Submerged caves of Croatia: distribution,classification and origin

Presently, 235 submerged caves and pits have been recorded along the Croatian coast and islands, partly or completely submerged by sea water. Contrary to the inland situation, recorded submerged features are predominantly horizontal (60%), though there are indications that the real situation is similar to that of the continental part where 69% are vertical pits. Completely marine conditions are established in 126 caves and the rest are anchihaline caves and submarine springs. Speleothems are found in more than 140 caves. By their origin, the investigated caves are all continental features formed in Mesozoic and Palaeogene carbonates, subsequently submerged owing to sea transgression. Due to the relatively low wave energy, rapid sea level rise and maturity of the host rock, they do not fit into concepts of a sea cave or a flank margin cave development, but they fulfil several conditions for being the blue holes. Since the term ‘blue hole’ is mainly associated with the Bahamian karst, our attempt is only to show the possible similarities with no intention of ascribing that term to the Croatian caves. Beside karstological issues, Croatian submerged caves are unique environmental, archaeological and tourism assets.     

Density variations in the thickened crust as a function of pressure, temperature, and composition

Constraints on density as a function of pressure, temperature, and composition are crucial to understand isostatic movements during geodynamic processes. Here, we provide a systematic series of density diagrams extracted from thermodynamic calculations for a variety of crustal compositions within a wide P–T range. We quantify systematic density changes in collisional settings for relevant compositional variations and attempt to simplify the density–composition relationships. Rock densities depend strongly on pressure, temperature, and composition. Densities at some selected pressure–temperature conditions increase linearly with increasing Al₂O₃ as well as MgO/FeO contents in pelitic rocks. Al- and Fe-rich pelites yield the highest densities, which is mostly due to the formation of garnet but also depends on other minerals and changes of reactions. The effect of loading on densities is investigated, and we show that for deep burial, a meta-pelite rich in Fe and Mg yields much larger density changes than a dry basalt and that the burial of such a rock with a composition close to typical lower crust may result in significant negative buoyancy. Metamorphism of hydrous lower crust due to pressurization and heating thus leads to densification of thickened lower crust, while heating of dry crust leads to a decrease in density. Hence, water-loaded isostatic subsidence due to metamorphism of water-saturated lower crust is substantial and increases with the thickness and depth of the reacting layer, while dry compositions show much less or only transient densification and subsidence. The density change due to thermal expansion, an extensively used concept in geodynamic models, predicts uplift under the same P–T conditions and is an order of magnitude smaller than the density variation calculated from petrologically consistent diagrams.     

Newly found Tunglo Active Fault System in the fold and thrust belt in northwestern Taiwan deduced from deformed terraces and its tectonic significance

We found active faults in the fold and thrust belt between Tunglo town and the Tachia River in northwestern Taiwan. The surface rupture occurred in 1999 and 1935 nearby the study area, but no historical surface rupture is recorded in this area, suggesting that the seismic energy has been accumulated during the recent time. Deformed fluvial terraces aid in understanding late Quaternary tectonics in this tectonically active area. This area contains newly identified faults that we group as the Tunglo Fault System, which formed after the area's oldest fluvial terrace and appears at least 16 km long in roughly N–S orientation. Its progressive deformations are all recorded in associated terraces developed during the middle to late Quaternary. In the north, the system consists of two subparallel active faults, the Tunglo Fault and Tunglo East Fault, striking N–S and facing each other from opposite sides of the northward flowing Hsihu River, whose course may be controlled by interactions of above-mentioned two active faults. The northern part of the Tunglo Fault, to the west of the river, is a reverse fault with upthrown side on the west; conversely the Tunglo East Fault, to the east, is also a reverse fault, but with upthrown side on the east. Both faults are marked by a flexural scarp or eastward tilting of fluvial terraces. Considering a Quaternary syncline lies subparallel to the east of this fault system, the Tunglo Fault might be originated as a bending moment fault and the Tunglo East Fault as a flexural slip fault. However, they have developed as obvious reverse faults, which have progressive deformation under E–W compressive stress field of Taiwan. Farther south, a west-facing high scarp, the Tunglo South Fault, strikes NNE–SSW, oblique to the region's E–W direction of compression. Probably due to the strain partitioning, the Tunglo South Fault generates en echelon, elongated ridges and swales to accommodate right-lateral strike–slip displacement. Other structures in the area include eastward-striking portion of the Sanyi Fault, which has no evidence for late Quaternary surface rupture on this fault; perhaps slip on this part of Sanyi Fault ceased when the Tunglo Fault System became active.     

