Factors influencing methane-derived authigenic carbonate formation at cold seep from southwestern Dongsha area in the northern South China Sea

This paper carried out mineral and geochemical studies on a profile through a diagenetic methane-derived authigenic carbonate sample that was collected from southwestern Dongsha area of the northern South China Sea. Five samples locating in the cross-sectional middle mainly consist of dolomite and quartz, and two samples close to the surface have a small amount of Mg-calcite. The δ¹³C values of the samples vary between ?30.59 and ?0.30 % VPDB, with δ¹⁸O values ranging from 3.07 to 3.59 % VPDB, δ^44/40Ca values ranging from 1.35 to 1.47 % SRM915a, indicating a contribution of methane to the carbon pool where the precipitation of authigenic carbonates occurred. Based on the isotope values alone, it can not be distinguished if the carbon source is thermogenic gas or a mixture of biogenic methane and marine dissolved inorganic carbon. The δ¹⁸O values are in general consistent with dolomite precipitation from a fluid similar to present seawater. The observed small variation might be related to the oxygen isotope composition of seep fluid. The relative small range in calcium isotope values suggests that relatively constant growth conditions and precipitation from seawater. The central part of the carbonate nodule formed under the strong influence of methane seepage, and the external part is less influenced by methane, either due to reduced methane flux to the surface or caused by erosional exhumation of the carbonate nodule from greater depth to the sediment surface.     

A New Family of Moths from the Middle Jurassic (Insecta: Lepidoptera)

<正>Three lepidopteran species,from the Middle Jurassic Daohugou beds(inner Mongolia,China),are described in a new family,Mesokristenseniidae,and new genus,Mesokristensenia,which could represent the sister group of the Micropterigidae.Mesokristensenia differs from all extant Lepidoptera,but one genus(Agathiphaga, Agathiphagidae),in retaining four median veins in the forewing,a plesiomorphy also present in many Trichoptera. Evidence for placing Mesokristensenia in the Lepidoptera includes four traits,notably a previously unrecorded autapomorphy of this insect order:beyond stem M1+2,vein M1 is bent and connected to cross-vein r-m(in both wing pairs).Among 24 characters taken into account to assess the systematic position of Mesokristensenia,12 are considered informative for a cladistic analysis involving this fossil taxon and the four suborders recognized in present-day Lepidoptera(Zeugloptera,Aglossata,Heterobathmiina,and Glossata).     

Moments in everyday/distant geopolitics: Young people’s fears and hopes

The everyday implications of a volatile geopolitical climate are increasingly recognised, but far less is known about how people’s emotional geographies are affected by geopolitical change. This paper offers a critical examination of how some young people in different parts of the world navigate fears and hopes that might be considered ‘global’ in nature, and those that might be considered ‘everyday’. We report from participatory research conducted with young people from a range of ethnic and cultural backgrounds living in New Zealand and the United Kingdom. We examine how personal fears and hopes intersect with wider anxieties about youth, urban crime and terrorism. The research suggests that global-everyday emotions are not separated out in young people’s analyses. They are critically reflexive about wider discourses of fear, while undertaking the day to day business of navigating what are sometimes challenging emotional topographies.     

Geoarchaeology of Pleistocene open-air sites in the Vila Nova da Barquinha-Santa Cita area (Lower Tejo River basin, central Portugal)

This paper aims to provide insight into human occupation and landscape change during the Pleistocene in a central area of the Lower Tejo basin (Portugal). Detailed geomorphological mapping, coupled with lithostratigraphy, sedimentology and luminescence dating, supports the identification of a complete terrace staircase sequence. It consists of six gravely terraces located below the culminant (Pliocene) basin unit. A chronological framework for the sedimentary sequences and associated human industries is proposed and correlated with marine oxygen isotope stages (MIS): T1 terrace, not dated; T2, not dated; T3, >300 ka; T4, ∼300-160 ka (MIS8, MIS7 and MIS6); T5, ∼136-75 ka (MIS5); T6, ∼62-30 ka (MIS3); colluvium and aeolian sands, ∼30-14 ka (MIS2); valley fill deposits, ∼14 ka to present (MIS1). The oldest artefacts were found at the base of the T4 terrace, with the local stratigraphic level dated to ≥175 ± 6 ka (Middle Pleistocene). The lithic assemblages collected from distinct stratigraphic levels (T4, T5 top, T6 terraces and colluvium) are characterized by the predominance of opportunistic technological choices, a feature that can be attributed partly to the preferential exploitation of the available raw material, dominated by local-sourced quartzites and quartz pebbles. The adaptation to local raw material (texture and volume), together with subsistence patterns and behaviours, could explain the rarity of Acheulian types (handaxes and cleavers) and picks in the T4 terraces of the Tejo tributaries; this is in contrast to the same terrace of the Tejo valley, in which these types are found. Interpretation of the environmental conditions (controlled by climate and glacio-eustatic sea-level changes) affecting the hunter-gatherer human groups is also presented.     

Overwash vulnerability assessment based on long-term washover evolution

An integrated methodology for evaluation of overwash vulnerability is developed with respect to the historical washover evolution of a barrier island system. Three different aspects of overwash are addressed in the vulnerability indices developed: overwashed shoreline ratio, maximum overwash intrusion recurrence, and complete barrier overwash. The indices were applied to the barriers in the Ria Formosa system in Southern Portugal using an aerial photography catalogue covering the period 1947–2001. Historical trends of washover evolution were observed to be different between the barriers analysed, but generally, there was a decrease in washover number and dimensions throughout the analysed period. The final overwash diagnostic obtained allowed an integrated overwash vulnerability rating to be defined for each barrier, with vulnerabilities ranging from low to extreme. The methodology has produced results that may assist coastal managers with information concerning barrier island system overwash hazard, define the temporal and geographical distributions of overwash, and provide indications as to where overwash is most likely to occur in the future.     

