Fig. 8: Three-scenario scheme of the continental margin carbon cycling before during and after the negative isotope excursion (NIE).
From: Multi-proxy evidence for sea level fall at the onset of the Eocene-Oligocene transition
a At higher sea-level (late Eocene) conditions, the weathering input is balanced by the burial of CaCO3 in neritic and deep ocean environments (Pacific carbonate compensation depth – CCD: ~4 km). b With early stage of sea-level regression, the enhanced weathering flux of organic carbon and nutrients from terrestrial and exposed marginal marine environments causes transient release of CO2; and together with nutrient-stimulated increase in pelagic primary production, causes a transient shoaling of the CCD (Pacific CCD shoals by ~100–200 m). c Further sea-level fall, reduced shelf area and reduced shallow water carbonate factory (and erosion where exposed) causes an imbalance between sources and sinks of alkalinity, resulting in the long-term enhanced preservation and burial of CaCO3 in deep-sea sediments, and the deepening of the CCD (early Oligocene Pacific CCD: > 4.5 km).
