Particulate organic carbon (POC) in surface sediments of the Baltic Sea   总被引：2，自引：2，他引：0  

Thomas Leipe  Franz Tauber  Henry Vallius  Joonas Virtasalo  Szymon U?cinowicz  Nicole Kowalski  Sven Hille  Susanna Lindgren  Tero Myllyvirta 《Geo-Marine Letters》2011,31(3):175-188

In this study, particulate organic carbon (POC) contents and their distribution pattern in surficial sediments of the Baltic Sea are presented for 1,471 sampling stations. POC contents range from approx. 0.1% in shallow sandy areas up to 16% in deep muddy basins (e.g. Gotland Basin). Some novel relationships were identified between sediment mass physical properties (dry bulk density (DBD), grain size) and POC levels. Notably, the highest POC concentrations (about 10–17 mg cm^–3) occur in sandy mud to mud (60–100% mud content) with intermediate POC contents of about 3–7% and DBDs of 0.1–0.4 g cm^–3. Areas with this range in values seem to represent the optimum conditions for POC accumulation in the Baltic Sea. The maximum POC contents (8–16%) are found in fluid mud of the central Baltic Sea characterized by extremely low DBDs (<0.1 g cm^–3) and moderate POC concentrations (4–7 mg cm^–3). Furthermore, sediment mass accumulation rates (MAR), based on ²¹⁰Pb and ¹³⁷Cs measurements and available for 303 sites of the Baltic Sea, were used for assessing the spatial distribution of POC burial rates. Overall, these vary between 14 and 35 g m^–2 year^–1 in the mud depositional areas and, in total, at least 3.5 (±2.9) Mt POC are buried annually. Distribution patterns of POC contents and burial rates are not identical for the central Baltic Sea because of the low MAR in this area. The presented data characterize Baltic Sea sediments as an important sink for organic carbon. Regional differences in organic carbon deposition can be explained by the origin and transport pathways of POC, as well as the environmental conditions prevailing at the seafloor (morphology, currents, redox conditions). These findings can serve to improve budget calculations and modelling of the carbon cycle in this large brackish-water marginal sea.  相似文献   

Downscaling projections of climate change in Sao Tome and Principe Islands,Africa     

Sin Chan Chou  Andr&#; de Arruda Lyra  Jorge Lu&#;s Gomes  Daniel Andr&#;s Rodriguez  Minella Alves Martins  Nicole Costa Resende  Priscila da Silva Tavares  Claudine Pereira Dereczynski  Isabel Lopes Pilotto  Alessandro Marques Martins  Lu&#;s Felipe Alves de Carvalho  Jos&#; Luiz Lima Onofre  Idal&#;cio Major  Manuel Penhor  Ad&#;rito Santana 《Climate Dynamics》2020,54(9):4021-4042

Sao Tome and Principe is a small insular African country extremely vulnerable to rising sea levels and impacts such as inundation, shore line change, and salt water intrusion into underground aquifers. Projections of climate change have considered coarse model resolutions. The objective of this work is to dynamically downscale the global model projections to 4-km resolution and to assess the climate change in the Sao Tome and Principe islands. The global climate projections are provided by the Canadian Earth System Model under two Representative Concentration Pathways greenhouse gas scenarios, RCP4.5 and RCP8.5. The downscaling is produced by the Eta regional climate model. The baseline period is taken between 1971 and 2000, and the future climate period is taken between 2041 and 2070. The 2-m temperature simulations show good agreement with station data. The model simulates temperature more accurately than precipitation. The precipitation simulations systematically show underestimation and delay of the rainy and the dry seasons by about 1 month, a feature inherited from the global climate model. In the middle of the 21st century, projections show the strongest warming in the elevated parts of the Sao Tome Island, especially in February under RCP8.5. Warmer nights and warmer days become more frequent in the islands when compared with those in the present. While under RCP4.5, precipitation increases in the islands; under RCP8.5, it decreases everywhere in both islands. Heavy precipitation rates should increase, especially in the south-southwestern parts of the Sao Tome islands. Detailed spatial variability of the temperature and precipitation changes in the islands can only be revealed at very high spatial model resolution. Implications for the potential energy production from two major river basins are assessed in this work.  相似文献   

Quasi-thermal Noise Spectra Measured by a Dipole Antenna in the Upper Hybrid frequency band     

Yury V. Chugunov  Anna Yu. Kazarova  Eugene A. Mareev  Michel Moncuquet  Karine Issautier  Nicole Meyer-Vernet 《Astrophysics and Space Science》2001,277(1-2):313-316

