Submarine canyons are the primary conduits for particulate transport from the continents to the deep sea, including sediments, organic carbon, and pollutants. Previously, focus has primarily been on transport due to downslope gravity currents. There is increasing recognition of the role internal tides may play, however, a lack of long-term seabed monitoring limits understanding of their significance. Here, we present novel near-seafloor monitoring data of breaking internal tides ('bores'), spanning one year within Whittard Canyon, a land-detached submarine canyon on the NE Atlantic margin. Throughout the year, these bores are energetic, with flow speeds regularly exceeding 0.5 m/s, and capable of resuspending seafloor sediments. Bores were observed for similar to 80 % of tidal cycles during the deployment. The shape and structure of bores varies throughout the year, in relation to spring-neap tidal cycles and longer-term seasonal changes. During the period of November-March, these bores generally attain higher speeds, show more abrupt changes in flow speed, and hold the greatest potential for up-canyon sediment transport. While fine-grained material may be moved throughout the year, this stronger winter activity has the greatest capacity to mobilize larger grains up-canyon. We show that bores, driven by internal tides, are an important, but previously poorly-observed agent for particulate transport. Bores occur frequently, yet exhibit variability at both seasonal and shorter time scales that may shape particulate transport within submarine canyons. These findings change our view of the general significance of internal tides in submarine canyons, with wide implications for hazards, tempo and fluxes of particulate transport.

To meet our Net Zero commitments, the past decade has seen a dramatic increase in wind power, with hundreds of thousands of wind turbines already in place. Many studies have focused on the environmental impact of windfarms; however, wind turbine-induced ground seismic vibrations have received less attention. Prior seismic observations near wind turbines show apparently contradictory spatio-temporal noise patterns and complex relationships to operational parameters. Here, we investigate these contradictions, categorizing seismic observations from wind farms worldwide, and explain the causes for this variation. We link the ground seismic response to the fundamentals of wind, the structural response of wind turbines, and the interactions of their foundations with variable geology. We summarise these approaches and discuss potential implementation in noise management, alongside noise suppression technologies. We finally explore the use of wind turbine noise as a seismic source to potentially monitor the structural health of wind turbine structures, and the subsurface. The latter is highly relevant to measurement, monitoring and verification of CO2 and H2 storage, where cost-effective and long-term monitoring solutions are necessary.

Small islands are among the most telecommunications-dependent communities on Earth, yet often the least resilient to network disruption, despite their importance for communications, education, healthcare and economic activity. However, global assessments of subsea cable vulnerability have largely overlooked the specific hazards and structural constraints affecting small islands. Here, we assess telecommunications resilience for small islands by integrating a 40-year global database of 5113 subsea cable faults with spatial analyses of environmental and anthropogenic hazard exposure. We analyse 24 island and island groups worldwide, representing diverse geological, economic, and oceanographic settings, and evaluate hazard exposure related to their offshore environments. We find that island-proximal environments are disproportionately hazardous for subsea cables, with over 75% of faults on island-connecting systems occurring within 300 km of island coastlines. Globally, 71.4% of faults are attributed to anthropogenic causes, and logistic regression shows that increased anthropogenic exposure significantly raises the likelihood of fault occurrence (odds ratio = 2.22, p = 0.006). In contrast, no significant relationship is observed between natural hazard exposure and fault occurrence (p > 0.4), suggesting that route design and engineering mitigation effectively reduce impacts from routine natural processes. However, extreme natural events can still cause widespread, multi-cable system failures. Small Island Developing States (SIDS) are particularly vulnerable, with fewer international cable connections (mean 3.9 vs 6.9 for non-SIDS) and greater distances from repair hubs (similar to 2200 km vs similar to 1800 km), increasing both the likelihood and duration of outages. These findings demonstrate that cable vulnerability is spatially concentrated and hazard-type dependent, requiring region-specific resilience strategies. Strengthening telecommunications resilience for small islands will require not only improved engineering and hazard assessment, but also increased network redundancy, regional cooperation, and targeted investment.

