Experimental evidence for the potential impact ejection of viable microorganisms from Mars and Mars-like planets

Bacterial spores (Bacillus subtilis), cyanobacteria (Chroococcidiopsis sp.), and lichen (Xanthoria elegans) embedded in martian analogue rock (gabbro) were exposed to shock pressures between 5 and 50 GPa which is the range of pressures observed in martian meteorites. The survival of Bacillus subtilis and Xanthoria elegans up to 45 GPa and of Chroococcidiopsis sp. up to 10 GPa supports the possibility of transfer of life inside meteoroids between Mars and Earth and it implies the potential for the transfer of life from any Mars-like planet to other habitable planets in the same stellar system.     

Automated and continual determination of radio telescope reference points with sub-mm accuracy: results from a campaign at the Onsala Space Observatory

The Global Geodetic Observing System (GGOS) requires sub-mm accuracy, automated and continual determinations of the so-called local tie vectors at co-location stations. Co-location stations host instrumentation for several space geodetic techniques and the local tie surveys involve the relative geometry of the reference points of these instruments. Thus, these reference points need to be determined in a common coordinate system, which is a particular challenge for rotating equipment like radio telescopes for geodetic Very Long Baseline Interferometry. In this work we describe a concept to achieve automated and continual determinations of radio telescope reference points with sub-mm accuracy. We developed a monitoring system, including Java-based sensor communication for automated surveys, network adjustment and further data analysis. This monitoring system was tested during a monitoring campaign performed at the Onsala Space Observatory in the summer of 2012. The results obtained in this campaign show that it is possible to perform automated determination of a radio telescope reference point during normal operations of the telescope. Accuracies on the sub-mm level can be achieved, and continual determinations can be realized by repeated determinations and recursive estimation methods.     

Organic carbon mobilization in a Bangladesh aquifer explained by seasonal monsoon-driven storativity changes

Currently, the most widely accepted hypothesis to explain high As concentrations in Bangladesh groundwaters is that dissolved organic C (DOC) reduces solid Fe (hydr)oxides and mobilizes sorbed arsenate. The nature of the DOC and its release mechanism are still controversial. Based on weekly to biweekly sampling over the course of one monsoon cycle at six monitoring wells of different depths, it is proposed that storativity changes drive natural DOC release from clay–peat layers to the adjacent aquifers. With a decrease in hydraulic heads during the dry season, total mineralization and DOC concentrations increased. With the onset of the rainy season and an increase in hydraulic heads, release of clay–peat derived components stopped and vertical water displacement due to groundwater recharge from rainwater occurred, causing aquifer flushing and a decrease in total mineralization and DOC concentrations. Total As and DOC concentrations correlated over depth. However, at the depth of maximum concentrations, the As peak was observed during the rainy season. At present, the reason for this inverse seasonal trend between As and DOC is unclear. Higher mineralization or DOC concentrations could lead to increased As sorption or the increased arsenite release is a time-lag abiotic or microbial response to the DOC peak. The vulnerability of the Pleistocene aquifer towards increased As concentrations was found to be much higher than previously assumed. Though sorption capacities were determined to be higher than in the Holocene aquifer, probably due to intact Fe (hydr)oxides, long-term continuous As input from overlying clay and peat layers by the proposed seasonal storativity changes has led to increased aqueous As concentrations of 85 μg/L, considerably higher than drinking water standards. Until now, aquifer and especially aquitard and aquiclude hydraulics have not been considered sufficiently when attempting to explain As mobilization in Bangladesh.     

Plume-lithosphere interactions in the ocean basins: constraints from the source mineralogy

Trace element relationships of near-primary alkalic lavas from La Grille volcano, Grande Comore, in the Indian Ocean, as well as those of the Honolulu volcanic series, Oahu, Hawaii, show that their sources contain amphibole and/or phlogopite. Small amounts of each mineral (2% amphibole in the source of La Grille and 0.5% phlogopite plus some amphibole in the source of the Honolulu volcanics) and a range of absolute degrees of partial melting from 1 to 5% for both series are consistent with the observed trace element variation. Amphibole and phlogopite are not stable at the temperatures of convecting upper mantle or upwelling thermal plumes from the deep mantle; however, they are stable at pressure-temperature conditions of the oceanic lithospheric mantle. Therefore, the presence of amphibole and/or phlogopite in the magma source region of volcanics is strong evidence for lithospheric melting, and we conclude that the La Grille and the Honolulu series formed by melting of the oceanic lithospheric mantle.

