Swedish Ordovician limestones: Problems in clarifying their directions of magnetizations

The easterly region of the Swedish Ordovician limestones (the Orthoceras Limestone) shows a fairly stable bulk magnetization of high positive (downward) inclination. A closer scrutiny reveals, however, that this magnetization is of polyphase structure, involving at least two axes of magnetization. The components have similar stability spectra, and alternating field demagnetization cannot separate them. Thermal demagnetization is more effective but no stable end-point has been reached.     

Study of Stratus-Lowering Marine-Fog Events Observed During C-FOG

Boundary-Layer Meteorology - Two stratus-lowering marine fog events observed on 28 September and 4 October 2018 during the Coastal Fog (C-Fog) field campaign that took place offshore of eastern...     

Influence of a Flood Event on Salinity and Nutrients in the Changshan Archipelago Area (Northern Yellow Sea)

River discharge can deliver nutrients to the coastal zone and change the hydrologic properties of the water column. Soon after a flash flood from the Yalu River (Northeast China) in August 2010, we investigated the salinity and nutrient concentrations, as well as other environmental conditions in the Changshan Archipelago area, located approximately 100 km west of the river mouth in the northern Yellow Sea. Diluted water was mainly observed in the upper layers shallower than 15 m, with surface salinity between 18.13 and 30.44 in the eastern study area and between 28.16 and 29.72 in the western area. Surface salinity showed a significant negative correlation with concentrations of dissolved nutrients (P < 0.05), but not with that of Chlorophyll-a (Chl-a), dissolved oxygen (DO), particulate materials or pH. The average concentrations of nitrite, nitrate, and silicic acid decreased from the surface layer to bottom layer and were significantly higher in the east area than in the west area (P < 0.05). In contrast, average ammonium and phosphate concentrations were highest in the bottom layer of both areas, with no significant spatial differences. DO varied between 6.06 and 8.25 mg L-1 in the surface layer, and was significantly higher in the eastern area than in the western area in the surface and middle layers. Chl-a concentration was constantly below 4.09 μg L-1. Our work demonstrated the strong influences of Yalu River on proportions of various nutrient components in the Changshan Archipelago area. Silicic acid and total inorganic nitrogen levels were significantly elevated comparing to phosphate in the eastern area. Such changes can potentially induce phosphate limit to phytoplankton growth.     

Assessment of drought hazard,exposure, vulnerability,and risk for rice cultivation in the Mun River Basin in Thailand

Natural Hazards - When assessing drought risk, most studies focus on hazard and vulnerability, paying less attention to exposure. Here, we propose a comprehensive drought risk assessment scheme...     

Detrital zircon U-Pb-He double dating: A method of quantifying long- and short-term exhumation rates in collisional orogens

A U-Pb-He double-dating method is applied to detrital zircons with core-rim structure from the Ganges River in order to determine average short- and long-term exhumation rates for the Himalayas. Long-term rates are calculated from the U/Pb ages of metamorphic rims of the grains that formed during the Himalayan orogeny and their crystallization temperatures, which are calculated from the Ti-in-zircon thermometer. Short-term rates are calculated from(U-Th)/He ages of the grains with appropriate closure temperatures. The results show that short-term rates for the Himalayas, which range from 0.70 ± 0.09 to 2.67 ± 0.40 km/Myr and average 1.75 ± 0.59(1±) km/Myr, are higher and more varied than the long-term rates, which range from 0.84 ± 0.16 to 1.85 ± 0.35 km/Myr and average 1.26 ± 0.25(1±) km/Myr. The differences between the long-term and short-term rates can be attributed to continuous exhumation of the host rocks in different mechanisms in continental collision orogen. The U/Pb ages of 44.0 ± 3.7 to 18.3 ± 0.5 Ma for the zircon rims indicate a protracted episode of ~25 Myr for regional metamorphism of the host rocks at deeper crust, whereas the(U-Th)/He ages of 42.2 ± 1.8 to 1.3 ± 0.2 Ma for the zircon grains represent a protracted period of ~40 Myr for exposure of the host rocks to shallower crustal level. In particular, the oldest(U-Th)/He ages of the zircon grains are close to the oldest U/Pb ages for the rims, indicating that some parcels of the rocks that contain zircons were rapidly exhumed from deep to shallow levels in the stage of collisional orogeny. On the other hand, some parcels of the rocks may have been carried upwards by thrust faults in the post-collisional stage. The parcels could be carried upwards by the thrust faults that steepen as they near the surface, or by transient movement faults so that areas of rapid exhumation became areas of slow exhumation and visa versa on a time scale of a few Myr in order to maintain the continuous exhumation. In this regard, the Ganges River must be preferentially sampling areas that are currently undergoing above average rates of uplift.     

