Clumped-isotope geochemistry of carbonates: A new tool for the reconstruction of temperature and oxygen isotope composition of seawater     

Stefano M. Bernasconi  Thomas W. Schmid  Anna-Lena Grauel  Joerg Mutterlose 《Applied Geochemistry》2011

Clumped-isotope geochemistry deals with the state of ordering of rare isotopes in molecules, in particular with their tendency to form bonds with other rare isotopes rather than with the most abundant ones. Among its possible applications, carbonate clumped-isotope thermometry is the one that has gained most attention because of the wide potential of applications in many disciplines of the earth sciences. In particular, it allows reconstructing the temperature of formation of carbonate minerals without knowledge of the isotopic composition of the water from which they were formed. In addition, the O isotope composition of the waters from which they were formed can be calculated using the δ¹⁸O of the same carbonate sample. This feature offers new approaches in paleoclimatology for reconstructing past global geochemical cycles. In this contribution two applications of this method are presented. First the potential of a new analytical method of measurement of clumped isotopes on small samples of foraminifera, for high-resolution SST and seawater δ¹⁸O reconstructions from marine sediments is shown. Furthermore the potential of clumped isotope analysis of belemnites, for reconstructing seawater δ¹⁸O and temperatures in the Cretaceous is shown.  相似文献   

Climate change effects on snow melt and discharge of a partly glacierized watershed in Central Switzerland (SoilTrec Critical Zone Observatory)     

Florian Kobierska  Tobias Jonas  Jan Magnusson  Massimiliano Zappa  Mathias Bavay  Thomas Bosshard  Frank Paul  Stefano M. Bernasconi 《Applied Geochemistry》2011

A comprehensive hydrological modeling study in the drainage area of a hydropower reservoir in central Switzerland is presented. Two models were tested to reproduce the measured discharge dynamics: (1) a detailed energy-balance model (ALPINE3D) primarily designed for snow simulations; (2) a conceptual runoff model system (PREVAH), including a distributed temperature-index snow and ice melt model. Considerable effort was put into distributing available meteorological station data to the model grids as forcing data. The recent EU regional climate modeling initiative ENSEMBLES provided up-to-date climate predictions for two 30-a periods in mid and late 21st century. These were used to estimate evolutions in the water supply of the hydropower reservoir in response to expected climate changes. The simulations suggest a shift of spring peak-flow by almost two months for the end of the century. Warmer winter temperatures will cause higher winter base-flow. Due to glacier retreat, late-summer flow will decrease at the end of the century.  相似文献   

Geological comparison of precambrian and early palaeozoic terrains between the Southern West Coast of Africa and the South-East Coast of South America     

A. Bernasconi 《Precambrian Research》1983,23(1):9-31

This paper describes a geological comparison of similar lithostratigraphic sequences of Proterozoic and early Palaeozoic ages between the southern west coast of Africa (Namibia and South Africa) and the south-east coast of South America (Brazil and Uruguay). The oldest terrains present within the compared regions are those comprising the Rio de la Plata and the Richtersveld Provinces of ~ 2000 Ma. Both provinces appear to have evolved from earlier Archaean terrains, i.e., the Guapore Craton in South America and the Kalahari Craton in southern Africa, during the Transamazonic and Eburnian orogenic cycles, respectively. Both the Namaqua Province, affected by the Kibaran orogenesis at ~ 1200 Ma, and the Sinclair Group of 1300 Ma seem to have no comparable geological counterparts in southern Brazil and Uruguay.The late Precambrian—early Palaeozoic successions of the Gariep and Ribeira belts investigated here seem to be remarkably similar and it is suggested that they were parts of the same geological unit, i.e., a mobile belt, developed during the Pan-African-Brasil- iano orogenesis. Geological comparisons are particularly good between the Gariep, Porongos and Lavalleja Groups, and stratigraphic correlations can be successfully at- tempted even between geological formations, i.e., Marica, Piedra de Afilar and Stink- fontein Formations.The lack of detailed geological maps for South America makes it difficult to separate different geological formations from broad lithostratigraphic successions and, consequent- ly, comparisons can only be drawn between subgroups and several geological formations, i.e., Vacacai and Minas Subgroups with Grootderm Holgat and Oranjemund Formations. The extensive magmatic activity generated during the Brasiliano orogenesis and only present in the south-east coast of South America has not affected the southern west coast of Africa. However, two post-tectonic complexes, i.e., the Kuboos—Bremen line of intrusives and the Sierra de Animas Complex appear to be geochronologically analogous and petrologically they seem to have certain similarities. It is also suggested that the Camaqua Group in southern Brazil and the Nama Group could perhaps have certain similarities within their lithological successions and their ages may be also com- parable.The late stages of the geological evolution of the basin, represented by molassic sediments, are only present in south-east Brazil. Finally an interpretation is given of the geological evolution of the Proterozoic—early Palaeozoic terrains compared in this work.  相似文献   

