Open-system chemical behavior in deep Wilcox Group mudstones,Texas Gulf Coast,USA

Wilcox Group mudstones have been mechanically and geochemically transformed over a temperature range of 20–200 °C. Our research controlled for provenance and age by sampling from five wells, parallel to the paleodepositional axis, all within the Houston delta system. Across the sampled depths, mudstone porosity has been reduced from ∼25 to <10% and bulk mineralogical change as documented by quantitative X-ray diffraction includes decreases in quartz, K-feldspar and kaolinite content whereas illite + illite − smectite, chlorite, and plagioclase increase. These mineral transformations transfer elements at a scale of less than 1 mm from one mineralogical form to another, however, X-ray fluorescence data suggest that among major elements only Al₂O₃ and TiO₂ are fully conserved within the system (trace-element ZrO₂ is also conserved). K₂O has been added to and SiO₂ released from the Wilcox Group mudstones. Cathodoluminescence and secondary electron imaging did not find this SiO₂ locally precipitated. We, therefore, document an open-system geochemical behavior.     

Flood effects on phosphorus immobilisation in a river water filled pit lake—Case study Lake Goitsche (Germany)

Between 1999 and 2002, a former open-cast mine was filled with river water forming the recent Lake Goitsche. During filling initially acid water was neutralised. Phosphorus (P) imported from Mulde River was nearly completely removed from the water column by co-precipitation with iron (Fe) and aluminium (Al) and deposited in the sediment.During extremely high waters of the Mulde River in 2002, a dike breach facilitated a second high import of P into Lake Goitsche with suspended and dissolved matter. The analysis of total phosphorus (TP), however, showed that P again had been eliminated from the water body a few months after the flood event. Sediment investigations before filling with river water, during filling, and after the flood event were used to analyse the process of P immobilisation in a lake with acid mine drainage history.The ratios of Fe to soluble reactive P (SRP) of sediment pore water were up to three orders of magnitudes higher than in natural lakes and can serve as an indicator for potential internal P loading from sediments. The SRP concentrations at the oxic/anoxic boundary were near or below the limit of quantification (< 0.2 μmol/L). Fe and manganese (Mn) redox cycling were responsible for hindering P dissolution from sediment to lake water.Finally it can be stated, that the risk of eutrophication for such a lake seems to be low.     

Socio-economic changes,social capital and implications for climate change in a changing rural Nepal

We investigate the use of social capital in the form of social ties in the face of commercialization, urbanization and climate change. While discussions of social capital often focus on whether people possess certain social ties or not our study shows that it is also necessary to consider under what circumstances people can make use of their ties. The use of different kinds of ties varies with context and is not as clear cut as suggested in the literature. For example families closer to the city are in a better position to take advantage of new opportunities. Using a combination of ties people have engaged in high-input agriculture, business and paid employment. Diversification of livelihoods has made many people less sensitive to climate change, but this does not translate into decreased vulnerability for the community. Intensive agriculture and lower community cohesion seems unsustainable in the long run. Thus, decreased vulnerability at the household level may come at the price of increased vulnerability at higher levels and negative consequences for the wider social–ecological system. Evaluating vulnerability and the role of social ties depends on the unit and sector of analysis, and the temporal and spatial scale.     

Active mud volcanoes on the upper slope of the western Nile deep-sea fan—first results from the P362/2 cruise of R/V Poseidon

In February 2008, cruise P362/2 was undertaken aboard R/V Poseidon to the Giza and North Alex mud volcanoes (MVs) on the upper slope of the western Nile deep-sea fan. Emitted fluids were strongly depleted in chloride and rich in hydrocarbons, predominantly of thermogenic origin. In-situ sediment temperature measurements indicate extremely high and moderate levels of activity for the North Alex MV and Giza MV, respectively, and suggest rapid changes from dormant to active stages. Both the physical properties of core sediments (e.g., color and magnetic susceptibility), and their assemblages of micro- and nannofossils point to different sources for the two mud volcanoes. Biostratigraphic dating suggests source depths of 2,100–2,450 mbsf for the Giza MV and 1,150–1,550 mbsf for the North Alex MV. Very high temperatures of up to 70°C in shallow sediments at the North Alex MV can be explained only if the fluid source were warmer and deeper than the sediment source.     

MedFlux: Investigations of particle flux in the Twilight Zone

The MedFlux project was devised to determine and model relationships between organic matter and mineral ballasts of sinking particulate matter in the ocean. Specifically we investigated the ballast ratio hypothesis, tested various commonly used sampling and modeling techniques, and developed new technologies that would allow better characterization of particle biogeochemistry. Here we describe the rationale for the project, the biogeochemical provenance of the DYFAMED site, the international support structure, and highlights from the papers published here. Additional MedFlux papers can be accessed at the MedFlux web site (http://msrc.sunysb.edu/MedFlux/).     

