in Wright Valley (77-32 S; 161-34 E), one of a group of ancient river and glacier-carved landforms that comprise the McMurdo Dry Valleys of Antarctica. The river is more than 30 km long and is the largest of the glacial meltwater streams that characterize this relatively ice-free region near the Ross Sea. The complete absence of rainfall in the region and the usually small contributions of glacially derived tributaries to the main channel make this a comparatively simple system for geochemical investigation. Moreover, the lack of human impacts, past or present, provides an increasingly rare window onto a pristine aquatic system.For all major ions and silica, we observe increasing concentrations with distance from Lake Brownworth down to the recording weir near Lake Vanda. Chemical weathering rates are unexpectedly high and may be related to the rapid dissolution of ancient carbonate deposits and to the severe physical weathering associated with the harsh Antarctic winter. Of the nutrients, nitrate and dissolved reactive phosphate appear to have quite different sources. Nitrate is enriched in waters near the Lower Wright Glacier and may ultimately be derived from stratospheric sources; while phosphate is likely to be the product of chemical weathering of valley rocks and soils. We confirm the work of earlier investigations regarding the importance of the Boulder Pavement as a nutrient sink.Dissolved Mn, Fe, Ni, Cu, and Cd are present at nanomolar levels and, in all cases, the concentrations of these metals are lower than in average world river water. We hypothesize that metal uptake and exchange with particulate phases along the course of the river may serve as a buffer for the dissolved load. Concurrent study of these three solute classes points out significant differences in the mechanisms and sites of their removal from the Onyx River.     

Palaeosecular variation in Central Mexico over the last 30 000 years: the record from lavas

13 lava flows of known age (ages from ¹⁴C dating), which have been erupted in the last 30 000 years, have been studied to determine the palaeosecular variation of the geomagnetic field in Central Mexico. Samples were taken from two different monogenetic volcanic fields: the Michoacan-Guanajuato volcanic field (six sites) and the Chichinautzin Formation (seven sites), both part of the Transmexican Volcanic Belt. The lavas were studied in detail using rock magnetic methods (magnetic susceptibility at room temperature, low-temperature susceptibility behaviour, hysteresis loops, Curie temperatures), combined with reflected light microscopy, in order to deduce their magnetic mineralogy and the domain states of the magnetic minerals. The magnetic carriers are titanomagnetites, which show differing degrees of high-temperature deuteric oxidation, and seem to be predominantly pseudo-single domain (PSD), though in many cases are probably a mixture of domain states. Mean palaeomagnetic directions and palaeointensity values using Shaw and Thellier techniques were obtained using several specimens from each flow. Our data seem to indicate a sharp easterly swing in declination about 5000 years ago, which is also observed in lake sediments from Central Mexico. The calculated values of the virtual dipole moment (VDM) range from 3.1 to 14.9 × 10²² A m². Our data indicate that the virtual dipole moment seems to have increased gradually in magnitude over the last 30 kyr, with a peak at about 9000 years BP. These are features that have been observed in other parts of the globe and are probably caused by variations in the dipole part of the geomagnetic field.     

Numerical technique for dynamic analysis of structures with friction devices

In recent years a number of studies on employing friction elements for the seismic protection of buildings has demonstrated conclusively that such devices can markedly reduce earthquake-induced vibrations. Any numerical estimate of the effectiveness of such isolation systems implies a correct solution of the pertinent nonlinear equations of motion. In direct integration algorithms, the phase transitions between adherence and sliding, or the sliding phase may be accompanied by marked high-frequency oscillation of the relative velocity difference. The paper presents a numerical technique for overcoming these problems, thus leading to increased accuracy of the solutions of equations of motions with Coulomb damping. Since only the damping matrix and the loading vector are involved, the procedure is also computationally efficient. In order to validate the proposed numerical technique, an experimental study of a friction system has been carried out. The dynamic response of a four-storey braced frame with friction devices is presented as an example for the practical application of the proposed numerical technique.     

An in vitro study of the effects of zinc on osmoregulatory processes

The short-circuited opercular epithelium of seawater-adapted killifish Fundulus heteroclitus was studied following addition of zinc to both serosal and mucosal sides of the preparation. Zn inhibited the short-circuit current which is a direct measure of the chloride transport across the epithelium. Light microscope observations showed that the mucosal side of the epithelium was completely desquamated after 1 h exposure to Zn. It is suggested that desquamation of gill epithelia described by several authors following in vivo Zn contamination is a direct consequence of the breakdown of osmoregulatory processes.     

