Circular polarimetry: why and how     

Jaap Tinbergen 《Astrophysics and Space Science》2003,288(1-2):3-14

Measurement of circular polarization is mostly looked upon as a specialist craft, applied by polarization freaks to answer uninteresting questions. This paper attempts to correct that view: some important questions can only be tackled by circular polarimetry, there is nothing very special about Stokes V and its measurement is entirely analogous to that of Q and U.Radio and optical polarimetry are covered, using both single telescopes and interferometers.  相似文献   

The carbon isotopic response of algae, (cyano)bacteria, archaea and higher plants to the late Cenomanian perturbation of the global carbon cycle: Insights from biomarkers in black shales from the Cape Verde Basin (DSDP Site 367)     

Jaap S. Sinninghe Damst  Marcel M.M. Kuypers  Richard D. Pancost  Stefan Schouten 《Organic Geochemistry》2008,39(12):1703

The stable carbon isotopic compositions of free and sulfur (S)-bound biomarkers derived from algae, (cyano)bacteria, archaea and higher plants and total organic carbon (TOC) during the first phase of the late Cenomanian/Turonian oceanic anoxic event (OAE) were measured in black shales deposited in the southern proto-Atlantic Ocean in the Cape Verde basin (DSDP Site 367) to determine the response of these organisms to this major perturbation of the global carbon cycle resulting from widespread burial of marine organic matter. The average positive isotope excursions of TOC and biomarkers varied from 5.1‰ to 8.3‰. The δ¹³C values were cross correlated to infer potential common sources of biomarkers. This revealed common sources for C₃₁ and C₃₂ hopanes but no 1:1 relationship for pristane and phytane. The correlation of δ¹³C_TOC with the δ¹³C value of sulfur (S)-bound phytane is the strongest. This is because S-bound phytane is derived from phytol that originates from all marine primary producers (algae and cyanobacteria) and thus represents a weighted average of their carbon isotopic compositions. The δ¹³C values of S-bound phytane and C₃₅ hopane were also used to estimate pCO₂ levels. Before the OAE burial event, pCO₂ levels are estimated to be ca. 1300 ppmv using both biomarkers and the independent maximum Rubisco fractionation factors. At times of maximum organic carbon burial rates during the OAE, reconstructed pCO₂ levels are estimated to be ca. 700 ppmv. However, compared to other C/T OAE sections the positive isotope excursion of S-bound phytane is also affected by an increased production during the OAE. When we compensate for this, we arrive at pCO₂ levels around 1000 ppmv, a reduction of ca. 25%. This indicates that burial of organic matter can have a large effect on atmospheric CO₂ levels.  相似文献   

Thermal stability of ladderane lipids as determined by hydrous pyrolysis   总被引：1，自引：0，他引：1  

Andrea Jaeschke  Michael D. Lewan  Ellen C. Hopmans  Stefan Schouten  Jaap S. Sinninghe Damst 《Organic Geochemistry》2008,39(12):1735

Anaerobic ammonium oxidation (anammox) has been recognized as a major process resulting in loss of fixed inorganic nitrogen in the marine environment. Ladderane lipids, membrane lipids unique to anammox bacteria, have been used as markers for the detection of anammox in marine settings. However, the fate of ladderane lipids after sediment burial and maturation is unknown. In this study, anammox bacterial cell material was artificially matured by hydrous pyrolysis at constant temperatures ranging from 120 to 365 °C for 72 h to study the stability of ladderane lipids during progressive dia- and catagenesis. HPLC-MS/MS analysis revealed that structural alterations of ladderane lipids already occurred at 120 °C. At temperatures >140 °C, ladderane lipids were absent and only more thermally stable products could be detected, i.e., ladderane derivatives in which some of the cyclobutane rings were opened. These diagenetic products of ladderane lipids were still detectable up to temperatures of 260 °C using GC-MS. Thus, ladderane lipids are unlikely to occur in ancient sediments and sedimentary rocks, but specific diagenetic products of ladderane lipids will likely be present in sediments and sedimentary rocks of relatively low maturity (i.e., C₃₁ hopane 22S/(22S + 22R) ratio <0.2 or ββ/(αβ + βα + ββ) ratio of >0.5).  相似文献   

Validating management simulation models and implications for communicating results to stakeholders     

Pastoors  Martin A.; Poos  Jan Jaap; Kraak  Sarah B. M.; Machiels  Marcel A. M. 《ICES Journal of Marine Science》2007,64(4):818-824

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Population dynamics of two marine polychaetes: the relative role of density dependence, predation, and winter conditions     

van der Meer  Jaap; Beukema  Jan J; Dekker  Rob 《ICES Journal of Marine Science》2000,57(5):1488-1494

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Assessing the population size of the European storm petrel (Hydrobates pelagicus) using spatial autocorrelation between counts from segments of criss-cross ship transects     

van der Meer  Jaap; Leopold  Mardik F. 《ICES Journal of Marine Science》1995,52(5):809-818

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Micromorphological characteristics of glacimarine sediments: implications for distinguishing genetic processes of massive diamicts     

Aoibheann A. Kilfeather  Colm Ó Cofaigh  Julian A. Dowdeswell  Jaap J. M. van der Meer  David J. A. Evans 《Geo-Marine Letters》2010,30(2):77-97

