苏北岸外辐射潮流沙脊群东沙浅滩沉积速率空间分布特征

江苏岸外发育典型的辐射状沙脊群,沙脊群的地貌与沉积变化是海岸海洋动力地貌研究的热点领域。东沙是辐射沙脊群的重要组成部分,2012年在东沙浅滩采集了18个柱状岩心,利用210Pb方法分析了柱状岩心沉积物210Pb比活度,计算获得了东沙地区10个站位的平均沉积速率。东沙地区平均沉积速率有"西部边缘低、东部边缘高"和"南北高、中间低"的空间分布特点。辐射沙洲东沙附近地形格局和潮流对沉积速率有至关重要的影响。     

Combining passive integrated transponder tags with conventional T‐bar tags to improve tag reporting rates in a rock lobster trap fishery

Tag reporting rate is an important parameter required for estimating fishing and natural mortality in fished populations. It is an extremely difficult parameter to estimate and can vary both during the fishing season and between fishing years. Improving tag reporting rates has been identified as a cost‐effective way of improving precision in fishing and natural mortality estimates derived from tagging data. In this study we evaluated the use of passive integrated transponder (PIT) tags to improve tag reporting rates in a lobster (Jasus edwardsii) trap fishery. To minimise the risk of PIT tag ingestion by consumers, we tested insertion of the PIT tag into the base of the antennae, the base of the walking leg, and the base of the telson. The base of the antennae proved to be the best option for lobster health although impacts were observed at all tag insertion sites. We further developed and tested a hybrid tag that combined a conventional external T‐bar tag with a PIT tag embedded within the shaft. PIT tag scanners were positioned in bottlenecks in the capture process so that all lobsters retained on board the vessel were passed through a scanner. Thus, the tag reporting rate was expected to be 100% for the subsample of the fleet fitted with scanners when scanners were operational. Scanner malfunction was a major issue and further engineering solutions are required to ensure that scanners are reliable when working in harsh marine conditions such as on‐board fishing vessels. Advantages of the hybrid tag are: the ability to be detected by both automatic detectors and fishers; known tag‐induced mortality and tag loss rates from previous research; and PIT tagging without risk of human ingestion.     

No evidence for a decrease of nuclear decay rates with increasing heliocentric distance based on radiochronology of meteorites

It has been argued that the decay rates of several radioactive nuclides are slightly lower at Earth’s aphelion than at perihelion, and that this effect might depend on heliocentric distance. It might then be expected that nuclear decay rates be considerably lower at larger distances from the sun, e.g., in the asteroid belt at 2–3 AU from where most meteorites originate. If so, ages of meteorites obtained by analyses of radioactive nuclides and their stable daughter isotopes might be in error, since these ages are based on decay rates determined on Earth. Here we evaluate whether the large data base on nuclear cosmochronology offers any hint for discrepancies which might be due to radially variable decay rates. Chlorine-36 (t_1/2 = 301,000 a) is produced in meteorites by interactions with cosmic rays and is the nuclide for which a decay rate dependence from heliocentric distance has been proposed, which, in principle, can be tested with our approach and the current data base. We show that compilations of ³⁶Cl concentrations measured in meteorites offer no support for a spatially variable ³⁶Cl decay rate. For very short-lived cosmic-ray produced radionuclides (half-lives < 10–100 days), the concentration should be different for meteorites hitting the Earth on the incoming vs. outgoing part of their orbit. However, the current data base of very short-lived radionuclides in freshly fallen meteorites is far from sufficient to deduce solid constraints. Constraints on the age of the Earth and the oldest meteorite phases obtained by the U–Pb dating technique give no hints for radially variable decay rates of the α-decaying nuclides ²³⁵U or ²³⁸U. Similarly, some of the oldest phases in meteorites have U–Pb ages whose differences agree almost perfectly with respective age differences obtained with “short-lived” radionuclides present in the early solar system, again indicating no variability of uranium decay rates in different meteorite parent bodies in the asteroid belt. Moreover, the oldest U–Pb ages of meteorites agree with the main-sequence age of the sun derived from helioseismology within the formal ∼1% uncertainty of the latter. Meteorite ages also provide no evidence for a decrease of decay rates with heliocentric distance for nuclides such as ⁸⁷Rb (decay mode β⁻) ⁴⁰K (β⁻ and electron capture), and ¹⁴⁷Sm (α).     

On the relationship between cycles of eruptive activity and growth of a volcanic edifice

The behaviour of a magma plumbing system during a cycle of volcanic edifice growth is investigated with a simple physical model. Loading by an edifice at Earth's surface changes stresses in the upper crust and pressures in a magma reservoir. In turn, these changes affect magma ascent from a deep source to the reservoir and from reservoir to Earth's surface. The model plumbing system is such that a hydraulic connection is maintained at all times between the reservoir and a deep magma source at constant pressure. Consequently the input rate of magma into the reservoir is predicted by the model rather than imposed as an input parameter. The open hydraulic connection model is consistent with short-term measurements of deformation and seismicity at several active volcanoes. Threshold values for the reservoir pressure at the beginning and end of eruption evolve as the edifice grows and lead to long-term changes of eruption rate. Depending on the dimensions and depth of the reservoir, the eruption rate follows different trends as a function of time. For small reservoirs, the eruption rate initially increases as the edifice builds up and peaks at some value before going down. The edifice size at the peak eruption rate provides a constraint on the reservoir shape and depth. Edifice decay or destruction leads to resumption of eruptive activity and a new eruption cycle. A simple elastic model for country rock deformation is valid over a whole eruptive cycle extending to the cessation of eruptive activity. For large reservoirs, an elastic model is only valid over part of an eruptive cycle. Long-term stress changes eventually lead to reservoir instability in the form of either roof collapse and caldera formation or reservoir enlargement in the horizontal direction.     