A comparison of biohydrodynamic interaction within mangrove and saltmarsh boundaries

Mangrove forests and saltmarshes are recognized for their roles in wave and current attenuation, although a comparison of in situ observations between woody and herbaceous plants is needed in order to understand the different mechanisms of bio‐physical interaction within coastal wetlands. The aim of our study was to compare the mechanisms of flow reduction and energy dissipation by mangrove trees and saltmarsh grass in a subtropical area where tidal currents dominate. Fieldwork was conducted to measure the hydrodynamic processes occurring at the boundaries between a bare mudflat and vegetated tidal flat, as the flow transitions from a bare mudflat to either mangrove or saltmarsh. Synchronous acoustic Doppler velocimetry (ADV) measurements at three sites revealed that the mangrove was more effective than the saltmarsh grass at flow reduction. In addition, a considerable rotation in flow direction was observed as the flow entered the mangrove trees, while rotation was considerably less pronounced within the saltmarsh edge. The mechanism for this difference was explained through a combination of changes in drag force and eddy viscosity over the two vegetation types. Although overall the mangrove was observed to dissipate energy more effectively than the saltmarsh, the relative efficiency of the vegetation at dissipating turbulent energy was found to vary with the maximum water level of tidal cycle. When the maximum water level remained below the mangrove canopy bottom (‘bio‐line’), the energy dissipation ability of the mangrove was relatively low, as a result of the presence of rigid, sparse trunks rather than denser saltmarsh grass found near the bed; when the maximum water level was sufficiently high to reach the mangrove canopy, the ability of the mangrove to dissipate energy was significantly increased, becoming more effective than the saltmarsh grass. Copyright © 2016 John Wiley & Sons, Ltd.     

人与保护区：理解态度差异 提高保护成效

When the attitudes of local people towards wildlife and conservation are not aligned with those of other stakeholders, significant conflicts can result, potentially undermining conservation efforts. We collected attitudinal data from 171 local people and 59 governmental staff from a Nature Reserve in southwestern China. These attitudinal questions covered key topics of ecosystem services, protected areas and human-wildlife coexistence. Statistically significant (p<0.05) similarities of responses between local people and staff were identified and the nature of any disparity was investigated. The majority of attitudes relating to protected areas (60%) and coexistence (100%) were statistically similar between the two groups, unlike 25% of responses relating to ecosystem services. Few characteristics of staff were statistically associated with their attitudes, whereas responses from local people were frequently associated with sub-village. Such attitudinal studies inform recommendations that consider the potential for future conflicts that might persist following attitudinal disparity between two key stakeholders.     

Wavelet transform-based seismic facies classification and modelling: application to a geothermal target horizon in the NE German Basin

At the geothermal test site near Groß Schönebeck (NE German Basin), a new 3D seismic reflection survey was conducted to study geothermal target layers at around 4 km depth and 150°C. We present a workflow for seismic facies classification and modelling which is applied to a prospective sandstone horizon within the Rotliegend formation. Signal attributes are calculated along the horizon using the continuous Morlet wavelet transform. We use a short mother wavelet to allow for the temporal resolution of the relatively short reflection signals to be analysed. Time-frequency domain data patterns form the input of a neural network clustering using self-organizing maps. Neural model patterns are adopted during iterative learning to simulate the information inherent in the input data. After training we determine a gradient function across the self-organizing maps and apply an image processing technique called watershed segmentation. The result is a pattern clustering based on similarities in wavelet transform characteristics. Three different types of wavelet transform patterns were found for the sandstone horizon. We apply seismic waveform modelling to improve the understanding of the classification results. The modelling tests indicate that thickness variations have a much stronger influence on the wavelet transform response of the sandstone horizon compared with reasonable variations of seismic attenuation. In our interpretation, the assumed thickness variations could be a result of variable paleo-topography during deposition of predominantly fluvial sediments. A distinct seismic facies distribution is interpreted as a system of thicker paleo-channels deposited within a deepened landscape. The results provide constraints for the ongoing development of the geothermal test site.     

Potentially mobile pools of phosphorus and silicon in sediment from the Bay of Brest: Interactions and implications for phosphorus dynamics

Competitive interactions between silicate and phosphate at ligand exchange sites in the sediment surface layer may increase the release of phosphorus (P) from the sediment into the water column. In this study, the role of silicon (Si) in the release of P from the sediment surface layer was studied in a marine estuarine environment, the Bay of Brest, with the aid of a sequential sediment fractionation procedure developed for P, and the addition of inorganic or diatom-bound Si to surface sediment samples in vitro. The potentially mobile pools of P in the surface sediment (loosely bound P + Fe/Al-bound-P) amounted to 5.0 μmol g⁻¹ dry sed., 42% of the total extractable and 33% of the total amount of P in the sediment, while the similarly extracted pools of Si were bigger (ca. 20 μmol g⁻¹ dry sed., 50% of the total extractable Si). Additions of inorganic Si increased the concentration of dissolved P in the sediment interstitial water in a bottle experiment, and the addition of both inorganic Si and cultivated diatoms to intact sediment cores increased the outward flux of dissolved P. Model calculations based on the regression equation from the bottle experiment and Si and P water column data showed that the sedimentation of spring diatoms could cause Si pulses to the sediment which would produce a P flux to the water column of ca. 44 μmol m⁻² d⁻¹. Field data from the bay show that in spring, decreases in P and Si and an increase in chl a due to diatom production are often followed by a small separate P peak which may be caused by Si-induced P fluxes from the sediment surface.