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We report some main results of multidisciplinary investigations carried out within the framework of the Indian National Gas Hydrate Program in [2002][2003] in the Krishna-Godavari Basin offshore sector, east coast of India, to explore indicators of likely gas hydrate occurrence suggested by preliminary multi-channel seismic reflection data and estimates of gas hydrate stability zone thickness. Swath bathymetry data reveal new evidence of three distinct geomorphic units representing (1) a delta front incised by several narrow valleys and mass flows, (2) a deep fan in the east and (3) a WNW-ESE-trending sedimentary ridge in the south.Deep-tow digital side-scan sonar, multi-frequency chirp sonar, and sub-bottom profiler records indicate several surface and subsurface gas-escape features with a highly resolved stratification within the upper 50 m sedimentary strata. Multi-channel seismic reflection data show the presence of bottom simulating reflections of continuous to discrete character. Textural analyses of 76 gravity cores indicate that the sediments are mostly silty clay. Geochemical analyses reveal decreasing downcore pore water sulphate (SO 4 2− ) concentrations (28.7 to <4 mM), increasing downcore methane (CH 4 ) concentrations (0-20 nM) and relatively high total organic carbon contents (1-2.5%), and microbial analyses a high abundance of microbes in top core sediments and a low abundance of sulphate-reducing bacteria in bottom core sediments.Methane-derived authigenic carbonates were identified in some cores. Combined with evidence of gasescape features in association with bottom simulating reflections, the findings strongly suggest that the physicochemical conditions prevailing in the study area are highly conducive to methane generation and gas hydrate occurrence. Deep drilling from aboard the JOIDES Resolution during 2006 has indeed confirmed the presence of gas hydrate in the KrishnaGodavari Basin offshore.

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The Oxygen Minimum Zone (OMZ) is a potential source of CO 2 to the atmosphere and the extensive OMZ spread to 1.37 x 10 6 km 2 in the northern Arabian Sea would be an important contributor to the CO 2 budget. In this perspective, we report here that the eastern Arabian Sea experienced coeval increase in productivity and denitrification from ~7 to 0 kyr, which coincides with minimum dissolved oxygen levels in bottom-waters. In addition, during the same period, an increased calcium carbonate dissolution occurred as evidenced by low CaCO 3 content, decreasing shell weights of planktonic foraminifer species Globigerinoides ruber with well-marked dissolution features on their shells. Therefore, this study has implications on the role of OMZ in governing CaCO 3 dissolution and contributing to an increase in atmospheric CO 2 .

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