Oceanic acidification undermines the chemical conditions that allow carbonate minerals to form and persist. Increasing atmospheric carbon dioxide drives more CO2 into sea water, reducing pH and lowering the concentration of carbonate ions. Richard A. Feely, NOAA Pacific Marine Environmental Laboratory, has documented how this shift decreases the carbonate saturation state that controls whether shells and skeletal fragments of organisms dissolve or accumulate. Bärbel Hönisch, Columbia University Lamont-Doherty Earth Observatory, has shown similar links between acidification and reduced preservation of biogenic carbonates in the sedimentary record.
Mechanisms on continental shelves
Continental shelves are zones of high biological production and active sedimentation where biogenic carbonate from foraminifera, coccolithophores, corals and molluscs supplies much of the sediment. When the aragonite and calcite saturation states fall below critical thresholds, fine carbonate particles and thin-shelled organisms become prone to dissolution before burial. Early diagenetic reactions in bottom waters and the upper sediment column amplify loss of carbonate by converting solid CaCO3 back into dissolved ions, a process that can temporarily increase alkalinity but reduces long-term carbonate burial. Shelf systems are especially sensitive because they receive terrestrial inputs and experience variable bottom-water chemistry; local eutrophication or freshening can exacerbate acidification effects.
Consequences for preservation and societies
Reduced preservation changes sediment composition, biasing the geological archive toward more refractory minerals and silicates and making paleoenvironmental reconstructions more challenging. Loss of carbonate sediment production can weaken natural coastal defenses built by reefs and carbonate platforms, with direct consequences for fisheries, tourism and shoreline protection in regions such as tropical continental shelves and island territories where carbonate systems dominate. Over geological timescales, diminished carbonate burial influences the global carbon cycle by slowing a sink that helps remove CO2 from the surface ocean and atmosphere, a linkage highlighted in national and international assessments by oceanographers and climate scientists.
Understanding these processes requires integrated observational and experimental work across shelf environments. Maintaining datasets and targeted experiments led by recognized research groups is essential to quantify how ongoing acidification will alter carbonate sediment preservation and the societal services that depend on carbonate-rich continental shelves.