http://irgu.unigoa.ac.in/drs/handle/unigoa/5627 Tue, 21 Jul 2026 06:38:40 GMT 2026-07-21T06:38:40Z http://irgu.unigoa.ac.in/drs/handle/unigoa/7892 The Bengal fan - Geomorphology and sediment distribution Nayak, G.N. The Bay of Bengal is a large but relatively shallow embayment of the northeastern Indian Ocean. It receives a significant amount of freshwater and sediment, approximately 2000 million tonnes annually, from the Himalayan and the Indian peninsular rivers during the North East (NE) and the South West (SW) monsoons, respectively. The sediment flux to the bay is among the highest globally due to its size, location, and the catastrophic deposition of sediments. Long paleo-synoptic reconstructions and paleomonsoon interpretations from sediment cores in the Bay of Bengal are limited. This is largely because the enormous sediment load that enters the Bay through river discharge occurs under high-energy conditions, making it challenging to retrieve turbidity-free and undisturbed sediment cores. However, some recent reports (Ponton et al., 2012; Tripathy et al., 2014) have documented variations in paleoclimate and geochemical cycles from the Last Glacial Maximum to the late Holocene period in the Bay of Bengal. Sedimentological and geochronological studies conducted on the eastern Bengal shelf studied by Kuehl et al. (1989) revealed that the highest sediment accumulation from the Ganges-Brahmaputra river system occurs near the head of the Swatch of No Ground, which is located west of the present river mouths of Ganges-Brahmaputra. Additionally, Kolla and Rao (1990) analyzed sediment sources from the Bay of Bengal and reported high quartz and low calcium carbonate percentages adjacent to the Indian subcontinent, likely due to a substantial influx of terrigenous clastics. Furthermore, investigations on the mineralogy and heavy minerals in sands suggest that sediments of the western Bengal Fan, characterized by high levels of smectite, sillimanite, and garnet, are derived from peninsular Indian rivers. Thu, 01 Jan 2026 00:00:00 GMT http://irgu.unigoa.ac.in/drs/handle/unigoa/7892 2026-01-01T00:00:00Z http://irgu.unigoa.ac.in/drs/handle/unigoa/7863 Seasonal variations in the optical properties of near-surface aerosols and the delineation of aerosol types at a tropical coastal site, Goa, adjoining the Eastern Arabian Sea Sen, A.; Shaikh, A.A.; Menon, H.B. A comprehensive study characterizing the extensive (scattering (sigma sca) and absorption (sigma abs) coefficients) and intensive (scattering Angstrom exponent (SAE), absorption Angstrom exponent (AAE), and single scattering albedo (SSA)) optical properties of near-surface aerosols, was conducted at a tropical coastal site adjoining the Eastern Arabian Sea (Goa, India) for the period from December 2019 to November 2020. Temporal (seasonal/diurnal) variations in aerosol extensive and intensive properties, and the roles of continental/marine air masses (long-range transport and land-sea-breeze circulation), boundary-layer evolution, and emission patterns in modulating the aerosol population have been examined. This is the first study at a coastal site in India to probe the SAE-AAE relationship for aerosol-type classification. Distinct seasonal variability was observed in sigma sca and sigma abs, with elevated aerosol concentrations during winter and post-monsoon, attributable to the influence of continental air masses and stagnant meteorological conditions, and reduced aerosol concentrations during monsoon owing to wet scavenging and marine air intrusion. Bimodal peaks in sigma sca and sigma abs during morning (08:00-09:00 h) and evening (20:00-22:00 h) indicated diurnal variations in aerosol concentrations driven by boundary-layer evolution and anthropogenic emissions, particularly during winter. Intensive optical properties revealed a seasonal transition from fine-mode, absorbing aerosols, associated with urban pollution during winter (SAE=1.19 plus-minus 0.15, AAE=1.02 plus-minus 0.18, SSA=0.86 plus-minus 0.04) and post-monsoon (SAE=1.30 plus-minus 0.19, AAE=0.99 plus-minus 0.19, SSA=0.90 plus-minus 0.04), to coarse-mode, scattering types in monsoon (SAE=0.40 plus-minus 0.43, AAE=0.94 plus-minus 0.26, SSA=0.93 plus-minus 0.04). The aerosol-type classification revealed low-absorbing small particles (SPLA), black carbon-dominated (BC-dominated), large particles and BC mixture (LP/BC mix), and low-absorbing large particles (LPLA) as the dominant near-surface aerosol types across seasons. Their seasonal distributions reflected a shift from continental to marine influence, with SPLA plus BC-dominated aerosol types prevalent during post-monsoon (92.2 percent) and winter (65.6 percent), and LPLA plus LP/BC mix (89.3 percent) during monsoon. The lowest mean SSA was observed for the BC-dominated aerosol type during winter (0.84), and the highest for LPLA (0.94) during monsoon. Diurnal variations were consistent across all seasons, with fine-mode (coarse-mode) aerosol types dominating during cooler nocturnal (warmer daytime) hours, indicating