Abstract
The hydrodynamics and the occurrence of topographic upwelling around the northern Brazilian seamount chain were investigated. Meteorological and physical oceanographic data collected under the REVIZEE-NE Program cruises around the Aracati Bank, the major and highly productive seamount in the area, were analyzed and used to force and validate simulations using the 3D Princeton Ocean Model (3D POM). The Tropical Water mass in the top 150-m layer and the South Atlantic Central Water (SACW) beneath it and down to a depth of 670 m was present. The thickness of the barrier layer varied seasonally, being thinner (2 m) during the austral spring (October–December) and thicker (20 m) during the austral autumn (April–June) when winds were stronger. The surface mixed and isothermal layers in the austral winter (July–September) were located at depths of 84 and 96 m, respectively. During the austral spring, those layers were located at depths of 6 and 8 m, respectively. The mean wind shear energy was 9.8 × 10–4 m2 s–2, and the energy of the surface gravity wave break was 10.8 × 10–2 m2 s–2, and both served to enhance vertical mixing in the area. A permanent thermocline between the 70- and 150-m depths was present throughout the year. The isohaline distribution followed an isotherm pattern of variation, but at times, the formation of low-salinity eddies was verified on the bank slope. The 3D POM model reproduced the thermohaline structure accurately. Temperature and salinity profiles indicated the existence of vertical water displacements over the bank and along the direction of the North Brazil Current, which is the strongest western boundary current crossing the equatorial Atlantic. The kinematic structure observed in the simulations indicated vertical velocities of O (10–3 m.s–1) in the upstream region of the bank during austral winter and summer seasons. During the summer, the most important vertical velocities were localized below the lower limit of the euphotic zone; while during the austral winter, these velocities were within the euphotic zone, thereby favoring primary producers.
Highlights
Oceanic islands, seamounts, and banks are associated with propitious fishing grounds worldwide, hosting abundant and diverse biomass and favoring the congregation of marine predators, such as tunas, dolphins, and seabirds (Morato et al, 2008; Pitcher et al, 2008)
The aim of this article was to investigate the effects of the flowtopography interaction on the thermohaline structure around the Aracati Bank, North Brazilian Chain (NBCh), analyzing potential locations where an enrichment of the mixed layer may occur
The analysis and treatment of in situ data allowed the identification of two main water masses in the Aracati Bank area (Table 4)
Summary
Seamounts, and banks are associated with propitious fishing grounds worldwide, hosting abundant and diverse biomass and favoring the congregation of marine predators, such as tunas, dolphins, and seabirds (Morato et al, 2008; Pitcher et al, 2008). These geological features serve as shelter and physical substrates for the development of several species and induce a variety of flow phenomena. Seamounts, characterized as submerged mountains that rise at least 1,000 m above the surrounding seabed, are one of the most common geological features on our planet. The interaction of marine currents with seamounts results in a complex system of circulation, which has been investigated from laboratory and in situ observations (Eiff and Bonneton, 2000; Mourino et al, 2001; Varela et al, 2007; Oliveira et al, 2016), as well as from analytical and numerical modeling studies (Boyer et al, 1987; Morato et al, 2009)
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