Global response of ocean stratification to climatic forcing

Oceanic stratification plays a key role in climate by modulating the ocean’s resistance to be mixed vertically. It has been traditionally assumed that, beyond the deepest reach of winter mixing, stratification is relatively invariant on the time scales of contemporary climate evolution. Here, we test this view 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 stratifications are found to exhibit spatially-structured, vertically-coherent, global-scale variations on seasonal-to-decadal time scales, suggesting that both stratifications are a rapidly-evolving, readily-interactive component 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 internal variability as important drivers of stratification changes. Our diagnosed patterns and forcings of stratification variability provide an important benchmark for advancing the climate models used to understand and predict the ongoing climate change