Interplay of eustatic,tectonic and autogenic controls on a Late Devonian carbonate platform,northern Canning Basin,Australia

Frasnian reef complexes along the northern margin of the Canning Basin in northwestern Australia evolved during rifting of the Fitzroy Trough. Geological investigations of the Frasnian Hull platform, which developed on an active tilted fault‐block, reveal significant lateral and vertical facies variations superimposed on prominent metre‐scale cyclicity. This study uses numerical analyses of facies and magnetic susceptibility data from three measured sections along the Hull platform to test whether a tectonic signal can be distinguished from eustatic and other signals. Geostatistical analysis of facies variations reveals an exponential distribution of thin (<3 m) facies, characteristic of stochastic depositional processes. Thick subtidal facies predominate in the Guppy Hills (GH) and southeastern Hull Range (SHR) sections near the hangingwall margin, and thick shallow‐subtidal to intertidal facies dominate the Horse Springs drillcore (HD 14) section near the footwall margin. Power and wavelet spectral analyses indicate a strong periodic component; Average Spectral Misfit and spectral optimisation methods confirm the presence of Milankovitch eccentricity signals and suggest the presence of obliquity and precession signals. However, the results also expose strong temporal and spatial variation providing evidence for tectonic control. Spectral analyses show strongest periodicity is recorded in short intervals that are not correlated across the platform and provide evidence of variations in sedimentation rate and hiatuses. Time series for the neighbouring GH and SHR sections show no overall statistical correlation, and Markov analysis indicates weakly ordered vertical facies transitions that do not correlate across the platform. Subtidal to intertidal facies data from HD 14 core suggest that at least 35% of the section is absent, almost obscuring the Milankovitch signal. The results indicate a complex set of controls on deposition on the Hull platform with local tectonic effects having produced spatio‐temporal moderation of the underlying eustatic signals and autogenic processes adding a localised stochastic response.     

The effect of Ni on element partitioning during iron meteorite crystallization

Abstract— ‐Iron meteorites exhibit a large range in Ni concentrations, from only 4% to nearly 60%. Most previous experiments aimed at understanding the crystallization of iron meteorites have been conducted in systems with about 10% Ni or less. We performed solid metal/liquid metal experiments to determine the effect of Ni on partition coefficients for 20 trace elements pertinent to iron meteorites. Experiments were conducted in both the end‐member Ni‐S system as well as in the Fe‐Ni‐S system with intermediate Ni compositions applicable to high‐Ni iron meteorites. The Ni content of the system affects solid metal/liquid metal partitioning behavior. For a given S concentration, partition coefficients in the Ni‐S system can be over an order of magnitude larger than in the Fe‐S system. However, for compositions relevant to even the most Ni‐rich iron meteorites, the effect of Ni on partitioning behavior is minor, amounting to less than a factor of two for the majority of trace elements studied. Any effect of Ni also appears minor when it is compared to the large influence S has on element partitioning behavior. Thus, we conclude that in the presence of an evolving S‐bearing metallic melt, crystallization models can safely neglect effects from Ni when considering the full range of iron meteorite compositions.     

Denitrification in a Laurentian Great Lakes coastal wetland invaded by hybrid cattail (Typha × glauca)

Wetland ecosystems maintain and improve water quality through the process of denitrification, an increasingly important ecosystem service due to global N pollution. Invasive plants have the potential to disrupt denitrification by altering the environmental conditions that facilitate this process. Great Lakes coastal wetlands are experiencing widespread invasion by highly productive hybrid cattail with largely uncertain biogeochemical effects. Through field and controlled mesocosm studies, we sought to determine the effects of cattail invasion through time on denitrification rates and associated environmental factors in a Great Lakes coastal wetland. In the field, we found that cattail density correlated with increased denitrification and a suite of environmental and plant community characteristics and denitrification rates were positively correlated with NH₄ ⁺, sediment organic matter, reduced water levels, and cattail stand age. Through our controlled mesocosm study, we documented conditions 1- and 5-year following invasion and found that denitrification rates and soil organic matter increased in year 5, and cattail and year-since-invasion altered plant communities and soil NH₄ ⁺. Only a weak correlation between denitrification rates and cattail treatments was noted, however, owing to high replicate variability. Our results indicate that with increasing cattail residence time, one ecosystem service, biodiversity, was negatively impacted, while two other services, denitrification and sediment carbon accumulation, were enhanced. Thus, this highly invaded wetland still provides valuable services to aquatic ecosystems and to society. A holistic perspective is therefore critical when evaluating invasive species impacts in which negative impacts are weighed against other ecosystem services, which may be stimulated.     