The Archaean terranes of central eastern Brazil: a review     

A. Bernasconi 《Precambrian Research》1983,23(2):107-131

This paper compiles and describes several lithostratigraphic sequences which have characteristics typical of granite-greenstone and granite-gneiss terranes. The Archaean high-grade metamorphic assemblages are also described and are considered to form part of the mobile belt areas. Three major Archaean domains appear to be present in central eastern Brazil, i.e., the São Francisco Craton and the Jequié and Goiás Mobile Belts. In addition, several other small, but no less important, ancient nuclei occur within the Tocantins Province, especially in central Goiás.The São Francisco Craton is mostly covered by thick platform sequences of Proterozoic age, and as a result it can be examined only around the margins where granite-greenstone terranes are partially exposed. There appears to be sufficient evidence to recognise a stable Archaean basement domain, except in the northeast where the craton has been largely affected by the Transamazonian cycle (2.2-1.8 Ga) and, therefore, may represent a separate province. The available data for the Jequié and Goiás belts suggest that these domains have been subjected to high-grade regional metamorphism, chiefly granulite facies, during the Jequié tectono-thermal event of ～2.7 Ga, equivalent to the Liberia-Limpopo events in Africa. The differentiated mafic to ultramafic complexes of central Goiás, of uncertain age, may also be related to the evolution of the Goiás Mobile Belt.In general, the Archaean terranes described here appear to display a rather fragmentary pattern with poorly defined boundaries due to substantial reworking, which makes them partially different from better preserved, major ancient domains in other continents.  相似文献   

Environmental changes and carbon cycle perturbations at the Triassic–Jurassic boundary in northern Switzerland     

Nathan Looser  Elke Schneebeli-Hermann  Heinz Furrer  Thomas M. Blattmann  Stefano M. Bernasconi 《Swiss Journal of Geoscience》2018,111(3):445-460

The Triassic–Jurassic boundary is characterized by strong perturbations of the global carbon cycle, triggered by massive volcanic eruptions related to the onset of the Central Atlantic Magmatic Province. These perturbations are recorded by negative carbon isotope excursions (CIEs) which have been reported worldwide. In this study, Triassic–Jurassic boundary sections from the southern margin of the Central European Basin (CEB) located in northern Switzerland are analyzed for organic carbon and nitrogen isotopes in combination with particulate organic matter (POM) analyses. We reconstruct the evolution of the depositional environment from Late Triassic to Early Jurassic in northern Switzerland and show that observed negative shifts in δ¹³C of the total organic carbon (δ¹³C_TOC) in the sediment are only subordinately influenced by varying organic matter (OM) composition and primarily reflect global changes in the carbon cycle. Based on palynology and the stratigraphic positions of isotopic shifts, the δ¹³C_TOC record of the studied sections is correlated with the GSSP section at Kuhjoch (Tethyan realm) in Austria and with the St. Audrie’s Bay section (CEB realm) in southwest England. We also show that in contrast to POM analyses the applicability of organic carbon/total nitrogen (OC/TN) atomic ratios and stable isotopes of total nitrogen (δ¹⁵N_TN) for detecting changes in source of OM is limited in marginal depositional environments with frequent changes in lithology and OM contents.  相似文献   

Coastal margin evolution and postulated “basin‐shipyard” area at ancient Locri‐Epizephiri,Calabria, Italy     

Maria Pia Bernasconi  Jean‐Daniel Stanley 《Geoarchaeology》2011,26(1):33-60

Environmental settings on the Ionian coastal plain and inner shelf seaward of Locri‐Epizephiri in Calabria, Italy, differed markedly before, during, and following settlement by the Greeks. Sediment core analyses and geophysical surveys in this study support recent archaeological findings and the hypothesis that the margin may once have served as a harbor and/or shipyard. The subsurface Holocene stratigraphy records that (1) the shoreline advanced to a maximum landward position before Greek settlement, then regressed offshore to what is now the inner shelf before once again migrating landward. These marked coastal shifts were triggered primarily by land uplift and probable subsidence offshore along this structurally active Calabrian Arc segment. Associated with this are: (2) a sediment fining‐upward sequence in Greek–Roman time that indicates only partial protection of the coastal area, and (3) possible presence of subsurface structures seaward of the city wall in a sector now positioned ∼200 m offshore. © 2010 Wiley Periodicals, Inc.  相似文献   

Computer Vision for the Solar Dynamics Observatory (SDO)     

P. C. H. Martens  G. D. R. Attrill  A. R. Davey  A. Engell  S. Farid  P. C. Grigis  J. Kasper  K. Korreck  S. H. Saar  A. Savcheva  Y. Su  P. Testa  M. Wills-Davey  P. N. Bernasconi  N.-E. Raouafi  V. A. Delouille  J. F. Hochedez  J. W. Cirtain  C. E. DeForest  R. A. Angryk  I. De Moortel  T. Wiegelmann  M. K. Georgoulis  R. T. J. McAteer  R. P. Timmons 《Solar physics》2012,275(1-2):79-113