Investigating the effect of ballasting by CaCO3 in Emiliania huxleyi, II: Decomposition of particulate organic matter

The quantitative relationship between organic carbon and mineral contents of particles sinking below 1800 m in the ocean indicates that organisms with mineral shells such as coccolithophores are of special importance for transporting carbon into the deep sea. Several hypotheses about the mechanism behind this relationship between minerals and organic matter have been raised, such as mineral protection of organic matter or enhanced sinking rates through ballast addition. We examined organic matter decomposition of calcifying and non-calcifying Emiliania huxleyi cultures in an experiment that allowed aggregation and settling in rotating tanks. Biogenic components such as particulate carbon, particulate nitrogen, particulate volume, pigments, transparent exopolymer particles (TEP), and particulate amino acids in suspended particles and aggregates were followed over a period of 30 d. The overall pattern of decrease in organic matter, the amount of recalcitrant organic matter left after 30 d, and the compositional changes within particulate organic matter indicated that cells without a shell are more subject to loss than calcified cells. It is suggested that biogenic calcite helps in the preservation of particulate organic matter (POM) by offering structural support for organic molecules. Over the course of the experiment, half the particulate organic carbon in both calcifying and non-calcifying cultures was partitioned into aggregates and remained so until the end of the experiment. The partial protection of particulate organic matter from solubilization by biominerals and by aggregation that was observed in our experiment may help explain the robustness of the relationship between organic and mineral matter fluxes in the deep ocean.     

Age,origin and climatic controls on vegetated linear dunes in the northwestern Negev Desert (Israel)

The stabilized northwestern (NW) Negev vegetated linear dunes (VLD) of Israel extend over 1300 km² and form the eastern end of the Northern Sinai – NW Negev Erg. This study aimed at identifying primary and subsequent dune incursions and episodes of dune elongation by investigating dune geomorphology, stratigraphy and optically stimulated luminescence (OSL) dating. Thirty-five dune and interdune exposed and drilled section were studied and sampled for sedimentological analyses and OSL dating, enabling spatial and temporal elucidation of the NW Negev dunefield evolution.In a global perspective the NW Negev dunefield is relatively young. Though sporadic sand deposition has occurred during the past 100 ka, dunes began to accumulate over large portions of the dunefield area only at ～23 ka. Three main chronostratigraphic units, corresponding to three (OSL) age clusters, were found throughout most of the dunefield, indicating three main dune mobilizations: late to post last glacial maximum (LGM) at 18–11.5 ka, late Holocene (2–0.8 ka), and modern (150–8 years). The post-LGM phase is the most extensive and it defined the current dunefield boundaries. It involved several episodes of dune incursions and damming of drainage systems. Dune advancement often occurred in rapid pulses and the orientation of VLD long axes indicates similar long-term wind directions. The late Holocene episode included partial incursion of new sand, reworking of Late Pleistocene dunes as well as limited redeposition. The modern sand movement only reactivated older dunes and did not lengthen VLDs.This aeolian record fits well with other regional aeolian sections. We suggest that sand supply and storage in Sinai was initiated by the Late Pleistocene exposure of the Nile Delta sands. Late Pleistocene winds, substantially stronger than those usually prevailing since the onset of the Holocene, are suggested to have transported the dune sands across Sinai and into the northwestern Negev.Our results demonstrate the sensitivity of vegetated linear dunes located along the (northern) fringe of the sub-tropical desert belt to climate change (i.e. wind) and sediment supply.     

Fine particulate organic matter (FPOM) transport and processing in littoral interstices – use of fluorescent markers

A fluorescent labelling method is presented as a new tool for the investigation of organic particle transport and biogenic carbon cycling processes in sandy littoral interstices at Lake Tegel, Berlin, Germany. Passive particle transport through the pore system was studied by in situ exposition of 2.4 μm monodisperse polymeric resin microparticles stained with 7-amino-4-methylcoumarin (AMC). Uptake of fluorescein-5-isothiocyanate (FITC)-labelled Chlorella vulgaris and fine particulate organic matter (FPOM) by the interstitial fauna was investigated in laboratory and field experiments. The major portion (>85%) of the FITC-labelled particles added to sediment cores was recovered from the topmost centimetre of sediment during the study period of 14 days. Uptake of FITC-labelled FPOM was observed in several benthic groups, e.g. chironomids, microcrustaceans, oligochaetes and tardigrads, whereas C. vulgaris was ingested by oligochaetes only. There is evidence to suggest that both are suitable materials for investigating the fragmentation and ingestion of organic material by herbivorous and detritivorous fauna. Field experiments with inert microparticles and FITC-labelled FPOM (<1 mm) prepared from dried alder leaves were carried out in plexiglass tubes as in situ whole core technique. Within the investigation period of two weeks, the transport of FPOM was restricted to the topmost 2–3 cm of sediment in conjunction with a distinct fragmentation to finer size classes with respect to increasing sediment depth. Vertical FPOM transport was hindered by a high interstitial concentration of natural POM and an intensive settlement of the interstices by algae (mainly epispammic algae, 65–96% of algae cell number) and extra-cellular polymeric substances (EPS), which formed a dense three-dimensional structure.