Alteration mineralogy of Home Plate and Columbia Hills—Formation conditions in context to impact,volcanism, and fluvial activity

The Mars Exploration Rover Spirit investigated the igneous and alteration mineralogy and chemistry of Home Plate and its surrounding deposits. Here, we focus on using thermochemical modeling to understand the secondary alteration mineralogy at the Home Plate outcrop and surrounding Columbia Hills region in Gusev crater. At high temperatures (300 °C), magnetite occurs at very high W/R ratios, but the alteration assemblage is dominated by chlorite and serpentine over most of the W/R range. Quartz, epidote, and typical high‐T phases such as feldspar, pyroxene, and garnet occur at low W/R. At epithermal temperatures (150 °C), hematite occurs at very high W/R. A range of phyllosilicates, including kaolinite, nontronite, chlorite, and serpentine are precipitated at specific W/R. Amphibole, with garnet, feldspar, and pyroxene occur at low W/R. If the CO₂ content of the system is high, the assemblage is dominated by carbonate with increasing amounts of an SiO₂‐phase, kaolinite, carpholite, and chlorite with lower W/R. At temperatures of hydrous weathering (13 °C), the oxide phase is goethite, silicates are chlorite, nontronite, and talc, plus an SiO₂‐phase. In the presence of CO₂, the mineral assemblage at high W/R remains the same, and only at low W/R, i.e., with increasing salinity, carbonate precipitates. The geochemical gradients observed at Home Plate are attributed to short‐lived, initially high (300 °C) temperature, but fast cooling events, which are in agreement with our models and our interpretation of a multistage alteration scenario of Home Plate and Gusev in general. Alteration at various temperatures and during different geological processes within Gusev crater has two effects, both of which increase the habitability of the local environment: precipitation of hydrous sheet silicates, and formation of a brine, which might contain elements essential for life in diluted, easily accessible form.     

Sedimentation patterns of diatoms in Lake Holzmaar, Germany - (on the transfer of climate signals to biogenic silica oxygen isotope proxies)

The seasonal sedimentation pattern of diatom valves in Lake Holzmaar was investigated during 1995 by deploying sediment traps at three different lake depths. According to the sedimentation pattern, the major reproduction zone of diatoms was restricted to the upper 6 m of the water body. The population growth started late in April and blooms of Cyclotella cf. comensis Grun., which dominates the plankton diatoms, and Fragilaria crotonensis Kitton were collected in traps during June and September, and July, respectively. During summer, the seasonal sedimentation pattern of each taxon, as collected in the upper traps, was reflected in the concentrations in the lowest trap. However, in May and from September onwards, the community composition in the lowest trap and augmented trapping rates suggest both sediment focusing and resuspension of bottom sediments.The temperature signals as recorded by 18O values of diatom valves should, therefore, reflect integrated temperatures between 0 and 6 m depth. However, temperatures during summer and autumn are expected to be accentuated in the sedimentary record since the isotopic signal is weighted by both the number and the weight-mass of the valves. During summer, the transfer of these signals by the sedimenting diatoms retains the information pattern recorded, while in spring and autumn/winter additional influxes caused by resuspension may somewhat alter those temperature informations. The proxy signals finally stored in the sediments, may, therefore, not precisely represent the successive temperatures currently recorded during 1995 within mid-lake.     

Cladoceran stratigraphy in two shallow brackish lakes with special reference to changes in salinity, macrophyte abundance and fish predation

Sub-fossils of Cladocera and Foraminifera were used to reconstruct changes since 1870 in the trophic dynamics of two brackish lakes, Glombak and Han Vejle, located in the Vejlerne nature reserve, Denmark, a site of international conservation importance. After creation of the lakes in the mid-1870s following land reclamation, the two lakes have developed quite differently; today Glombak is turbid, while Han Vejle is clear. In both lakes, stratigraphic changes in the assemblages of foraminifers and cladocerans indicate an abrupt shift from marine to brackish conditions at the end of the 19th century, coinciding with land reclamation. However, the composition of the fossil invertebrate assemblages in the 20th century implies differences in the exposure to salinity, in fish predation and in habitat diversity. In Glombak, the cladoceran record suggests relatively saline conditions in the first quarter of the last century and high macrophyte abundance followed by lower salinities and subsequently a major decrease in macrophyte abundance and an increase in fish predation during the past ca. 40 years. By contrast, in Han Vejle low salinity, high abundance of macrophytes and only minor changes in fish predation seem to have prevailed throughout most of the 20th century. The results are consistent with recent contemporary data, the few historical records, as well as with trends in the records of diatoms and macrofossils. This study highlights the potential of using crustacean remains as indicators of long-term changes in the trophic dynamics of brackish lakes.     

Density control in Potamogeton perfoliatus L. and Potamogeton pectinatus L.

