Ca and Mg ions that are abundant in sea water and that carry two positive charges. The formation of these insoluble crystals increases the density of these marine microgels and results in sedimentation falling to the bottom of the ocean, excluding their organic matrix from the food chain and eventually creating a carbon sink. In this fashion, carbon joins the chalky sediments at the bottom of the sea. The rate of carbon burial is also affected by pH and temperature. If the oceans are slightly more alkaline than pH 8.5, or if the oceans cool a bit, there is a higher rate of crystallization.
Higher crystallization means higher carbon burial and less recycling.
Verdugo claimed that he needed to research the matter further, but agreed that higher levels of CO2, which dissolves easily in sea water forming carbonic acid and calcium carbonate, could eventually lead to more mineralization. Life has survived massive bolide impacts from outer space, huge variations in solar output, gripping ice ages, the shifting of the Earth's magnetic field and a host of other disasters that would make human perturbations seem puny by comparison. Life has already maintained a tenacious hold on this planet for some 3.8 billion years, and will exist here for another 5.5 billion years or so, until the world's oceans boil from the heat emitted from an exhausted red sun. Gaia evolved ways of coping with all sorts of disasters long before there were humans. She will survive us, too.