Bottom water flow through the Kane Gap, Sierra Leone Rise, Atlantic Ocean

Abstract

Continuous seismic profiling, detailed temperature versus depth measurements, heat flow measurements, and a bottom photograph in the Kane Gap on the Sierra Leone Rise in the Atlantic Ocean suggest that a bottom current of cold water flows along the floor of the gap. The layer of cold water is 320 m thick and is marked by a large temperature gradient at the top. The layer is nearly isothermal at 2.28°C, which is 0.12°C colder than the water 500 m off the bottom. A channel exists in flat-lying sediments, which in turn overlay thicker, dipping sediments which exhibit internal evidence for erosion or selective nondeposition. This suggests a three-step depositional history: (1) erosion of a sequence of thick, dipping sediments, (2) deposition of flat-lying sediments, and (3) erosion of small channels in flat-lying sediments. It is not possible to determine conclusively the velocity or direction of flow of the bottom current from our data. The bottom photograph suggests flow to the north. This current probably reflects the effects on eastern basin circulation of the crossing of Antarctic bottom water through the Mid-Atlantic Ridge at either the Romanche fracture zone or the Vema fracture zone.