Stratospheric Ozone Depletion Drives Tropical Pacific Thermocline Variability via Enhanced UVB Penetration to the Upper Ocean

Stratospheric ozone is a key modulator of Earth's radiative balance, yet its role in driving tropical ocean variability remains uncertain. Here, using 40 years (1980–2020) of satellite and reanalysis data, we demonstrate that stratospheric ozone anomalies precede and predict changes in thermocline depth in the tropical Pacific through a direct radiative pathway. In this case, ozone depletion opens a "window" that allows enhanced ultraviolet-B (UVB) radiation to penetrate to the upper ocean (15–25 m depth), directly heating the thermocline layer. In the South Pacific (9–12°S, 130–110°W), stratospheric ozone and the depth to the 20°C isotherm (Z20) are strongly anticorrelated (r = − 0.61), with ozone leading Z20 by 5–10 months and accounting for 37% of its variance. Granger causality tests confirm unidirectional forcing from ozone to Z20 (peak F = 5.1 at 3-month lag; p < 0.001), with no significant reverse causality. This establishes ozone as an active driver rather than a passive response. Impulse response functions quantify a robust pathway in which a one-standard-deviation ozone-depletion shock deepens the thermocline by 218 cm within 4–7 months. A process that is driven by enhanced UVB absorption at the thermocline depth. The signal is strongest during extreme ENSO events and persists after detrending, confirming its origin in interannual dynamics. This stratosphere-to-ocean radiative teleconnection provides a physically grounded predictor with potential to extend ENSO forecast skill by 5–10 months.