Regional geomorphology of the continental slope of NW India: Delineation of the signatures of deep‐seated structures

Geomorphological features (derived from 16,000 lkm of echo‐sounding and bathymetric data) and deep‐seated tectonic structures of the continental margin off NW India are presented. The shelf break over the entire region occurs between 80 to 154 m water depth, and adjacent to Saurashtra and Bombay High the depth and orientation of the shelf edge show marked variations. The boundary of the slope is shallower in the northern portion (about 1450 m in the vicinity of the Indus) than in the southern region (2900 m off Bombay).

The steep slope off the Gulf of Kachchh has relatively smooth physiography due to higher input of fluvial sediment and burial of structures. The gentler slope off Saurashtra and the Bombay High area has numerous complex features, the most prominent among them being benches at depths of 180–230 m (width 2–10 km) and 650–780 m and a series of bathymetric highs and lows. Slope breaks are also observed between 400 and 600 m off Bombay and between 560 and 960 m off Saurashtra. These features are surface manifestations of the anticlinal features extending along the shelf in this region. Unevenness (order of 100–300 m) due to slumping is also observed at the base of the slope.

Based on the correlation between tectonic structures of this area and these subphysiographic features, extension of the Saurashtra Anticline onto the slope, a new strike slip fault (the southern boundary fault of Narmada graben) and an along‐shelf anticlinal structure off Saurashtra are delineated.     

Ice Height and Backscattering Coefficient Variability over Greenland Ice Sheets Using SARAL Radar Altimeter

Ice sheets investigation is important with regard to climate change and contribution to the sea level rise or fall. Radar altimetry in complement with laser altimetry can serve as a suitable candidate for precise monitoring of ice sheet evaluations. SARAL due to higher observation into the polar region (up to 82.5°N) can cover nearly 100% of the Greenland ice sheet. Continuous ice tracking mode retracker can provide useful information about ice surfaces, that is, determining the snow coverage, ice sheet transaction margin, and the evolution of snow depth during winter more accurately. This study present the results obtained with SARAL satellite Altika radar altimeter over the Greenland ice sheet region. The altimeter high rate waveforms products are used for utilizing the full capability of the instrument. High resolution DEM (1 km) generated using ICESAT/GLAS altimeter has been used for selecting the good quality data over the study region. Four different retrackers—Ocean, ICE-1, ICE-2, and Sea-Ice—were tested on the SARAL altimeter data set and compared with the DEM extracted ice sheet elevations. Three different data analysis—region of interest (ROI), track analysis, and cross-over analysis—were performed for in-depth analysis of the ice height changes and back scattering coefficient variability. ROI's (1° × 0.5°) were selected based on accumulation dry snow zone, percolation zone, wet snow zone, and ablation zone. Finally to observe the effect of Ka band, SARAL results has been compared with the Envisat altimeter in terms of back scatter and error in the height retrieval due to penetration problem within the ice sheet layer. The new SARAL data set confirms the potential of ice altimetry and provides a new opportunity to monitor the ice sheet surface topography evolution.     

Vertical diffuse attenuation coefficient (Kd) based optical classification of IRS-P3 MOS-B satellite ocean colour data

The optical classification of the different water types provides vital input for studies related to primary productivity, water clarity and determination of euphotic depth. Image data of the IRSP3 MOS-B, for Path 90 of 27th February, 1998 was used for deriving vertical diffuse attenuation coefficient (K_d) and an optical classification based onK _d values was performed. An atmospheric correction scheme was used for retrieving water leaving radiances in blue and green channels of 412, 443, 490 and 550 nm. The upwelling radiances from 443 nm and 550 nm spectral channels were used for computation of vertical diffuse attenuation coefficientK _d at 490 nm. The waters off the Gujarat coast were classified into different water types based on Jerlov classification scheme. The oceanic water type IA (K _d range 0.035-0.040m^-1), type IB (0.042-0.065 m^-1), type II (0.07-0.1m^-1) and type III (0.115-0.14m^-1) were identified. For the coastal waters along Gujarat coast and Gulf of Kachchh, K_d(490) values ranged between 0.15 m^-1 and 0.35 m^-1. The depth of 1% of surface light for water type IA, IB, II and III corresponds to 88, 68, 58 and 34 meters respectively. Classification of oceanic and coastal waters based onK _d is useful in understanding the light transmission characteristics for sub-marine navigation and under-water imaging.     

Remote Sensing of suspended sediments along the Tamil Nadu coastal waters

Indian Remote Sensing satellite (IRS) 1A & 1B digital data in combination with field measurement were used to map distribution and concentration of suspended sediments along the Tamil Nadu coastal waters for monsoon and non-monsoon periods. Qualitative suspended sediment mapping was done for entire Tamil Nadu coast while quantitative studies were taken at two selected sites (eg. Tuticorin and Ennore). For qualitative mapping both monsoon (17-12-90) and non-monsoon (18-4-90) season data were analysed by level slicing technique and a qualitative scale was assigned to different sediment classes based on tonal variations. The suspended sediment concentration (SSC) samples were collected on April 15, 1992 and March 10, 1992 around Ennore and Tuticorin coastal waters respectively, synchronous to IRS-1A satellite overpass. This data was used for quantitative estimation of SSC using digital chromaticity technique. The study shows that the plumes of high suspended sediment concentration are contributed from the nearshore wetlands and river mouths and were finally dispersing towards Jaffna coast. Different classes of high to low SSC values ranging from less than 5 mg/L in offshore areas to 21 mg/L in nearshore of Tuticorin were also delineated. The dispersal pattern of the sediments on different is discussed.     

