Preservation of organic matter in marine sediments by inner-sphere interactions with reactive iron.
Interactions between organic matter and mineral matrices are critical to the preservation of soil and sediment organic matter. In addition to clay minerals, Fe(III) oxides particles have recently been shown to be responsible for the protection and burial of a large fraction of sedimentary organic carbon (OC). Through a combination of synchrotron X-ray techniques and high-resolution images of intact sediment particles, we assessed the mechanism of interaction between OC and iron, as well as the composition of organic matter co-localized with ferric iron. We present scanning transmission x-ray microscopy images at the Fe L3and C K1edges showing that the organic matter co-localized with Fe(III) consists primarily of C=C, C=O and C-OH functional groups. Coupling the co-localization results to iron K-edge X-ray absorption spectroscopy fitting results allowed to quantify the relative contribution of OC-complexed Fe to the total sediment iron and reactive iron pools, showing that 25-62% of total reactive iron is directly associated to OC through inner-sphere complexation in coastal sediments, as much as four times more than in low OC deep sea sediments. Direct inner-sphere complexation between OC and iron oxides (Fe-O-C) is responsible for transferring a large quantity of reduced OC to the sedimentary sink, which could otherwise be oxidized back to CO2.
GEOTOP and the Department of Chemistry and Biochemistry, Concordia University, 7141 Sherbrooke West, Montréal, Quebec, H4B 1R6, Canada.
Andrew
A
Barber
Skidaway Institute of Oceanography, University of Georgia, 10 Ocean Science Circle, Savannah, GA, 31411, USA.
Jay
J
Brandes
Department of Natural Sciences, Marymount Manhattan College, 221 E 71st St., New York, New York, 10021, USA.
Alessandra
A
Leri
GEOTOP and the Department of Chemistry and Biochemistry, Concordia University, 7141 Sherbrooke West, Montréal, Quebec, H4B 1R6, Canada.
Karine
K
Lalonde
GEOTOP and the Department of Chemistry and Biochemistry, Concordia University, 7141 Sherbrooke West, Montréal, Quebec, H4B 1R6, Canada.
Kathryn
K
Balind
National Synchrotron Light Source, Brookhaven National Laboratory, Upton, NY, 11973, USA.
Sue
S
Wirick
Canadian Light Source Inc, Saskatoon, Saskatchewan, S7N 0X4, Canada.
Jian
J
Wang
GEOTOP and the Department of Chemistry and Biochemistry, Concordia University, 7141 Sherbrooke West, Montréal, Quebec, H4B 1R6, Canada. yves.gelinas@concordia.ca.
Yves
Y
Gélinas