Observations of sea and swell using directional wave buoy

Directional wave data collected during an experiment at a location on the continental shelf of the south west coast of India using a WAVEC buoy, have been analysed based on the technique of Kuiket al (1988). The observed wave spectra indicate that the wave field is composed of sea waves (with peaks around 0·18 and 0·23 Hz) travelling nearly in the wind direction (WNW-N), and lower frequency (0·09 Hz) swell waves from the South. The parameterization of the wave directional spread shows that both local wind conditions and nonlinear wave-wave interactions control the shape of the directional distribution. The directional distribution is generally bimodal in the transition region between sea and swell and at higher frequencies when rapid changes in wind speed and direction occur.     

Morphology and evolution of an alluvial fan-a case study of Kalanutala,Prakasam district,A.P.

Alluvial fans are the dominant landforms of the semi-aird and arid environments of the world. Studies on alluvial fans elsewhere suggest that there is a close relationship between the morphology of the fan and the drainage basin area; lithology, mean slope, vegetation, climatic and tectonic environments of the source area. An alluvial fan at Kalanutala village, in Prakasam district of Anthra Pradesh, has been studied in detail in order to analyse it's morphology and arrive at its geomorphic evolution. From a study of fan morphology and it's composition, it has been arrived, at the conclusion that there is a relationship between the fan and it's drainage basin (Kompayasela). Further, this study reveals that the apparent segmentation of the fan is not because of tectonic movement but due to the underlying topography of pediment. The study of fan morphology and its materials suggests that the initial deposition of fan took place in a humid climate, but gradually changed to the present arid climate.     

Oxygen and carbon isotope composition of cold-water Berriedale Limestone (Lower Permian), Tasmania, Australia

The Berriedale Limestone formed at about 80°S paleolatitude and contains many glacial dropstones. It formed during a period of major Gondwana deglaciation.

The Berriedale Limestone contains mostly bryozoans, brachiopods and bivalves, with some intraclasts and rare pellets. The faunal diversity is low and the fauna are similar to the modern cold-water foramol faunal assemblage. Micrite, microspar and spar occur as equant to well developed rhombs of calcite. The coarse spar cements are bored and are ruptured by dropstones, indicating submarine origin of low-Mg calcite at water-temperatures of around 3°C. The mixing zone cementation was preceded by erosion of early formed crystals. The eroded crystals occur as inclusions in mixing zone cements.

The fauna are characterized by heavy δ¹³C and light δ¹⁸O. The whole-rock field of δ¹⁸O-δ¹³C falls at the edge of “Normal Marine Limestone” and deviates to lighter δ¹⁸O values (down to −16.7‰ PDB). Lightest δ¹⁸O values ( −22‰ PDB) of fresh-water sparry calcite cement are similar to those in the Early Permian continental tillites, suggesting that the Permian sea was diluted by isotopically light melt waters. Micrite δ¹⁸O values (−9.2 to −12.6‰ PDB) are within the range of whole-rock values. The δ¹⁸O values of calcite in shales are lighter than limestone values.

The δ¹⁸O values of the fauna give an unrealistic range of sea-water temperatures because the fauna have equilibrated with variable amounts of melt waters. However, calculated original δ¹⁸O values of the fauna indicate temperatures < 4°C. The heaviest δ¹⁸O of fauna gives cold temperatures of 9°C (with δ_w −2.8‰) and −3°C (with δ_w −6‰). The lightest values of sparry calcite cements (−22‰ PDB) indicate that the limestone reacted with cold melt waters.

The δ¹⁸O of Permian sea is estimated to be about +1.2‰ and was diluted by melt waters as light as −27‰ SMOW.     

Spectral width parameter for wind-generated ocean waves

An evaluation of the spectral width parameter for wind-generated ocean waves is presented based on the analysis of wave data obtained through the ship-borne wave recorder fitted to RVGaveshani. The coverage of wave data includes deep as well as shallow waters on the east and west coasts of India. Considering that the spectral width parameter ?₀ derived from Tucker's wave analysis provides a reasonably accurate estimate, a comparative study has been made for the other band-width definitions available in the literature. The results indicate some bias in the estimation of spectral width information using higher-order moments, e.g. ? _S andv, and with the alteration of spectral forms that are usually associated with multiple- or single-peaked wave spectra. Such a bias is not seen in the case of Goda's peakedness parameterQ _p with variation of spectral form. The effect of the ratio of the high-frequency cut-off to the spectral peak period on ? _S ,v andQ _p is also investigated.     

Very low frequency electromagnetic prospecting method—A few field applications in India

The very low frequency electromagnetic prospecting equipment measures different space and phase components of the electromagnetic field in the frequency range 15–25 kHz emanating from distant naval radio stations. The field application of the equipment designed and constructed for this purpose has demonstrated the usefulness of the investigations in groundwater and geological mapping. The amplitude measurements necessitate correction of the diurnal variations of the electromagnetic field at the observation point.     

Satellite image based quantification of invasion and patch dynamics of mesquite (Prosopis juliflora) in Great Rann of Kachchh,Kachchh Biosphere Reserve,Gujarat, India

The invasion of alien species is a significant threat to global biodiversity and the top driver of climate change. The present study was conducted in the Great Rann of Kachchh, part of Kachchh Biosphere Reserve, Gujarat, India, which has been severely affected by invasion of Prosopis juliflora. The invasive weed infestation has been identified using multi-temporal remote sensing datasets of 1977, 1990, 1999, 2005 and 2011. Spatial analyses of the transition matrix, extent of invasive colonies, patchiness, coalescence and rate of spread were carried out. During the study period of three and half decades, almost 295 km² of the natural land cover was converted into Prosopis cover. This study has shown an increment of 42.9% of area under Prosopis cover in the Great Rann of Kachchh, part of the Kachchh Biosphere Reserve during 1977 to 2011. Spatial analysis indicates high occupancy of Prosopis cover with most of the invasion (95.9%) occurring in the grasslands and only 4.1% in other land cover types. The process of Prosopis invasion shows high patch initiation, followed by coalescence, indicating aggressive colonization of species. The number of patches within an area of < 1 km² increased from 1977 to 2011, indicating the formation of new Prosopis habitats by replacing the grasslands. The largest patch of Prosopis cover increased from 144 km² in 1977 to 430 km² in 2011. The estimated mean patch size was 7.8 km² in 1977. The mean patch size was largest during 2011, i.e., 9 km². The annual spread rate for Prosopis has been estimated as 2.1% during 2005–2011. The present work has investigated the long term changes in Prosopis cover in the Great Rann of Kachchh, part of Kachchh Biosphere Reserve. The spatial database generated will be useful in preparing strategies for the management of Prosopis juliflora.