Changes in the cosmic-ray background of the Earth can impact the ozone layer. High-energy cosmic events (e.g., Supernova, SN) or rapid changes in the Earth's magnetic field (e.g., Geomagnetic Excursion, GE) can lead to a cascade of cosmic rays. Ensuing chemical reactions can then cause thinning/destruction of the ozone layer — leading to enhanced penetration of harmful UV radiation towards the Earth's surface. However, observational evidence for such UV ‘windows’ is still lacking. Here, we conduct a pilot study and investigate this notion during two well-known events: the multiple SN event (≈10 kBP) and the Laschamp GE event (≈41 kBP). We hypothesize that ice-core-Δ33S records—originally used as volcanic fingerprints—can reveal UV-induced background-tropospheric- photochemical imprints during such events. Indeed, we find non-volcanic S-isotopic anomalies (Δ33S≠0 ‰) in background Antarctic-ice-core sulfate during GE/SN periods, thereby confirming our hypothesis. This suggests that ice-core-Δ33S records can serve as a proxy for past ozone-layer-depletion events.