There WERE carbon sinks. They used photosynthesis. They released oxygen to the troposphere. An entire global ecosystem died. The bleaching didn't recover and the corals died. Globally.
Oxygen levels (click here) are decreasing globally due to fossil-fuel burning. The changes are too small to have an impact on human health, but are of interest to the study of climate change and carbon dioxide. These plots show the atmospheric O2 concentration relative to the level around 1985. The observed downward trend amounts to 19 'per meg' per year. This corresponds to losing 19 O2 molecules out of every 1 million O2 molecules in the atmosphere each year.
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