Brazil-Malvinas Confluence upper ocean temperature anomalies induced by an ENSO wind forcing

Abstract

The Brazil-Malvinas Confluence (BMC) region constitutes one of the most important ocean features in the South Atlantic Ocean basin. Understanding the BMC upper ocean temperature variability could represent one of the key factors to understanding its connection to local and global ocean circulation. Some important local and remote ocean processes are related to the annual and interannual variability of its thermal/salt front position. This paper investigates the upper ocean variability in the BMC region under the influence of an El Niño/Southern Oscillation-type wind stress field using an oceanic general circulation model (Modular Ocean Model version 4.0). The results revealed the occurrence of positive anomalies, with values ranging from 0.5ºC to 1.0ºC (centered at 40.5ºS and 55.0ºW), near the BMC region associated with upper ocean velocity anomalies during the peak of the ocean kinetic energy phase. This mechanism was a response of a volume transport balance between the Brazil Current (BC) and the Malvinas Current (MC), the latter being accelerated by the Antarctic Circumpolar Current (ACC). The occurrence of positive anomalies was always associated with an enhanced BC meridional surface volume transport, together with a decrease of the ACC zonal volume transport, vertically integrated across the Drake Passage, and a correspondent decrease in the upper layer MC volume transport. It was possible to see negative upper layer temperature anomaly predominance just before the peak ocean kinetic energy month and positive anomaly predominance immediately following this month. The occurrence of upper layer temperature anomalies in the BMC region was not restricted to just the peak ocean kinetic energy month since they occurred throughout the perturbed experiment integration time.