
Just a small sampling of the forms that are made of CaCO3 (Calcium Carbonate). Every molecule has a carbon atom in it. More common are the innumerable foraminifera, which live in the upper 300 ft. of the oceans, and form the basis of marine food chains. So, yes, there is a tremendous amount of biologically fixed carbon which ends up as anything from carbonate ooze to reef rock and carbonate beach sand.
That
Climate scientists underestimated this is no surprise, they seem to ignore the carbon dioxide which is used by plants in photosynthesis, too.