The identification of amphibole ± phlogopite in the source region of both series implies that the metasomatism by fluids or volatile-rich melts occurred prior to melting. The presence of hydrous phases results in a lower solidus temperature of the lithospheric mantle, which can be reached by conductive heating by the thermal plumes. Isotope ratios of the La Grille and the Honolulu series display a restricted range in composition and represent compositional end-members for each island. Larger isotopic variations in shield lavas, represented by the contemporaneous Karthala volcano on Grande Comore and the older Koolau series on Oahu, reflect interaction of the upwelling thermal plumes with the lithospheric mantle rather than the heterogeneity of deep-seated mantle plume sources or entrainment of mantle material in the rising plume. Literature OsSr isotope ratio covariations constrain the process of plume-lithosphere interaction as occurring through mixing of plume melts and low-degree melts from the metasomatized oceanic lithospheric mantle.

The characterization of the lithospheric mantle signature allows the isotopic composition of the deep mantle plume components to be identified, and mixing relationships show that the Karthala and Koolau plume end-members have nearly uniform isotopic compositions. Based on independent arguments, isotopic variations on Heard and Easter islands have been shown to be a result of mixing between deep plume sources having distinct isotopic compositions with lithosphere or shallow asthenospheric mantle. To the extent that these case studies are representative of oceanic island volcanism, they indicate that interaction with oceanic lithospheric mantle plays an important role in the compositions of lavas erupted during the shield-building stage of plume magmatism, and that isotopic compositions of deep mantle plume sources are nearly uniform on the scale that they are sampled by melting.     

The influence of numerical advection schemes on the results of ocean general circulation models

The dependence of results from coarse-resolution models of the North Atlantic circulation on the numerical advection algorithm is studied. In particular, the sensitivity of parameters relevant for climate simulations as e.g., meridional transport of mass and heat and main thermocline thickness is investigated. Three algorithms were considered: (a) a central difference scheme with constant values for horizontal and vertical diffusion, (b) an upstream scheme with no explicit diffusion, and (c) a flux-corrected transport (FCT) scheme with constant and strictly isopycnal diffusion. The temporal evolution of the three models on time scales of centuries is markedly different, the upstream scheme resulting in much shorter adjustment time whereas the central difference scheme is slower and controlled by vertical diffusion rather than advection. In the steady state, the main thermocline structure is much less diffusive in the FCT calculation which also has much lower heat transport. Both horizontal circulation and overturning in the meridional-vertical plane are strongest in the upstream-model. The results are discussed in terms of the effective vertical (diapycnal) mixing in the different models. A significant increase in vertical resolution would be required to eliminate the high sensitivity due to the numerical algorithms, and allow physically motivated mixing formulations to become effective.This paper was presented at the International Conference on Modelling of Global Climate Change and Variability, held in Hamburg 11–15 September 1989 under the auspices of the Meteorological Institute of the University of Hamburg and the Max Planck Institute for Meteorology. Guest Editor for these papers is Dr. L. Dümenil     

Tracing sediment pathways by zircon fission track analysis: Oligocene marine connections in Central Europe

In this study, we use contrasting zircon fission track age signatures of Alpine detritus and detritus derived from the Variscan realm to trace sediment pathways in Central Europe. Our data show that the Molasse Basin was connected with the Rhine Graben Sea during the Mid-Oligocene, thus joining the North Sea to the Paratethys. Within the Rhine Graben Sea, fairly strong south–north directed currents existed, transporting sand-sized Alpine detritus nearly 300 km towards the north. A connection between the Rhône-Bresse Graben and the Rhine Graben and/or the French Molasse Basin and the Swiss Molasse Basin, by contrast, is not supported by the fission track data. This may be explained by the existence of submarine rises that hampered the transport of sand-sized sediment towards the north/northeast.