Deep time climatic oscillations regulated by shallow-water carbonates

The long-term climate depend on continental weathering, hydrothermal fluxes, and carbonate sequestration in the oceans, but a coherent explanation is missing. Here, we investigate the role of neritic carbonate accumulation, by plugging a macro-ecological model for shallow-water carbonates onto a combined set of state-of-the-art tectonic, climatic and physiographic reconstructions. Our model introduces and quantifies neritic habitability as a primordial climatic control. Our model confirms the role of deep ocean carbonate habitability -when carbon sources exceed the accumulation capacity of warm water carbonates, expanding carbon storage to the abyss- as a cooling factor, and reveals an unidentified alternative warm regime, controlled by the exceeding capacity of warm-water carbonates to capture Ca2+ and alkalinity fluxes. This regime depletes the oceans of its alkalinity, shoals the carbonate compensation depth, and releases carbon from the deep ocean to the atmosphere. These contrasted regimes, that we refer to as habitability-limited and calcium-limited, largely explain longterm climatic excursions, as revealed by the geological archive.