Novel sensor array helps to understand submarine cable faults off West Africa

Abstract

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 14-16 th 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 9 th 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 (72,000m 3 ) recorded at Kinshasa since the early 1960s, and this flood peak reached the river mouth on ~30 th December 2019. However, the cable-breaking turbidity currents occurred 2-10 weeks

Plio‐Pleistocene Ocean Circulation Changes in the Gulf of Alaska and Its Impacts on the Carbon and Nitrogen Cycles and the Cordilleran Ice Sheet Development

“…The 30% contribution of benthic diatoms to the total diatom MAR at Site U1417, despite its location at 4,218 m water depth (Jaeger et al, 2014), points to the transport of shallow water habitat assemblages towards the Surveyor Fan (McGee et al, 2008). The early Pliocene lithology at Site U1417 contains gravity flow deposits, while the tectonic history in the GOA and coastal Alaska during the Pliocene (Enkelmann et al, 2015) may result in slope instability and distal transport of shallow species to Site U1417, which lies ~700 km from the coastline (comparable to distances observed in turbidity current transports offshore West Africa, Talling et al, 2021). Relatively high terrestrial n-alkane MAR (Figure 4C) suggest enhanced flux of terrestrial OM input and rapid burial during gravity flows, which may also account for the peaks in TOC (e.g., Hage et al, 2020).…”

Longest sediment flows yet measured show how major rivers connect efficiently to deep sea

“…Subsequently, moored ADCPs were used to record more detailed (every ~30 s) velocity profiles through flows in the upper canyon in 2010-13 [31][32][33] . However, no previous study had deployed ADCP-moorings at multiple sites to the end of a deep-sea canyon-channel, as occurred during this 2019-2020 project 9 (Figs. 1 and 2).…”

“…These findings underpin a generalised model for how turbidity currents transfer globally significant sediment volumes from major rivers to the deep-sea. Finally, the wider implications of this study are outlined for efficiency of organic carbon transfer to the deep-sea [15][16][17] , predicting hazards to seabed telecommunication cables 9,[22][23][24][25] , and how future climate or land-use changes may impact the deep-sea.…”

“…It was previously thought that directly measuring powerful turbidity currents that reached the deep-sea was impractical 8 . However, here we describe direct monitoring of deep-sea turbidity currents in the Congo Canyon offshore West Africa 9 , whose timing was captured by an array of seabed moorings and seabed telecommunication cable breaks (Figs. 1 and 2).…”

“…The January 2020 flow described here broke both telecommunication cables (Figs. 1 and 2) connecting to West Africa, causing the internet to slow significantly from Nigeria to South Africa 9 , and these cables were broken again by turbidity currents in March 2020, April 2021 and January 2022 (Supplementary Table 1), including during coronavirus (CoV-19) related lockdown when internet bandwidth was particularly critical. Understanding why these cables broke is important, especially as they had not broken in the preceding 18 years (Supplementary Table 1).…”