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published: 30 June 2022
dol: 10.3389/mars.2022.910979
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Two Decades of Full-Depth Current
Velocity Observations From a
Moored Observatory in the Central
Equatorial Atlantic at O°N, 23°W
Franz Philip Tuchen!**, Peter Brandt!?*, Johannes Hahn“, Rebecca Hummels.
Gerd Krahmann, Bernard Bourles®, Christine Provost®, Michael J. McPhaden”
and John M. Toole®
GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany, ° NOAA/Atlantic Oceanographic and Meteorological
Laboratory, Miami, FL, United States, 3 Faculty of Mathematics and Natural Sciences, Kiel University, Kiel, Germany,
* Federal Maritime and Hydrographic Agency, Hamburg, Germany, © Centre IRD de Bretagne, IMAGO, Technopole
Pointe du Diable, Plouzane, France, © Laboratoire LOCEAN-IPSL, Sorbonne Universite, Paris, France, 7 NOAA/Pacific Marine
Environmental Laboratory, Seattle, WA, United States, 8 Woods Hole Oceanographic Institution, Woods Hole,
MA, United States
OPEN ACCESS
Edited by:
Sabrina Speich,
Ecole Normale Superieure, France
Reviewed by:
Riccardo Farneti,
he Abdus Salam International Centre
for Theoretical Physics (ICTP), Italy
Igor V. Polyakov,
University of Alaska Fairbanks,
United States
*Correspondence:
Franz Philip Tuchen
franz.philip.tuchen@noaa.g0ov
Peter Brandt
pbrandt@geomar.de
Keywords: ocean observations, physical oceanography, equatorial Atlantic circulation, ocean currents, moored
Observations. celimate variabilitv
INTRODUCTION
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
ıropical current system with impacts on societally relevant climate hazards such as anomalous
rainfall or droughts over the surrounding continents (Bourles 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 sl and maximum variability on seasonal time scales (Brandt et al., 2014;
"ohns 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);
‚Ohnson 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
2t 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.
While variability in the zonal velocity component on the equator is focused on seasonal to
interannual time scales (Brandt et al., 2016; Claus et al., 2016; Kopte et al., 2018), meridional velocity
Äuctuations dominate the intraseasonal period range (20 to 50 days) due to the presence and
passage of westward propagating Tropical Instability Waves (TIWs; Grodsky et al., 2005; Bunge
et al., 2007; Wenegrat and McPhaden, 2015; Tuchen et al., 2018; Specht et al., 2021). In general,
Specialty section:
Ihis article was submitted to
Ocean Observation,
a section of the journal
Frontiers in Marine Science
Received: 01 April 2022
Accepted: 18 May 2022
Published: 30 June 2022
Citation:
Tuchen FP, Brandt P, Hahn J,
Hummels R. Krahmann G, Bourles B,
Drovost C, McPhaden MJ and
"oole JM (2022) Two Decades of Full-
Depth Current Velocity Observations
From a Moored Observatory in the
Central Equatorial Atlantic at 0O°N, 23°W.
Front. Mar, Sci. 9:970979.
dot: 10.3389/mars. 2022.910979
Zrantiers in Marine Science | www frontiersin oru
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