In Fall 2008 NASA selected a large international consortium to produce a comprehensive automated feature-recognition system for the Solar Dynamics Observatory (SDO). The SDO data that we consider are all of the Atmospheric Imaging Assembly (AIA) images plus surface magnetic-field images from the Helioseismic and Magnetic Imager (HMI). We produce robust, very efficient, professionally coded software modules that can keep up with the SDO data stream and detect, trace, and analyze numerous phenomena, including flares, sigmoids, filaments, coronal dimmings, polarity inversion lines, sunspots, X-ray bright points, active regions, coronal holes, EIT waves, coronal mass ejections (CMEs), coronal oscillations, and jets. We also track the emergence and evolution of magnetic elements down to the smallest detectable features and will provide at least four full-disk, nonlinear, force-free magnetic field extrapolations per day. The detection of CMEs and filaments is accomplished with Solar and Heliospheric Observatory (SOHO)/Large Angle and Spectrometric Coronagraph (LASCO) and ground-based Hα data, respectively. A?completely new software element is a trainable feature-detection module based on a generalized image-classification algorithm. Such a trainable module can be used to find features that have not yet been discovered (as, for example, sigmoids were in the pre-Yohkoh era). Our codes will produce entries in the Heliophysics Events Knowledgebase (HEK) as well as produce complete catalogs for results that are too numerous for inclusion in the HEK, such as the X-ray bright-point metadata. This will permit users to locate data on individual events as well as carry out statistical studies on large numbers of events, using the interface provided by the Virtual Solar Observatory. The operations concept for our computer vision system is that the data will be analyzed in near real time as soon as they arrive at the SDO Joint Science Operations Center and have undergone basic processing. This will allow the system to produce timely space-weather alerts and to guide the selection and production of quicklook images and movies, in addition to its prime mission of enabling solar science. We briefly describe the complex and unique data-processing pipeline, consisting of the hardware and control software required to handle the SDO data stream and accommodate the computer-vision modules, which has been set up at the Lockheed-Martin Space Astrophysics Laboratory (LMSAL), with an identical copy at the Smithsonian Astrophysical Observatory (SAO).  相似文献   

Diatom-inferred late Pleistocene and Holocene palaeolimnological changes in the Ioannina basin, northwest Greece     

Timothy D. Jones  Ian T. Lawson  Jane M. Reed  Graham P. Wilson  Melanie J. Leng  Merle Gierga  Stefano M. Bernasconi  Rienk H. Smittenberg  Irka Hajdas  Charlotte L. Bryant  P. C. Tzedakis 《Journal of Paleolimnology》2013,49(2):185-204

The character and impact of climate change since the last glacial maximum (LGM) in the eastern Mediterranean region remain poorly understood. Here, two new diatom records from the Ioannina basin in northwest Greece are presented alongside a pre-existing record and used to infer past changes in lake level, a proxy for the balance between precipitation and evaporation. Comparison of the three records indicates that lake-level fluctuations were the dominant driver of diatom assemblage composition change, whereas productivity variations had a secondary role. The reconstruction indicates low lake levels during the LGM. Late glacial lake deepening was underway by 15.0 cal kyr BP, implying that the climate was becoming wetter. During the Younger Dryas stadial, a lake-level decline is recorded, indicating arid climatic conditions. Lake Ioannina deepened rapidly in the early Holocene, but long-term lake-level decline commenced around 7.0 cal kyr BP. The pattern of lake-level change is broadly consistent with an existing lake-level reconstruction at Lake Xinias, central Greece. The timing of the apparent change, however, is different, with delayed early Holocene deepening at Xinias. This offset is attributed to uncertainties in the age models, and the position of Xinias in the rain shadow of the Pindus Mountains.  相似文献   

A multi‐method field experiment to determine local groundwater flow in a glacier forefield          下载免费PDF全文

Florian Kobierska  Tobias Jonas  Nena Griessinger  Christian Hauck  Stephan Huxol  Stefano M. Bernasconi 《水文研究》2015,29(6):817-827

We implemented multiple independent field techniques to determine the direction and velocity of groundwater flow at a specific stream reach in a glacier forefield. Time‐lapse experiments were conducted using two electrical resistivity tomography (ERT) lines installed in a cross pattern. A circular array of groundwater tubes was also installed to monitor groundwater flow via discrete salt injections. Both inter‐borehole and ERT results confirmed this stream section as a losing reach and enabled quantification of the flow direction. Both techniques yielded advection velocities varying between 5.7 and 21.8 m/day. Estimates of groundwater flow direction and velocity indicated that groundwater infiltrates from the stream nearby and not from the adjacent lateral moraine. Groundwater age estimated from radon concentration measurements supported this hypothesis. Despite uncertainties inherent to each of the methods deployed, the combination of multiple field techniques allowed drawing consistent conclusions about local groundwater flow. We thus regard our multi‐method approach as a reliable way to characterize the two‐dimensional groundwater flow at sites where more invasive groundwater investigation techniques are difficult to carry out and local heterogeneities can make single measurements unreliable. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Functional measures and food webs of high elevation springs in the Swiss alps     

Christopher Thomas Robinson  Dominik Schmid  Matthias Svoboda  Stefano M. Bernasconi 《Aquatic Sciences - Research Across Boundaries》2008,70(4):432-445

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