Freezing and thawing can speed soil carbon loss in cold regions, and climate change is altering how often these events occur. We incubated soils from different depths under freeze–thaw patterns and measured carbon dioxide release and dissolved carbon. Thaw bursts weakened with repeated cycles, yet higher frequency produced more total carbon loss. Dissolved carbon best predicted losses at all depths, while deeper soils relied more on enzymes and surface soils on organic matter protection.