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

Abstract

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.

Burial of Organic Carbon in Swedish Fjord Sediments: Highlighting the Importance of Sediment Accumulation Rate in Relation to Fjord Redox Conditions

“…This implies that rivers, while not dominant sources of particulates to these fjords, are the dominant source of OC terr to these systems. Mass wasting events are dominant sources of OC terr in high relief watersheds of New Zealand, Canadian, Chilean, and Alaskan fjords (Cui, Bianchi, Jaeger, & Smith, 2016; Cui et al., 2017; Hage et al., 2022; Korup et al., 2019; Ramirez et al., 2016). Landslides have been recorded in Swedish fjord sediments (Polovodova et al., 2011), but are likely not an important point source of OC terr inputs to the fjords because of the relatively low relief of these fjord basins.…”

Predicting turbidity current activity offshore from meltwater-fed river deltas

“…Estimates of maximum suspended sediment concentrations for the Homathko River are 0.5-0.7 kg m −3 ; such concentrations are not sufficient for wholescale plunging of (hyperpycnal) river floodwater (Bornhold et al, 1994;Mulder and Syvitski, 1995). The Southgate River has only been gauged since June 2021, with measurements of discharge approximately 50% of the Homathko River (Hage et al, 2022).…”

“…These two channels join, forming a single submarine channel that continues down-fjord for 40 km to a water depth of 660 m where the channel transitions to a depositional lobe (Conway et al, 2012;Heijnen et al, 2020). This submarine channel is highly active with tens of turbidity currents frequently occurring in the upper channel during the freshet (Bornhold et al, 1994;Pope et al, 2022), and therefore acts as an efficient mechanism for the transport and burial of organic carbon supplied by the Homathko and Southgate Rivers (Hage et al, 2022).…”

“…Submarine sediment flows, known as turbidity currents, sculpt the deepest canyons (Harris and Whiteway, 2011;Shepard, 1972) and form some of the largest sediment accumulations on our planet (Talling, 2014). Turbidity currents dominate the transport and burial of terrestrial derived sediments (Talling, 2014), organic matter (Dai et al, 2012;Galy et al, 2007;Hage et al, 2022Hage et al, , 2020Lee et al, 2019), and pollutants, such as litter (Pierdomenico et al, 2019;Zhong and Peng, 2021) and plastics (Pierdomenico et al, Khripounoff et al, 2009). Despite this, the number of turbidity currents recorded at a single site via direct monitoring has limited statistical analysis to univariate approaches (i.e.…”

Understanding the Role of Terrestrial and Marine Carbon in the Mid‐Latitude Fjords of Scotland

“…Both the outer sill depth and tidal range can be seen as proxies for the restrictiveness of the fjord which likely governs both the input of OC mar and the retention of OC terr within the fjord as conceptualized by Fuast and Knies (2019). When the outer sill depth and tidal range are compared with F terr Other Vegetated Fjord Systems Scotland 2.88 ± 1.99 −27.7-−17.5 2.36-9.5 Bottrell et al, 2009;Hunt et al, 2020;Loh et al, 2008;Smeaton et al, 2016;Smeaton, Cui, et al, 2021;Smeaton, Hunt, et al, 2021; Alaska 5.08 ± 2.44 −22.4-−21.0 - Cui et al, 2016b;Jaeger et al, 1998;Walinsky et al, 2009 Canada 3.37 ± 2.50 −27.0-−22.6 - Hage et al, 2022;Ingall et al, 2005;Louchouarn et al, 1997;Nuwer & Keil, 2005;Smith & Walton, 1980;Smittenberg, Pancost, et al, 2004;St-Onge & Hillaire-Marcel, 2001 Chile 1.79 ± 0.76 −29.0-−19.1 1.3-9.0 Bertrand et al, 2012;Mayr et al, 2014;Rebolledo et al, 2019;Ríos et al, 2020;Ruiz-Ruiz et al, 2021;Sepúlveda et al, 2005Sepúlveda et al, , 2011Silva et al, 2011;Silva & Prego, 2002Norway 8.82 ± 4.20 −23.8-−20.9 4.69-6.9 Duffield et al, 2017Faust et al, 2014;Faust & Knies, 2019;Huguet et al, 2007;Müller, 2001;Skei, 1983;Smittenberg, Pancost, et al, 2004;Smittenberg et al, 2005;Velinsky & Fogel, 1999New Zealand 3.74 ± 1.86 −28.2-−19.1 4.55 ± 2.59 Cui, Bianchi, Savage, & Smith, 2016Hinojosa et al, 2014;Knud...…”