Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

T. M. Balakrishnan Nair ¹, V. Ramaswamy ¹, G. Parthiban ¹, R. Shankar ²

Affiliations
1 National Institute of Oceanography, Dona Paula, Goa - 403 004, IN
2 Department of Marine Geology, Mangalore University, Mangalagangotri - 574 199, IN

Abstract

Particle fluxes were measured using six time-series sediment traps at three sites in the western (16°20' N; 60°30' E), central (14°31' N; 64°46' E) and eastern (15°31' N; 68°43' E) Arabian Sea. Trap deployment depths were between 900 and 3000 m and collection period was from December 1992 to February 1994.

Annual particle fluxes showed an east-west trend with minimum fluxes (22.25 gm^-2) in the eastern Arabian Sea and maximum fluxes (69.81 g m^-2) in the western Arabian Sea. Carbonates, contributed mainly by foraminifers and coccolithophorids, are the dominant component in all the traps. Opal fluxes were maximum in the western Arabian Sea. At all the locations, lithogenic percentages increased with depth whereas organic carbon percentages decreased. Particle flux patterns show a strong seasonality with peak fluxes during the southwest (SW) monsoon (June to September). Relatively high fluxes were also observed during the northeast (NE) monsoon (December to February).

In the western Arabian Sea, particle fluxes are dominated mainly by carbonates during the early SW monsoon but by biogenic silica during the fate SW monsoon. The increase in particle fluxes during the early SW monsoon is related to variations in the mixed layer depth which, in turn, is controlled by the strength of the Findtater Jet and the curl of the wind stress. The increase in biogenic silica fluxes during the late SW monsoon is related to the advection of nutrient-rich water from the Oman and Somali upwelling areas. In the eastern Arabian Sea, particle fluxes are high during the NE monsoon due to the effects of winter cooling.

Keywords

Oceanography, Particle Flux, Sediment Trap, Sea Surface Temperature, Arabian Sea.

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J. N. Pattan ¹, G. Parthiban ¹

Affiliations
1 National Institute of Oceanography, Dona Paula, Goa - 403 004, IN

Abstract

Five buried ferromanganese nodules were recovered at different depths of 167-169 cm (A), 172- 174 cm (B), 228-230 cm (C), 328-330 cm (D) and 418-420 cm (E) in a 5 m sediment core from the siticeous sediment of Central Indian Basin (Lat 9°00' S , Long 76°00' E) at a water depth of 5260 m. These nodules were analysed for major, trace and rare earth element(REE) concentrations to understand their genesis and compare with the surface and burled nodules in the top 1 in of the sediment column from the same basin. Nodules A, B, C are of an early diagenetic(Mn/Fe ratio between 9 3 and 15 I), nodule D IS of hydrogenetic(Mn/Fe ratio 1 6) and nodule E is of diagenetic(Mn/Fe ratio 3 0) origin. Total REE concentration ranges between 164 and 497 ppm (av-348 ppm) and is nearly 2 to 3 fold lower than the surface and burled nodules REE are conveyed from the seawater to the nodules In association with a combined phase consistnig of Fe - Ti - P. The shale (NASC) - Normalized REE pattern displays a small convex pattern with a positive Ce-anomaly indicating an oxidized environment while, the presence of positive E u-anomaly in nodules A, B and C probably suggest an aeolian dust. These burled nodules show a moderate middle and heavy REE enrichment (strong in nodules B and C) compared to light REE, but fractionation between middle and heavy REE is not very clear It appears that not much significant Post -Depositional changes have occurred in these buried nodules.

Keywords

Buned Fe-Mn Nodules, Chemical Composlition, Genesis, REE Patterns, Central Indian Ocean Basin.

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