Sources of fluids and gases expelled at cold seeps offshore Georgia, eastern Black Sea   总被引：1，自引：0，他引：1  

Anja Reitz  Thomas Pape  Mark Schmidt  Florian Scholz  Giovanni Aloisi  Stephan M. Weise 《Geochimica et cosmochimica acta》2011,75(11):3250-46

Four seep sites located within an ∼20 km² area offshore Georgia (Batumi seep area, Pechori Mound, Iberia Mound, and Colkheti Seep) show characteristic differences with respect to element concentrations, and oxygen, hydrogen, strontium, and chlorine isotope signatures in pore waters, as well as impregnation of sediments with petroleum and hydrocarbon potential. All seep sites have active gas seepage, near surface authigenic carbonates and gas hydrates. Cokheti Seep, Iberia Mound, and Pechori Mound are characterized by oil-stained sediments and gas seepage decoupled from deep fluid advection and bottom water intrusion induced by gas bubble release. Pechori Mound is further characterized by deep fluid advection of lower salinity pore fluids. The Pechori Mound pore fluids are altered by mineral/water reactions at elevated temperatures (between 60 and 110 °C) indicated by heavier oxygen and lighter chlorine isotope values, distinct Li and B enrichment, and K depletion. Strontium isotope ratios indicate that fluids originate from late Oligocene strata. This finding is supported by the occurrence of hydrocarbon impregnations within the sediments. Furthermore, light hydrocarbons and high molecular weight impregnates indicate a predominant thermogenic origin for the gas and oil at Pechori Mound, Iberia Mound, and Colkheti Seep. C₁₅₊ hydrocarbons at the oil seeps are allochtonous, whereas those at the Batumi seep area are autochthonous. The presence of oleanane, an angiosperm biomarker, suggests that the hydrocarbon source rocks belong to the Maikopian Formation. In summary, all investigated seep sites show a high hydrocarbon potential and hydrocarbons of Iberia Mound, Colkheti Seep, and Pechori Mound are predominantly of thermogenic origin. However, only at the latter seep site advection of deep pore fluids is indicated.  相似文献   

Use of sedimentary diatoms from multiple lakes to distinguish between past changes in trophic state and climate: evidence for climate change in northern Germany during the past 5,000 years     

Mirko Dreßler  Anja Schwarz  Thomas Hübener  Sven Adler  Burkhard W. Scharf 《Journal of Paleolimnology》2011,45(2):223-241

Fossil diatoms from lake sediments have been used to infer both past trophic state and climate conditions. In Europe, climate reconstructions focused on northern and alpine regions because these areas are climatically sensitive and anthropogenic impact was low. In contrast, anthropogenic impact was often high in the central European lowlands, such as northern Germany, beginning in the Neolithic Age, ~3700 BC. Since that time, trophic state change was the main factor that affected diatom assemblages in central European lowland lakes. Therefore, it was considered difficult or impossible to identify climate changes in the region using sedimented diatoms. We used diatom assemblage changes, diatom-inferred total phosphorus concentrations and the relative abundance of planktonic diatoms from sediments of three lakes that differ in their location, size, morphology, catchment area and current trophic state to test whether we could distinguish between trophic state and climate signals over the past 5,000 years in northern Germany. In this study, changes in trophic state and climate were well differentiated. In the study lakes, relative abundance of planktonic diatoms seems to be linked to the length of lake mixing phases. Planktonic diatom abundance decreased during years with shorter mixing duration, and these shorter mixing times probably reflect colder winters. The diatom-inferred periods of short mixing phases from 1000 BC to AD 500 and from AD 1300 to 1800 coincide well with two known cooling phases in Europe and the North Atlantic region.  相似文献   

A Comparison of the Sequential Gaussian and Markov-Bayes Simulation Methods for Small Samples     

Anja Kannengieser Fredericks  Ken B. Newman 《Mathematical Geology》1998,30(8):1011-1032

We compared the performance of sequential Gaussian simulation (sGs) and Markov-Bayes simulation (MBs) using relatively small samples taken from synthetic datasets. A moderate correlation (approximately r = 0.70) existed between a continuous primary variable and a continuous secondary variable. Given the small sample sizes, our objective was to determine whether MBs, with its ability to incorporate the secondary information, would prove superior to SgS. A split-split-plot computer experiment was conducted to compare the two simulation methods over a variety of primary and secondary sample sizes as well as spatial correlations. Using average mean square prediction error as a measure of local performance, sGs and MBs were roughly equivalent for random fields with short ranges (2 m). As range increased (15 m) the average mean square prediction error for sGs was less than or equal to that for MBs, even when number of noncollocated secondary observations was twice the number of collocated observations. Median variance within nonoverlapping subregions was used as a measure of the local heterogeneity or surface texture of the image. In most situations sGs images more faithfully reflected the true local heterogeneity, while MBs was more erratic, sometimes oversmoothing and sometimes undersmoothing.  相似文献   

Spatio‐temporal variability of zooplankton biomass and environmental control in the Northern Benguela Upwelling System: field investigations and model simulation          下载免费PDF全文

