Abstract
Abstract. We study low-frequency properties of the Antarctic Bottom Water (AABW) flow through the Kane Gap (9° N) in the Atlantic Ocean. The measurements in the Kane Gap include five visits with CTD (Conductivity-Temperature-Depth) sections in 2009–2012 and a year-long record of currents on a mooring using three AquaDopp current meters. We found an alternating regime of flow, which changes direction several times during a year. The seasonal signal seems to dominate. The maximum daily average values of southerly velocities reach 0.20 m s−1, while the greatest north-northwesterly velocity is as high as 0.15 m s−1. The velocity and transport at the bottom are aligned along the slope of a local hill near the southwestern side of the gap. The distribution of velocity directions at the upper boundary of AABW is wider. The transport of AABW (Θ < 1.9 °C) based on the mooring and LADCP (Lowered Acoustic Doppler Current Profiler) data varies approximately within ±0.35 Sv in the northern and southern directions. The annual mean AABW transport through the Kane Gap is almost zero.
Highlights
Cold bottom waters over the major part of the Atlantic Ocean are of the Antarctic origin
We follow the definition of these waters given in Wüst (1936) and name Antarctic Bottom Water (AABW) all the bottom waters propagating in the Atlantic Ocean from Antarctica to the north
During the first visit to the Kane Gap in May 2009, when only one CTD cast with an LADCP instrument was carried out near the main sill of the Gap (Fig. 5), we unexpectedly revealed a southeasterly abyssal current from the Gambia Abyssal Plain to the Sierra Leone Basin with a sufficient velocity of about 10 cm s−1
Summary
Cold bottom waters over the major part of the Atlantic Ocean are of the Antarctic origin. Mantyla and Reid (1983) conclude that the waters that propagate through the Romanche Fracture Zone influence only the regions of the Guinea, Sierra Leone, and partly Angola basins, whereas the waters that flow through the Vema Fracture Zone influence the Gambia Abyssal Plain, the Canary, and possibly the Iberian basins (van Aken, 2000) They fill the entire bottom layer in the northeastern Atlantic Ocean. Antarctic Bottom Water propagates to the eastern Atlantic Ocean through two main passages in the Mid-Atlantic Ridge: the Vema Fracture Zone (at 11◦ N) and Romanche and Chain fracture zones (at the Equator) and reaches the Kane Gap west of Guinea According to these observations the current was directed to the northwest, from the Sierra Leone Basin to the Gambia Abyssal Plain (Hobart et al, 1975)
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