Australasian microtektites from Antarctica: XAS determination of the Fe oxidation state

The Fe oxidation state and coordination number of 29 impact glass spherules recently recovered from the Transantarctic Mountains (Antarctica) have been determined by X‐ray absorption near edge structure (XANES) spectroscopy. Based on geochemical, isotopic, and fission track data, these spherules are considered as microtektites from the Australasian tektite/microtektite strewn field. Their find location is the farthest so far discovered from the possible source crater region, and their alkali content is the lowest compared with other published data on Australasian microtektite glasses. The Fe³⁺/(Fe²⁺+Fe³⁺) ratio, determined from the analysis of the pre‐edge peak energy position and integrated intensity, is below 0.1 (±0.04) for all the samples, and is comparable to that of most tektites and microtektites from the Australasian strewn field. Also, the pre‐edge peak integrated intensity, which is sensitive to the average Fe coordination geometry, is comparable to that of other Australasian microtektites reported in the literature. The agreement of the Fe oxidation state and coordination number, between the Transantarctic Mountain microtektites (TAM) and the Australasian tektites and microtektites, further confirms the impact origin of these glass spherules and provides an independent suggestion that they represent a major extension southeastward of the Australasian strewn field. The fact that similar redox conditions are observed in tektites and microtektites within the Australasian strewn field regardless of the distance from the source crater area (up to approximately 11000 km) could be an important constraint for better understanding the different processes affecting microtektite formation and transport. The fact that the Fe oxidation state of microtektites does not increase with distance, as in the case of North American microtektites, means that thermal and redox histories of Australasian and TAM microtektites could differ significantly from those of North American microtektites.     

Nachocho — an example of the change of the living sphere of the Maasai of Northern Tanzania

The example of Nachocho's enkang shows the recent socio-economic changes taking place in the southern Maasai Steppe of N Tanzania. The initial point is the traditional living community in the enkang and the form of pastoralism which are the basis of the economic and social security systems of the Maasai. The state land use policy, however, leads to the strong restriction of the grazing potential. In order to secure land titles for themselves, the Maasai try to pursue agropastoral activities, although they have had, until recently, no contact or experience with farming at all. In this transitional situation, their old pastoral economic basis is strongly endangered, although no useful alternative has been found, so far. For the Maasai of the Tanzanian Steppe a process of impoverishment is thus being triggered off.     

Petrography and geochemistry of granitoid and metamorphite pebbles from the early Archaean Moodies Group,Barberton Mountainland/South Africa

Pebbles of potassic granitoids and metamorphites constitute up to 5% of the basal conglomerate of the Moodies Group in a ratio of 2 : 1. The granitoid pebbles frequently show micrographic quartz–feldspar intergrowth, whereas the metamorphites—of a modal composition similar to that of the granitoids—are characterized by large quartz grains which could represent original quartz phenocrysts in felsic volcanic precursors.The granitoids show high K₂O, Sr, K₂O/Na₂O, and K/Rb, small enrichment of light REE, large negative Eu-anomalies, and slightly depleted and fractionated heavy REE. Compared to the granitoids the metamorphites show higher Fe₂O₃, TiO₂, and Cr concentrations, greater enrichment of light REE, and also large negative Eu-anomalies.There is little similarity between the Moodies pebbles and the majority of the rocks of the Ancient Gneiss Complex of Swaziland (AGC). There is only some similarity of the REE distribution patterns between the pebbles and the Mkhondo Metamorphic Suite, possibly an areally restricted phase of the AGC. The geochemical data, and especially the large negative Eu-anomalies suggest that the Moodies pebbles were derived from granites which represent residual magmas from which much plagioclase had been removed. The granites crystallized at depths of < 7 km from magmas with low H₂O-pressures in a rather thick sialic crust. It appears possible that the pre-Moodies granitoids originated through partial melting of low-Al₂O₃ siliceous gneisses of the AGC. A chronologic connection of the formation of the granitoids with the late Onverwacht Group volcanicity is possible.     