land-sea-breeze circulation as the primary driver. These findings underscore the complex interplay among local and upwind emission sources and atmospheric processes in shaping the aerosol regimes over tropical coastal environments. Thu, 01 Jan 2026 00:00:00 GMT http://irgu.unigoa.ac.in/drs/handle/unigoa/7863 2026-01-01T00:00:00Z http://irgu.unigoa.ac.in/drs/handle/unigoa/7852 Analysis of bio-optical properties in estuarine and coastal waters-study through in-situ and remote sensing observations. Patil, Partha Estuarine and coastal waters are characterised by highly variable and optically complex conditions resulting from spatially and temporally heterogeneous distributions of optically ac tive constituents (OACs), notably phytoplankton pigments, total suspended matter (TSM), and chromophoric dissolved organic matter (CDOM). These aquatic environments, generally clas sified as Case II waters, challenge conventional remote sensing methodologies due to the non linear and spectrally overlapping contributions of absorption and scattering processes governed by these constituents. This thesis presents a comprehensive investigation of the bio-optical dynamics of estuarine and coastal ecosystems through an integrative approach combining multi-seasonal in-situ radiometric, spectrophotometric, and remote sensing observations with satellite-derived ocean colour products. The research specifically emphasizes the quantification and remote sensing of CDOM and its implications for radiative transfer processes and coastal ecosystem functioning. A semi-analytical retrieval algorithm was developed for the robust esti mation of CDOM absorption at 440 nm (a440 CDOM) across diverse optical regimes by isolating the CDOMsignal influencing the spectral reflectance and minimising the attenuation by the other OACs. Thedevelopedalgorithmwasoftheform, a440 the three wavelength index given as x = ( 1 R412 rs cdom = −0.01368x2+0.102x+0.02295, with − 1 ) ×R560 R490 rs rs . This algorithm was formulated and validated using an extensive global dataset of in-situ measurements comprising absorption and attenuation coefficients, water-leaving radiance, and CDOM spectral slopes, acquired from estuarine and nearshore coastal zones. Comparative evaluation against widely adopted empiri cal and semi-analytical algorithms demonstrated superior performance of the proposed model, yielding the highest coefficient of determination (r2 = 0.64) and the lowest error metrics (rmse = 0.1039, mae = 0.064, mape = 51.96%). Notably, its accuracy improved under conditions where CDOM exerted a dominant influence on the total absorption budget. The validation using satellite-derived data from MODIS-Aqua and Sentinel-3 OLCI further substantiated the algorithm’s applicability across a spectrum of Case II waters Sun, 01 Jun 2025 00:00:00 GMT http://irgu.unigoa.ac.in/drs/handle/unigoa/7852 2025-06-01T00:00:00Z http://irgu.unigoa.ac.in/drs/handle/unigoa/7807 Assessment of microplastic contamination and associated risks in agricultural soils: a case study along the National Highway-66, Goa, India Chodankar, R.; Kalangutkar, N.G. Agricultural soils near major transportation corridors increasingly act as repositories for anthropogenic debris, yet the dynamics of this contamination in tropical paddy fields remain under-researched. This study investigates the abundance, morpho-chemical characteristics, and calculated ecological risks of microplastics in paddy field soils along National Highway 66 in Goa, India. Using Raman spectroscopy, scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), and standardized hazard indices, microplastic contamination was found to be ubiquitous, with concentrations ranging from 250 to 423 MP/kg (mean: 336.7 plus-minus 55.47 MP/kg). Population density and proximity to urban centers were key drivers of accumulation, with low-lying paddy regions functioning as depositional sinks for pollutants transported via runoff. Morphological analysis revealed a predominance of fibers (63 percent) and fine-sized particles (0.1-0.063 mm), indicating high potential for soil mobility. Polypropylene (51.85 percent) and polycarbonate (17.59 percent) were the dominant polymers identified. Notably, while the study area is traffic-influenced, tire-wear particles were not detected within the analytical range of the Raman technique employed, with the profile instead reflecting agricultural and consumer-related inputs. SEM analysis highlighted extensive surface weathering, while elemental profiling confirmed the adsorption of heavy metals (Pb, Cu, Fe), establishing these particles as active vectors for contaminants. Ecological risk assessments using the Polymer Hazard Index (PHI), Pollution Load Index (PLI), and Potential Ecological Risk Index (PERI) demonstrated a disconnect between abundance and hazard. These findings suggest that mitigation must prioritize hazard-weighted assessment over simple abundance monitoring to protect agricultural soil health. Thu, 01 Jan 2026 00:00:00 GMT http://irgu.unigoa.ac.in/drs/handle/unigoa/7807 2026-01-01T00:00:00Z