Significance: A key factor regulating the air−sea balance of carbon dioxide (CO ₂ ) is the sinking of particles containing organic carbon from the surface to the deep ocean. The depth at which this carbon is released back into the water (remineralization) has a strong influence on atmospheric CO ₂ concentration. Here we show a significant relationship between the remineralization depth of sinking organic carbon flux in the upper ocean and water temperature, with shallower remineralization in warmer waters. Our results contrast with data from deep-sea sediment traps, highlighting the importance of upper ocean remineralization to our understanding of the ocean’s biological carbon pump. Our results suggest that predicted future increases in ocean temperature will result in reduced CO ₂ storage by the oceans.