Seawater generally forms stratified layers with lighter waters near the surface and denser waters at greater depth. This stable configuration acts as a barrier to water mixing that impacts the efficiency of vertical exchanges of heat, carbon, oxygen and other constituents. Previous quantification of stratification change has been limited to simple differencing of surface and 200-m depth changes and has neglected the spatial complexity of ocean density change. Here, we quantify changes in ocean stratification down to depths of 2,000 m using the squared buoyancy frequency N² and newly available ocean temperature/salinity observations. We find that stratification globally has increased by a substantial 5.3% [5.0%, 5.8%] in recent decades (1960–2018) (the confidence interval is 5–95%); a rate of 0.90% per decade. Most of the increase (~71%) occurred in the upper 200 m of the ocean and resulted largely (>90%) from temperature changes, although salinity changes play an important role locally.

海水通常形成分层的层，其表层附近的水较轻，深度较深的水较稠密。这种稳定的配置成为水混合的障碍，影响了热量，碳，氧和其他成分的垂直交换效率。先前对分层变化的量化仅限于对表面变化和200-m深度变化进行简单区分，而忽略了海洋密度变化的空间复杂性。在这里，我们使用平方浮力频率N ²来量化直到2,000 m深度的海洋分层变化以及最新的海洋温度/盐度观测。我们发现，最近几十年（1960年至2018年），全球分层增加了5.3％[5.0％，5.8％]（置信区间为5–95％）；每十年0.90％的比率。尽管盐度变化在当地起着重要的作用，但大部分增加（〜71％）发生在海洋的200 m上部，主要是由于温度变化（> 90％）。