Spatial scale and habitat-dependent diversity patterns in nematode communities in three seepage related sites along the Norwegian Sea margin     

Saskia Van Gaever  Maarten Raes  Francesca Pasotti  & Ann Vanreusel 《Marine Ecology》2010,31(1):66-77

Assessing the relative contribution of local diversity to regional biodiversity may be the key to understanding large-scale and even global patterns in species diversity. Here, the contribution of habitat heterogeneity of cold seeps at three spatial scales [micro-scale (ms), macro-scale (10 to 100s of ms), and mega-scale (10 to 100s of km)] to the total nematode biodiversity (genus level) along the Norwegian continental margin is evaluated. Due to the development of higher resolution bathymetry and increased bottom sampling in recent years, continental margins, once regarded as monotonous landscapes, are now acknowledged to have a high degree of habitat complexity and diversity. By calculating the additive partitioning of gamma diversity in alpha and beta fractions, we examined to what extent habitat diversity of seep sites significantly increases the nematode genus composition and diversity at different spatial scales. Siboglinidae patches and control sediments yielded comparably high levels of nematode genus richness. They exhibited low turnover rates within and across the different seep sites. In contrast, the bacterial mats at Håkon Mosby Mud Volcano (HMMV) and the reduced sediments at the Nyegga pockmarks harboured genus-poor nematode communities with an equally high dominance of one or two species, which were different for each seep. Different habitats, in particular at the HMMV, contributed significantly to the seep nematode richness. This study demonstrates that the presence of distinct habitat types within multiple seep sites contributes to the high diversity of nematode communities inhabiting the seeps in the Norwegian deep sea.  相似文献   

Water transport at subtidal frequencies in the Marsdiep inlet   总被引：1，自引：0，他引：1  

Maarten C. Buijsman  Herman Ridderinkhof 《Journal of Sea Research》2007,58(4):255-268

Long-term time series of subtidal water transport in the 4-km wide Marsdiep tidal inlet in the western Dutch Wadden Sea have been analysed. Velocity data were obtained between 1998 and the end of 2002 with an acoustic Doppler current profiler that was mounted under the hull of the ferry ‘Schulpengat’. Velocities were integrated over the cross-section and low-pass filtered to yield subtidal water transport. A simple analytical model of the connected Marsdiep and Vlie tidal basins was extended to include wind stress and water-level and density gradients and applied to the time series of subtidal water transport. In accordance with the observations, the model calculates a mean throughflow from the Vlie to the Marsdiep basin. The mean water transport through the Marsdiep inlet consists of an export due to tidal stresses and freshwater discharge and an import due to southwesterly winds. In contrast, the variability in the subtidal water transport is mainly governed by wind stress. In particular, southwesterly winds that blow along the main axis of the Marsdiep basin force a throughflow from the Marsdiep to the Vlie basin, whereas northwesterly winds that blow along the main axis of the Vlie basin force a smaller mean water transport in the opposite direction. The contribution of remote sea-level change to the water transport, or coastal sea-level pumping, has been found to be much smaller than the contribution of local wind stress.  相似文献   

Fast reconnaissance of carbonate dissolution based on the size distribution of calcareous ooze on Walvis Ridge, SE Atlantic Ocean     

Jan-Berend W. Stuut  Maarten A. Prins  J. H. Fred Jansen 《Marine Geology》2002,190(3-4):581-589

We present a new index of carbonate fragmentation based on the size distribution of bulk sediments in core MD962094 from Walvis Ridge (SE Atlantic Ocean). The carbonate fragmentation index is constructed by taking a ratio of the two coarsest fractions in the grain size distributions of the bulk calcareous ooze. The coarsest two fractions (25–90 μm and >90 μm) of the bulk sediments consist primarily of complete shells and fragments of adult foraminifera shells, and juvenile foraminifera shells and fragments, respectively. The ratio of the proportions of the two fractions is interpreted as a measure of fragmentation of the foraminifera shells caused by carbonate dissolution. Downcore changes in our carbonate fragmentation index compare very well with those in the coarse-carbonate fragmentation index in sediments from a nearby core on Walvis Ridge. The latter commonly used fragmentation index is defined as a ratio of foraminifera fragments over whole foraminifera in the >150-μm fraction as seen with a light microscope. Fragmentation is relatively high during glacial stages and relatively low during interglacial stages during the last 300 kyr, caused by the combined effect of wind-driven upwelling of corrosive water and increased production of organic matter, decreasing the preservation potential of carbonates both during and after deposition. The carbonate fragmentation index we present here provides a precise and fast method to establish a downcore fragmentation record. It can be applied to bulk sediments that are carbonate-rich (CaCO₃>68%) and to all other deep-marine sediments of which the grain size distribution of the carbonate-free fraction is available.  相似文献   

Seismic evidence for long-term history of glaciation on central East Greenland shelf south of Scoresby Sund     

K. Vanneste  G. Uenzelmann-Neben  H. Miller 《Geo-Marine Letters》1995,15(2):63-70

A seismic reflection transect crossing the central East Greenland continental margin south of the Scoresby Sund fjord system provides information regarding the long-term history of expansion and retreat of the Inland Ice. The shelf and slope sediments can be divided into three first-order units; the upper unit is interpreted to have a glacial origin. Within the up to 1000-m-thick glacial unit, six sequences were identified, representing at least as many phases of extensive ice sheet grounding on the shelf. Varying amounts of progradation and aggradation probably reflect successive phases in the glacial evolution of the region.  相似文献   