Quasi-thermal noise (QTN) spectroscopy is one of the most effective tools for in situ diagnostics in space plasmas (Meyer-Vernet et al., 1998; Meyer-Vernet and Perche, 1989; Chugunov and Trakhtengerts, 1978). This method produces routine measurements of the bulk electron density and temperature; recently it has been extended to measure the ion bulk speed. Among the advantages of the method its immunity to spacecraft potential and photoelectron perturbations should be noted. Quasi-thermal noise spectroscopy is used particularly on Ulysses and Wind. However for the interpretation of QTN data the calculation of the noise voltage induced on antennas under different conditions is necessary. This question is especially complicated and so far insufficiently studied in magnetized plasmas. In the present paper we calculate the spectrum of the noise voltage induced on a dipole antenna in the upper hybrid frequency range. The computations are adapted to the interpretation of data acquired on the Ulysses and Wind spacecraft. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Cataclysmic variables with evolved secondaries and the progenitors of AM CVn stars     

Ph. Podsiadlowski  Z. Han  S. Rappaport 《Monthly notices of the Royal Astronomical Society》2003,340(4):1214-1228

  相似文献   

Molluscan successions from the Holocene tufa of St Germain‐le‐Vasson,Normandy (France) and their biogeographical significance     

Nicole Limondin‐Lozouet  Richard C. Preece 《第四纪科学杂志》2004,19(1):55-71

A detailed molluscan succession from a 10 m thick deposit of Holocene tufa at St Germain‐le‐Vasson, Normandy, provides the most complete record from northern France and has shed new light on the historical biogeography of several species of land snail. The succession has been reconstructed from four profiles and a chronology provided by accelerator mass spectrometry radiocarbon dating of charcoal, wood and shell. The onset of tufa formation occurred after 9700±90 yr BP and persisted until 4213±77 yr BP. The tufa appears to have accumulated at a remarkably constant rate (14.4–16.5 cm 100 yr^?1), except for the upper levels, where the rate increases fourfold. The succession has been divided into six local molluscan zones. An early assemblage consisting of ecologically tolerant species and those indicative of marshy grassland is replaced by a sequence of shade‐demanding taxa, reflecting the encroachment of woodland. Shaded conditions persist until the end of the sequence but the most hygrophilous elements decline after 5422±60 yr BP (zone 5), a change also reflected in the tufa lithology by the development of silty grey horizons. Notable species recovered from the tufa include Acicula fusca, Vertigo substriata, V. alpestris, V. moulinsiana (all rare or unknown living in northern France). Hygromia limbata, a twentieth century introduction to Britain, was previously thought to be a relatively recent arrival in northern France, but its record at St Germain shows that it has been present in Normandy since 6500 yr BP. Azeca goodalli, another shade‐demanding species, appeared at St Germain much later, just after 4420±65 yr BP. Several other species present in the tufa, such as Pomatias elegans, no longer live on the site, adding to the evidence for a distributional decline in Normandy and elsewhere. Perhaps the most noteworthy record is that of Leiostyla anglica, between about 8500 yr BP and 5000 yr BP, because this constitutes its only Holocene occurrence from mainland Europe. Following this discovery it seems likely that further Holocene sites with L. anglica may be found along the western seaboard of Europe connecting populations in Iberia with those of the British Isles. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Perturbed particle disks     

Nicole Borderies  Peter Goldreich  Scott Tremaine 《Icarus》1983,55(1):124-132

The Boltzmann moment equations are solved to determine the velocity ellipsoid in a particle disk near an isolated satellite resonance. In a coordinate frame which rotates with the pattern speed of the perturbation potential, the solutions are stationary functions of the azimuthal angle. From the velocity ellipsoid we obtain the stress tensor due to particle collisions and consequently, the viscous angular momentum flux. We show that the magnitude of the rate of deformation tensor in a perturbed particle disk is bounded from above by $\text{KΩ(1 + τ}{}^2\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{,}\text{where}\text{Ω}$ is the orbital angular velocity, τ is the optical depth, and K is a dimensionless constant of order unity. It is also found that in sufficiently perturbed regions there are ranges of azimuthal angle within which the radial component of the angular momentum flux is negative. It is even possible for the angular momentum luminosity, the radial flux integrated over azimuth, to be negative. These results are important for understanding sharp edges and the decay of density waves in planetary rings. They are also relevant to the damping of differential precession and eccentricity in narrow ringlets.  相似文献   

