Deep overflows across the saddles on the Ninetyeast Ridge are essential for the deep limb of the Indian Ocean meridional overturning circulation. However, the volume transport or temporal variability of these overflows remains poorly understood. Based on a 17-month moored record of velocity profiles, the time-averaged volume transport of the overflow across the saddle near 10°S is estimated to be 1.3 Sv (1 Sv = 1×10⁶ m³/s) which closely aligns with the result diagnosed from a rotating hydraulic theory and early hydrographic observations. The overflow transport exhibits significant variabilities on intraseasonal (73 days) and semi-annual scales (170 days), and is closely correlated to the wind stress curl to the east of the Ninetyeast Ridge. These variabilities are attributed to vertically propagating Rossby waves generated by remote wind stress curl anomalies, which is indicated by the analysis on numerical model outputs utilizing spectral empirical orthogonal function decomposition and ray tracing techniques.

Ninetyeast Ridge,Volume Transport,Deep Overflow,Southeast Indian Ocean