Carbonate deposition, climate stability, and Neoproterozoic ice ages
Andy J. Ridgwell, Martin J. Kennedy & Ken Caldeira
In the Neoproterozoic, climate was greatly influenced by sea level change. A reduction in sea level would have dramatically increased carbonate ion concentration in the ocean by reducing shallow water deposition areas, which would have in turn reduced atmospheric CO2 and lowered temperature. This effect is not seen in modern climate systems due to the rise of planktic calcifiers that allow for carbonate buildup in the deep sea. It is suggested here that a drastic lowering of sea level could have contributed to the Neoproterozoic ice ages, which lasted for millions of years.
The evolutionary success of planktic calcifiers during the Phanerozoic stabilized the climate system by introducing a new mechanism that acts to buffer ocean carbonate-ion concentration: the saturation-dependent preservation of carbonate in sea-floor sediments. Before this, buffering was primarily accomplished by adjustment of shallow-water carbonate deposition to balance oceanic inputs from weathering on land. Neoproterozoic ice ages of near-global extent and multimillion-year duration and the formation of distinctive sedimentary (cap) carbonates can thus be understood in terms of the greater sensitivity of the Precambrian carbon cycle to the loss of shallow-water environments and CO2-climate feedback on ice-sheet growth.