Bettina Martin  Anja Eggert  Rolf Koppelmann  Rabea Diekmann  Volker Mohrholz  Martin Schmidt 《Marine Ecology》2015,36(3):637-658

Spatial and temporal distribution patterns of zooplankton are highly variable in the Northern Benguela Upwelling System. We studied the distribution of zooplankton (size class ≥ 0.33 mm) and used field data from four cruises that took place between March 2008 and February 2011, as well as simulation results of a regional ecosystem model. Remotely sensed sea surface temperatures (SST) and surface chlorophyll concentrations were analysed to investigate environmental influences on zooplankton biomass. The Intense Benguela Upwelling Index showed a distinct seasonal signal throughout the years and the highest upwelling peaks in August/September. Even though surface chlorophyll concentrations were very variable throughout the year, the highest concentrations were always detected in September, following the upwelling of nutrient‐rich water. In field catches, zooplankton biomass concentration in the upper 200 m was highest above the outer shelf and shelf‐break in December 2010 and February 2011, i.e. 6 months after the upwelling peaks. In contrast, zooplankton biomass simulated by the model in the surface water was highest in September. In March/April, biomass maxima were typically measured in the field at intermediate water depths, but the vertical distribution was also affected by extensive oxygen minimum zones. The ecosystem model reproduced this vertical pattern. Although general trends were similar, simulation data of zooplankton standing stocks overestimated the field data by a factor of 3. In upwelling systems, food webs are generally considered to be short and dominated by large cells. However, our field data indicate more small‐sized zooplankton organisms above the shelf than offshore.  相似文献   

Major and trace element geochemistry of superficial sediments and suspended particulate matter of shallow saline lakes in Eastern Austria     

Anja Stojanovic  Daniel Kogelnig  Dieter Mader  Rudolf Krachler 《Chemie der Erde / Geochemistry》2009,69(3):223-234

General geochemical parameters of water, superficial sediments, and suspended particulate matter (SPM) were determined from small shallow saline lakes (soda ponds) as well as from lake Neusiedlersee in eastern Austria. Additionally, instrumental neutron activation analysis (INAA) was used to determine the distribution of major, rare earth and other trace elements in superficial sediments and SPM. Chemical results show remarkable differences in salinity and ionic strength between the investigated ponds. Anthropogenic effects, such as drawdown of ground water level and a loss of lake water due to drainage, are clearly reflected in obtained chemical and geological data. Due to a strong dependence of the complexation and scavenging behavior of the rare earth elements (REE) on ionic strength, a significant difference between REE concentrations in soda ponds with different anthropogenic impact was found. The content and composition of authigenic evaporitic minerals in superficial sediments and SPM clearly differ with a fluctuating water level and salt concentration. Furthermore, we determined the distribution of major and trace elements in superficial sediments of a nearby fluvial system. Our results show a clear correlation between REE superficial sediment concentrations in anthropogenically degraded soda ponds and fluvial system. Therefore, we assume that REE concentrations of sediments and SPM are suitable for the study of geochemical changes of inland saline lakes due to anthropogenic impacts on water balance.  相似文献   

Variations in the characteristics of cyclonic activity and cloudiness in the atmosphere of extratropical latitudes of the Northern Hemisphere based from model calculations compared with the data of the reanalysis and satellite data     

I. I. Mokhov  A. V. Chernokul’skii  M. G. Akperov  J. -L. Dufresne  H. Le Treut 《Doklady Earth Sciences》2009,424(1):147-150

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The Chemical Evolution of the Universe on its Smallest Scales: Dust in Stars,Disks and Planets     

Christiane Helling  Jane Greaves  Anja C. Andersen 《Astronomische Nachrichten》2007,328(7):645-660

D15 Dust and gas in the inner accretion disk around the Herbig star MWC 147 resolved with infrared spectro‐interferometry D21 The effective temperature of OGLE‐TR‐10 – The Balmer α line D29 Metal Injection into the Intracluster Medium D30 Eigenmodes of circumstellar dust shells D40 Numerical Modelling Approach of Circumstellar Dust Shells Around Pulsating AGB Stars Aiming at Multi Time Scale Processes D45 UV radiation induced CO molecule formation patterns in low density PDRs D46 IR properties of calcite and dolomite at low temperatures D47 Observations and Models of Dusty Giants – Past and Present D51 A multi‐method approach to the outer layers of AGB stars D53 On the convective energy transport in M‐type brown dwarf atmospheres D70 Structure and Dust Composition of the TW Hya Disc D75 Chemical Abundances in the Carina Dwarf Spheroidal Galaxy D76 Kinematic and chemical constraints on the formation of M31's inner halo structures D77 IR band profiles of silicate and oxide dust obtained by laboratory measurements of free‐flying particles D98 Dust particle growth in protoplanetary disks D134 Comparative study of dust cloud modelling for substellar atmospheres D137 Photometric study of neglected binary DV Psc D154 Quantitative Spectroscopy of Deneb D160 Hot subluminous Ostars from the SDSS D166 Simultaneous Observations of Solar Ca II H and Ca II 8662 lines and Numerical Simulation of these lines D182 Present‐day carbon abundances in the solar vicinity D189 Detection of a giant planet around a pulsating extreme horizontal branch star: the oldest known planet? D200 Confirmation of a very young binary brown dwarf candidate with disk in Chamaeleon D208 Galaxy ages and metallicities in the cluster A1314 D217 Charge‐dipole induced dust gelation – fastening the process of dust growth in protoplanetary disks D246 Protoplanetary Disk Structure and Evolution  相似文献   

