Ocean stratification is an important factor controlling biogeochemical cycles and affecting marine ecosystems. WGI AR6 Section 9.2.1.3  assessed that it is virtually certain that stratification in the upper 200 m of the ocean has been increasing since 1970. Recent evidence has strengthened estimates of the rate of change , with an estimated increase of 1.0 + 0.3%  per decade over the period 1970-2018  , higher than assessed in SROCC. It is very likely that stratification in the upper few hundred metres of the ocean will increase substantially in the 21st century in all ocean basins, driven by intensified surface warming and near-surface freshening at high latitudes .
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report