Description: This dataset includes organic carbon measurements on sediment samples collected in Bute Inlet (British Columbia, Canada) in October 2016 (cruise number PGC2016007) and October 2017 (cruise number PGC2017005) aboard the research vessel CCGS Vector. The cruise PGC2016007 took place between 7 October and 17 October 2016 and was led by Gwyn Lintern. The cruise PGC2017005 took place between 19 and 29 October and was led by Cooper Stacey. River samples were taken in the Homathko and Southgate rivers using Niskin bottles in the water column and a grab sampler in the river beds and the river deltas

Description: This dataset includes organic carbon measurements on sediment samples collected in Bute Inlet (British Columbia, Canada) in October 2016 (cruise number PGC2016007) and October 2017 (cruise number PGC2017005) aboard the research vessel CCGS Vector. The cruise PGC2016007 took place between 7 October and 17 October 2016 and was led by Gwyn Lintern. The cruise PGC2017005 took place between 19 and 29 October and was led by Cooper Stacey. Marine sediment samples were collected in Bute Inlet using a box corer for the sandy samples in the submarine channel and a piston corer for the muddy samples in the overbanks and distal basin.

Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Hage, S., Galy, V., Cartigny, M., Heerema, C., Heijnen, M., Acikalin, S., Clare, M., Giesbrecht, I., Gröcke, D., Hendry, A., Hilton, R., Hubbard, S., Hunt, J., Lintern, D., McGhee, C., Parsons, D., Pope, E., Stacey, C., Sumner, E., Tank, S., & Talling, P. Turbidity currents can dictate organic carbon fluxes across river‐fed fjords: an example from Bute Inlet (BC, Canada). Journal of Geophysical Research: Biogeosciences, 127(6), (2022): e2022JG006824, https://doi.org/10.1029/2022jg006824.

Description: 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.

Description: S.H. acknowledges funding by the IAS postgraduate grant scheme, a Research Development funds offered by Durham University, and the NOCS/WHOI exchange program. S.H. has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement no. 899546. The field campaign and geochemical analyses were supported by Natural Environment Research Council grants NE/M007138/1, NE/W30601/1, NE/N012798/1, NE/K011480/1 and NE/M017540/1. M.J.B.C. was funded by a Royal Society Research Fellowship (DHF\R1\180166). M.A.C. was supported by the U.K. National Capability NERC CLASS program (NE/R015953/1) and NERC grants (NE/P009190/1 and NE/P005780/1). C.J.H. and M.S.H. were funded by the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement no. 721403 - ITN SLATE. E.L.P. was supported by a Leverhulme Early Career Fellowship (ECF-2018-267).

