HR: 1400h
AN: GS23B-08    [Abstracts]
TI: Age and Variability of Riverine Dissolved Organic Carbon in the St. Lawrence River
AU: * Moingt, M
EM: matthieumoingt@yahoo.fr
AF: Université Paris-Sud XI, Bāt. 504 Faculté des sciences, Orsay, F-91405, France
AU: * Moingt, M
EM: matthieumoingt@yahoo.fr
AF: GEOTOP-UQAM-McGill, 201 Av. du Président Kennedy, Montreal, Qc H2X-3Y7, Canada
AU: Hillaire-Marcel, C
EM: chenv@uqam.ca
AF: GEOTOP-UQAM-McGill, 201 Av. du Président Kennedy, Montreal, Qc H2X-3Y7, Canada
AU: Dever, L
EM: dever@geol.u-psud.fr
AF: Université Paris-Sud XI, Bāt. 504 Faculté des sciences, Orsay, F-91405, France
AU: Gelinas, Y
EM: ygelinas@alcor.concordia.ca
AF: Chemistry and Biochemistry Department, Concordia University, 7141 Sherbrooke St. West, Montreal, Qc H4B-1R6, Canada
AU: Barbecot, F
EM: florent.barbecot@u-psud.fr
AF: Université Paris-Sud XI, Bāt. 504 Faculté des sciences, Orsay, F-91405, France
AB: Riverine export of dissolved organic carbon (DOC) to the global ocean represents about 0.25 x 10E15gC/yr.Various studies have shown that this DOC mainly derives from terrestrial organic matter (OM). It is generally considered to be refractory and transported conservatively to the ocean. However, recent work has shown that many rivers carry a high-14C content DOC. Knowledge of the age (residence time) of both labile/refractory components of DOC and of its variability is essential for a robust assessment of riverine DOC role in the global carbon budget. Here, we report chemical and isotopic composition of DOC from the St. Lawrence River, with a focus on 14C ages of labile vs. total fractions, and on the spatial, seasonal to interannual variability of DOC-export. Alkaline CuO oxidation was used to collect refractory fractions of DOC and to identify sources and degradation stages of terrestrial organic matter. Our results indicate some variability in total DOC from year to year, but more notably, in temporal and spatial variability of 14C-activities of refractory components, which represent approximately 5 to 15% of total DOC and yielded 14C-activities ranging between 75 and 96% of modern carbon (pMC). From these values, 14C-activities of labile compound were estimated. They range from 100 to 111pMC. It is concluded that labile DOC compounds have a very young age/short residence time. This residence time is much shorter than the one estimated for water in the Great Lakes/St. Lawrence River system, thus suggesting prominent terrestrial sources for this reactive organic carbon. Although representing lesser overall fluxes, refractory material display ages pointing towards their previous significant residence time in soils.
DE: 1030 Geochemical cycles (0330)
DE: 1040 Radiogenic isotope geochemistry
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1055 Organic and biogenic geochemistry
SC: Geochemical Society [GS]
MN: 2007 Joint Assembly