Dynamics of summer monsoon current around Sri Lanka

Ocean Dynamics - From June–September, the summer monsoon current (SMC) flows eastward south of Sri Lanka and bends northeastward to form a swift jet that enters the Bay of Bengal (BoB). This...     

Tidally‐averaged flows in the interior Sacramento–San Joaquin River Delta: Trends and change attribution

The hydrology of the San Francisco Bay‐Delta estuary (the Delta) has been significantly modified over the past 150 years to serve a variety of human needs for water supply and food production, albeit with adverse ecological impacts. These adverse impacts, in concert with evolving societal values, have motivated change in the estuary's water management to promote ecosystem restoration goals while continuing to support human uses. Understanding historical flow patterns, as well as the environmental functions provided by these flow patterns, is critical to restoration planning. Building upon previous work on outflow trends from the Delta to San Francisco Bay, this paper evaluates historical trends in key interior Delta flows spanning nine decades (1922–2016) and presents an attribution of these trends to various anthropogenic drivers. We reconstructed historical time series records at four key locations in the interior of the Delta; these time series represent tidally‐averaged flows that are intensively managed and are of great importance to the beneficial uses of water in the region. We derived several scenario‐based flow time series at these same four locations to assist in attributing change to a variety of drivers, including reservoir and export pumping operations, in‐Delta barrier and gate operations, and upstream water diversions. Flow changes were measured relative to 1920‐level land use and water management conditions. We find the four interior Delta locations to have distinct seasonal flow trends and, in general, unique responses to various drivers of change. Our work highlights the complex nature of historical flow changes in a highly‐managed estuarine ecosystem, and the types of modifications that would be necessary to reverse these changes.     

Identification of uncertainties in the shape of geophysical objects with level sets and the adjoint method

A shape reconstruction method for geophysical objects by temperature measurements is presented which uses adjoint equations and a level set function approach. Temperature is measured on subdomains, e.g., representing boreholes. This information is used to reconstruct the shape of the geophysical layers. For this purpose, shape optimization techniques are applied. The method uses a representation of the layers by a so-called level set function. The evolution of this level set function is then used to determine the optimal shape. The “speed” of the evolution is computed using adjoint equations. Synthetic examples demonstrate the use of the inverse method and its behavior in different configurations.     

Occurrence of PGE mineralisation in Bangur,Kendujhar district,Odisha

PGE mineralisation of significant grade and extent is reported from Bangur chromite mining area, Kendujhar district, Odisha, located to the south of the well known Baula-Nuasahi ultramafic complex. The hitherto unknown PGE mineralisation is established in a ferritchromit rich breccia zone occurring within Bangur litho-mélange. The mineralized breccia zone is traced for about 550m with a mean width of 12m in NW-SE direction. Chemical analysis of drill core samples by ICP-MS indicates an average ΣPGE content of 3.2 ppm dominated by Pt and Rh. Occurrence of discrete grains of PGM in sizes up to 45 microns is confirmed by SEM-EDX and EPMA study. Delineation of this PGE bearing zone stresses the need for preservation of gangue/matrix of the breccia zone, along with ferritchromit clasts, in the ongoing selective mining of chromite in Bangur.     

Audiomagnetotelluric investigations of shallow sedimentary basins in northern Sudan

Audiomagnetotelluric (AMT) investigations were carried out to study shallow sedimentary basins in northern Sudan and southern Egypt. Unlike recordings in settled areas, the natural variations (atmospherics) in the eastern Sahara were completely unperturbed by cultural noise, usually yielding very high data quality. Typical recordings and spectra are presented. The atmospherics show distinct daily variations, with maximum amplitudes in the local afternoon/night hours. As a sort of calibration, AMT measurements together with DC-resistivity and electromagnetic soundings were conducted at several groundwater boreholes. Under favourable conditions, a vertical anisotropy may be resolved by joint inversion of DCR and AMT data. The results of a case study in the Es Safya basin (NW Sudan) are presented. The investigations were aimed at determining basement depths and groundwater levels, as well as the direction and dip of major bounding faults. 2-D modelling and inversion revealed the overall conductivity structure of this shallow graben. The AMT method proved to be a valuable tool for a comparatively swift reconnaissance study of shallow structures.     

Very high electrical conductivity beneath the Münchberg Gneiss area in Southern Germany: implications for horizontal transport along shear planes

New magnetotelluric data from the Münchberg Gneiss complex in Southern Germany reveal a zone of extremely high electrical conductivity. 1-D modelling of the data is justified in the period range 0.01 to 10  s. At least three layers are required to explain the steepness of the apparent resistivity curves, and the best-fitting models comprise four layers with successively higher conductivities. The layers of highest conductivity at depths between 2.2 and 3.6  km correlate with pronounced bands of high seismic reflectivity (profile DEKORP 85-4N). The Münchberg complex is today widely recognized as a tectonic klippe, consisting of rocks whose metamorphic and stratigraphic order is inverted rather than overturned. The material was transported into its present position by predominantly horizontal tectonic forces along shear zones. We interpret the high conductivity and high reflectivity as remnants of this transport process.