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41.
Cornelia Iulia Blaga Gert-Jan Reichart Oliver Heiri Jaap S. Sinninghe Damsté 《Journal of Paleolimnology》2009,41(3):523-540
We studied the distribution of glycerol dialkyl glycerol tetraethers (GDGTs) in water-column particulate matter and the top
5 cm of sediment from 47 lakes along a transect from southern Italy to the northern part of Scandinavia. Our objective was
to investigate the biological sources and potential palaeoenvironmental applications of GDGTs in lacustrine sediments. Both
archaea-derived isoprenoid and bacteria-derived branched GDGTs, produced by yet unknown soil bacteria, were identified in
all lake sediments. GDGT distributions varied substantially. Crenarchaeotal GDGTs, including the characteristic GDGT crenarchaeol,
were found in varying relative concentrations, and were more dominant in lakes from the Alps and some of the lakes from the
more southern part of the latitudinal transect. In some lakes, we observed high amounts of the GDGT with no cyclopentane moieties
relative to crenarchaeol. As methanogenic Euryarchaeota are known to biosynthesise this GDGT predominantly, these Archaea,
rather than Crenarchaeota, may be its dominant biological source. In most of the lakes, high amounts of soil-bacteria-derived,
branched GDGTs (>40% of total GDGTs) indicated a substantial contribution from soil erosion. Branched GDGTs dominated, especially
in the northern lakes, possibly related to high soil-erosion rates. In many of the lakes, soil input affects the distribution
of isoprenoidal GDGTs and prevents the reliable application of the TEX86 temperature proxy for lake water temperature, which is based on in situ crenarchaeotal GDGTs production. In 9 out of the
47 lakes studied, the TEX86 temperature proxy could be used reliably. When we compared the TEX86 correlation with annual and winter lake-surface temperature, respectively, the relationship between TEX86 and winter temperature was slightly stronger. This may indicate the season in which these GDGT-producing organisms have their
peak production. 相似文献
42.
High precision trace element data obtained by inductively coupled plasma mass spectrometry and Sr–Nd isotope analyses are presented for mafic volcanic rocks from Gough Island, South Atlantic. The new data reveal negative Ce anomalies, with Ce/Ce? values in Gough lavas extending down to ～ 0.92. Ce is only fractionated from other rare earth elements (REE) due to formation of Ce4+ under oxidizing conditions of near-surface environments while other REE remain trivalent. Ce anomalies in convergent margin magmas have been shown to indicate a contribution of a subducted sediment component. In contrast, Ce anomalies in intra-plate basalts have been attributed to weathering processes, but can be excluded here based on element–element systematics indicating magmatic trends rather than weathering-induced element mobility. Shallow-level contamination by local marine sediments with negative Ce anomaly inherited from seawater can be excluded because Gough lavas with increasingly negative Ce anomalies do not trend towards low Ce/Pb ratios characterizing such sediments. Rather, it is argued that the negative Ce anomalies in Gough Island lavas are consistent with variable amounts of a sediment component in the mantle plume source. Mixtures between estimates of subducting sediment columns with negative Ce anomaly and mantle capable of giving rise to Gough Island magmas without Ce anomalies reproduce the Gough compositional array with the exception of highly fluid-mobile elements. The calculated trace element composition of the deeply recycled sediment in the Gough plume source is depleted in fluid-mobile elements such as Ba and Pb relative to the composition of some present-day subducting sediments. This loss is attributed to the dehydration or flushing of sediment in the subduction factory, consistent with constraints from arc magmas. 相似文献
43.
某些大洋玄武岩具有异常的同位素特征,不同于同一空间的地幔羽但却是古老的大陆岩石圈地幔（如Hawkesworth等,1986）或古老的下陆壳（Kamenetsky等,2001）的典型特征。这些异常组分被认为是大陆开裂期间分离出来并被运移到大洋地幔浅处的岩石圈物质。羽状物的热侵蚀和裂谷作用导致的构造分离都被认为是可能的分离过程, 相似文献
44.
We investigate the response of the Nordic seas-Arctic Ocean system to surface freshwater flux anomalies that we regard as typical for long-term atmospheric variability. We employ response experiments with a coupled sea ice-ocean model where we introduce a surface freshwater flux anomaly (A) over the Norwegian Sea and (B) in the Laptev Sea. Case A offers an explanation for the intermediate depth salinity changes observed in the Amundsen Basin. The signal observed there belongs to an original perturbation that, according to the model, occurred around a decade earlier. Salinity fluctuations in the Laptev Sea could play a role in changes in the near surface salinity in the Amundsen Basin. 相似文献
45.
