Recent sedimentation in the southeast Indian Ocean with special reference to the effects of Antarctic Bottom Water circulation

Abstract

In the southeast Indian Ocean the influence of the Anarctic Bottom Water (AABW) on sedimentation is evidenced by the intensity of the water turbidity near the bottom, and by the mineralogy (carbonate and quartz abundances) of the sediments and current markings on the sea floor. In the deep basins south of 50°S (South Indian and Tasman basins), besides high biogenic siliceous opal productivity, the greater influence of AABW is recorded in shallower carbonate compensation depths (<4000 m) than is the case in basins north of 50°S (5000–5200 m). Spreading of the AABW from the regions south of the Southeast Indian Ridge to the regions north of it is through fracture zones in the ridge at about 123–126°E and 145–155°E. These bottom-water passages are characterized by (1) low carbonate, high quartz, or high clay contents in the sediments, (2) distinct current markings suggesting the northward flow, and (3) high bottom-water turbidity. In large basins such as the South Indian and Tasman basins which have moderate-to-high near-bottom turbidity, central portions tend to be less turbid than the margins, suggesting strong marginal circulation. The Emerald Basin, situated east of the Tasman Basin and north of the Indian-Pacific Ridge, has high near-bottom turbidities. This suggests that the AABW in the Emerald Basin is derived directly from the source regions south of the ridge although some of the water may also be spreading from the Tasman Basin.