CoAuthors

Sang-Ki Lee (NOAA-AOML, USA); Arnold Gordon (Lamont-Doherty Earth Observatory, Columbia University, USA); Michael Rudko (University of Miami, RSMAS, USA)

A decade-long increase of sea level and heat content in the South Indian Ocean (SIO) in 2004-2013 ended with an unprecedented drop below the values observed back in 2004. This basin-wide heat release was associated with one of the strongest on record El Niño events in 2014-2016. Surprisingly, the SIO heat content and sea level quickly recovered during the weak La Niña in 2017-2018. Here, we show that the 2014-2016 El Niño did contribute to the observed cooling in the SIO through an unusual combination of both the reduced heat advection from the Pacific (‘ocean tunnel’ effect) and the basin-wide cyclonic wind anomaly and associated Ekman upwelling (‘atmospheric bridge’ effect); with the former mechanism being more dominant in the eastern SIO and the latter in the western SIO. The ensuing recovery in 2017-2018 was mainly forced by an anticyclonic wind anomaly associated with stronger trade winds that caused deepening of isotherms and upper-ocean warming, effectively suppressing the 2014–2016 cooling signal propagating from the eastern boundary.