Inter-relationship between Nuclei and Gross Characteristics of Manganese Nodules,Central Indian Ocean Basin

More than 200 samples of manganese nodules from the Central Indian Ocean Basin (CIOB) were studied for their different parameters. The study included various aspects such as morphology, texture, mineralogy, and composition of the nodules. The nuclei of the nodules were also examined along with the oxide layers. We attempt to correlate the nucleus (their type and abundance) with the nodule parameters such as their external morphology, chemical composition, and suitable location of formation, amongst others. We found various nucleating materials and these include rock fragments (fresh and altered), clay, pumice and sharks' teeth. In a majority of the cases, rock fragments are dominant in the core of the nodules and these conform to that of the seafloor basalts. The shape of the nuclei influences that of the nodules, especially during their initial period of growth. Irrespective of the kind of nuclei, todorokite is the main mineral of the nodules. The nodules of the CIOB were formed mostly due to hydrogenous accretion of ferromanganese oxides while diagenetic contribution of metals is less common.     

Understanding heavy mineral dynamics using magnetic fingerprinting technique: a case study of North Maharashtra Coast,India

Environmental magnetic and grain size measurements were carried out on sand samples collected from nine sand pits along a 20-km coastal stretch of Arnala Beach, North Maharashtra, India. This study sets out to identify the potential heavy (magnetite) mineral-rich sites in a dynamic coastal system and decipher their enrichment processes. Combination of rock-magnetic and grain size data of the sand pits mirrors the differential heavy mineral fluxes along the coast. Two distinct and well-separated bands of magnetite enrichments were identified. The upper magnetite band (UMB) is more pronounced and shows uniform magnetite enrichment representing the present-day beach erosional state. A well-separated lower magnetite band (LMB) had highest magnetite concentration at Vaitarna River mouth and depicts a strong decrease in magnetite content and clastic (mean) grain size away from the river mouth. This suggests that the NW–SE-directed coast-parallel sediment transport in the past played a major role in the formation of magnetite-rich layers of LMB. A non-enriched zone (NEZ) between UMB and LMB is magnetically weak and showed large variations in clastic grain sizes and possibly represents a period of sediment accretion. A strong correlation between magnetite concentration and magnetic grain size was found for all the sand pit samples, with highest magnetic susceptibility values being dominated by coarser magnetic grains. This relationship needs to be further exploited as a potential fingerprint to identify the heavy mineral lag deposits in coastal environments. Our study explores the potential of using environmental magnetism and sedimentological methods to identify the potential areas enriched in heavy (magnetic) minerals and explains the mechanism of their formation.     

Accumulation of hexavalent chromium by an exopolysaccharide producing marine Enterobacter cloaceae

An exopolysaccharide producing Enterobacter cloaceae (AK-I-MB-71a) was tested for its Cr (VI) tolerance. This isolate was not only resistant to this heavy metal but also showed enhanced growth and exopolysaccharide production in the presence of Cr (VI) at 25, 50 and 100 ppm concentrations. XRF analysis of both the biomass as well as the exopolysaccharide revealed that a sum total of about 60-70% chromium was accumulated by this bacterium. This indicated that this organism could prove to be a potential candidate in the field of bioremediation with respect to chromium removal.     

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.     

Mineral chemistry of Carlsberg Ridge basalts at 3°35′–3°41′N

Mineral chemical analyses of transitional basalts from the Carlsberg Ridge show plagioclase (An ~ 87 mole %), phenocrysts, and microphenocrysts have a K₂O depletion as compared to the laths (An ~ 79 mole %). Olivine (Fo ~ 91 mole %) are few and rarely zoned. The composition of plagioclase and olivine indicate low pressure equilibrium crystallization. The basalts were probably derived through fractional crystallization at shallow depths under low partial melting conditions. Morphology of plagioclase phenocrysts and bulk rock chemistry suggest magma mixing and fractional crystallization for the origin of these basalts. (Detailed chemical analyses can be obtained from the authors.)     

The economics of mining seabed manganese nodules: A case study of the Indian Ocean nodule field

Abstract

Because of ever-growing demand for strategic metals, the focus of the international community has fallen on deep sea manganese nodules occurring at a water depth of more than 4500?m. We present an economic appraisal and strategy for mining of nodules from the Indian Ocean Nodule Field- one of the four economically potential areas in the world oceans. In contrast to the prevailing perception of non-viability of nodule mining, our analysis indicates a fair degree of economic feasibility and commercial sustainability to mine the deep-sea manganese nodules.     

Comparative study of scintillations at the magnetic equator and at the crest region of the equatorial anomaly in Indian zone

Using simultaneous long-term observations of ionospheric scintillation at equator and anomaly crest region in the same longitude (Indian) zone comparative features of scintillation occurrence are brought out. The salient features are: (a) predominantly pre-midnight occurrence of scintillation at equator during winter and equinox seasons, (b) increase of pre-midnight scintillation occurrence with solar activity (c) shifting of occurrence peak during summer from post-midnight in low to pre-midnight in high solar activity periods (d) similarity of scintillation behaviour at these locations during winter and equinoxes but dissimilarity during summer. The solar activity response and magnetic effects indicate that the scintillations at the anomaly crest region in winter and equinox, particularly during high solar activity periods, are of equatorial origin while the summer events may be of local or mid-latitude origin.