Effect of enhanced water exchange on ecosystem functions in backwaters of an urban floodplain

This study evaluated the effects of a controlled surface water connectivity scheme on several backwaters in an urban floodplain within the city limits of Vienna, the Upper Lobau. A phosphorus budget and ecosystem metabolism measurements were used to assess the reaction of two trophically distinct floodplain backwater sections on changed connectivity conditions. The surface water connection led to a reduction of the retention times in the backwater system. The water column nutrient concentrations in the individual backwater sections approached those of the source water body. The significance of these effects, however, depends on the historical and current trophic situation of the respective water bodies. Generally, the surface water connectivity introduced particulate phosphorus export up to 30% increase over the influent loading and dissolved phosphorus up to 14% increase over the influent loading. However, in sections with submersed macrophyte development, which provided enhanced filtering capacities for particulate matter, sediment and phosphorus accumulation rates were increased. At the same time, water transparency increased resulting in a positive feedback supporting further macrophyte development. Based on these findings, the evaluation of restoration measures in urban floodplains needs to consider the spatial and temporal dynamics of nutrients and ecosystem processes such as gross primary production and community respiration to predict long-term development.     

Oceans and human health: Emerging public health risks in the marine environment

There has been an increasing recognition of the inter-relationship between human health and the oceans. Traditionally, the focus of research and concern has been on the impact of human activities on the oceans, particularly through anthropogenic pollution and the exploitation of marine resources. More recently, there has been recognition of the potential direct impact of the oceans on human health, both detrimental and beneficial. Areas identified include: global change, harmful algal blooms (HABs), microbial and chemical contamination of marine waters and seafood, and marine models and natural products from the seas. It is hoped that through the recognition of the inter-dependence of the health of both humans and the oceans, efforts will be made to restore and preserve the oceans.     

Regional modeling of carbonaceous aerosols over Europe—focus on secondary organic aerosols

In this study, an improved and complete secondary organic aerosols (SOA) chemistry scheme was implemented in the CHIMERE model. The implementation of isoprene chemistry for SOA significantly improves agreement between long series of simulated and observed particulate matter concentrations. While simulated organic carbon concentrations are clearly improved at elevated sites by adding the SOA scheme, time correlation are impaired at low level sites in Portugal, Italy and Slovakia. At several sites a clear underestimation by the CHIMERE model is noticed in wintertime possibly due to missing wood burning emissions as shown in previous modeling studies. In Europe, the CHIMERE model gives yearly average SOA concentrations ranging from 0.5 μg m ^− 3 in the Northern Europe to 4 μg m ^− 3 over forested regions in Spain, France, Germany and Italy. In addition, our work suggests that during the highest fire emission periods, fires can be the dominant source of primary organic carbon over the Mediterranean Basin, but the SOA contribution from fire emissions is low. Isoprene chemistry has a strong impact on SOA formation when using current available kinetic schemes.     

The 2nd century AD earthquake in central Italy: archaeoseismological data and seismotectonic implications

The 2nd century AD earthquake in central Italy is only known by an epigraph that mentions restorations to a damaged weighing-house at the ancient locality of Pagus Interpromium. The available seismic catalogues report this event with the conventional date of 101 AD, a magnitude M _aw of 6.3, and an epicentral location at the village of San Valentino in Abruzzo Citeriore, in the province of Pescara. In order to improve the knowledge of the damage pattern, we gathered all the archaeological data collected during modern excavations at sites located in the area, which were presumably struck by the earthquake. This information is mainly represented by (1) stratigraphic units due to the sudden collapse of buildings over still frequented floors; (2) stratigraphic units demonstrating restoration or re-building of edifices; (3) stratigraphic units formed as the result of the abandonment of sites or of their lack of frequentation for decades or centuries. Only stratigraphic evidence consistent with an earthquake occurrence during the 2nd century AD has been considered. The most recent archaeological material found in a collapsed unit is a coin of Antoninus Pius, dated at 147–148 AD. This may represent a post quem date very close to the occurrence of the earthquake. The gathered information, plus the stratigraphic data that excluded the earthquake occurrence at some sites, has allowed us to roughly delineate an area of possible damage, including the Sulmona Plain and surrounding areas. Comparisons between the possible 2nd century damage distribution and (i) the damage patterns of more recent historical events that have struck the investigated area, (ii) the distribution of virtual intensities obtained by simulating an earthquake having an epicenter in the Sulmona Plain and applying an intensity attenuation relationship and (iii) a shaking scenario obtained by modelling the activation of the major active fault of the Sulmona Plain area (the Mt. Morrone fault) have revealed consistency between the ancient earthquake and the activation of this fault. Since no other historical events can be attributed to this active fault, we conclude that the time that has elapsed since the last fault activation should be in the order of 1,850 years, i.e. a time span that is very close to the recurrence interval of Apennine seismogenic sources. Moreover, considering the fault length, the causative source may be responsible for earthquakes with M up to 6.6–6.7. The comparison between the presumed 2nd century damage and the shaking scenario suggests that the magnitude mentioned is consistent with the presumed effects of the ancient earthquake. Finally, considering that Sulmona (the most important town in the region investigated) is located in the middle of the Mt. Morrone fault hanging wall, we consider it as the probable epicentral area. Therefore, to summarise the information on the 2nd century AD earthquake, we can conclude that (i) it occurred shortly after 147–148 AD; (ii) a magnitude M _w 6.6–6.7 can be attributed to it and (iii) the probable macroseismic epicentral area was Sulmona.     