Description: Seabed telecommunication cables can be damaged or broken by powerful seafloor flows of sediment (called turbidity currents), which may runout for hundreds of kilometres into the deep ocean. These flows have the potential to affect multiple cables near-simultaneously over very large areas, so it is more challenging to reroute traffic or repair the cables. However, cable-breaking turbidity currents that runout into the deep ocean were poorly understood, and thus hard to predict, as there were no detailed measurements from these flows in action. Here we present the first detailed measurements from such cable-breaking flows, using moored-sensors along the Congo Submarine Canyon offshore West Africa. These turbidity currents include the furthest travelled sediment flow (of any type) yet measured in action on Earth. The SAT-3 (South Atlantic 3) and WACs (West Africa Cable System) cables were broken on 14-16th January 2020 by a turbidity current that accelerated from 5 to 8 m/s, as it travelled for 〉 1,130 km from river estuary to deep-sea, although a branch of the WACs cable located closer to shore survived. The SAT-3 cable was broken again on 9th March 2020 due to a second turbidity current, this time slowing data transfer during regional coronavirus (COVID-2019) lockdown. These cables had not experienced faults due to natural causes in the previous 19 years. The two cable-breaking flows are associated with a major flood along the Congo River, which produced the highest discharge (72,000m3) recorded at Kinshasa since the early 1960s, and this flood peak reached the river mouth on ~30th December 2019. However, the cable-breaking turbidity currents occurred 2-10 weeks after the flood peak and coincided with unusually large spring tides. Thus, the large cable-breaking flows in 2020 are caused by a combination of a major river flood and tides; and this can provide a basis for predicting the likelihood of future cable-breaking flows. Older (1883-1937) cable breaks in the Congo Submarine Canyon occurred in temporal clusters, sometimes after one or more years of high river discharge. Increased hazards to cables may therefore persist for several years after one or more river floods, which cumulatively prime the river mouth for cable-breaking flows. The 14-16th January 2020 flow accelerated from 5 to 8 m/s with distance, such that the closest cable to shore did not break, whilst two cables further from shore were broken. The largest turbidity currents may increase in power with distance from shore, and are more likely to overspill from their channel in distal sites. Thus, for the largest and most infrequent turbidity currents, locations further from shore can face lower-frequency but higher-magnitude hazards, which may need to be factored into cable route planning. Observations off Taiwan in 2006-2015, and the 2020 events in the Congo Submarine Canyon, show that although multiple cables were broken by fast (〉 5 m/s) turbidity currents, some intervening cables survived. This indicates that local factors can determine whether a cable breaks or not. Repeat seabed surveys of the canyon-channel floor show that erosion during turbidity currents is patchy and concentrated around steeper areas (knickpoints) in the canyon profile, which may explain why only some cables break. If possible, cables should be routed away from knickpoints, also avoiding locations just up-canyon from knickpoints, as knickpoints move up-slope. This study provides key new insights into long runout cable-breaking turbidity currents, and the hazards they pose to seafloor telecommunication cables.

Description: Landslide-dams, which are often transient, can strongly affect the geomorphology, and sediment and geochemical fluxes, within subaerial fluvial systems. The potential occurrence and impact of analogous landslide-dams in submarine canyons has, however, been difficult to determine due to a scarcity of sufficiently time-resolved observations. Here we present repeat bathymetric surveys of a major submarine canyon, the Congo Canyon, offshore West Africa, from 2005 and 2019. We show how an ~0.09 km3 canyon-flank landslide dammed the canyon, causing temporary storage of a further ~0.4 km3 of sediment, containing ~5 Mt of primarily terrestrial organic carbon. The trapped sediment was up to 150 m thick and extended 〉26 km up-canyon of the landslide-dam. This sediment has been transported by turbidity currents whose sediment load is trapped by the landslide-dam. Our results suggest canyon-flank collapses can be important controls on canyon morphology as they can generate or contribute to the formation of meander cut-offs, knickpoints and terraces. Flank collapses have the potential to modulate sediment and geochemical fluxes to the deep sea and may impact efficiency of major submarine canyons as transport conduits and locations of organic carbon sequestration. This has potential consequences for deep-sea ecosystems that rely on organic carbon transported through submarine canyons.

Description: Here we show how major rivers can efficiently connect to the deep-sea, by analysing the longest runout sediment flows (of any type) yet measured in action on Earth. These seafloor turbidity currents originated from the Congo River-mouth, with one flow travelling 〉1,130 km whilst accelerating from 5.2 to 8.0 m/s. In one year, these turbidity currents eroded 1,338-2,675 [〉535-1,070] Mt of sediment from one submarine canyon, equivalent to 19–37 [〉7–15] % of annual suspended sediment flux from present-day rivers. It was known earthquakes trigger canyon-flushing flows. We show river-floods also generate canyon-flushing flows, primed by rapid sediment-accumulation at the river-mouth, and sometimes triggered by spring tides weeks to months post-flood. It is demonstrated that strongly erosional turbidity currents self-accelerate, thereby travelling much further, validating a long-proposed theory. These observations explain highly-efficient organic carbon transfer, and have important implications for hazards to seabed cables, or deep-sea impacts of terrestrial climate change.