Near-IR Integral Field Spectroscopy of High-z Galaxies     

Andrew Bunker  Annette Ferguson  Rachel Johnson  Richard McMahon  Ian Parry  Max Pettini  Alfonso Aragón-Salamanca  Rachel Somerville  Nicole Vogt 《Astrophysics and Space Science》2002,281(1-2):529-529

  相似文献   

Grosvenor Mountains 95 howardite pairing group: Insights into the surface regolith of asteroid 4 Vesta          下载免费PDF全文

Nicole G. Lunning  Kees C. Welten  Harry Y. McSween Jr  Marc W. Caffee  Andrew W. Beck 《Meteoritics & planetary science》2016,51(1):167-194

Regolithic howardites are analogs for the surface materials of asteroid 4 Vesta, recently mapped by the Dawn spacecraft. Rigorously evaluating pairing of howardites recovered in 1995 in the Grosvenor Mountains (GRO 95), Antarctica, enables an examination of a larger, more representative regolith sample. Previous work on two of the howardites studied here concluded that GRO 95602 and GRO 95535 are solar wind‐rich surface regolith samples and that they are not paired with each other, leading to uncertainty regarding pairing relationships between the other GRO 95 howardites. Based on petrology, cosmic‐ray exposure history, and terrestrial age, four GRO 95 howardites are paired. The paired howardites (GRO 95534, 95535, 95574, 95581) were from a meteoroid with radius of 10–15 cm, a preatmospheric size comparable to that of Kapoeta, the largest known regolithic howardite. The paired GRO 95 howardites contain clasts of at least 18 separate HED lithologies, providing evidence they were assembled from diverse source materials. The total eucrite:diogenite mixing ratio (ratio of all eucrite lithologies to all diogenite lithologies) in the paired GRO 95 howardites is ~2:1. Petrographically determined basaltic eucrite:cumulate eucrite ratios in regolithic howardites, studied here and previously, vary more widely than total eucrite:diogenite ratios. Relative to eucritic pyroxene, plagioclase is depleted in these howardites, which provides evidence that plagioclase is preferentially comminuted in the vestan regolith. The extent of plagioclase depletion could be an indicator of regolith maturity.  相似文献   

Microbiological processes in banded iron formation deposition     

Nicole R. Posth  Kurt O. Konhauser  Andreas Kappler 《Sedimentology》2013,60(7):1733-1754

Banded iron formations have been studied for decades, particularly regarding their potential as archives of the Precambrian environment. In spite of this effort, the mechanism of their deposition and, specifically, the role that microbes played in the precipitation of banded iron formation minerals, remains unresolved. Evidence of an anoxic Earth with only localized oxic areas until the Great Oxidation Event ca 2·45 to 2·32 Ga makes the investigation of O₂‐independent mechanisms for banded iron formation deposition relevant. Recent studies have explored the long‐standing proposition that Archean banded iron formations may have been formed, and diagenetically modified, by anaerobic microbial metabolisms. These efforts encompass a wide array of approaches including isotope, ecophysiological and phylogeny studies, molecular and mineral marker analysis, and sedimentological reconstructions. Herein, the current theories of microbial processes in banded iron formation mineral deposition with particular regard to the mechanisms of chemical sedimentation and post‐depositional alteration are described. The main findings of recent years are summarized and compared here, and suggestions are made regarding cross‐disciplinary information still required to constrain the role of the biosphere in banded iron formation deposition.  相似文献   

Does martian soil release reactive halogens to the atmosphere?     

Suniti Karunatillake  Yu-Yan Sara Zhao  Scott M. McLennan  J.R. Skok  Nicole E. Button 《Icarus》2013

Detailed statistical examination of Cl, Br, and S distributions, in martian soil profiles at Gusev Crater and Meridiani Planum, indicates decreasing Br abundance and weakening Br–S association towards the surface. All three elements decrease towards the surface in the order Cl < S < Br. Furthermore, Br variability decouples from potential cations such as Mg at the surface relative to the subsurface. These observations support a relative loss of surficial Br compared to S and Cl, all highly mobile elements in aqueous environments. We propose that Br may have converted preferentially to gas phases (e.g., BrO), driven either by UV photolysis or by chemical oxidants. Such volatilization pathways may in turn impart a global signature on Mars by acting as controls on oxidants such as ozone and perchlorates. S/Cl mass ratios vary with depth (∼4–5 in the subsurface; 1.8–3.6 on the surface) as well, with a strong correlation of S and Cl near the surface but more variable at depth, consistent with differential vertical mobility, but not volatilization of Cl. Elevated S/Cl in subsurface soil also suggests that the ratio may be higher in bulk soil – a key repository of martian geologic and climatic records – than previously thought.  相似文献