Distribution of Crenarchaeota tetraether membrane lipids in surface sediments from the Red Sea

The Red Sea represents an extreme marine environment, with high salinity, high temperature and low level of nutrients, complicating the application of standard geochemical palaeotemperature proxies. In order to investigate the applicability of the TEX₈₆ (TetraEther indeX of GDGTs with 86 carbons) proxy for sea surface temperature (SST) in the Red Sea, the distribution of glycerol dialkyl glycerol tetraether membrane lipids (GDGTs) in sediments from the Red Sea and the Gulf of Aden were examined. Against expectations, TEX₈₆ values for the Red Sea do not show a simple linear relationship with SST and deviate from the global core top calibration. In the northern Red Sea, at temperatures between 25 and 28 °C, the values increase linearly with SST, whereas in the southern Red Sea, at temperatures above 28 °C, TEX₈₆ decreases with increasing temperature. Factors like seasonality and depth of production, salinity and nutrient availability, as well as diagenetic overprint or influence of allochtonous terrestrial lipids, cannot explain this pattern. However, the observed TEX₈₆ relationship with SST could be explained by the presence of a hypothetical endemic Crenarchaeota population in the Red Sea with a specific TEX₈₆ vs. SST relationship. In the Southern Red Sea, a two-component mixing model implies an exponential decrease in the endemic population towards the Gulf of Aden. Thus, the application of the TEX₈₆ as a palaeotemperature proxy in the Red Sea is likely only possible for the northern Red Sea area with the specific SST vs. TEX₈₆ relationship determined in this study and potentially for the whole Red Sea basin during glacials, when water exchange with the Indian Ocean was more restricted than today and the endemic archaeal lipid distribution was not affected by transport from the Indian Ocean. Our results suggest that distinct populations of Crenarchaeota in extreme environments such as evaporitic basins may have different membrane composition, necessitating application of another calibration than the global core top calibration for TEX₈₆ palaeothermometry.     

Optical afterglows of gamma-ray bursts: a bimodal distribution?

The luminosities of the optical afterglows of gamma-ray bursts, 12 h (rest-frame time) after the trigger, show a surprising clustering, with a minority of events being at a significantly smaller luminosity. If real, this dichotomy would be a crucial clue to understand the nature of optically dark afterglows, i.e. bursts that are detected in the X-ray band, but not in the optical. We investigate this issue by studying bursts of the pre- Swift era, both detected and undetected in the optical. The limiting magnitudes of the undetected ones are used to construct the probability that a generic burst is observed down to a given magnitude limit. Then, by simulating a large number of bursts with pre-assigned characteristics, we can compare the properties of the observed optical luminosity distribution with the simulated one. Our results suggest that the hints of bimodality present in the observed distribution reflect a real bimodality: either the optical luminosity distribution of bursts is intrinsically bimodal, or there exists a population of bursts with a quite significant grey absorption, i.e. wavelength-independent extinction. This population of intrinsically weak or grey-absorbed events can be associated with dark bursts.