Peatland ferruginization during late Quaternary in the Uberaba Plateau (South-Eastern Brazil)
Résumé
Due to the poor preservation of old peat formations and the limited research developed on them, the contribution of peat oxidation to the global C cycle at geological scales is poorly understood. Iron duricrusts containing abundant well-preserved plant structures have been reported above Humic Gleysols in the Uberaba Plateau (Brazil). We show that the iron accumulation results from an in-situ impregnation of peat, fast enough to preserve the plant structures. The formation of iron oxides results from two processes: precipitation in the pores and C/Fe replacement. The iron duricrusts were probably triggered by oxidation of the peatland following dry climatic events during the last 50 kyr. The large amount of iron dissolved in peatland waters was immobilized contemporaneously with the destruction of organic matter. The oxidation of organic matter from the lower peat, dated at ca 24-27 kyr BP, may have released between 0.08 and 2.26 kg CO2 m(-2) yr(-1) in the atmosphere. These rates are in a good agreement with present-day measurements of CO2 release from drained peatlands. Although peatland formation has been identified as a significant contributor to the global CO2 uptake, our findings suggest that natural peatland oxidation should also be considered as a source of atmospheric CO2 during past climate change.