Population genetics of cold‐water coral associated Pleustidae (Crustacea,Amphipoda) reveals cryptic diversity and recent expansion off Iceland

Amphipoda are a diverse and important faunal component of deep‐sea habitats worldwide. However, relatively little is known about species that are associated with cold‐water corals, in particular concerning their genetic diversity, population genetic processes, population differentiation, and potential host specificity. We exemplarily investigate these questions studying three pleustid species—Stenopleustes aff. malmgreni (Boeck, 1871), Stenopleustes aff. nodifera (Sars, 1883) and Neopleustes aff. boecki (Hansen, 1888)—that are associated with cold‐water corals and polychaete assemblages along the Reykjanes Ridge southwest of Iceland. We sequenced mitochondrial COI and performed ddRAD to study thousands of nuclear loci. These species and a pair of morphologically cryptic species within Stenopleustes aff. nodifera were consistently delimited by COI and ddRAD. We conclude that all of our studied species are new to science, raising the number of pleustids reported from cold‐water corals to six. Two species were collected only once, and these species exhibited high levels of inbreeding, suggesting little exchange with other populations, which might be a result of strong host specificity. The other two species were wider distributed, with very low differentiation among populations, even between populations separated by 130 km. These species showed signs of recent population expansions, possibly in relation to changes in the cold‐water coral associated ecosystem (e.g., due to glacial cycles and/or volcanic or geothermal activities). They had lower levels of inbreeding and were each associated with three different host coral species, which might facilitate dispersal and gene flow. Our results show divergent population genetic patterns for the studied pleustid species. These might be attributed to the species’ host specificity and highlight important differences among species with seemingly similar life‐styles. Species diversities appear to be greatly underestimated, limiting our abilities to truly assess the vulnerability of the fauna living in these threatened cold‐water coral habitats.     

The effect of mantle composition on density in the extending lithosphere

The density distribution of the lithosphere is non-linear and discontinuous due to complex mineralogy and, most importantly, phase transitions. We evaluate the influence of changes in mantle composition on lithospheric density and its evolution during horizontal stretching, using thermodynamic calculations of the density as a function of pressure, temperature and composition. We also develop a simple parameterization based on end-member mineral reactions and geometric relationships between the geotherm and the phase boundary for comparison. The garnet–spinel peridotite transition leads to a moderate decrease in density of the mantle part of the lithospheric column at the initial stages of stretching. When the crust is sufficiently thinned and temperature is relatively high, plagioclase peridotite becomes stable in the upper part of the mantle. The density reduction due to the plagioclase-in reaction is controlled by bulk Al₂O₃ in the mantle and by the depth of the plagioclase-in reaction, which is mainly governed by the Na₂O/Al₂O₃ ratio. Since Na₂O and Al₂O₃ increase with the fertility of the mantle the phase transition effect is most pronounced for relatively fertile mantle (and strong extension) and can lead to 2.3% density reduction. This is equivalent to heating the entire lithosphere by 700 °C if only the effect of thermal expansion on density is taken into account. The formation of plagioclase peridotite can explain syn-rift uplift in sedimentary basins that experienced large mantle stretching without invoking an unrealistically strong increase in temperature. It might also be responsible for the break-up unconformity observed at continental margins.     

