Abstract
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