The sequestration of carbon in sediments results in an overall removal of CO2 from the atmosphere (Burdige, 2006) and an understanding of both how and how much carbon is sequestered in sediments is crucial to understand the carbon cycle. Here we present evidence for the first time on the sequestration of carbon by manganese oxides, and specifically the intercalation, stabilisation and subsequent fractionation of dissolved organic matter (DOM) as molecularly uncharacterised carbon (MUC) within birnessite. We will examine in detail the physiochemical relationships between the MUC and birnessite which is present as coatings on sand grains in a water treatment works filter bed (Mosswood WTW, Northumberland, UK, Co. Durham, UK, 54°51°N - 53°59°W). Total organic carbon (TOC) in the birnessite is 3.0% (n=6) and total inorganic carbon (TIC) is 0.5% (n=6). The birnessite coating is analysed using thermogravimetric analysis (TGA) combined with differential scanning calorimetry (DSC) and mass spectroscopy. Carbon dioxide (m/z 44) is detected in the 200-375oC and the 550-750oC range and the DSC curve detects exothermic reactions at 270oC and 600oC, that could be associated with labile and refractory carbon (Lopez-Capel et al, 2005) and a small endothermic reaction at 712oC, which could be associated with inorganic carbon (as calcium carbonate). Intriguingly, a significant proportion of the labile MUC has been fractionated and has a heavier delta 13C signature (-24.8) from the original DOM (-27). We conclude that the role of manganese oxides in sequestering, stabilising and fractionating carbon in sediments has been overlooked, and that more research is needed in order to fully understand the preservation mechanisms for carbon in sediments.
CORE (COnnecting REpositories)
CORE (COnnecting REpositories)