Provenance of gravity-flow sandstones from the Upper Jurassic–Lower Cretaceous Farsund Formation,Danish Central Graben,North Sea

Through the Upper Jurassic and Lower Cretaceous gravity-flow sandstones were deposited in the Danish Central Graben. These gravity-flow sandstones were deposited within mudstones of the Farsund Formation which is the main source rock in the area, and they are thus potential oil and gas reservoirs. The petrography and geochemistry of the sandstones show good intra well relations and several local geographical relations, which may indicate that they were derived from multiple locally sourced flows and not merely by one basin-axial flow system. The gravity-flow sandstones deposited in the eastern part of the basin are less mature and richer in, especially, carbonates and albite compared to previously deposited Jurassic sandstones and simultaneously deposited sandstones in the western part of the Danish area. This may indicate a division of the basin in an eastern and a western provenance province. This study addresses the provenance of the gravity-flow sandstones by petrographical and geochemical analyses in order to derive possible shared detrital sources as a means of understanding the transport system(s) of the gravity flows.     

Solute transport scales in an unsaturated stony soil

Solute transport parameters are known to be scale-dependent due mainly to the increasing scale of heterogeneities with transport distance and with the lateral extent of the transport field examined. Based on a transect solute transport experiment, in this paper we studied this scale dependence by distinguishing three different scales with different homogeneity degrees of the porous medium: the observation scale, transport scale and transect scale. The main objective was to extend the approach proposed by van Wesenbeeck and Kachanoski to evaluating the role of textural heterogeneities on the transition from the observation scale to the transport scale. The approach is based on the scale dependence of transport moments estimated from solute concentrations distributions. In our study, these moments were calculated starting from time normalized resident concentrations measured by time domain reflectometry (TDR) probes at three depths in 37 soil sites 1 m apart along a transect during a steady state transport experiment. The Generalized Transfer Function (GTF) was used to describe the evolution of apparent solute spreading along the soil profile at each observation site by analyzing the propagation of the moments of the concentration distributions. Spectral analysis was used to quantify the relationship between the solid phase heterogeneities (namely, texture and stones) and the scale dependence of the solute transport parameters. Coupling the two approaches allowed us to identify two different transport scales (around 4-5 m and 20 m, respectively) mainly induced by the spatial pattern of soil textural properties. The analysis showed that the larger transport scale is mainly determined by the skeleton pattern of variability. Our analysis showed that the organization in hierarchical levels of soil variability may have major effects on the differences between solute transport behavior at transport scale and transect scale, as the transect scale parameters will include information from different scales of heterogeneities.     

Sharing as sociomaterial practice: Car sharing and the material reconstitution of automobility

Sharing has become one of the buzzwords of contemporary urban life and scholarship, as cities and social lives are transformed by the share economy and collaborative consumption. This paper advances critical analysis of sharing economies through an investigation of the ways in which objects are mobilized in the practice of sharing. Drawing on an empirical base of 35 interviews conducted with Sydney residents using car sharing as a form of transport, we explicate the material entanglements that constitute car sharing in order to highlight the complex intersections of the object being shared, the constellations of objects brought into the orbit of the practice, and the code that flows through each. Bringing together a material-focused analysis into conversation with the concepts of share economies as both performed and hybrid, we advance the concepts of sharing as a set of socio-material entanglements. We argue that the divergent spatialities and temporalities of objects and humans both hold together and tear apart the experiences of sharing, which in turn underpins car sharing’s implications for the reconstitution of automobility.     

Characterizing solute transport with transient storage across a range of flow rates: The evidence of repeated tracer experiments in Austrian and Italian streams

Solute transport in rivers and streams with hyporheic zone exchange and/or in-stream storage is typically affected by the prevailing flow rate. The research reported here focuses on stream tracer experiments repeated many times along the same Austrian (Mödlingbach) and Italian (Torrente Lura) channel reaches to characterize parameter dependency on flow rate. Both groups of data sets showed an increase of storage zone area and main stream area with discharge. In either case, a strong negative correlation was obtained between storage zone residence time and flow rate. From the Mödlingbach data, no clear relationship with Q emerged for the dispersion coefficient and the dead zone ratio, whereas Torrente Lura showed a clear positive correlation of the dispersion coefficient with the flow rate and a slightly negative Q-dependency for the dead zone ratio. Mödlingbach and Torrente Lura results are presented against the background of other repeat experiments reported in literature.     

Magma eruption rates of Merapi volcano,Central Java,Indonesia during one century (1890–1992)

The magma eruption rates of Merapi volcano form 1890 to 1992 are re-examined chronologically. For this volcano, movements of extruded lavas and domes as well as their extrusions are important because they control the modes of the subsequent activities and cause nuées ardentes and lahars. The monthly eruption rates varied widely, but the cumulative volume of lavas has increased linearly and is expressed as 0.1x10⁶ m³/month. The magma production rate of this volcano may have been constant for these 100 years. Recurrent excessive effusion of lavas is tentatively interpreted by assuming a magma reservoir. The averaged eruption rate is small in comparison with other volcanoes such as Nyramuragia, Kilauea and Vesuvio. However, it is remarkable that the activity has been continuous for these 100 years and the total amount of lava discharged during this period reached more than 10⁸ m³. A simple model for the formation of the 1992 lava dome is presented. The viscosity of the lavas is probably between 10⁶ and 10⁷ P and the length of the magma conduit is probably less than 10 km.