Thermohaline circulation in the Central Indian Basin (CIB) during austral summer and winter periods of 1997

As a part of Indian Deep Sea Environment Experiment (INDEX) aimed at assess ing the environmental impact of manganese nodule mining in the Central Indi an Basin (CIB), a study on baseline physical conditions of water column viz . potential temperature (theta), salinity and potential density together wi th geostrophic circulation regime in the deeper depths of the basin was con ducted. The hydrography data used in the present analysis were collected ov er a wide area of the western part of CIB (71 degrees -79 degrees E; 9 degr ees -14 degreesS) during austral summer (January 1997) from the Indian rese arch vessel ORV Sagar Kanya, while during the austral winter season (June-J uly 1997), hydrographical stations were occupied by Russian research vessel RV Yuzhmorgeologia in the central part of CIB (75 degrees -77 degreesE; 9 degrees -11 degreesS) where a benthic disturbance on experimental scale was carried out. The spatial variations in the physical parameters decreased b elow 3500 m, inferring a restricted basin-scale deep circulation. The dynam ic topography field at 5000 m relative to 2000 db surface in the central pa rt of CIB, representing the abyssal circulation, was generally characterize d by a southwestward weak flow around 10 degreesS flanked by cyclonic and a nti-cyclonic eddies on its right and left sides, respectively. This flow re gime agreed with the earlier one inferred by Warren (J. Mar. Res. 40 (1982) 823) linking the source of deep water in CIB to a saddle overflow across N inetyeast Ridge from West Australian Basin around 10 degreesS. (C) 2001 Els evier Science Ltd. All rights reserved.