Satellite free-air gravity anomaly contour map at 5 mGal interval, seismic reflection and bathymetric data lead to the identification of deformed crustal structure of the Central Indian Ocean Basin. Twenty-three NE-SW trending deformed crustal features have been identified between 5°S to 4°N and 77° to 89°E. Pattern of deformation varies with large relief anticlines in the west, numerous long wavelength anticlinal basement rises in the middle of the basin, and zones of high-angle reverse faults and low-amplitude broad basement rises dominated with reverse faults in the east. Their disposition and deformation pattern record excess folding and shortening in the east of the basin. A chain of near circular free-air anomalies due to volcanic constructs that trend in arcuate shape from north to south parallel to 82.5°E are noted as southern continuity of the 85°E Ridge, which terminates at the Afanasy Nikitin seamount. Change in rheology of the crustal rocks and deformation in the east appear to result due to high heat-flow in the middle of the basin and intense seismicity of the eastern part of the basin. The present plate boundary forces contribute to the change in physical state and architecture of deformation of crust and result in vast area undergoing NNW-SSE to NW-SE compression.
Bengal Fan is one of the world's largest submarine fans having an area of 2.8-3.0 xl0 6 sq.km. It extends from Ganges/Brahmaputra delta around 20° N latitude to south of 7° S, with a maximum width of about 1000 km around 15 N latitude. Large volume of continental sediments are being discharged by Ganges and Brahmaputra Rivers into the Bay of Bengal and the finer sediment particles reach even 7° S latitude. The sediments rest on the early Cretaceous ocean floor characterized by the Mesozoic anomalies M11 through M0. Pattern of sediment deposition, tracing the imprints of sediment movement, turbidity current flows. paleo channels, their migration in time and space and sea level fluctuations by facies identification can be used to reconstruct the development history of the Fan. After India's soft collision with the Eurasian plate, these events may have played a critical role in shaping various morphological features since late Eocene in the Bay of Bengal. The present 12 kHz Echo sounder data collected along the NW-SE trending long profiles spaced at 30 nautical miles aided to improve the bathymetry chart of the Bay of Bengal. The echograms show some important geo-morphological features of the seafloor. One such feature is the Swatch of no ground which resembles a deep Canyon/Channel/ valley. Several longitudinal channels appear to drain the sediments from the mighty rivers Ganges and Brahmaputra into the Bengal Fan. Levees and abandoned channels are also present on the seafloor. The eastern continental margin is characterized by narrow shelf followed by steep slope. Bathymetry in the adjacent Bengal fan varies from 4000 m. The echograms along some profiles depict an irregular and rugged topography immediately beyond the shelf break. The seafloor is very stable and smooth except few places beyond shelf break. At some locations in the distal Bengal fan, isolated local highs dominate the seafloor with a positive relief of 500 to 900 m from the mean seabed and these features are associated with positive magnetic anomalies. The newly reported bathymetric high (R) is characterized with three peaks, and associated with a positive magnetic anomaly. This positive topographic high is surrounded by abandoned channels with levees and the fan divisions.
Bathymetry and magnetic studies (part of the Trans Indian Ocean Geotraverse investigations) in the northeastern Indian Ocean revealed seafloor topographic features, magnetic lineations (19 through 32B) and abandoned spreading centers. The seafloor topography of the Ninetyeast Ridge is relatively wider and shallower south of 15°S. The magnetic anomalies indicate nine fracture zones. Two of them are newly identified. Some of the fracture zones are reflected in the bathymetry. Abandoned spreading centers between 86°E Fracture Zone (FZ) and 92°E FZ are interpreted as the western extensions of the Wharton Ridge. They ceased spreading along with other spreading centers in the Wharton Basin soon after the formation of magnetic anomaly 19 (around 42 Ma) and merged the Indian and Australian plates as single Indo‐Australian plate. The pattern of magnetic lineations between 86°E FZ and 90°E FZ indicate a series of southerly ridge jumps at anomalies 30, 26 (Royer et al., 1991 and other workers) and 19. These ridge jumps transferred portions of the Antarctic plate to the Indian plate. The captured portions and offset along 86°E FZ between India‐Antartica Ridge and Wharton Ridge resulted in an anomalous extra oceanic crust between 86°E FZ and Ninetyeast Ridge spanning 11° in latitude.
Vibrio cholerae, the bacterium responsible for the disease cholera, is a naturally-occurring bacterium, commonly found in many natural tropical water bodies. In the context of the U.N. Sustainable Development Goals (SDG) targets on health (Goal 3), water quality (Goal 6), life under water (Goal 14), and clean water and sanitation (Goal 6), which aim to “ensure availability and sustainable management of water and sanitation for all”, we investigated the environmental reservoirs of V. cholerae in Vembanad Lake, the largest lake in Kerala (India), where cholera is endemic. The response of environmental reservoirs of V. cholerae to variability in essential climate variables may play a pivotal role in determining the quality of natural water resources, and whether they might be safe for human consumption or not. The hydrodynamics of Vembanad Lake, and the man-made barrier that divides the lake, resulted in spatial and temporal variability in salinity (1–32 psu) and temperature (23 to 36 °C). The higher ends of this salinity and temperature ranges fall outside the preferred growth conditions for V. cholerae reported in the literature. The bacteria were associated with filtered water as well as with phyto- and zooplankton in the lake. Their association with benthic organisms and sediments was poor to nil. The prevalence of high laminarinase and chitinase enzyme expression (more than 50 µgmL−1 min−1) among V. cholerae could underlie their high association with phyto- and zooplankton. Furthermore, the diversity in the phytoplankton community in the lake, with dominance of genera such as Skeletonema sp., Microcystis sp., Aulacoseira sp., and Anabaena sp., which changed with location and season, and associated changes in the zooplankton community, could also have affected the dynamics of the bacteria in the lake. The probability of presence or absence of V. cholerae could be expressed as a function of chlorophyll concentration in the water, which suggests that risk maps for the entire lake can be generated using satellite-derived chlorophyll data. In situ observations and satellite-based extrapolations suggest that the risks from environmental V. cholerae in the lake can be quite high (with probability in the range of 0.5 to 1) everywhere in the lake, but higher values are encountered more frequently in the southern part of the lake. Remote sensing has an important role to play in meeting SDG goals related to health, water quality and life under water, as demonstrated in this example related to cholera.
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