Glacimarine diamicts are produced by diverse processes, and genetic differentiation is often problematic using macro-sedimentological criteria alone. Micromorphology offers a potentially helpful tool in such investigations. Macroscopically massive diamict samples of known glacimarine origin, from the Polar North Atlantic, Antarctica and north Irish Sea, were prepared for micromorphological analysis to (1) identify microstructures unique to different modes of sedimentation and (2) interpret genetic processes from those structures. The samples comprised examples of debris-flow, iceberg-turbate and suspension settling deposits from late Quaternary glacier-influenced marine environments: tidewater glacier, sub- or pro-ice shelf and continental slopes in front of ice stream termini. Results show two significant features of debris-flow sediments: a bimodal grain fabric of near-horizontal and -vertical grains, and laminated clay and silt coatings on sand and pebble grains. Coatings are best developed in sediments with finer grain-size distributions and in debris-flow sediments which have had relatively long run-out distances on trough-mouth fans, suggesting continuous rotation of grains in a buoyant, turbulent aqueous environment. This is significant because it precludes debris-flow delivery by plug flow. The micromorphology of iceberg turbate has not been described previously. It contains structures similar to those described in tills, so that unambiguous identification of these sediments seems unlikely based on micromorphological criteria alone. Suspension sediments range from fine-grained massive diamicts containing microfossils to more heterogeneous coarser sediments characterised by abrupt textural variations, from ice-distal and ice-proximal glacimarine environments respectively. The ice-proximal sediments contain fine vertical lineations marking the trajectories of dropstones through wet matrix. These dropstone tracks have not been reported in previous studies.  相似文献   

A combined pyrolysis mass spectrometric and light microscopic study of peatified Calluna wood isolated from raised bog peat deposits     

Edwin van der Heijden  Jaap J. Boon 《Organic Geochemistry》1994,22(6)

Stem wood of the Angiosperm Calluna vulgaris (Scotch heather), isolated at different depths from a selection of raised bog peat deposits, was chemically characterized using in-source pyrolysis mass spectrometry (Py-MS) and Curie-point pyrolysis gas chromatography mass spectrometry (Py-GC-MS). Light microscopy was performed to relate mass spectrometric characteristics with anatomical features. Peatified wood samples, isolated from increasing depth show a gradual decrease in carbohydrate content. This decrease in anatomically reflected in a selective removal of secondary cell wall material from the fibre-tracheids and wood parenchyma. During prolonged peatification a selective removal of hemicellulose sugars is observed, while a part of the cellulose fraction is preserved. This highly resistant cellulose is mainly located in the secondary cell walls of the vessels. The lignin macromolecule is preserved, but a gradual decrease in syringyl to guaiacyl ratio (S/G) is observed during peatification. Because no increase in catechol and phenolic compounds is observed, we conclude that S/G shifts are due to removal the of syringyl-rich secondary cell wall material and the retention of guaiacyl-rich compound middle lamella. Small chemical changes in the lignin macromolecule involve shifts in oxygen substitutions on the aliphatic side chains of the methoxyphenolics and the occurrence of aromatic acids.  相似文献   

Sulphur-containing compounds in sulphur-rich crude oils from hypersaline lake sediments and their geochemical implications   总被引：1，自引：0，他引：1  

Guoying Sheng  Jiamo Fu  S. C. Brassell  A. P. Gowar  G. Eglinton  Jaap S. Sinninghe Damste  Jan W. de Leeuw  P. A. Schenck 《中国地球化学学报》1987,6(2):115-126

Three sulphur-rich commercial crude oils have been studied, which contain sulphur as high as up to 4–12%. These samples were collected from Tertiary hypersaline lake sediments of the Jianghan Basin, Hubei Province at different depths, but above the oil generation threshold (2200m). FPD-GC and GC-MS data show that aromatic fractions of the crude oils are composed of different homologues of sulphur-containing compounds, including long-chain normal alkyl-thiophenes and-thiolanes, long-chain isoprenoid-thiophenes and -thiolanes, and benzothiophenes. It is worth noting that the distribution patterns of long-chain alkyl-thiophenes and -thiolanes from two shallow-seated crude oils are quite similar to those of normal alkanes showing marked even-odd predominance. It seems that the even-odd predominance of sulphur-containing compounds decreases with increasing burial depth of the crude oils. The major component of aliphatic fraction is phytane, and similarly the major peaks of aromatic fractions also represent C₂₀ isoprenoid thiophenes. Some preliminary conclusions have been drawn from the above discussion: (1) Abundant sulphur-containing compounds may be used as an indicator of low mature or immature crude oils produced from hypersaline lake sediments; (2) Sulphur-containing compounds are considered to be early diagenetic products of reactions between elemental sulphur or sulfides and alkanes or their precursors (phytols, fatty acids, alcohols, etc.), or of bacterial activities, but not direct inputs of organisms.  相似文献   

Micromorphological Analysis of Coastal Sediments from Willapa Bay, Washington, USA: A Technique for Analysing Inferred Tsunami Deposits     

Aoibheann A. Kilfeather  Jeffrey J. Blackford  Jaap J. M. van der Meer 《Pure and Applied Geophysics》2007,164(2-3):509-525

Tsunami deposits are provisionally distinguished in the field on the basis of anomalous sand horizons, fining-up and fining-landward, coupled with organic-rich, fragmented `backwash' sediments. In this paper, micromorphological features of a sediment sequence previously interpreted as being of tsunami origin are described. These characteristics are shown to be consistent with the macro-scale features used elsewhere, but show additional details not seen in standard stratigraphies, including possible evidence for individual waves, possibly wave-magnitude progression, organic fragment alignment and intraclast microstructures. Although replication and more complete studies are needed, this analysis confirms the identification of a tsunami in Willapa Bay in ca.1700 AD, while demonstrating a widely applicable technique for confirming or refuting possible tsunami deposits.  相似文献