旱作地膜小麦-玉米带田一膜两用热效应显著

旱作地膜小麦－玉米带田一膜两用技术热效应显著，可提高地温２—６℃，保证了小麦安全越冬，促进了作物早发；热资源利用率高达０．９７７，比单作提高了２５％－４０％；变作物一年一熟为一年两熟，亩产可达到４４０—６１０ｋｇ，比单作增产２０％－８０％．     

The contribution of Dutch landscape painters to the conservation of geoheritage

Landscape images are a way to register geoheritage, and we have applied it here in a consideration of the landscapes of the Netherlands. Before the 1950s these landscapes were documented chiefly by landscape painters; with useful photographs of limited availability. We have looked through a large number of paintings of Dutch landscapes to assess their geoheritage value, and present here a first reconnaissance.     

Living Shorelines Support Nearshore Benthic Communities in Upper and Lower Chesapeake Bay

Human population growth and sea-level rise are increasing the demand for protection of coastal property against shoreline erosion. Living shorelines are designed to provide shoreline protection and are constructed or reinforced using natural elements. While living shorelines are gaining popularity with homeowners, their ability to provide ecological services (e.g., habitat provision and trophic transfer) is not well understood, and information is needed to improve coastal and resource management decision-making. We examined benthic community responses to living shorelines in two case-study subestuaries of Chesapeake Bay using a before-after control-impact study design. At Windy Hill, a bulkhead was removed and replaced by three tombolos, sand fill, and native marsh vegetation. At Lynnhaven, 25 m of eroding marsh shoreline was stabilized with coir logs, sand fill, and native marsh vegetation. Communities of large (>?3 mm) infauna adjacent to living shorelines at both locations tended to increase in biomass by the end of the study period. Community compositions changed significantly following living shoreline construction at Windy Hill, reflecting a trend toward higher density and biomass of large bivalves at living shorelines compared to pre-construction. Increasing trends in density and biomass of clams and simultaneously decreasing density and decreasing trends in biomass of polychaetes suggest a transition toward stable infaunal communities at living shorelines over time, though longer-term studies are warranted.     

Geoid and topography of Venus in various thermal convection models

Important though indirect information about the internal structure of Venus is provided by its topography and geoid. In the last decades this information has been used to constrain the Venus mantle viscosity structure and its dynamic regime. Recently, the geodynamic inversion of the Venus?? geoid and topography resulted in a group of best fitting viscosity profiles. We use these viscosity models here as an input to our mantle convection code. We carry out simulations of the Venus?? mantle evolution in a 3D spherical shell with depth dependent viscosity and check whether the character of the dynamic topography and the geoid represented by their power spectra fits the observed quantities. We compare the results with several other models obtained for different viscosity stratifications (constant, constant with highly viscous lithosphere, linear increase of viscosity). Further, we estimate the effect of other factors such as internal heating and varying Rayleigh number. We use a 2D spherical axisymmetric convection code to study the effect of lateral viscosity variations. In these 2D models we monitor the topography and the geoid developing above the axisymmetric plume and compare them with the observed elevations of Venus?? geoid and topography in several Regia. Though none of the models fits observed data perfectly, we can generally conclude, that the best fit between the observed and predicted quantities is reached for viscosity profiles with 200 km thick lithosphere followed by a gradual increase of viscosity with depth and with the upper mantle viscosity of 2 × 10 ²¹ Pa s. For all viscosity profiles the predicted geoid and topography spectra match the observed ones only up to the degree 40, thus indicating other than dynamic origin of these quantities for higher degrees.     

Stratospheric dust loading from early 1981 to September 1985 based on the twilight sounding method and stratospheric dust collections

Stratospheric aerosol loading from early 1981 to late 1985 was investigated by remote optical measurements using the twilight sounding method and by in situ mineral dust collections. Both experiments tracked the decay of aerosol abundances after the El Chichón eruption. A comparison between the remote optical observations and dust samplings suggests that aerosol maxima in 1985 were probably associated with a minor eruption of the Bezymianny volcano. Considering the different dynamical behavior of volcanic ash and condensed sulfuric acid aerosol, we traced the origin of collected dust to a minor eruption of Una Una volcano. This collected dust that could not be detected by remote sensing techniques against the high background level due to condensed aerosol from El Chichón highlights the complimentary nature of stratospheric dust collections and the twilight sounding method.