Observed Climatic Variability of Global Ocean Stratification

Abstract Oceanic stratification plays a key role in climate by modulating the ocean's resistance to be mixed vertically. However, the climatic variability of stratification remains little documented beyond the deepest reach of winter mixing. Here, we address this gap by performing a global investigation of the spatio‐temporal variability of stratification from the surface to the main pycnocline, using 20 years (2003–2022) of data from the Argo float array. Both near‐surface and main pycnocline stratification are found to exhibit spatially structured, vertically coherent, global‐scale variations on seasonal‐to‐decadal time scales, suggesting that stratification at both levels are rapidly‐evolving and responsive components of the climate system. Variability in stratification is organized into well‐defined patterns that replicate the spatial footprints and time scales of major climate modes, pointing to these modes of variability as important drivers of stratification changes. Our diagnosed patterns and forcings of stratification variability provide a benchmark for advancing the climate models used to understand and predict the ongoing climate change.