Routing of terrestrial organic matter from the Congo River to the ultimate sink in the abyss: a mass balance approach (André Dumont medallist lecture 2017)

Baudin, François; Dennielou, Bernard

doi:10.20341/gb.2020.004

Cited by 17 publications

(33 citation statements)

References 67 publications

(161 reference statements)

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“…In the case of freshwater lakes, the required sediment concentration is very low, about 1 kg.m -3 (Mulder and Syvitski 1995). Hyperpycnal flows have been proved to be also an important contributor to the flux of land-derived organic carbon towards distal, central basin areas (Zavala et al 2012;Liu et al 2013;Baudin et al 2017Baudin et al , 2020.…”

Section: Towards a Rational Classification Of Deltas And Their Depositsmentioning

confidence: 99%

Deltas: a new classification expanding Bates’s concepts

et al. 2021

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Deltas constitute complex depositional systems formed when a land-derived gravity-flow (carrying water and sediments) discharges into a marine or lacustrine standing body of water. However, the complexity of deltaic sedimentary environments has been oversimplified by geoscientists over the years, considering just littoral deltas as the unique possible type of delta in natural systems. Nevertheless, a rational analysis suggests that deltas can be much more complex. In fact, the characteristics of deltaic deposits will depend on a complex interplay between the bulk density of the incoming flow and the salinity of the receiving water body. This paper explores the natural conditions of deltaic sedimentation according to different density contrasts. The rational analysis of deltaic systems allows to recognize three main fields for deltaic sedimentation, corresponding to (1) hypopycnal (2) homopycnal and (3) hyperpycnal delta settings. The hypopycnal delta field represents the situation when the bulk density of the incoming flow is lower than the density of the water in the basin. According to the salinity of the receiving water body, three different types of hypopycnal littoral deltas are recognized: hypersaline littoral deltas (HSLD), marine littoral deltas (MLD), and brackish littoral deltas (BLD). The basin salinity will determine the capacity of the delta for producing effective buoyant plumes, and consequently the characteristics and extension of prodelta deposits. Homopycnal littoral deltas (HOLD) form when the density of the incoming flow is roughly similar to the density of the water in the receiving basin. This situation is typical of clean bedload-dominated rivers entering freshwater lakes. Delta front deposits are dominated by sediment avalanches. Typical fallout prodelta deposits are absent or poorly developed since no buoyant plumes are generated. Hyperpycnal deltas form when the bulk density of the incoming flow is higher than the density of the water in the receiving basin. The interaction between flow type, flow density (due to the concentration of suspended sediments) and basin salinity defines three types of deltas, corresponding to hyperpycnal littoral deltas (HLD), hyperpycnal subaqueous deltas (HSD), and hyperpycnal fan deltas (HFD). Hyperpycnal littoral deltas are low-gradient shallow-water deltas formed when dirty rivers enter into brackish or normal-salinity marine basins, typically in wave or tide-dominated epicontinental seas or brackish lakes. Hyperpycnal subaqueous deltas represent the most common type of hyperpycnal delta, with channels and lobes generated in marine and lacustrine settings during long-lasting sediment-laden river-flood discharges. Finally, hyperpycnal fan deltas are subaqueous delta systems generated on high-gradient lacustrine or marine settings by episodic high-density fluvial discharges.

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Section: Towards a Rational Classification Of Deltas And Their Depositsmentioning

confidence: 99%

Deltas: a new classification expanding Bates’s concepts

et al. 2021

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“…However, remineralization was shown to occur in small proportions in the Congo system, based on in situ measurements of total oxygen uptake made on the lobe sediments (Rabouille et al, 2019). Finally, we note that undersampling of the Congo Canyon and Channel occurred in past studies due to the difficulty with sampling sandy deposits (Baudin et al, 2020). This undersampling of the canyon and channel may result in underestimation of OC burial rates in the Congo Channel, similar to the Bute Inlet channel where only 30-cm-long sediment cores could be retrieved.…”

Section: Comparison With Larger Deep-sea Turbidity Current Systemsmentioning

confidence: 74%

“…This is the Congo River to the Congo Fan (Baudin et al, , 2020Coynel et al, 2005), where burial rates are calculated over centennial timescales that are comparable to the longer timescales considered in this study. Using a source to sink approach, Baudin et al (2020) found that 33%-69% of the annual OC delivered by the Congo River is buried in the Congo turbidity current system. This burial efficiency is similar to, if slightly lower than, our estimate in Bute Inlet (52%-72%), highlighting the difficulty in closing budgets between river source and marine sinks fed by turbidity currents (Baudin et al, 2020).…”

Section: Comparison With Larger Deep-sea Turbidity Current Systemsmentioning

confidence: 90%

“…The OC burial rates (Kt/year) in the fjord are calculated using Equation (Table 2; Baudin et al., 2020) as follows:

\boldsymbol{A}\mathbf{\times }\mathbf{T}\mathbf{O}\mathbf{C}\mathbf{\times }\boldsymbol{\rho }\mathbf{\times }\mathbf{(}\mathbf{1}\mathbf{-}\boldsymbol{\phi }\mathbf{)}\mathbf{\times }\mathbf{S}\mathbf{R},

where A is the surface area of a subenvironment (m 2 ), TOC is the total OC content (%) averaged between samples from a given subenvironment, ρ is the grain density (kg/m 3 ), φ is the porosity (%), and SR is the sedimentation rate (m/year).…”

Section: Methodsmentioning

confidence: 99%

“… b Assumed sedimentation rates in the channel and lobe are based on c and Baudin et al. (2020); see Supporting Information . …”

Section: Methodsmentioning

confidence: 99%

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Turbidity Currents Can Dictate Organic Carbon Fluxes Across River‐Fed Fjords: An Example From Bute Inlet (BC, Canada)

et al. 2022

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The delivery and burial of terrestrial particulate organic carbon (OC) in marine sediments is important to quantify, because this OC is a food resource for benthic communities, and if buried it may lower the concentrations of atmospheric CO2 over geologic timescales. Analysis of sediment cores has previously shown that fjords are hotspots for OC burial. Fjords can contain complex networks of submarine channels formed by seafloor sediment flows, called turbidity currents. However, the burial efficiency and distribution of OC by turbidity currents in river‐fed fjords had not been investigated previously. Here, we determine OC distribution and burial efficiency across a turbidity current system within Bute Inlet, a fjord in western Canada. We show that 62% ± 10% of the OC supplied by the two river sources is buried across the fjord surficial (30–200 cm) sediment. The sandy subenvironments (channel and lobe) contain 63% ± 14% of the annual terrestrial OC burial in the fjord. In contrast, the muddy subenvironments (overbank and distal basin) contain the remaining 37% ± 14%. OC in the channel, lobe, and overbank exclusively comprises terrestrial OC sourced from rivers. When normalized by the fjord’s surface area, at least 3 times more terrestrial OC is buried in Bute Inlet, compared to the muddy parts of other fjords previously studied. Although the long‐term (>100 years) preservation of this OC is still to be fully understood, turbidity currents in fjords appear to be efficient at storing OC supplied by rivers in their near‐surface deposits.

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The Rock‐Eval Method

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Routing of terrestrial organic matter from the Congo River to the ultimate sink in the abyss: a mass balance approach (André Dumont medallist lecture 2017)

Cited by 17 publications

References 67 publications

Deltas: a new classification expanding Bates’s concepts

Deltas: a new classification expanding Bates’s concepts

Turbidity Currents Can Dictate Organic Carbon Fluxes Across River‐Fed Fjords: An Example From Bute Inlet (BC, Canada)

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