The significance of the personal within disability geography

Drawing on in-depth qualitative data, this article critically examines disability geography as a subfield where the personal is highly valued. The value and the risks inherent in this personal approach will be evaluated, including the usefulness of being an 'insider' and the difficulties of being reflexive and critically making use of one's positionality. The article concludes with reflections regarding how disability geography can confront its marginal status, appealing to researchers who claim no experience of disability while also supporting and encouraging those with personal experiences of disability to participate in the field.     

THE MARBLE BEACHES OF TUSCANY*

ABSTRACT. Beach‐nourishment operations designed to replace sediment lost through erosion change the identity and meaning of coastal landscapes. Seven beaches in Tuscany, nourished with marble‐quarry waste, reveal how an industrial byproduct is naturalized by particle rounding and sorting and can become a positive symbol of human‐altered nature. The marble was placed on formerly sandy beaches, resulting in different grain size and color of sediments, beach morphology, and value for human use. The abrasion rate of marble makes the nourished beaches unsatisfactory when viewed solely as protection structures, but the rapid particle rounding and aesthetic appeal of marble increase the acceptability of the beaches for recreation.     

Climatic influences on riverine nitrate flux: Implications for coastal marine eutrophication and hypoxia

The average nitrate flux of the lower Mississippi River increased 3.3-fold between 1954–1967 and 1983–2000. During the same time period, the average nitrate concentration increased 2.3-fold while the average discharge increased 40%. Partitioning of the observed trend in nitrate flux among the two flux components, nitrate concentration and discharge, revealed that about 80% of the observed increase in flux could be explained by the increase in nitrate concentration. This indicates that a historical increase in the anthropogenic nutrient inputs has had a far greater impact on the lower Mississippi River nitrate flux than a change in climate. The influence of climatic factors on nitrate flux has been significant and may further increase as a result of global climate change. This argument is supported by two lines of evidence. The residual component of nitrate flux, obtained by removing a trend from the time series, is controlled primarily by the variability in discharge, i.e., climatic factors. Also, there is a highly significant relationship between discharge and nitrate concentration at the low end of the discharge spectrum (<13,000 m³ s^?1). The differences in nitrate flux between flood and drought years are significantly larger than the variations in discharge. This makes the Mississippi River nitrate flux potentially sensitive to future changes in the frequency of extreme climatic events. Because of the importance of nitrate for the productivity of coastal phytoplankton, future climate change would likely have important implications for coastal marine eutrophication and hypoxia.     

THE DECLINE OF PARTY VOTING: A GEOGRAPHICAL ANALYSIS OF THE 1978 MASSACHUSETTS ELECTION

A factor analysis of the 1978 Massachusetts election is undertaken to investigate whether the alleged decline of political parties in the United States can be distinguished at the state scale. Four factors are identified, two of which relate to the voting patterns of state-wide candidates. The main factor is easily seen to represent a “party voting”pattern and the fourth factor suggests a nonparty pattern of support associated with the Democratic candidate for governor, Edward King. It is suggested that this separation of the voting pattern for Democratic candidates may possibly reflect party decomposition in Massachusetts.     

