Antarctic bottom water flow in the western part of the Romanche Fracture Zone based on the measurements in October of 2011

Abstract

The properties of the Antarctic Bottom Water flow in the region of its inflow to the channel of the Romanche Fracture Zone at 22°10′–22°30′ W are studied on the basis of CTD and LADCP profiling in the western part of the equatorial fracture zone. A deep water cataract was found at the sill over the southern wall of the fracture with a depth of approximately 4600 m, which is associated with the abyssal flow, whose potential temperature is lower than 1°C. The inflow of water into the channel of the fracture in this temperature range is fully localized over this sill. The minimum potential temperature θ recorded in 2011 near the bottom was equal to 0.51°C, which is lower approximately by 0.12°C than the minimum temperatures ever measured in the western part of the fracture. The water transport in the cataract was estimated at 0.2 Sv (1 Sv = 10⁶ m³/s), which is approximately 30% of the known estimates of the total transport of Antarctic Bottom Water (θ < 1.9°C) through the fracture. The extremely high intensity of the cross isothermal mixing in the cataract region was found. The analysis of the bottom topography data, including the historical WOD09 dataset, shows that the inflow of water with 1.00° < θ < 1.70°C into the channel of the fracture is most likely fully localized in a few passages in the region of the survey in 2011, while the water exchange with the abyssal waters with θ > 1.70°C through the Romanche Fracture Zone between the West and East Atlantic can also occur through the depressions in the southern and northern walls of the fracture in the region of the Vema Deep.