This study reveals a 3.9 ± 1.6% global intensification of the sea surface temperature (SST) seasonal cycle over the past four decades (1983–2022), with hotspots like northern subpolar gyres experiencing up to 10% intensification. Increased greenhouse gases are the primary driver, aided by decreased anthropogenic aerosols. These changes lead to shallower mixed layers, reduced thermal inertia, and enhanced SST seasonality. The intensification extends throughout the mixed layer and impacts seasonal oxygen variation, crucial for ocean ecosystems.

Fukai Liu, Fengfei Song, Yiyong Luo