On the circulation of bottom water in the region of the Vema Channel |
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Affiliation: | 1. Wuxi Fisheries College, Nanjing Agricultural University, Wuxi 214081, China;2. Key Laboratory of Freshwater Fisheries and Germplasm Resources Utilization, Ministry of Agriculture and Rural Affairs, Freshwater Fisheries Research Center, Chinese Academy of Fishery Sciences, Wuxi 214081, China;1. Instituto de Geociências, Universidade Federal do Rio Grande do Sul, Brazil;2. Instituto de Geociências, Universidade de Brasilia, Brazil;3. Institut des Sciences de la Terre (ISTerre), Université Joseph Fourier, France;1. Jilin University, College of GeoExploration Science and Technology, Changchun 130000, China;2. Key Laboratory of Submarine Geoscience, State Oceanic Administration, Hangzhou 310012, China;3. Second Institute of Oceanography, State Oceanic Administration, Hangzhou 310012, China;4. China University of Geoscience, Wuhan 430000, China;5. Jilin University, College of Instrument Science & Electrical Engineering, Changchun 130000, China |
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Abstract: | The circulation and transport of Antarctic Bottom Water (σ4<45.87) in the region of the Vema Channel are studied along three WOCE hydrographic lines, the geostrophic velocities referenced to previously published direct current measurements. The primary supply of water to the deep Vema Channel is from the Argentine Basin's deep western boundary current, with no indication of an inflow from the southeast. In the northern Argentine Basin, detachment of lower North Atlantic Deep Water from the continental slope is associated with a deep thermohaline front near 34°S. To the north of this front, the upper part of the AABW bound for the Vema Channel (σ4<46.01) exhibits a significant NADW influence. Further modification of the throughflow water occurs near 30°30′S, where the channel orientation changes by ∼50°. Southward flow of bottom water on the eastern flank of the Vema Channel, amounting to ∼1.5 Sv, represents a significant countercurrent to the deep channel transport. Inclusion of this countercurrent reduces the net flow of AABW through the Vema Channel from 3.2±0.7 to 1.7±1.1 Sv. Water properties imply that the near-zero net flow over the Santos Plateau results from a near-closed cyclonic circulation fed by the deep Vema Channel throughflow. A disruption of the northward boundary current in the upper AABW (lower circumpolar water) is required by this flow pattern. The extension of the cyclonic circulation on the Santos Plateau enters the Brazil Basin as a ∼1 Sv flow distinct from the outflow in the Vema Channel Extension (6.2 Sv). The high magnitude of the latter suggests a southward recirculation of bottom water near the western boundary to the north of the region of study. |
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