Glacially derived material in an Inner Mongolian desert lake during Marine Isotope Stage 2

Establishing the precise timing of continental glacial dynamics and abrupt high‐latitude climate events is crucial to understanding the causes of global climate change. Here we present multi‐proxy records in a lake sediment core from arid Inner Mongolia (Wuliangsuhai Lake) that show two distinct glacially derived sedimentation events at ～26.2–21.8 and ～17.3–11.5k cal a BP. Fine sediments from the Last Glacial Maximum separate these glacially derived coarse sediments. Within these intervals, the occurrence of granite clasts at ～24–23.5, 17.3–17 and 15.6–14.1k cal a BP implies either sediment discharge by meltwater as well as strong current flow in the Yellow River and/or sediment influx through hill‐slope mass wasting and landsliding from the nearby Yin Mountains. Surface microfeatures of quartz grains and spot elemental analysis of black specks in these intervals, however, indicate that physical weathering is dominant and that the provenance of the rocks is probably from a glacial source. To the best of our knowledge, this is the first time glacier‐derived materials have been detected in any desert lake in the Yellow River basin. The occurrence of granite clasts roughly correlates with Heinrich events in the North Atlantic, suggesting synchronous ice sheet dynamics in high‐ and mid‐latitude regions during the Last Glacial period. Although our data provide unprecedented evidence for the influence of glacier‐related processes in arid Inner Mongolia, further well‐dated records are clearly needed to re‐evaluate the correlative inference drawn between granite clast layers in Wuliangsuhai Lake and Heinrich events in the North Atlantic. Copyright © 2012 John Wiley & Sons, Ltd.     

What drives nearshore sediment transport controls on the depletion of beach placers at Manavalakurichi,Southwest Coast of India?

An in-depth analysis has been made to simulate hydrodynamic scenarios for understanding the nearshore sediment transport controls of placer mineral depletion at Manavalakurichi, India. From the analyses of topographic configuration (extracted from Hydrographic Nautical Chart No. 2048 and data generated during year 2010), we inferred that the 5-m isobaths had broadened and exhibited shallowness. Distances between the coastline and the isobaths were found to have increased significantly over the past five decades. Along with this, the 10 and 20-m contours were found to have shifted about 35–100?m horizontally landward. These changes led to severe sediment deposition in these regions due to the changed wave energy levels and refraction patterns. Numerical simulations linking bathymetry, hydrodynamics, sediment load, and significant wave heights revealed that changes in bathymetry would amplify the wave heights and convergence of wave energy. Associated removal of sand from the high-energy zones will eventually lead to sediment starvation situations and depletion of placers in the adjacent beaches. As the observed trends of depletion generate great concern, detailed oceanographic investigations should be taken up immediately in the region. Fine-resolution hydrodynamic data-sets should prove useful for further evaluating the physical responses of the system to the altered geometry and for exploring remedial measures for restoring the heavy mineral content of the beach sand.     

Microbiologically influenced corrosion in dairy effluent

In the dairy industry mild steel is used as the construction material for the effluent treatment plants, pipelines, reinforcement in concrete structures etc. The steel exposed to the dairy effluent faces corrosion due to the microbes. In the present study the role of microbes in dairy effluent on the corrosion of mild steel has been investigated. Pseudomonas sp., Streptococcus sp., Micrococcus sp., Bacillus sp., Neisseria sp. and Lactobacillus sp. were identified in dairy effluent. Corrosion rate has been estimated by weight loss measurements and polarization technique. The Fourier transform infrared spectroscopy (FTIR) and X-ray diffractometer (XRD) studies were found helpful in investigating the chemical pathway leading to the formation of corrosion products on the mild steel during fermentation. Initiation of pitting corrosion was noticed on steel specimens by scanning electron microscope (SEM). A mechanism has been proposed for microbiologically influenced corrosion in dairy effluent.     

Characteristic Study of the Boundary Layer Parameters over the Arabian Sea and the Bay of Bengal Using the QuikSCAT Dataset

The marine atmospheric boundary layer （MABL） plays a vital role in the transport of momentum and heat from the surface of the ocean into the atmosphere. A detailed study on the MABL characteristics was carried out using high-resolution surface-wind data as measured by the QuikSCAT （Quick scatterometer） satellite. Spatial variations in the surface wind, frictional velocity, roughness parameter and drag coefficient for the different seasons were studied. The surface wind was strong during the southwest monsoon season due to the modulation induced by the Low Level Jetstream. The drag coefficient was larger during this season, due to the strong winds and was lower during the winter months. The spatial variations in the frictional velocity over the seas was small during the post-monsoon season （-0.2 m s^-1）. The maximum spatial variation in the frictional velocity was found over the south Arabian Sea （0.3 to 0.5 m s^-1） during the southwest monsoon period, followed by the pre-monsoon over the Bay of Bengal （0.1 to 0.25 m s^-1）. The mean wind-stress curl during the winter was positive over the equatorial region, with a maximum value of 1.5×10^-7 N m^-3, but on either side of the equatorial belt, a negative wind-stress curl dominated. The area average of the frictional velocity and drag coefficient over the Arabian Sea and Bay of Bengal were also studied. The values of frictional velocity shows a variability that is similar to the intraseasonal oscillation （ISO） and this was confirmed via wavelet analysis. In the case of the drag coefficient, the prominent oscillations were ISO and quasi-biweekly mode （QBM）. The interrelationship between the drag coefficient and the frictional velocity with wind speed in both the Arabian Sea and the Bay of Bengal was also studied.     