Interaction of acid mine drainage with waters and sediments at the Corona stream, Lousal mine (Iberian Pyrite Belt, Southern Portugal)

This study investigates the geochemical characteristics of the acid mine drainage discharged from the abandoned mine adits and tailing piles in the vicinity of the Lousal mine and evaluates the extent of pollution on water and on the stream sediments of the Corona stream. Atmospheric precipitation interacting with sulphide minerals in exposed tailings produces runoff water with pH values as low as 1.9–2.9 and high concentrations of (9,249–20,700 mg l⁻¹), Fe (959–4,830 mg l⁻¹) and Al (136–624 mg l⁻¹). The acidic effluents and mixed stream water carry elevated Cu, Pb, Zn, Cd and As concentrations that exceed the water quality standards. However, the severity of contamination generally decreases 4 km downstream of the source due to mixing with fresh waters, which causes the dilution of dissolved toxic metals and neutralization of acidity. Some natural attenuation of the contaminants also occurs due to the general reduced solubility of most trace metals, which may be removed from solution, by either co-precipitation or adsorption to the iron and aluminium precipitates.     

Mercury Redox Chemistry in the Negro River Basin, Amazon: The Role of Organic Matter and Solar Light

Pristine water bodies in the Negro River basin, Brazilian Amazon, show relatively high concentrations of mercury. These waters are characterized by acidic pH, low concentrations of suspended solids, and high amounts of dissolved organic matter and are exposed to intense solar radiation throughout the year. This unique environment creates a very dynamic redox chemistry affecting the mobility of mercury due to the formation of the dissolved elemental species (Hg⁰). It has been shown that in this so-called black water, labile organic matter from flooded forest is the major scavenger of photogenerated H₂O₂. In the absence of hydrogen peroxide, these black waters lose their ability to oxidize Hg⁰ to Hg²⁺, thus increasing Hg⁰ evasion across the water/atmosphere interface, with average night time values of 3.80 pmol m^?2 h^?1. When the dry period starts, labile organic matter inputs gradually diminish, allowing the increasing concentration of H₂O₂ to re-establish oxidative water conditions, inhibiting the metal flux across the water/atmosphere interface and contributing to mercury accumulation in the water column.     

Short- and Long-Term Chlorophyll a Variability in the Shallow Microtidal Patos Lagoon Estuary, Southern Brazil

In the shallow microtidal Patos Lagoon estuary, southern Brazil (32° 07′ S–52° 06′ W), chlorophyll a (Chl a) variability was studied at different time scales during the last 25 years (hourly–daily sampling in 1984/1985; weekly sampling in 1986 and from 1988 to 1990; monthly sampling from 1993 to 2008). Phytoplankton biomass variation seems to be most influenced by hydrology, which is primarily driven by meteorological factors like wind, rainfall, and evaporation. However, it was observed that the hydrological driving forces play different roles at different time scales. For instance, short-term Chl a variability is mainly controlled by winds, while long-term changes are related to the freshwater input by rainfall. Significant correlation was found between the total amount of rain in the year and the mean annual value of Chl a, though this relationship was linear until 1,500 mm of rain per year. After this threshold, mean annual Chl a values dropped significantly, probably due to a washout of the produced biomass from the estuary. Similarly, low rainfall levels and drought years lead to small phytoplankton biomass due to scarcity of nutrient, mainly silicate, or a possible inhibitory effect generated by high ammonium concentration. In this sense, large-scale Chl a variability would be related to the El Ni?o-Southern Oscillation climatic anomaly, which influences the rainfall levels in Southern Brazil, though sampling periodicity has also great influence on this relationship. No Chl a or nutrient enrichment was observed in the estuarine region along the last years, indicating that this estuary is not subject to an eutrophication process. In contrast, signals of an ongoing oligotrophication are observed, possibly a remote effect of the eutrophication in the Northern area of the lagoon where the phytoplankton nutrients uptake may act as a biological filter mechanism.     

Environmental Forcing of Phytoplankton in a Mediterranean Estuary (Guadiana Estuary,South-western Iberia): A Decadal Study of Anthropogenic and Climatic Influences

Phytoplankton seasonal and interannual variability in the Guadiana upper estuary was analyzed during 1996–2005, a period that encompassed a climatic controlled reduction in river flow that was superimposed on the construction of a dam. Phytoplankton seasonal patterns revealed an alternation between a persistent light limitation and episodic nutrient limitation. Phytoplankton succession, with early spring diatom blooms and summer–early fall cyanobacterial blooms, was apparently driven by changes in nutrients, water temperature, and turbulence, clearly demonstrating the role of river flow and climate variability. Light intensity in the mixed layer was a prevalent driver of phytoplankton interannual variability, and the increased turbidity caused by the Alqueva dam construction was linked to pronounced decreases in chlorophyll a concentration, particularly at the start and end of the phytoplankton growing period. Decreases in annual maximum and average abundances of diatoms, green algae, and cyanobacteria were also detected. Furthermore, chlorophyll a decreases after dam filling and a decrease in turbidity may point to a shift from light limitation towards a more nutrient-limited mode in the near future.