Northern Svalbard represents a basement high surrounded by the Norwegian‐Greenland Sea/Fram Strait, Eurasian Basin, the Barents Shelf and the onshore Central Tertiary Basin (CTB). Published apatite fission track (AFT) data indicate Mesozoic differential, fault‐controlled uplift and exhumation of the region. Thermal history modelling of published and new AFT and (U–Th–Sm)/He ages of 51–153 Ma in the context of regional stratigraphy and geomorphology implies at least two, possibly three, uplift and exhumation stages since late Mesozoic, separated by episodes of subsidence and sediment deposition. Late Cretaceous/Palaeocene exhumation and subsequent burial appear to be related with the transition of compressional to transpressional collision of Svalbard and Greenland during the Eurekan Orogeny. Renewed exhumation since the Oligocene probably results from passive margin formation after the separation of Svalbard and Greenland, when a new offshore sedimentary basin opened west of Svalbard. Final uplift since the Miocene eventually re‐exposed the palaeosurface of northern Svalbard. 相似文献
46.
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. 相似文献
47.
Cornelia I. Blaga Gert-Jan Reichart André F. Lotter Jaap S. Sinninghe Damsté 《Geochimica et cosmochimica acta》2011,75(21):6416-6428
To determine where and when glycerol dialkyl glycerol tetraether (GDGT) membrane lipids in lakes are produced, we collected descending particles in Lake Lucerne (Switzerland) using two sediment traps (at 42 and 72 m water depth) with a monthly resolution from January 2008 to late March 2009. Suspended particulate matter (SPM) was monthly filtered from the water column at three different depths. The potential application of GDGTs in palaeoenvironmental and palaeoclimatic reconstructions was investigated by comparing core lipids and their relative GDGT distribution, with lake water temperatures throughout the year. Fluxes of GDGTs and their concentrations in the water column vary according to a seasonal pattern, showing a similar trend in the SPM and sediment traps. Fluxes and concentrations of isoprenoid GDGTs increase with depth, maximum values being observed in the deeper part of the water column, indicating production of isoprenoid GDGTs by Thaumarchaeota in the deep (∼50 m), aphotic zone of Lake Lucerne. The flux-weighted averages of the proxies TEX86 (0.27) and BIT (0.03) based on the total extracted GDGTs are similar at both trap depths. A sediment core from the same location showed that in the first few centimetres of the core TEX86 and BIT values of 0.29 and 0.07, respectively, are similar to those recorded for descending particles and SPM, indicating that the sedimentary TEX86 records the annual mean temperature of deeper waters in Lake Lucerne. TEX86 values are slightly higher below 20 cm in the core. This offset is interpreted to be caused by the present-day trophic state of the lake, which probably resulted in a deeper niche of the Thaumarchaeota. Branched GDGTs represent only a minor fraction of the total GDGTs in the lake and their origin remains unclear. Our data reveal that GDGTs in lakes have a large potential for palaeoclimatic studies but indicate that knowledge of the system is important for accurate interpretation. 相似文献
48.
Sergey Oladyshkin Holger Class Rainer Helmig Wolfgang Nowak 《Computational Geosciences》2011,15(3):565-577
CO2 storage in geological formations is currently being discussed intensively as a technology with a high potential for mitigating
CO2 emissions. However, any large-scale application requires a thorough analysis of the potential risks. Current numerical simulation
models are too expensive for probabilistic risk analysis or stochastic approaches based on a brute-force approach of repeated
simulation. Even single deterministic simulations may require parallel high-performance computing. The multiphase flow processes
involved are too non-linear for quasi-linear error propagation and other simplified stochastic tools. As an alternative approach,
we propose a massive stochastic model reduction based on the probabilistic collocation method. The model response is projected
onto a higher-order orthogonal basis of polynomials to approximate dependence on uncertain parameters (porosity, permeability,
etc.) and design parameters (injection rate, depth, etc.). This allows for a non-linear propagation of model uncertainty affecting
the predicted risk, ensures fast computation, and provides a powerful tool for combining design variables and uncertain variables
into one approach based on an integrative response surface. Thus, the design task of finding optimal injection regimes explicitly
includes uncertainty, which leads to robust designs with a minimum failure probability. We validate our proposed stochastic
approach by Monte Carlo simulation using a common 3D benchmark problem (Class et al., Comput Geosci 13:451–467, 2009). A reasonable compromise between computational efforts and precision was reached already with second-order polynomials.
In our case study, the proposed approach yields a significant computational speed-up by a factor of 100 compared with the
Monte Carlo evaluation. We demonstrate that, due to the non-linearity of the flow and transport processes during CO2 injection, including uncertainty in the analysis leads to a systematic and significant shift of the predicted leakage rates
toward higher values compared with deterministic simulations, affecting both risk estimates and the design of injection scenarios. 相似文献
49.
50.
Dieter Stöffler Gerda Horneck Sieglinde Ott Ulrich Hornemann Charles S. Cockell Ralf Moeller Cornelia Meyer Jean-Pierre de Vera Jörg Fritz Natalia A. Artemieva 《Icarus》2007,186(2):585-588
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. 相似文献