The seasonal and interannual variabilities of the barrier layer thickness in the tropical Indian Ocean

Abstract. The seasonal and interannual variations of the barrier layer thickness (BLT) in the tropical Indian Ocean (TIO) is investigated in this study using the Simple Ocean Data Assimilation (SODA) version 3 reanalysis dataset from 1980 to 2015. BLT presents a significant seasonal variation in the TIO, mainly attributed to the variations of the sea surface salinity (SSS) and the thermocline. In particular, BLT anomalies are negatively correlated to SSS anomalies in the western TIO, except in summer. In the eastern TIO, the thermocline anomalies positively impact BLT anomalies in all seasons. However, the dependency of BLT anomalies on thermocline in the western TIO is only observed during winter. Furthermore, It is found that BLT could feedback on SSS, as BLT of the spring-time can negatively affect the SSS of the summer-time in the western TIO. In terms of the interannual BLT variation, we found that both the Indian Ocean Dipole (IOD)and El Nino South Oscillation (ENSO) events could impact the variation of BLT by affecting the thermocline, especially in the eastern TIO. In addition, BLT in the western TIO presents remarkable seasonal phase locking feature during the El Nino years. During the developing and mature phases of El Nino, thicker BLT is due to the change of thermocline, while during the decaying phase of El Nino BLT opposing to the weakened thermocline change becomes more significant because of the change of SSS.