Web-based resources on software GPS receivers

This column provides the Web-based GPS resources and their technical background information. Its purpose is to inform the reader about the data, software, electronic documents that are available online. This column is coordinated by Dr. Jinling Wang, The University of New South Wales, Sydney. Comments and suggestions are appreciated (jinling.wang@unsw.edu.au). In this issue’s column, Mr. Ravindra Babu introduces the online resources on software GPS receivers.     

Seismic Anisotropy and Velocity Variations in the Mantle beneath the Saxothuringicum-Moldanubicum Contact in Central Europe

—We report on results of a passive seismic experiment undertaken to study the 3-D velocity structure and anisotropy of the upper mantle around the contact zone of the Saxothuringicum and Moldanubicum in the western margin of the Bohemian Massif in central Europe. Spatial variations of P-wave velocities and lateral variations of the particle motion of split shear waves over the region monitor changes of structure and anisotropy within the deep lithosphere and the asthenosphere. A joint interpretation of P-residual spheres and shear-wave splitting results in an anisotropic model of the lithosphere with high velocities plunging divergently from the contact of both tectonic units. Lateral variations of the mean residuals are related to a southward thickening of the lithosphere beneath the Moldanubicum.     

Stability of a sand spit due to dredging in an adjacent creek

The Jatadharmohan creek lies between Mahanadi and Devi Rivers along the Orissa coast and it is separated from the sea by an elongated sand spit. It was proposed to mine a volume of 15×10⁶ m³ of sand from the creek for land filling, but maintaining the spit intact. For this, the stability of sand spit is studied with different criteria. The results confirm that the creek mouth is a near permanent zone of deposition. The model results obtained for various depth scenarios show that the magnitude of currents would increase considerably when depth is increased by 7.0 m and marginally for further increase in depth by 10.0 m. Accordingly, a dredging scheme has to be designed without affecting the spit stability. Considering the existing hydrodynamics in the creek system, it is recommended that a bed slope of 1:6 (9.5°) be maintained during dredging, which is much less than 13.75°—the evaluated critical slope at the site when seepage flow is parallel to the bed slope. It is observed during monitoring that the creek is very productive, and the sand spit is totally intact.     

Effect of Salinity and Currents on Sea Level Variation Along the Indian Coast: A Numerical Study

The process of upwelling/sinking and associated sea level variations are seen as a response of coastal ocean to pure wind stress forcing. Further,precipitation and monsoonal floods, apart from the marine meteorological parameters, are expected to influence the sea level fluctuations along the coast. This study comprises determining the sea level from the various parameters together with the pure wind stress forcing, which is compared with the observed cycle. However, it is found that there is considerable difference between the computations and observations. This suggests that the sea level is dependent not just on the local forcing alone, but also on the induced background circulation as well. For example, the sea level changes along the east coast of India, particularly the northern region, are more sensitive to freshwater discharge from various rivers joining the Bay of Bengal. This is due to more frequently occurring pre- and postmonsoon cyclonic storms and the associated surges in the Bay of Bengal as compared to the Arabian Sea. Hence the salinity effects are particularly important in the coastal waters off the east coast of India during monsoon months (June-September). For the west coast of India, however, it is expected that the large-scale coastal circulation may play a role in determining sea level changes in addition to other forcings. The salinity effects are negligible along the west coast in the absence of any major river systems that join the Arabian Sea. The local advection currents caused by the offshore directed freshwater discharge from various estuaries joining the coastal bay also seemed to influence the sea level. In order to elucidate the essential dynamics involved and to study the effect of the remote forcing, a three-dimensional baroclinic, nonlinear numerical model is used with appropriate open boundary conditions. The local effect of the current has been incorporated in the west coast model by means of opening a channel at Cochin through which the rainwater is carried away to the model ocean. The low saline plume, cascading from north along the east cost of India, has been incorporated in the east coast model through a proper forcing applied at the northern boundary of the model. With the inclusion of these remote forcings in the models, the disagreement between the simulations and the observations is minimized.     

Liquefaction analysis and soil improvement in Beydag dam

Beydag dam is under construction on Kucukmenderes River for irrigation purposes. Due to the scarcity of core material and liquefaction of alluvium at the dam site, the original design was changed to Roller Compacted Concete (RCC) from rockfill dam with claycore. Although the new design was safer, it nearly doubled the cost of the dam, so the owner, State Hydraulic Works of Turkey, (DSI) set out to find more economical but equally safe alternative. Since jet-grouting is a cheap ground improvement tool in Turkey, such an alternative was developed for the ground improvement against liquefaction together with concrete face rockfill dam sitting on top of improved ground. This paper presents a detailed discussion of how the new alternative was developed and evaluated: it discusses the determination of jet grouting pattern, the placement of jet grouted blocks, and the assesment of liquefaction. On one hand the soil cement strength of jetgrout columns, internal friction angle of alluvium and rockfill were important in determining the dimensions of the blocks, on the other hand the location of the blocks were highly affected by the areas where liquefaction occurred. One of the most important parameter that has a considerable influence in delineating the boundary betweeen liquefaction and non-liquefaction was the value of stress reduction coefficient (r _d), being primarily sensitive to the weight of overburden, which is calculated by the height from the face of dam to the depth where the calculation was made. This approach is justified by two-dimensional ground response analysis. Most importantly, this paper shows that there exists an alternative solution for building dams on the liquefaction prone sites without removing alluvium by using a well known jet grouting technique for improving ground at only selected places.