The authors did a neat job of putting this all together to show us the HOW and WHY this happens in our oceans. In a sterile world, this might happen a bit as we'd expect from inorganic chemistry. On Earth, with abundant microbes, we get this feedback of microbial growth, metabolism, and localized CO2 concentration that promotes dissolution of descending carbonates faster and shallower than expected, helping sequester CO2 away into the deeper ocean reservoirs. Thanks, microbes! [/end thread]