The influence of iron and manganese oxides on the production of marine sedimentary cerium anomalies

Abstract

Cerium is the only metal in the yttrium and rare earth element (YREE) series that can be oxidized under natural conditions, resulting in anomalous Ce distributions relative to those of the other YREE. Marine sedimentary cerium anomaly records have thus been used to signify relative shifts in bottom water oxygenation. However, Ce anomalies form via several pathways often not considered in paleo-oceanographic interpretations. To determine the relative influence of two important marine particulate components, Fe and Mn, on Ce oxidation, YREE sorption was investigated under anaerobic conditions in 0.5 M NaCl solutions over a range of pH (4-8) on hydrous ferric, manganese(IV) and ferromanganese oxides. Non-electrostatic surface complexation models were developed that describe non-oxidative sorption mechanisms on each surface. Cerium oxidation occurred on all sorbents containing Mn, indicating that sedimentary Ce records cannot be directly related to past marine oxygen conditions, even in the presence of relatively little manganese.