Recent satellite observations reveal that the annual cycles of tropical sea surface salinity (SSS) minimum (Smin) and subtropical SSS maximum (Smax) are phased locked, with the former leading the latter by six months. The evidence suggests an interconnected nature between the 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 Intertropical Convergence Zones. 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 El Niño - Southern Oscillation (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 domain 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.

最近的卫星观测表明，热带海面盐度（SSS）最小值（Smin）和副热带海面盐度最大值（Smax）的年周期是阶段性锁定的，前者领先后者六个月。证据表明盐度极值之间存在相互关联的性质，激发了对潜在机制的研究。研究发现，由信风驱动的极地埃克曼输运是连接热带淡水影响和副热带海洋高盐度影响的关键通道。有两个关键方面对于平流海洋通道的运行至关重要。一是每年由来自双热带辐合带的淡水通过埃克曼辐合形成的近赤道Smin带。^{另一个是埃克曼运输机以大约 7 cm s -1}的平均速度行驶所花费的平流时间。这一速度使得近赤道盐度异常能够在六个月内传播到副热带Smax边缘，与观测到的Smin和Smax之间的半年相移密切相关。近十年来厄尔尼诺-南方涛动（ENSO）暖冷事件期间，近赤道低盐度异常向极地传播尤为突出，导致副热带太平洋地表大幅清新。有趣的是，ENSO 触发的 SSS 异常的纬度传播仅限于极地埃克曼输运的范围内。这种限制重申了热带Smin和亚热带Smax区域之间的内在联系，揭示了海洋过程、水循环和 SSS 分布之间复杂的相互作用。