Hersh, C., Gebbie, G., Wijffels, S.A., and Forget, G. (2026)
Presented at:
Ocean Sciences Meeting 2026In the global subtropical oceans, water mass properties (e.g. salinity, temperature) are set at the surface and subducted along ventilated pathways that flow toward upwelling sites in the tropics. Earlier work has indicated that some interannual anomalies of these properties can be tracked to western boundary and equatorial current systems. They therefore have the potential to affect remote climate variability through ocean “tunnels” along which heat anomalies propagate. We have shown that Estimating the Circulation and Climate of the Ocean (ECCO) state estimate version 4 release 4 sufficiently captures water mass variability along subtropical-to-tropical pathways as observed in a gridded Argo data product. We perform a suite of experiments in the ECCO-configured Massachusetts Institute of Technology General Circulation Model (MITgcm) in which we modify the interannual frequency band of the input surface forcing over different ocean regions. This allows us to describe the pathways and quantify the impact strength of subtropically-forced water mass anomalies on equatorial variability. We find that interannual forcing over each of the five global subtropical basins creates a detectable impact on equatorial water properties, although the strength varies greatly between basins. ECCO experiments suggest that the most likely locations for anomalies forced over the subtropics to re-emerge into the equatorial mixed layer are the eastern Pacific Ocean (from South Pacific anomalies), the western Indian Ocean (from South Indian anomalies), and the western Atlantic Ocean (from South Atlantic anomalies). Closing the loop, we also investigate impacts in the reverse direction, from variability forced over the equator toward the subtropics, and demonstrate potential ocean-based mechanisms through which such variability can propagate.