New perspectives on ethnic segregation over time and space. A domains approach     

Maarten van Ham  Tiit Tammaru 《Urban geography》2016,37(7):953-962

Ethnic segregation has most often been studied at the place of residence, segregation being defined on the basis of the relative presence of different groups within city neighbourhoods. It is increasingly recognized, however, that segregation occurs in different ways in different domains (such as the workplace, leisure, social media, etc.), the residential domain being just one of many in which segregation can occur. In this research note we present the domains approach to segregation and outline some its conceptual, methodological and empirical underpinnings and challenges.  相似文献   

Mesozoic exhumation of the southern Cape, South Africa, quantified using apatite fission track thermochronology   总被引：4，自引：2，他引：2  

Justine Tinker  Maarten de Wit  Roderick Brown   《Tectonophysics》2008,455(1-4):77-93

Southern Africa's topography is distinctive. An inland plateau of low relief and high average elevation is separated from a coastal plane of high relief and low average elevation by a steeply dipping escarpment. The origin and evolution of this topography is poorly understood because, unlike high plateaus elsewhere, its development cannot be easily linked to present day compressional plate boundary processes. Understanding the development of this regional landscape since the break-up of Gondwana is a first order step towards resolving regional epeirogenesis. We present data that quantifies the timing and extent of exhumation across the southern Cape escarpment and coastal plane, using apatite fission track analysis (AFTA) of 25 outcrop samples and 31 samples from three deep boreholes (KW1/67, SA1/66, CR1/68). Outcrop fission track (AFT) ages are Cretaceous and are significantly younger than the stratigraphic ages of their host rocks, indicating that the samples have experienced elevated paleotemperatures. Mean track lengths vary from 11.86 to 14.23 μm. The lack of Cenozoic apatite ages suggests that major cooling was over by the end Cretaceous. The results for three boreholes, situated seaward (south) of the escarpment, indicate an episode of increased denudation in the mid-late Cretaceous (100–80 Ma). An earlier episode of increased denudation (140–120 Ma) is identified from a borehole north of the escarpment. Thermal modelling indicates a history involving 2.5–3.5 km of denudation in the mid-late Cretaceous (100–80 Ma) at a rate of 175 to 125 m/Ma. The AFT data suggest that less than 1 km of overburden has been eroded regionally since the late Cretaceous (< 80 Ma) at a rate of 10 to 15 m/Ma, but do not discount the possibility of minor (in relative amplitude) episodes of uplift and river incision through the Cenozoic. The reasons for rapid denudation in these early and mid-Cretaceous episodes are less clear, but may be related to epeirogenic uplift associated with an increase in mantle buoyancy as reflected in two punctuated episodes of alkaline intrusions (e.g. kimberlites) across southern Africa and contemporaneous formation of two large mafic igneous provinces (~ 130 and 90 Ma) flanking its continental margins. Because Cenozoic denudation rates are relatively minimal, epeirogenic uplift of southern Africa and its distinct topography cannot be primarily related to Cenozoic mantle processes, consistent with the lack of any significant igneous activity across this region during that time.  相似文献   

How climate metrics affect global mitigation strategies and costs: a multi-model study     

Mathijs J. H. M. Harmsen  Maarten van den Berg  Volker Krey  Gunnar Luderer  Adriana Marcucci  Jessica Strefler  Detlef P. Van Vuuren 《Climatic change》2016,135(2):203-209

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Kinematics of elliptical galaxies with a diffuse dust component – III. A Monte Carlo approach to include the effects of scattering     

Maarten Baes †  Herwig Dejonghe 《Monthly notices of the Royal Astronomical Society》2002,335(2):441-458

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Reply to comment by F. A. Dahlen and G. Nolet on 'On sensitivity kernels for 'wave-equation' transmission tomography'     

Maarten V. de Hoop  Robert D. van der Hilst 《Geophysical Journal International》2005,163(3):952-955

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Late Cenozoic evolution of the western Barents Sea-Svalbard continental margin     

Jan Inge Faleide  Anders Solheim  Anne Fiedler  Berit O. Hjelstuen  Espen S. Andersen  Kris Vanneste 《Global and Planetary Change》1996,12(1-4)

Seven regionally correlatable reflectors, named R7 (oldest) to R1, have been identified in the Upper Cenozoic sedimentary succession along the western continental margin of Svalbard and the Barents Sea. Regional seismic profiles have been used to correlate between submarine fans that comprise major depocentres in this region. Glacial sediment thicknesses reach up to 3 seconds two-way time, corresponding to 3.5–4 km. Despite limited chronostratigraphic control, ages have been assigned to the major sequence boundaries based on ties both to exploration wells and to shallow boreholes, and by paleoenvironmental interpretations and correlations with other regions. Lateral and vertical variations in seismic facies, between stratified and chaotic with slump structures, have major implications for the interpretation of the depositional regime along the margin. The main phases of erosion and deposition at different segments of the margin are discussed in the paper, which also provides a regional seismic stratigraphic framework for two complementary papers in the present volume. Reflector R7 marks the onset of extensive continental shelf glaciations, but whereas the outer Svalbard shelf has been heavily and frequently glaciated since R7 time, this did not occur, or occurred to a much less extent, until R5 time in the southern Barents Sea. The present study provides the background for a quantification of the late Cenozoic glacial erosion of Svalbard and the Barents Sea. The rates of erosion and deposition exhibit large temporal and spatial variations reflecting the importance of glacial processes in the Late Cenozoic development of this nearly 1000 km long margin.  相似文献