[23-Feb-2024] Yu, L.
Presented at the 2024 Ocean Sciences MeetingTraditionally, tropical salinity minima (Smin) and subtropical salinity maxima (Smax) have been considered as separate entities due to their distinct characteristics and geographical separation. However, recent analysis of satellite sea surface salinity (SSS) observations reveals that the two salinity extrema are phase connected, with the tropical Smin leading the subtropical Smax by six months. The evidence suggests an interconnected nature between salinity extrema, motivating an investigation into the underlying mechanisms. It is found that the poleward Ekman transport, driven by trade winds, stands as a pivotal conduit linking the influence of tropical freshwater to high salinities in the subtropical oceans. Two key aspects are central to the operation of this advective oceanic pathway. One is the annual formation of the near-equatorial Smin zones by Ekman convergence of the freshwater sourced from the double ITCZ. The other is the advection time taken by Ekman transport traveling at an average speed of approximately 7 cm s^-1. This speed allows the near-equatorial salinity anomalies to be carried to the subtropical Smax fringes in six months, aligning closely with the observed semi-annual phase shift between Smin and Smax. During ENSO warm and cold episodes in recent decade, poleward propagation of near-equatorial low salinity anomalies was particularly prominent, leading to substantial surface freshening in the subtropical Pacific. Interestingly, the latitudinal spread of the ENSO-triggered SSS anomalies is confined within the impact zone of the poleward Ekman transport. This confinement reaffirms the inherent connection between the tropical Smin and subtropical Smax regions, shedding light on the intricate interplay between oceanic processes, the water cycle, and SSS distributions. Subsequently, there is a need to reevaluate methodologies for deriving information about changes in the ocean water cycle from SSS observations.