The formation of asymmetric submarine channels and canyons is the result of multiple processes, including bottom currents, Coriolis forcing, and centrifugal forces, acting on turbidity flows. Despite increasing studies of asymmetric submarine canyons and channels and recognition of the influence of bottom currents on turbidity flows, the relative contributions of these factors remain poorly constrained, often resulting in contradictory interpretations. In this study, we investigate whether morphometric characteristics of submarine canyons and channels – specifically relief and width asymmetries, and cross-sectional slope angles – can indicate the most likely processes responsible for their asymmetry, such as Coriolis effect versus bottom currents. We systematically analysed 24 asymmetric canyons and channels from diverse settings, integrating their morphometric data with environmental parameters including latitude, water depth, slope angle, and bottom current intensity and direction.Our results reveal substantial variability in channel asymmetry along their lengths: the positions of the higher margin, thalweg, steeper margin, and the degree of asymmetry often change within a system, so that a single channel cannot be consistently described with one asymmetry value. Depth-dependent variations in slope, water-mass structure, turbidity current dynamics, and bottom-current intensity, combined with temporal variability in both turbidity-current characteristics and bottom-current velocities, create locally coherent, but non-predictive asymmetry. Thus, our observations suggest that morphological characteristics alone are insufficient to identify the main forces controlling channel asymmetry. We propose a classification scheme to aid interpretation of channel asymmetry and potential bottom current interactions, emphasizing the complexity of channel formation.

The 2022 Hunga volcano eruption generated one of the largest and most destructive volcanic tsunamis ever recorded. We interpret the timing, nature and relative hazard of volcanic-tsunamigenic processes by combining geophysical, oceanographic, atmospheric, and eye-witness observations of this event. Hydro-acoustic signal ( T waves) detected on seismic stations up to 2600 km away provided a key to discerning tsunami triggers from explosions, volcanic mass flows, and caldera subsidence. The largest tsunami was generated by the first of at least two sudden caldera-subsidence events. This occurred 1 hour after globally detected explosions that produced smaller tsunami. Our results provide rare insights into the rates of caldera subsidence and highlight the complex multiple sources of tsunamis resulting from eruptions of oceanic volcanoes.

Underwater sediment density currents triggered by marine volcanic eruptions threaten island communities and infrastructure, while their deposits provide archives of past eruptions. Despite their significance, scarce real-time density current observations and concurrent deposit samples limit our understanding of their behaviour and relationship to varying volcanic mechanisms. Using data acquired following the explosive, VEI 6, shallow-submarine eruption of Hunga Volcano in 2022, we show that syn-eruptive delivery of pyroclastic material into the ocean via low-column collapses and fountaining triggered the multidirectional dispersal of highly-concentrated underwater density currents. Rapid supply of > 6.5 km3 of dense pyroclastic material onto the steep volcanic flanks over minutes-to-hours generated currents that maintain high density and velocity 10-100s of kilometres from the volcano. We outline diagnostic criteria to differentiate deposits of shallow-submarine generated underwater currents from other volcanic processes - enabling better reconstruction of the records of volcanic activity in marine sediments and enhancing hazard assessments in submerged volcanic settings worldwide.

Abstract The drive to cut carbon emissions and harness renewable energy has spurred rapid industrialization of the seas. Current estimates of seabed modification due to offshore windfarms (ca. 1% of a windfarm’s area) do not account for enhanced seabed mobility due to monopile wakes. Here we demonstrate how turbulence emanating from windfarm infrastructure mobilizes seabed sediments. Whilst mean flow conditions in our laboratory experiment could mobilize fine sand, near-bed turbulence from monopile’s wake could mobilize sand 17 monopile diameters ( D ) downstream. Related bedform formation coincided spatially with downwelling of the monopile’s turbulent wake, indicating that the 3D wake flow structure both creates and defines enhanced sediment mobility. We introduce a method for predicting this region of enhanced transport capacity by combining bed shear stress from near-bed turbulence with that from mean flow; and our field evidence at an operational offshore windfarm validates this approach. Our results show bed stress amplification is expected cover 3-8% of a typical windfarm area. Enhanced seabed mobility can alter seabed habitats and should be factored into impact assessment and marine planning.

Microplastics pervade the global seafloor, yet the mechanisms by which this pollutant is increasingly transported to the deep sea remain unclear. Fast-moving sediment avalanches (called turbidity currents) are hypothesized to efficiently transport microplastics into the deep sea. However, while this has been inferred from field sampling of the seafloor, it has never been demonstrated outside of a laboratory setting. Here, we provide direct field-scale evidence that turbidity currents in submarine canyons not only transport globally significant volumes of mineral and organic matter into the deep sea but also carry large quantities of anthropogenic particles, including microfibers and microplastic fragments. In situ hydrodynamic monitoring, coupled with direct sampling of the seafloor and material suspended by turbidity currents, reveals that even a submarine canyon whose head lies hundreds of kilometers from land acts as an efficient conduit to flush sediment and pollutants from the continental shelf to water depths greater than 3200 m. Frequent and fast turbidity currents supply oxygen and nutrients that sustain deep-sea biodiversity and fishing grounds in, and adjacent to, such canyons. Our study therefore confirms that these biodiversity hotspots are colocated with microplastic hotspots, indicating that the more than 5000 land-detached canyons worldwide can be important but previously unproven conveyors of anthropogenic pollution to the deep sea.

