Exploring structured scripting cartographic technique of GMT for ocean seafloor modeling: A case of the 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.

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Seasonal variations in the Indian Ocean along 110°E. I. Hydrological structure of the upper 500 m

Marine and Freshwater Research ◽

10.1071/mf9690001 ◽

1969 ◽

Vol 20 (1) ◽

pp. 1 ◽

Cited By ~ 62

Author(s):

DJ Rochford

Keyword(s):

Indian Ocean ◽

Surface Waters ◽

Water Masses ◽

Surface Currents ◽

Temperature Changes ◽

East Indian ◽

Hydrological Structure ◽

The Indian Ocean ◽

The Tropics ◽

East Indian Ocean

Tropical and subtropical water masses at surface and subsurface depths were separated by their salinity, temperature, oxygen, and nutrient characteristics. The annual mean depths and latitudinal extent of these water masses were determined. Annual changes in the upper 50 m were generally so small relative to those found in other oceans that advection and mixing must have been less important in their genesis than local climatic changes. There was a barely significant seasonal rhythm in surface phosphate and nitrate, with peak occurrences of each some 6 months apart. At each latitude the permanent thermal discontinuity centred around a particular isotherm varied little in intensity during the year, but rose and fell in accordance with surface currents. The thermocline south of c. 18�S. varied little in depth but greatly in intensity during the summer. The depth of the mixed layer was much less in summer and at all times shallower in the tropics. The depth of this layer was governed more by the accumulation of surface waters by zonal currents and eddies, than by wind stress or convective overturn. Therefore there was little difference from south to north, or month to month, in average nutrient values of this mixed column. The movement of the various surface waters, deduced from salinity and temperature changes during the year, usually agrees with geostrophic currents across 110�E, and ships' observations of surface currents in the south-east Indian Ocean.

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Hydrology of the Indian Ocean. I. The Water Masses in Intermediate Depths of the South-East Indian Ocean

Marine and Freshwater Research ◽

10.1071/mf9610129 ◽

1961 ◽

Vol 12 (2) ◽

pp. 129 ◽

Cited By ~ 16

Author(s):

DJ Rochford

Keyword(s):

Indian Ocean ◽

West Indian ◽

Water Masses ◽

The South ◽

North West ◽

East Indian ◽

The North ◽

The Indian Ocean ◽

The Antarctic ◽

East Indian Ocean

Three water masses have been identified from maxima and minima in temperature-salinity diagrams for intermediate depths of the south-east Indian Ocean. (1) The Antarctic Intermediate occurred as a salinity minimum within the density range of 7.00-27.28 σt. (2) The North-West Indian Intermediate was found as a salinity maximum within the σt range 27.20-27.50. (3) The Banda Intermediate, lying below the North-West Indian Intermediate, had the characteristic of a salinity minimum within the σt range of 27.28-27.59. Preformed phosphate has been found useful as a third conservative property for the identification of major paths of spreading. The distribution and paths of spreading of the three water masses are shown in charts of the Indian Ocean east of 90�E.

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