The effect of density on the growth, recruitment of new ramets, biomass allocation, rhizome spacer length and rhizome branching of the submersed macrophyte Potamogeton perfoliatus L. was experimentally evaluated in a mesocosm with three different initial shoot densities. The findings suggest that the number of primary shoots available in the beginning of the season can strongly influence patterns of growth and clonal reproduction. In contrast to many studies that found decreasing production parameters with plant density, ramet and biomass production of Potamogeton perfoliatus plants were highest at medium plant density. This is probably due to negative feed-back through crowding at high density and unclear negative effects at low density. Shoot allocation tended to increase with density, rhizome allocation tended to decrease with density and root biomass remained unchanged. At low density Potamogeton perfoliatus produced longer rhizome spacers and more branchings than at higher densities. Shorter rhizome spacers at high plant density probably restrict patch expansion and cause discrete patch shapes. A likely mechanism for plastic changes in clonal architecture is increasing competition for light at increasing density, but other density-dependent factors may also contribute.Investigations on propagule numbers of tubers and turions show that self-regulation of ramet number was associated with self-regulation of propagule number in both Potamogeton perfoliatus and Potamogeton pectinatus, with higher densities producing less propagules per plant.     

Mining candidate causal relationships in movement patterns

In many applications, the environmental context for and drivers of movement patterns are just as important as the patterns themselves. This article adapts standard data mining techniques, combined with a foundational ontology of causation, with the objective of helping domain experts identify candidate causal relationships between movement patterns and their environmental context. In addition to data about movement and its dynamic environmental context, our approach requires as input definitions of the states and events of interest. The technique outputs causal and causal-like relationships of potential interest, along with associated measures of support and confidence. As a validation of our approach, the analysis is applied to real data about fish movement in the Murray River in Australia. The results demonstrate that the technique is capable of identifying statistically significant patterns of movement indicative of causal and causal-like relationships.     

Perceived deficiencies in the provision of climate and weather information for tourism: A New Zealand media analysis

Climate and weather are important for tourism and leisure as they impact on destination attractiveness and subsequent visitation. Through an archive analysis of media articles and a content analysis of Regional Tourism Organisation (RTO) websites, this paper explores perceived deficiencies in the currently available climate and weather information for tourists in New Zealand. While media reports focused on concern by many RTOs over the poor regional images generated by inaccurate and poorly presented climate and weather data, the RTO websites were found to contain limited climate and weather information. There is considerable potential for RTOs to improve in this respect.     

‘Ageing in place’: experiences of older adults in Amsterdam and Portland

This article addresses the importance and meanings of formal and informal social support relationships and neighbourhood ties for older adults ‘ageing in place’ in urban neighbourhoods in two different welfare state settings: Portland (Oregon, the United States) and Amsterdam (the Netherlands). The rising number of people growing old(er) in urban environments raises new demands and pressing challenges for urban development. The majority of older adults are and will be ageing in their homes and communities, as opposed to institutionalized care facilities and settings. At the same time, the provision of formal and public care is being increasingly challenged by government cutbacks. On top of this, the formerly strong welfare states in many European countries have weakened. In-depth interviews with 40 older adults and key informants in two neighbourhoods in each city provide the empirical basis for this study. In Portland, there are widespread local civic initiatives related to care provision for older adults. The city has a long tradition both of individual responsibility and community culture, which has emerged from and appears to compensate for the overall lack of state services and support. Amsterdam has a long tradition of state provision, but is experiencing a policy shift towards a stronger reliance on private market-led services, and an emphasis on family and community as providers of support. Although a few emerging local initiatives for elderly care in Amsterdam were identified, it is unclear whether this form of community support can compensate for decreasing state provision in Amsterdam. This study raises concerns about the future of care provision for older adults living in unsupportive urban neighbourhoods, without financial resources or nearby relatives.     

Extended larval development compensates for sublethal effects of fish predation in a mayfly population (Rhithrogena semicolorata, Ephemeroptera)

Many predation experiments in streams are carried out in enclosures. Hence, the relevance of their results to predict population dynamics is often unclear due to the relatively small spatial and temporal scale of the experiments. To enhance the transferability of experimental results on the ecosystem scale the impact of fish predators on a prey population was observed in a reach scale approach over 2 years in a natural stream. A 400-m reach inhabited by the small benthivorous fishes gudgeon (Gobio gobio) and stone loach (Barbatula barbatula) was compared with a fishless reference reach.It was shown that fish predation may affect the population of the grazing mayfly Rhithrogena semicolorata on the ecosystem scale. Although the larvae grew slower in the fish reach than in the fishless reach, the adults reached the same size and fecundity because they emerged 2–3 weeks later. By this compensation, the prey species avoided a reduction of their individual fecundity. On the other hand, the extended exposure to the fish predators resulted in an enhanced mortality and a reduced density of adult mayflies. Thus, there was obviously a trade-off between maximising fecundity and minimising mortality from fish predation.The observed differences were almost certainly caused be fish predation and not by natural differences of the reaches. This was concluded from results gained after eliminating all benthivorous fish from the former fish reach.With the help of scenario analyses based on our empirical data and simple model assumptions we could demonstrate that compensating the potential loss in fecundity by extending development time led to higher average fitness of the prey population than emerging at an earlier fixed time to avoid additional predation losses. Therefore, we concluded that this strategy was adaptive in the presence of benthivorous fish.