Abstract
AbstractThe great ocean conveyor presents a time-mean perspective on the interconnected network of major ocean currents. Zonally integrating the meridional velocities, either globally or across basin-scale domains, reduces the conveyor to a 2D projection widely known as the meridional overturning circulation (MOC). Recent model studies have shown the MOC to exhibit variability on near-inertial time scales, and also indicate a region of enhanced variability on the equator. We present an analysis of three integrations of a global configuration of a numerical ocean model, which show very large amplitude oscillations in the MOCs in the Atlantic, Indian, and Pacific Oceans confined to the equatorial region. The amplitude of these oscillations is proportional to the width of the ocean basin, typically about 100 (200) Sv (1 Sv ≡ 106 m3 s−1) in the Atlantic (Pacific). We show that these oscillations are driven by surface winds within 10°N/S of the equator, and their periods (typically 4–10 days) correspond to a small number of low-mode equatorially trapped planetary waves. Furthermore, the oscillations can be well reproduced by idealized wind-driven simulations linearized about a state of rest.
Highlights
The large-scale global meridional ocean overturning circulation (MOC) gained widespread recognition through its depiction as the ‘‘Great Ocean Conveyor Belt’’ (Broeker 1987)
To investigate the mechanisms behind this localized increase in variability we perform an experiment using NEMO, a widely adopted numerical ocean model used in ocean-only applications, including data assimilation, and a variety of coupled configurations such as the U.K
Examining the CONTROL simulation, we find that the large equatorial MOC variability observed in all basins exhibits peaks in the power spectra that correspond to periods of 10 and 4 days
Summary
The large-scale global meridional ocean overturning circulation (MOC) gained widespread recognition through its depiction as the ‘‘Great Ocean Conveyor Belt’’ (Broeker 1987). Its portrayal as such gives the impression of a slow and steady transport of water, along with heat, salt, carbon, and other tracers around the global oceans. Sustained observations by the RAPID–MOCHA–WBTS (Western Boundary Time Series) array at 26.58N (Rayner et al 2011) revealed much greater MOC variability than was previously known to exist, with short-term values ranging from 25 to 35 Sv (1 Sv [ 106 m3 s21), around a mean state of ;17 Sv (McCarthy et al 2015, 2012; Smeed et al 2014, 2018). Models are well suited to identifying the physical processes governing AMOC variability: short-time-scale Ekman (wind-driven) variability in the surface ocean; longer-time-scale wind-driven variability through mechanisms such as Sverdrup transport due to Ekman pumping at higher/lower latitudes (Duchez et al 2014b); changes in the eastern and western boundary densities
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
