scholarly journals Geomorphology of the Ninety East Ridge

2021 ◽  
Vol 20 (3) ◽  
pp. 195-212
Author(s):  
Polina Lemenkova ◽  
Keyword(s):  
Indian Ocean ◽  
High Precision ◽  
Gravity Data ◽  
Cross Sectional ◽  
The Indian Ocean ◽  
Geomorphological Features ◽  
Topographic Structure

This paper explores the geomorphological features of the Ninety East Ridge (NER), Indian Ocean. NER presents especially long and linear topographic structure formed as a result of complex regional geophysical and geologic development. The research is based on high precision bathymetric, geological and gravity data. The submarine geomorphology of NER was digitized as three cross-sectional profiles. The profiles were selected in northern, central and southern segments. The depths were visualized in graphs, compared and statistically analyzed by histograms. The study contributes to the geophysical studies of the Indian Ocean.

scholarly journals Exploring structured scripting cartographic technique of GMT for ocean seafloor modeling: A case of the East Indian Ocean

2021 ◽  
Vol 3 (2) ◽  
pp. 162-184
Author(s):  
Polina Lemenkova
Keyword(s):  
Indian Ocean ◽  
Western Slope ◽  
Cross Sectional ◽  
Marine Research ◽  
East Indian ◽  
Eastern Flank ◽  
Trench Structure ◽  
The Indian Ocean ◽  
Topographic Depressions ◽  
East Indian Ocean

This paper examines spatial variations in the geomorphology of the Ninety East Ridge (NER), located in the Indian Ocean. The NER is an extraordinary long linear bathymetric feature with topography reflecting complex geophysical setting and geologic evolution. The research is based on a compilation of high-resolution bathymetric, geological, and gravity datasets clipped for the study area extent  (65° -  107°E, 35°S - 21°N): General Bathymetric Chart of the Oceans (GEBCO), Earth Gravitational Model (EGM2008, EGM96). The submarine geomorphology of the NER was modeled by digitized cross-sectional profiles using Generic Mapping Tools (GMT). The availability of the method is explained by 1) the free datasets; 2) the open source GMT toolset; 3) the available tutorials of the GMT and the codes explained in this work. Three segments of the NER were selected, digitized, and modeled: 1) northern 89°E, 7°S to 90°E, 7°N; 2) central 88.4°E, 14.7°S to 88.8°E, 8.2°S; 3) southern 87.9°E, 17°S to 87.5°E, 27°S. Measured depths were visualized in graphs, compared, and statistically analyzed by the histograms. The northern segment has a steepness of 21.3° at the western slopes, and 14.5° at the eastern slope. The slopes on the eastern flank have dominant SE orientation. The central segment has a bell-shaped form, with the highest steepness comparing to the northern and southern segments. The eastern flank has a steepness of 49.5°. A local depression at a distance of 50 km off from the axis (90°E) continues parallel to the NER, with the shape of the narrow minor trench. The western slope has a steepness of 57.6°, decreasing to 15.6°. The southern segment has a dome-like shape form. Compared to the northern and central segments, it has a less pronounced ridge crest, with a steepness of 24.9° on the west. The eastern flank has a steepness of 36.8° until 70 km, gradually becoming steeper at 44.23°. A local minor trench structure can be seen on its eastern flank (100 km off the axis). This corresponds to the very narrow long topographic depressions stretching parallel to this segment of the NER at 90.5°E. The study contributes to regional geographic studies of Indian Ocean geomorphology and cartographic presentation of GMT functionality for marine research and oceanographic studies.

The Indian Ocean paradox revisited: HIV and sexually transmitted infections in the Comoros

2007 ◽  
Vol 18 (9) ◽  
pp. 596-600 ◽  
Author(s):  
Yasmina Dada ◽  
François Milord ◽  
Eric Frost ◽  
Jean-Pierre Manshande ◽  
Aloys Kamuragiye ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Sex Workers ◽  
Female Sex Workers ◽  
Adult Population ◽  
Adverse Outcomes ◽  
Transmitted Infection ◽  
Cross Sectional ◽  
Sexually Transmitted ◽  
Number Of Sexual Partners ◽  
The Indian Ocean

The combination of high sexually transmitted infection (STI) prevalence and low HIV prevalence has been described as the Indian Ocean paradox. To investigate current epidemiology of HIV and STI in the Comoros, we conducted cross-sectional surveys of a representative sample of the adult population, and convenience samples of female sex workers and male STI patients. Only one (0.025%) of 3990 community participants was HIV-infected, while 142 (3.6%) had treponemal antibodies. Treponemal antibodies were not associated with past genital ulcers, number of sexual partners or adverse outcomes of pregnancies; their prevalence did not increase with age and there was no concordance within couples. Thus, most individuals with treponemal antibodies were probably infected during childhood with a non-venereal treponematosis. Only 1/70 (1.4%) and 0/83 sex workers sampled in 2004 and 2005 were HIV-infected. The Comoros have been protected by their insular status, male circumcision and paucity of syphilis. HIV control should focus on sex workers.

scholarly journals Insights on the Indian Ocean Tectonics and Geophysics Supported by GMT.

2020 ◽  
Vol 27 (2) ◽  
pp. 67-83
Author(s):  
Polina Lemenkova
Keyword(s):  
Indian Ocean ◽  
Gravity Data ◽  
Geological Structure ◽  
Climatic Conditions ◽  
Seafloor Topography ◽  
High Resolution Data ◽  
Free Air ◽  
The Indian Ocean ◽  
Free Air Gravity ◽  
Spreading Rates

This paper presented analyzed and summarized data on geological and geophysical settings about the tectonics and geological structure of the seafloor of the Indian Ocean by thematic visualization of the topographic, geophysical and geological data. The seafloor topography of the Indian Ocean is very complex which includes underwater hills, isolated mountains, underwater canyons, abyssal and accumulative plains, trenches. Complex geological settings explain seismic activity, repetitive earthquakes, and tsunami. Understanding and prognosis of the disastrous and catastrophic geological events is strongly based on correct data analysis, modelling and visualization. An important feature of this paper is mapping multi-source high-resolution data by GMT. Data include raster grids in NetCDF and GRD formats: ETOPO1, geologic and marine free-air gravity data, EGM96, age, spreading rates, and spreading asymmetry of the ocean crust by NOAA, total sediment thickness. Data were visualized by GMT modules to compare and analyze geophysical and geological settings of the Indian Ocean. Visualization reveled correlations between high bathymetric variations of the oceanic seafloor, distribution of main geological seafloor fabric: Southwest, Southeast, Mid and Carlsberg ridges. Tectonic maps were plotted to perform comparative analysis of several variables: crust age, spreading half rates (mm/yr), asymmetries in crustal accretion on conjugate ridge flanks (%), variations in the geopotential and gravimetric models. Being the warmest of the world’s ocean, Indian Ocean has specific climatic conditions (repetitive monsoons, tsunamis, cyclones and storms), complex geologic seafloor structure with triple junction and unique geographic settings. Presented paper contribut ed to the regional studies of the Indian Ocean.

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