Abyssal Channels in the Atlantic Ocean: Water Structure and Flows

This book is dedicated to the study of structure and transport of deep and bottom waters above and through underwater channels of the Atlantic Ocean. The study is based on recent observations, analysis of historical data, and literature reviews. This approach allows us to understand how water transport and water mass prop- ties have changed over the last years and decades. The focus of our study is on the propagation of bottom waters in the Atlantic Ocean based on new field data at key points. At the end of the 1920s, the first integral study of water masses and bottom topography of the Central and South Atlantic was carried out from the German - search vessel Meteor. This German Atlantic Expedition was one of the first cruises equipped with the newly developed echo sounder (fathometer): an obligatory p- requisite for the investigation of bottom morphology in the deep sea on an - erational base. The results of the expedition were published by Wüst, Defant, and colleagues in the multivolume METEOR publication series starting with the cruise report by the ship’s commander (Spiess 1928, 1932). Historically, this series of p- lications, intermittently interrupted by World War II, was the basis for many years of research into the development of modern concepts about Atlantic water masses and their circulation schemes.

This book is dedicated to the study of structure and transport of deep and bottom waters through underwater channels of the Atlantic Ocean. The study is based on recent observations, analysis of historical data, and literature review.
A strong flow of Antarctic Bottom Water from the Argentine Basin to the Brazil Basin through the Vema Channel (32-27 S) is studied on the basis of CTD sections combined with LADCP profiling carried out annually and long-term moored measurements. The flow in the Vema Channel is mixed in the vertical direction but horizontally stratified. The mean speed of the flow is 30 cm/s and water transport is approximately 3.5 Sv. Owing to the bottom Ekman friction the dense core of the flow is usually displaced to the eastern wall of the channel. A temperature increase was found in the deep Vema Channel, which has been observed for 30 years already.
The further flow of bottom water in the Brazil Basin splits in the northern part of the basin. Part of water flows to the East Atlantic basins through the Romanche and Chain fracture zones. The other part is a northwestern flow to the North American Basin. Part of the northwesterly flow propagates through the Vema Fracture Zone (11 N) into the Northeastern Atlantic basins.
Flows in the Romanche, Chain, and Vema fracture zones were studied recently by CTD and LADCP profiling. An underwater cataract was found in the Chain Fracture Zone. Recent measurements in the Kane Gap show that the flow of bottom water there is characterized by alternative transport in time. The Northeastern Atlantic basins are filled with the bottom water flowing through the Vema Fracture Zone. The flows of bottom waters through the Romanche and Chain fracture zones do not spread to the Northeast Atlantic due to strong mixing in the equatorial zone and enhanced transformation of bottom water properties.

Extra material:
The CTD data sets collected in abyssal channels of theAtlantic Ocean can be downloaded from http://extras.springer.com. The access to the data is organized either by means of a clickable map or tables. Investigators can download individual casts organized by the year of the experiment or its location. The CTD data are organized in the form of a heading and three columns (pressure, temperature, salinity). The style is similar to the WOCE format. A line with coordinates is added to the heading.