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Carbon and silica megasink in deep-sea sediments of the Congo terminal lobes

Abstract : Carbon and silicon cycles at the Earth surface are linked to long-term variations of atmospheric CO2 and oceanic primary production. In these cycles, the river-sea interface is considered a biogeochemical hotspot, and deltas presently receive and preserve a major fraction of riverine particles in shallow water sediments. In contrast, periods of glacial maximum lowstand were characterized by massive exports of sediments to the deep-sea via submarine canyons and accumulation in deep-sea fans. Here, we calculate present-day mass balances for organic carbon (OC) and amorphous silica (aSi) in the terminal lobe complex of the Congo River deep-sea fan as an analogue for glacial periods. We show that this lobe complex constitutes a megasink with the current accumulation of 18 and 35% of the OC and aSi river input, respectively. This increases the estimates of organic carbon burial by 19% in the South Atlantic Ocean in a zone representing less than 0.01% of the basin. These megasinks might have played a role in carbon trapping in oceanic sediments during glacial times.
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Christophe Rabouille, B. Dennielou, François Baudin, Mélanie Raimonet, L. Droz, et al.. Carbon and silica megasink in deep-sea sediments of the Congo terminal lobes. Quaternary Science Reviews, Elsevier, 2019, 222, pp.105854. ⟨10.1016/j.quascirev.2019.07.036⟩. ⟨hal-02429997⟩



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