Mapping of hydrothermally altered zones in Aravalli Supergroup of rocks around Dungarpur and Udaipur,India, using Landsat-8 OLI and spectroscopy

We explored the utilization of Landsat-8 Operational Land Imager (OLI) data for mapping of hydrothermal alteration zones. The region in and around the cities of Dungarpur and Udaipur of Rajasthan state in India was selected for this study. The rock types of Dungarpur and Udaipur are serpentinites, talc-carbonate, talc-schist, and quartzite of the Aravalli Supergroup. Hydrothermally altered zones and resultant hydrous minerals play an important role in the genesis of these rocks. We aimed to identify possible locations of hydrothermally altered zones in regional context around Dungarpur and Udaipur using Landsat-8 OLI data. False-color composite maps and band ratios were prepared from Landsat-8 bands. Band ratios such as band 6/band 7 (short-wave infrared 1 (SWIR1)/short wave infrared 2 (SWIR2)), band 4/band 3 (red/green), and band 5/band 6 (near infrared (NIR)/SWIR1) and visual interpretation techniques were used to identify the hydrothermally altered zones. Spectroscopic analyses of field rock samples were done to validate the hydrothermal alteration zones delineated from the analysis of Landsat-8 data. We present the combined results of Landsat-8 and field spectroradiometer analysis which brings out the hydrothermal alteration zones associated with hydrous minerals (antigorite, lizardite, montmorillonite, vermiculite, talc, and saponite). The study demonstrates the utility Landsat-8 OLI (with field spectroradiometer data) in the mapping of hydrothermally altered zones as a key in understanding geological processes.     

Differential behaviour of a Lesser Himalayan watershed in extreme rainfall regimes

Climatic extremes including precipitation are bound to intensify in the global warming environment. The present study intends to understand the response of the Tons sub-watershed in Lesser Himalaya, in 3 years with entirely different hydrological conditions (July 2008–June 2011) in terms of discharge, sediment flux and denudation rates. Within an uncertainty limit of ±20%, the mean interannual discharge (5.74 ± 1.44 m ³ s ^?1) (±SE), was found highly variable (CV: 151%; 0.8–38 m ³ s ^?1). In a normal rainfall year (2008–2009; ～1550 mm), the discharge was 5.12 ± 1.75 m ³ s ^?1, whereas in a drought year (2009–2010), it reduced by 30% with the reduction in ～23% rainfall (CV: 85%). In an excessive rainfall year (once-in-a-century event) (2010–2011; ～3050 mm), discharge as well as total solid load was ～200% higher. Monsoon months (July–September) accounted for more than 90% of the annual solid load transport. The ratio of dissolved to suspended solid (C/P ratio) was consistently low (<1) during monsoon months and higher (1–7) during the rest of the dry period. C/P ratio was inversely (R ²=0.49), but significantly (P <0.001) related to the rainfall. The average mechanical erosion rate in the three different rainfall years was 0.24, 0.19 and 1.03 mmyr ^?1, whereas the chemical erosion was estimated at 0.12, 0.11 and 0.46 mmyr ^?1, respectively. Thus, the average denudation rate of the Tons sub-watershed has been estimated at 0.33 mmyr ^?1 (excluding extreme rainfall year: 1.5 mmyr ^?1). Our results have implications to understand the hydrological behaviour of the Lesser Himalayan watersheds and will be valuable for the proposed and several upcoming small hydropower plants in the region in the context of regional ecology and natural resource management.     

Evaluation of fertility indicators associated with arsenic-contaminated paddy fields soil

Emerging environmental issues related to heavy metal contamination in rice draw great concern about the soil quality of paddy farming lands irrigated with groundwater. Investigating the functioning of soil microorganisms exposed to heavy metal contamination is imperative for agricultural soil manipulations. The current study accentuates the influence of heavy metals on microbial activity and community composition in arable soil of West Bengal State of India. The result revealed that the fertility indicators (activity of all soil enzymes) and growth-limiting factors (soil N and P) were negatively correlated with the heavy metal stress except the soil total organic content which demonstrated significant positive correlation with the heavy metals. In case of functional diversity of soil, all the considered diversity indices exhibited no specific pattern along with the availability of heavy metals. Further, despite the heavy metal contamination, we observed a very complex and indifferent pattern of bacterial community composition along the heavy metal contamination sites. Overall, we found that γ-Proteobacteria had been the most abundant bacterial community followed by Actinobacteria, Firmicutes, β-Proteobacteria and α-Proteobacteria. Commemorating all the results, we can infer that arsenic and other heavy metal contamination is deteriorating the soil quality and hence warrants immediate attention of concerned soil scientist and agronomists.     

Depositional environments inferred from variations of calcium carbonate,organic carbon,and sulfide sulfur: A core from southeastern Arabian Sea

The variations in CaCO₃ and organic carbon and their inter-relationship in a core from the southeastern Arabian Sea (water depth 2,212 m) have been used to demarcate the Holocene/Pleistocene boundary; an increased terrigenous deposition during Late Pleistocene has been inferred. The higher contents of organic carbon and sulfide sulfur and their negative relationship clearly establish the existence of a reducing environment below 65 cm subbottom depth. The occurrence of pyrite framboids and crystals, present only on the surface of fecal pellets (80–85 cm), has been discussed in terms of significance of reducing microenvironment.