![submarine canyon submarine canyon](https://i0.wp.com/www.geological-digressions.com/wp-content/uploads/2018/04/Pt-Lobos-canyon-close-view.jpg)
![submarine canyon submarine canyon](https://images.assettype.com/tgdaily%2F2016-09%2F80b38e01-2dcf-410d-b326-d031530dc472%2Fsubmarinecanyons.jpg)
This issue is particularly compounded for broad continental shelves, which were extensively flooded following the Last Glacial Maximum. In contrast, land-detached canyons that do not, or barely, incise into the continental shelf are generally considered to be inactive during sea level highstands, only switching on during lowstands 11, 23. The head of Monterey Canyon (California) lies only a few metres from shore, intersecting two littoral cells that directly funnel sediment into the canyon head 25, 26. For instance, the Congo Canyon (W Africa) extends into the estuary to provide direct connection to the high-discharge Congo River across all sea-level stands 23, 24. Where canyons cut sufficiently far landward into the continental shelf (land-attached), they maintain direct connection with fluvial or long-shore sediment supplies on the inner shelf during both sea-level high- and lowstands 11. The current paradigm holds that turbidity current activity should vary between different canyon types, as a function of their physiography and relative sea level 20, 21, 22, 23. It is therefore important to understand the frequency, magnitude and controls on turbidity current activity and how this varies between submarine canyons worldwide. The fast and dense nature of these currents also poses a threat to the network of seafloor cables that underpins the internet and global communications 18, 19. Turbidity currents that flow along submarine canyons can travel 1000s of km, transporting more sediment than rivers on land, and efficiently burying large quantities of organic carbon, thus contributing to regulation of climate on geological timescales 15, 16, 17. The resultant biodiversity hotspots underpin diverse and important ocean ecosystems 12, 13, 14. These incised conduits provide the dominant connection for sediment, nutrients and pollutants from continental shelves to the deep sea, enhance primary productivity, and locally steer ocean currents 3, 4, 5, 6, 7, 8, 9, 10, 11. Submarine canyons are found on all the world’s submerged continental margins, often dwarfing onshore river systems 1, 2.
![submarine canyon submarine canyon](https://i1.wp.com/www.extremescience.com/graphics/zhemchug-canyon.jpg)
As >1000 other canyons have a similar configuration, we propose that contemporary deep-sea particulate transport via such land-detached canyons may have been dramatically under-estimated. Major triggers such as storms or earthquakes are not required instead, seasonal variations in cross-shelf sediment transport explain temporal-clustering of flows, and why the storm season is surprisingly absent of turbidity currents. Here we present the most detailed field measurements yet of turbidity currents within a land-detached submarine canyon, documenting a remarkably similar frequency (6 yr −1) and speed (up to 5-8 ms −1) to those in large land-attached submarine canyons. Existing models therefore assume that land-detached submarine canyons are dormant in the present-day however, monitoring has focused on land-attached canyons and this paradigm remains untested. Post-glacial sea-level rise disconnected more than three quarters of the >9000 submarine canyons worldwide from their former river or long-shore drift sediment inputs. Sediment, nutrients, organic carbon and pollutants are funnelled down submarine canyons from continental shelves by sediment-laden flows called turbidity currents, which dominate particulate transfer to the deep sea.