Life cycle and population structure of the polychaeteFicopomatus enigmaticus (Serpulidae) in Mar Chiquita coastal lagoon,Argentina

Ficopomatus enigmaticus, a polychaete inhabiting the subtidal zone in the Mar Chiquita coastal lagoon, builds reef-like aggregates that facilitate silt accumulation. To describe the life cycle, samples were take monthly from September 1984 to September 1985. In contrast with other polychaetes, it has two oocyte generations per year; maturation of the oocytes takes approximately 4 mo. Temperature level and day length regime do not appear as environmental signals to the onset of oogenesis, although they possibly affect oogenesis growth. Two periods of spawning and recruitment were observed in November–December and April–May, when water temperature is above 18°C. Hermaphroditic individuals were not found. Sex ratio was male-biased in all months, significantly in November, February, and August (p<0.001). Monthly size-frequency distributions show distinct year-classes with early (November–December) and late (April–May) recruitment. Early recruited cohorts have two spawning periods during a 24-mo lifespan. Late cohorts have one spawning period during their 20-mo lifespan. The life cycle of this species can be summarized as follows: annual iteroparous—1 to 2 batches of small eggs per female during each lifespan, free spawning, planktotrophic larvae, sedentary suspension-feeder worms.     

Learning and earning: relational scales of children's work

There is an important dissonance in recent studies of children's work between the global efforts to eradicate abusive forms of child labour on the one hand and, on the other hand, local settings where children's work plays an important role in social reproduction, socialization and skill acquisition. This research explores the reasons for this dissonance by eliding both the global perspectives of children's rights and the local realities of children's daily geographies. By closing the gap between global knowledge about children (from above) and children's knowledge and agency in their own environments (from below), we seek to present a relational account of children's work within the context of their daily geographies. We draw on data collected with child workers in Tijuana, Mexico to demonstrate the complex role that children's work often plays in the daily geographies of young people.     

The potential of using LiDAR and color-infrared aerial imagery for palustrine wetland typology and change

Wetlands are dynamic landscapes and their spatial extent and types can change over time. Mapping wetland locations, types, and monitoring wetland typological changes have important ecological significance. The National Wetlands Inventory data suffer from two problems: the omission error that some wetlands are not mapped, and the out-of-date wetland types in many counties of the United States. To address these two problems, we proposed an automatic wetland classification model for newly mapped (or existing) wetland polygons lacking typological information. The research goals in this study were (1) to develop a nonparametric and automatic rule-based model to assign wetland types to palustrine wetlands using high-resolution remotely sensed data and (2) to quantify wetland typological changes based on the wetland types obtained from the previous step. The model is a direct application of the Cowardin et al. (1979) wetland classification system without modification. The input information for the proposed model includes Light Detection and Ranging (LiDAR)-derived vegetation height and color infrared aerial imagery-derived vegetation spectral information. We tested the model for the palustrine wetlands in Horry County, SC, and analyzed 29,090 palustrine wetland polygons (101,427 ha). The model achieved an overall agreement of 87% for wetland-type classification and showed the dynamics of wetland typological changes. This nonparametric model can be easily applied to other areas where wetland inventory needs updating.     

Benthic foraminifera in a deep-sea high-energy environment: the Moira Mounds (Porcupine Seabight,SW of Ireland)

Cold-water coral ecosystems represent unique and exceptionally diverse environments in the deep-sea. They are well developed along the Irish margin, varying broadly in shape and size. The Moira Mounds, numerous small-sized mounds, are nestled in the Belgica Mound Province (Porcupine Seabight, North-East Atlantic). The investigation of living (Rose Bengal stained) and dead benthic foraminiferal assemblages from these mounds allowed to describe their distribution patterns and to evaluate their response to environmental variability. Quantitative data was statistically treated to define groups of species/genera associated to specific habitats. The Moira Mounds differ from their larger neighbours by the reduced spatial variability of benthic foraminiferal assemblages, living assemblages only distinguishing coral-rich and coral-barren areas. The ecological needs of corals are highlighted by the abundance of Alabaminella weddellensis and Nonionella iridea, phytodetritus-feeding species in coral supporting sediments. Living foraminifera in sediments from the Moira Mounds concentrate in the upper first centimetre. Infaunal species may be affected by bioturbation and/or reworking by the strong currents in the area. Dead foraminiferal assemblages from the Moira Mounds resemble those described for the sandwave facies in adjacent giant mounds, suggesting similar processes in facies deposition.     

Detection of integron integrase genes on King George Island,Antarctica

The presence and diversity of class 1 integrase gene (intI) sequences were evaluated by PCR using previously designed primers. Two clone libraries were constructed from DNA in sediment and microbial ma...     

Modelling flood events with a cumulant CO lattice Boltzmann shallow water model

Natural Hazards - In this work the development of a semiautomatic procedure based on the coupled use of a GIS subroutine and a two-dimensional hydraulic lattice Boltzmann model solving the shallow...