Recent findings by Viljoen et al. (2024, Nature Climate Change) reveal contrasting phytoplankton trends above and below the mixed layer depth in the Sargasso Sea between 2011 and 2022, linked to ongoing ocean warming. Building on these observations, the current study by Zheng et al. seeks to replicate the detected patterns and unravel the drivers of these decadal changes. To this end, the authors develop a two-layer ecosystem model that conceptualizes stratified ocean systems as comprising two distinct ecological regimes: one within the surface mixed layer and another beneath it. Their results offer valuable insights into how phytoplankton communities may respond to future climate-driven stratification and highlight the critical need for improved monitoring efforts capable of capturing subsurface biological dynamics beyond the reach of satellite observations.