The Levantine Basin in the eastern Mediterranean Sea is one of the most nutrient-poor marine regions on Earth. Using a detailed model and observations, we studied how oxygen changes from 2013 to 2020. We found that winter cooling draws oxygen into the sea and moves it to deeper waters, while warmer months release some back. Overall, the basin absorbs more oxygen than it releases, and winter heat loss and circulation patterns strongly control how oxygen is stored and transported.