The luminescence decay-time of Mn2+ activated calcite

Luminescence decay time data are presented for 17 samples of synthetic calcite and a natural calcite between room temperature and approximately 15 K. The majority of the samples have Mn concentration in the range 0.0001–0.01 atoms per formula unit (apfu). Their spectra are consistent with a single exponential decay. It was necessary to use a “stretched” exponential to obtain adequate fits to the spectra of two samples having Mn concentrations of 0.036 and 0.091 apfu. The decay time at room temperature ranges from approximately 40–57 ms. At low temperature the corresponding range is 51–120 ms, indicating that thermal quenching of the decay time takes place. The decay time is dependent on the concentration of Mn, reaching a maximum (at both room- and low-temperature) in the range 0.001–0.003 apfu. The composition dependence is greater at low temperature. The results are discussed in terms of the Mott-Seitz and multiphonon mechanisms of thermal quenching. It is concluded that the latter provides a better fit to the data and is more consistent with models of the luminescence process in calcite:Mn.     

Relationships among satellite chlorophylla, river inputs, and hypoxia on the Louisiana Continental shelf, Gulf of Mexico

SeaWiFS ocean color measurements were used to investigate interannual, monthly, and weekly variations in chlorophylla (chla) on the Louisiana shelf and to assess relationships with river discharge, nitrate load, and hypoxia. During the study period (2000–2003), interannual changes in shelf-wide chla concentrations averaged over January–July ranged from +57% to −33% of the 4-yr average, in accord with freshwater discharge changes of +20% to −29% and nitrate load changes of +20% to −35% from the Mississippi and Atchafalaya Rivers. Chla variations were largest on the shelf between the Mississippi and Atchafalaya Deltas. Within this region, which corresponds spatially to the area of most frequent hypoxia, lowest January–July mean chla concentrations (5.5 mg m⁻³ over 7,000 km²) occurred during 2000, the year of lowest freshwater discharge (16,136 m³ s⁻¹) and nitrate load (55,738 MT N d⁻¹) onto the shelf. Highest January–July mean chla concentrations (13 mg m⁻³ over 7,000 km²) were measured in 2002, when freshwater discharge (27,440 m³s⁻¹) and nitrate load (101,761 MT N d⁻¹) were highest and second highest, respectively. Positive correlations (R²=0.4–0.5) were found between chla and both fresh water and nitrate loads with 0 to 1 month lags, with the strongest relationships just west of the Mississippi Delta. In 2001, unusually clear skies allowed the identification of distinct spring and summer chla blooms west of the Mississippi Delta 4–5 wk after peaks in river discharge. East of the delta, the chla concentrations peaked in June and July, following the seasonal reversal in the coastal current. A clear linkage was not detected between satellite-measured chla and hypoxia during the 4-yr period, based on a time series of bottom oxygen concentrations at one station within the area of most frequent hypoxia. Clear relationships are confounded by the interaction of physical processes (wind stress effects) with the seasonal cycle of nutrient-enhanced productivity and are influenced by the prior year's nitrate load and carbon accumulation at the seabed.     

Aeolian sediment transport on a human‐altered foredune

Changes in wind speed and sediment transport are evaluated at a gap and adjacent crest of a 2 to 3 m high, 40 m wide foredune built by sand fences and vegetation plantings on a wide, nourished fine sand beach at Ocean City, New Jersey. Anemometer masts, cylindrical sand traps and erosion pins were placed on the beach and dune during two obliquely onshore wind events in February and March 2003. Results reveal that: (1) changes in the alongshore continuity of the beach and dune system can act as boundaries to aeolian transport when winds blow at an angle to the shoreline; (2) oblique winds blowing across poorly vegetated patches in the dune increase the potential for creating an irregular crest elevation; (3) transport rates and deflation rates can be greater within the foredune than on the beach, if the dune surface is poorly vegetated and the beach has not had time to dry following tidal inundation; (4) frozen ground does not prevent surface deflation; and (5) remnant sand fences and fresh storm wrack have great local but temporary effect on transport rates. Temporal and spatial differences due to sand fences and wrack, changes in sediment availability due to time‐dependent differences in surface moisture and frozen ground, combined with complex topography and patchy vegetation make it difficult to specify cause–effect relationships. Effects of individual roughness elements on the beach and dune on wind flow and sediment transport can be quantified at specific locations at the event scale, but extrapolation of each event to longer temporal and spatial scales remains qualitative. Copyright © 2006 John Wiley & Sons, Ltd.