Two Decades of Full-Depth Current Velocity Observations From a Moored Observatory in the Central Equatorial Atlantic at 0°N, 23°W

Regional climate variability in the tropical Atlantic, from interannual to decadal time scales, is
inevitably connected to changes in the strength and position of the individual components of the
tropical current system with impacts on societally relevant climate hazards such as anomalous
rainfall or droughts over the surrounding continents (Bourlès et al., 2019; Foltz et al., 2019).
Furthermore, the lateral supply of dissolved oxygen in the tropical Atlantic upper-ocean is closely
linked to the zonal current bands (Brandt et al., 2008; Brandt et al., 2012; Burmeister et al., 2020) and
especially to the Equatorial Undercurrent (EUC) and its long-term variations with potential
implications for regional marine ecosystems (Brandt et al., 2021). The eastward flowing EUC is
located between 70 to 200 m depth and forms one of the strongest tropical currents with maximum
velocities of up to 1 m s
and maximum variability on seasonal time scales (Brandt et al., 2014;
Johns et al., 2014). In the intermediate to deep equatorial Atlantic, variability on longer time scales is
mainly governed by alternating, vertically-stacked, zonal currents (equatorial deep jets (EDJs);
Johnson and Zhang, 2003). At a fixed location, the phases of these jets are propagating downward
with time, implying that parts of their energy must propagate upward towards the surface (Brandt
et al., 2011). In fact, a pronounced interannual cycle of about 4.5 years, that is associated with EDJs,
is projected onto surface parameters such as sea surface temperature or precipitation (Brandt et al.,
2011) further demonstrating the importance of understanding equatorial circulation variability and
its role in tropical climate variability.


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