Submarine canyons are important conduits for microplastic transport to the deep sea, but the processes involved in that transport and how faithfully seafloor deposits record trends in pollution remain unclear. We use sediment push-cores for microplastic and sediment grain-size analysis from two transects across the Whittard Canyon, UK, to investigate the roles of near-bed flows and sub-seafloor processes in the transport and burial of microplastics and semi-synthetic microfibres. Microplastic and microfibre pollution is pervasive across the canyon at both transects, from the thalweg and from 500 m higher on the flanks, despite turbidity currents being confined to the canyon thalweg. We calculate sediment accumulation rates from 210 Pb dating and show that microplastic concentrations remain similar at sediment depths down to 10 cm. Throughout the Whittard Canyon there is an observed uniformity in the gradual decline in microfibre concentration with sediment depth, despite the variable sample locations and marked variations in sediment accumulation rates. Furthermore, the huge global increase in plastic production rates over time is not recorded, and microplastics are present in sediments that pre-date the mass-production of plastic. The interaction of turbidity currents, deep tidally-driven currents, and sub-seafloor processes affects microfibre burial processes in the deep sea and shreds any potential signal that microplastics may provide as indicators of historical plastic production rates; complicating the use of microplastics as fully-reliable markers of Anthropocene onset.

Most volcanic eruptions on Earth take place below the ocean surface and remain largely unobserved. Reconstruction of past submerged eruptions has thus primarily been based on the study of seafloor deposits. Rarely before the 15 January 2022 eruption of Hunga volcano (Kingdom of Tonga) have we been able to categorically link deep‐sea deposits to a specific volcanic source. This eruption was the largest in the modern satellite era, producing a 58‐km‐tall plume, a 20‐m high tsunami, and a pressure wave that propagated around the world. The eruption induced the fastest submarine density currents ever measured, which destroyed submarine telecommunication cables and traveled at least 85 km to the west to the neighboring Lau Basin. Here we report findings from a series of remotely operated vehicle dives conducted 4 months after the eruption along the Eastern Lau Spreading Center‐Valu Fa Ridge. Hunga‐sourced volcaniclastic deposits 7–150 cm in thickness were found at nine sites, and collected. Study of the internal structure, grain size, componentry, glass chemistry, and microfossil assemblages of the cores show that these deposits are the distal portions of at least two ∼100‐km‐runout submarine density currents. We identify distinct physical characteristics of entrained microfossils that demonstrate the dynamics and pathways of the density currents. Microfossil evidence suggests that even the distal parts of the currents were erosive, remobilizing microfossil‐concentrated sediments across the Lau Basin. Remobilization by volcaniclastic submarine density currents may thus play a greater role in carbon transport into deep sea basins than previously thought.

When the first transoceanic telegraph cables were laid in the mid-1800s, rapid communication between continents became possible. The advent of fibre-optic submarine cables in the 1990s catalyzed a global digital revolution. Today, a network of > 1.7 million kilometres of fibre-optic cables crosses the oceans, carrying more than 99

Deep-sea transport of sediment and associated matter, such as organic carbon, nutrients and pollutants, is controlled by near-bed currents. On the continental slope, these currents include episodic down-slope gravity-driven turbidity currents and more sustained thermohaline-driven along-slope contour currents. Recent advancements in deep-sea monitoring have catalysed a step change in our understanding of turbidity currents and contour currents individually. However, these processes rarely operate in isolation and the near-bed current regime is still to be quantified in a mixed system. Such measurements are crucial for understanding deep-sea particulate transport, calibrating numerical models and reconstructing palaeoflow. Here we use 4 years of observations from 34 instrument moorings in a mixed system offshore of Mozambique to show that near-bed currents are highly dynamic. We observe spatial variability in velocity over tidal and seasonal timescales, including reversals in current direction, and a strong steering and funnelling influence by local seabed morphology. The observed near-bed currents are capable of mobilizing and distributing sediments across the seabed, therefore complicating deep-sea particulate transport and reconstruction of palaeoceanographic conditions. Mooring observations suggest that deep-sea currents exhibit substantial variability over tidal and seasonal timescales, driving a complex pattern of sediment transport.

