The mid-depth circulation of the northwestern tropical Atlantic observed by floats

• Published in: Deep Sea Research Part I: Oceanographic Research Papers
• Main Authors: Lankhorst, Matthias, Fratantoni, David, Ollitrault, Michel, Richardson, Philip, Send, Uwe, Zenk, Walter
• Other Authors: Leibniz-Institut für Meereswissenschaften (IFM-GEOMAR), Scripps Institution of Oceanography (SIO - UC San Diego), University of California San Diego (UC San Diego), University of California (UC)-University of California (UC), Woods Hole Oceanographic Institution (WHOI), Laboratoire de physique des océans (LPO), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2009
• Subjects: Floats; Tropical Atlantic; Antarctic Intermediate Water; North Atlantic Deep Water; Equatorial currents; [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography; Antarctic; The Antarctic; Mid-Atlantic Ridge; Antarc*; North Atlantic
• Online Access: https://hal.science/hal-00501642; https://doi.org/10.1016/j.dsr.2009.06.002

International audience A comprehensive analysis of velocity data from subsurface floats in the northwestern tropical Atlantic at two depth layers is presented: one representing the Antarctic Intermediate Water (AAIW, pressure range 600–1050 dbar), the other the upper North Atlantic Deep Water (uNADW, pressure range 1200–2050 dbar). New data from three independent research programs are combined with previously available data to achieve blanket coverage in space for the AAIW layer, while coverage in the uNADW remains more intermittent. Results from the AAIW mainly confirm previous studies on the mean flow, namely the equatorial zonal and the boundary currents, but clarify details on pathways, mostly by virtue of the spatial data coverage that sets float observations apart from e.g. shipborne or mooring observations. Mean transports in each of five zonal equatorial current bands is found to be between 2.7 and 4.5 Sv. Pathways carrying AAIW northward beyond the North Brazil Undercurrent are clearly visible in the mean velocity field, in particular a northward transport of 3.7 Sv across 16°N between the Antilles islands and the Mid-Atlantic Ridge. New maps of Lagrangian eddy kinetic energy and integral time scales are presented to quantify mesoscale activity. For the uNADW, mean flow and mesoscale properties are discussed as data availability allows. Trajectories in the uNADW east of the Lesser Antilles reveal interactions between the Deep Western Boundary Current (DWBC) and the basin interior, which can explain recent hydrographic observations of changes in composition of DWBC water along its southward flow.