Diatom-inferred late Pleistocene and Holocene palaeolimnological changes in the Ioannina basin, northwest Greece

The character and impact of climate change since the last glacial maximum (LGM) in the eastern Mediterranean region remain poorly understood. Here, two new diatom records from the Ioannina basin in northwest Greece are presented alongside a pre-existing record and used to infer past changes in lake level, a proxy for the balance between precipitation and evaporation. Comparison of the three records indicates that lake-level fluctuations were the dominant driver of diatom assemblage composition change, whereas productivity variations had a secondary role. The reconstruction indicates low lake levels during the LGM. Late glacial lake deepening was underway by 15.0 cal kyr BP, implying that the climate was becoming wetter. During the Younger Dryas stadial, a lake-level decline is recorded, indicating arid climatic conditions. Lake Ioannina deepened rapidly in the early Holocene, but long-term lake-level decline commenced around 7.0 cal kyr BP. The pattern of lake-level change is broadly consistent with an existing lake-level reconstruction at Lake Xinias, central Greece. The timing of the apparent change, however, is different, with delayed early Holocene deepening at Xinias. This offset is attributed to uncertainties in the age models, and the position of Xinias in the rain shadow of the Pindus Mountains.     

Hammer Efficiency and Correction Factors for the TxDOT Texas Cone Penetration Test

This study analyzes blowcount data from instrumented Texas Cone Penetration (TCP) tests. TCP hammer efficiency, rod length influence on the hammer efficiency, and overburden pressure correction factors for the TCP blowcounts (N_TCP) are explored. Results are compared to published correction factors for the standard penetration test (SPT). The final dataset analyzed for this study consisted of 293 TCP tests from which 135 tests were instrumented. TCP hammer efficiency values for automatic trip hammers ranged from 74 to 101% with an average of 89%. Analyses showed a statistically-significant relationship between the TCP hammer efficiency and the rod length below ground surface. Statistical models were developed for undifferentiated soils, and corresponding rod length correction factors for the TCP test (C_R-TCP) were obtained ranging from 0.90 to 1.00. In a second analysis, the relationship between the overburden pressure and N_TCP was explored and a mathematical expression for the overburden correction factor for the TCP blowcount value (C_N-TCP) was determined. This work represents the first study where corrections to N_TCP are explored, and the outcome of this research benefits the geotechnical engineering community using the TCP test and its associated foundation design method.     

STRUCTURAL TENSION,MIGRATION, AND DEVELOPMENT: A CASE STUDY OF VENEZUELA*

Mismatch of labor demand and supply, resulting from economic growth, is referred to here as structural tension. Spatial variations in structural tension are identified for Venezuelan states in 1971. Positive tension, indicating overutilization of human resources, prevails in urban areas. By contrast, rural locales exhibit underutilization due to rapid labor force growth without parallel increases in employment opportunities. Influence of structural tension, coupled with other migration determinants, upon destination choice by economically active immigrants is explored. Structural tension emerges as strongly significant for the total sample, displacing wages from the model. This is consistent with our contention that wages are a less precise indicator of labor supply and demand.     

Constraints on a soft X-ray excess in the quasar 3C 279

We present the results of a three-week daily monitoring campaign of the quasar 3C 279 by the X-ray satellites RXTE ROSAT . A cross-correlation provides no evidence for any time lag between the very similar soft and hard X-ray light curves, and the source shows no significant spectral variability over the observing period. There is no evidence to support the presence of a soft excess, with a 99 per cent upper limit on any such component of 25 per cent of the total observed luminosity in the 0.1–2 keV band (<3 × 10³⁸ W). This fraction (but not the luminosity) is significantly lower than that of the soft excess observed in 3C 273.     

Impact of mineral fouling on hydraulic behavior of permeable reactive barriers

This paper describes reactive transport simulations conducted to assess the impact of mineral fouling on the hydraulic behavior of continuous-wall permeable reactive barriers (PRBs) employing granular zero-valent iron (ZVI) in carbonate-rich alluvial aquifers. The reactive transport model included a geochemical algorithm for simulating corrosion and mineral precipitation reactions that have been observed in ZVI PRBs. Results of simulations show that porosity and hydraulic conductivity of the ZVI decrease over time and that flows are redistributed throughout the PRB in response to fouling of the pore space. Under typical conditions, only subtle changes occur within the first 10 years (i.e., duration of the current field experience record with PRBs), and the most significant changes do not occur until the PRB has operated for at least 30 years. However, changes can occur sooner (or later) if the rate at which mineral-forming ions are delivered to the PRB is higher (or lower) than that expected under typical conditions (i.e., due to higher/lower flow rate or inflowing ground water that has higher/lower ionic strength). When the PRB is more permeable than the aquifer, the median Darcy flux in the PRB does not change appreciably over time because the aquifer controls the rate of flow through the PRB. However, seepage velocities in the PRB increase, and residence times decrease, due to porosity reductions caused by accumulation of minerals in the pore space. When fouling becomes extensive, bypassing and reductions in flow rate in the PRB occur.     

The tropical cyclone threat to the Queensland Gold Coast

The Queensland Gold Coast has been Australia's premier holiday resort for more than 20 years, and has had increasing attraction as a retirement area for people from elsewhere in Australia. A mixture of canal estates, beach-front residences, retail trade outlets and high-rise apartment and hotel buildings extends onto the fore-dune. Tropical cyclones approaching the area have caused widespread damage to public and private property, and a recent analysis has pointed to the Gold Coast as one of the areas potentially vulnerable to the effects of super tropical cyclones. The nature and extent of hazard awareness and of public and private loss mitigation measures and their overall effectiveness are critical, if property damage and threats to life and the local economy are to be kept to a minimum. Surveys of hazard awareness of Gold Coast residents and of their approaches to loss mitigation and adjustment indicate a low level of preparedness despite past tropical cyclones, and point to the need for better public education.     

Macro‐ and micro‐sedimentology of a modern melt‐out till – Matanuska Glacier,Alaska, USA

The macro‐ and micro‐sedimentology of a supraglacial melt‐out till forming at the Matanuska Glacier was examined in relationship to the properties of the stratified basal zone ice and debris from which it is originating. In situ melting of the basal ice has produced a laminated to bedded diamicton consisting mainly of silt. Macroscopic properties include: discontinuous laminae and beds; lenses of sand, silt aggregates and open‐work gravel; deformed and elongate clasts of clay; widely dispersed pebbles and cobbles, those that are prolate usually with their long axes subparallel to parallel to the bedding. Evidence for deformation is absent except for localized bending of beds over or under rock clasts. Microscopic properties are a unique element of this work and include: discontinuous lineations; silt to granule size laminae; prolate coarse sand and rock fragments commonly with their long axis subparallel to bedding; subangular to subrounded irregular shaped clay clasts often appearing as bands; sorted and unsorted silt to granule size horizons, sometimes disrupted by pore‐water pathways. Limited deformation occurs around rock clasts and thicker parts of lamina. This study shows that in situ melting of debris‐rich basal ice can produce a laminated and bedded diamicton that inherits and thereby preserves stratified basal ice properties. Production and preservation of supraglacial melt‐out till require in situ melting of a stagnant, debris‐rich basal ice source with a low relief surface that becomes buried by a thick, stable, insulating cover of ice‐marginal sediment. Also required are a slow melt rate and adequate drainage to minimize pore‐water pressures in the till and overlying sediment cover to maintain stability and uninterrupted deposition. Many modern and ancient hummocky moraines down glacier of subglacial overdeepenings probably meet these process criteria and their common occurrence suggests that both modern and pre‐modern supraglacial melt‐out tills may be more common than previously thought.