Property Changes of Deep and Bottom Waters in the Western Tropical Atlantic

• Published in: Deep Sea Research Part I: Oceanographic Research Papers
• Main Authors: Herrford, Josefine, Brandt, Peter, Zenk, Walter
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2017
• Subjects: Antarctic; Antarc*; NADW; North Atlantic Deep Water; North Atlantic
• Online Access: https://oceanrep.geomar.de/id/eprint/37561/; https://oceanrep.geomar.de/id/eprint/37561/1/1-s2.0-S0967063716300498-main.pdf; https://oceanrep.geomar.de/id/eprint/37561/7/1-s2.0-S0967063716300498-main.pdf; https://doi.org/10.1016/j.dsr.2017.04.007

Highlights: • Analysis of hydrographic and current observations (1989–2014) in the western equatorial Atlantic. • Lower NADW and lighter AABW form an interactive transition layer in the northern Brazil Basin. • Proof of long-term abyssal warming on isobars in the western tropical Atlantic. • Warming of densest AABW is mainly caused by descent of isopycnal surfaces and volume loss of dense water masses. • Changes on isopycnal surfaces show warming in the 1990s and cooling in the 2000s. Abstract: The flow of North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW) contributes to the Atlantic meridional overturning circulation. Changes in the associated water mass formation might impact the deep ocean's capacity to take up anthropogenic CO2 while a warming of the deep ocean significantly contributes to global sea level rise. Here we compile historic and recent shipboard measurements of hydrography and velocity to provide a comprehensive view of water mass distribution, pathways, along-path transformation and long-term temperature changes of NADW and AABW in the western South and Equatorial Atlantic. We confirm previous results which show that the northwest corner of the Brazil Basin represents a splitting point for the southward/northward flow of NADW/AABW. The available measurements sample water mass transformation along the two major routes for deep and bottom waters in the tropical to South Atlantic – along the deep western boundary and eastward, parallel to the equator - as well as the hot-spots of extensive mixing. We find lower NADW and lighter AABW to form a highly interactive transition layer in the northern Brazil Basin. The AABW north of 5 °S is relatively homogeneous with only lighter AABW being able to pass through the Equatorial Channel (EQCH) into the North Atlantic. Spanning a period of 26 years, our data also allow an estimation of long-term temperature trends in abyssal waters. We find a warming of 2.5 ± 0.7∙10−3 °C yr−1 of the waters in the northern Brazil Basin at temperatures colder ...