“…Thus, the effect of geogenic CO 2 on the contents of pedogenic oxides is expressed by diminished availability of O 2 . Further, CO 2 has not only a quantitative effect on pedogenic oxides, but also a qualitative one, as ferric (hydr)oxides once formed tend to remain poorly crystalline and/or small, as deduced from a positive correlation between the ratio of oxalate-to dithionite-extractable Fe with the CO 2 partial pressure (Rennert and Pfanz, 2015). Similarly, Casanova et al (1999) detected two-line ferrihydrite rich in Al, Si and Ca precipitated in the vicinity of a CO 2 spring in the Massif Central, France.…”