article · Nature Communications
Direct observations of seafloor turbidity currents originating at the mouth of the Congo River reveal how major rivers transport material directly into the deep sea. One recorded sediment flow travelled more than 1,130 kilometres, accelerating from 5.2 to 8.0 metres per second along its path. Over a single year, these currents eroded between 1,338 and 2,675 megatonnes of sediment from one submarine canyon, equalling up to 37 per cent of the global annual suspended sediment flux from modern rivers. The measurements confirm that river floods can generate canyon-flushing flows when rapid sediment accumulation at river mouths is subsequently triggered by spring tides weeks to months later. These findings validate the theory that strongly erosive flows self-accelerate, driving long-distance transport of organic carbon.
Submarine sediment flows can severely damage critical seafloor infrastructure and play a vital role in global carbon cycling. Understanding how terrestrial river floods and oceanic tides interact to trigger these powerful currents helps researchers anticipate how climate change will influence deep-sea environments and threats to undersea telecommunications networks.
The findings inform geohazard risk assessments for subsea telecommunications cable operators and marine infrastructure developers routing assets across submarine canyons. This is early-stage natural hazard research, providing foundational data to improve seabed routing strategies and predictive risk models rather than delivering an immediately deployable commercial product.
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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.
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DOI: 10.1038/s41467-022-31689-3
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