Late Holocene tsunami traces on the western and southern coastlines of the Peloponnesus (Greece)   总被引：1，自引：0，他引：1  

Anja Scheffers  Dieter Kelletat  Andreas Vtt  Simon Matthias May  Sander Scheffers 《Earth and Planetary Science Letters》2008,269(1-2):271-279

Greece, in particular the western and southern parts close to the subduction zone of the Hellenic Trench, experiences strong earthquakes and subsequent tsunamis. Nevertheless, field evidence of tsunamis from the late Holocene is extremely rare. Our research along the coastlines of the western and southern Peloponnesus resulted in new findings of tsunami impacts in the form of clusters and ridges of large boulders and thick tsunamigenic sand layers encountered in vibracores. Many boulders contained attached marine organisms, which prove that they were transported from the foreshore environment against gravity by extreme wave events. The attached organisms, which have been dated by ¹⁴C-AMS, suggest that historical tsunami events of great energy occurred around 1300 cal AD. A wood fragment found at the base of tsunami deposits in a vibracore from Cape Punta was dated to ~ 250 cal AD.  相似文献   

Coarse clast ridge sequences as suitable archives for past storm events? Case study on the Houtman Abrolhos,Western Australia     

Anja M. Scheffers  Sander R. Scheffers  Dieter H. Kelletat  Peter Squire  Lindsay Collins  Yuexing Feng  Jian‐Xin Zhao  Renaud Joannes‐Boyau  Simon Matthias May  Gerhard Schellmann  Heather Freeman 《第四纪科学杂志》2012,27(7):713-724

Prehistoric storm records are relatively scarce in most parts of the world. This article presents storm records derived from coral rubble‐based geological archives of the Houtman Abrolhos Archipelago located off the west coast of Australia, where the southernmost coral reefs of the Indian Ocean are found. Winter storm swell from the circum‐Antarctic ‘Brave Westerlies’, as well as tropical cyclone waves, have left numerous ridge systems on dozens of islands of the archipelago, all composed of coral rubble from adjacent reefs. At three islands, seven ridge systems were dated by three different methods: U‐series (68 dates), radiocarbon (64 dates), electron spin resonance (7 dates); 139 radiometric dates span the last 5500 years of the Holocene. In contrast to the geomorphological interpretation, the age sequences show ‘inversions’, hiatuses and different ages for the same ridge, all pointing to complicated ridge formation processes. Time gaps, some exceeding 1000 years, are interpreted as phases of erosion and not as phases without storm activity. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Traces of historical tropical cyclones and tsunamis in the Ashburton Delta (north‐west Australia)          下载免费PDF全文

Simon Matthias May  Dominik Brill  Max Engel  Anja Scheffers  Anna Pint  Stephan Opitz  Volker Wennrich  Peter Squire  Dieter Kelletat  Helmut Brückner 《Sedimentology》2015,62(6):1546-1572

Although the north‐western coast of Western Australia is highly vulnerable to tropical cyclones and tsunamis, little is known about the geological imprint of historic and prehistoric extreme wave events in this particular area. Despite a number of site‐specific difficulties such as post‐depositional changes and the preservation potential of event deposits, both tropical cyclones and tsunamis may be inferred from the geomorphology and the stratigraphy of beach ridge sequences, washover fans and coastal lagoons or marshes. A further challenge is the differentiation between tsunami and storm deposits in the geological record, particularly where modern deposits and/or historical reports on the event are not available. This study presents a high‐resolution sedimentary record of washover events from the Ashburton River delta (Western Australia) spanning approximately the last 150 years. A detailed characterization of event deposits is provided, and a robust chronostratigraphy for the investigated washover sequence is established based on multi‐proxy sediment analyses and optically stimulated luminescence dating. Combining sedimentological, geochemical and high‐resolution optically stimulated luminescence data, event layers are assigned to known historical events and tropical cyclone deposits are separated from tsunami deposits. For the first time, the 1883 Krakatoa and 1977 Sumba tsunamis are inferred from sedimentary records of the north‐western part of Western Australia. It is demonstrated that optically stimulated luminescence applied in coastal sedimentary archives with favourable luminescence characteristics can provide accurate chronostratigraphies even on a decadal timescale. The results contribute to the data pool of tropical cyclone and tsunami deposits in Holocene stratigraphies; however, they also demonstrate how short‐lived sediment archives may be in dynamic sedimentary environments.  相似文献