Turbidity current behaviour is affected by interactions with seafloor topography. Changes in flow dynamics will depend on the physiographic configuration of the topography (orientation and gradient), and the character of the incoming flow (magnitude and rheology). A better understanding of how unconfined turbidity currents interact with topography will improve interpretations of the stratigraphic record; we address this using 3D flume tank experiments with unconfined saline density currents interacting with a ramp orientated perpendicular to flow direction. The incoming flow parameters remained constant, whilst the slope angle was independently varied. On a 20 slope, super-elevation of the flow and flow stripping of the upper, dilute region of the flow occurred high on the slope surface. This resulted in a strongly divergent flow and the generation of complex multidirectional flows (i.e., combined flows). The super-elevation and extent of flow stripping decreased as the slope angle increased. At 30 and 40, flow reflection and deflection, respectively, are the dominant flow process at the base of slope, with the reflected or deflected flow interacting with the parental flow, and generating combined flows. Thus, complicated patterns of flow direction and behaviour are documented even on encountering simple topographies; a planar slope orientated perpendicular to flow direction. Combined flows in deep-water settings have been linked to the interaction of turbidity currents with topography and the formation of internal waves with a dominant oscillatory flow component. Here, combined flow occurs in the absence of an oscillatory component. A new process model for the formation and distribution of hummock-like bedforms in deep-marine systems is introduced. This bedform model is coupled to a new understanding of the mechanics of onlap styles (draping versus abrupt pinchout) and triggers for soft-sediment deformation processes to produce a spatial model of gravity-current interaction, and deposition, on slopes to support palaeogeographic reconstructions.

Low volcanic explosivity index (VEI) eruptions are common occurrences in the Southwest Pacific but, as demonstrated by the 2021/2022 eruption of Hunga Volcano, submerged calderas in the region are also capable of producing much larger and more hazardous eruptions. As such, characterising smaller events from potentially hazardous systems is essential. The 2019 eruption of Volcano-F, a submerged caldera, would likely have gone totally undetected had it not produced a pumice raft that inundated beaches in Fiji and eventually washed up in Australia. New data, acquired 5 months after the eruption, reveal the development of a new vent and the accumulation of at least 3.1*107 m3 bulk volume (dense rock equivalent of 5.6*106 m3) of material on the seafloor. Between 30 and 70% of erupted material entered the raft, while the rest remained near to or was dispersed down-current of the vent. This previously unaccounted for material increases the volume estimate for the eruption, confirming it as a VEI 3 event and highlights the importance of considering not just the floating component of a pumice raft forming eruption for VEI estimation. Geochemical analysis reveals the eruption comprised a homogenous batch of dacitic magma, with compositional characteristics similar to that erupted from the same volcano in 2001, and an until-now-unidentified pumice raft in the Coral Sea in 1964. Volcano-F therefore appears to have had at least three explosive eruptions in the last 60 years, indicating it is significantly at unrest. Repeated eruptions of similar composition and low crystal content magma over decadal to centennial scales indicate the existence of a melt-dominant magma body beneath the volcano. Submerged calderas, like Volcano-F, are common in the wider Southwest Pacific region, with many such calderas producing regular eruptions, implicating active magmatic recharge. Our findings motivate a need to carefully monitor and characterise even apparently small eruptions at this volcano, and others along the Tonga-Kermadec Arc. This is because such eruptions have the potential to subsequently prime or trigger more explosive eruptions and provide critical geochemical evidence about the plumbing system and evolution of the volcano, essential for understanding the diverse hazards they pose.

The largest canyons on Earth occur on the seafloor, and seabed sediment flows called turbidity currents play a key role in carving these submarine canyons. However, the processes by which turbidity currents erode submarine canyons are very poorly documented and understood. Here we analyse the first detailed time-lapse bathymetric surveys of a large submarine canyon, and its continuation as a less-deeply incised channel. These are also the most comprehensive time-lapse surveys before and after a major canyon-channel flushing turbidity current. These unique field data come from the Congo Submarine Fan offshore West Africa, where canyon flushing turbidity currents between 2019 and 2020 eroded 2.65 km3 of seabed sediment, as they travelled for over 1100 km at speeds of 5-8 m/s. This eroded sediment volume is equivalent to 19-33 % of global sediment flux from all rivers to the oceans. The time-lapse surveys cover 40 % of the 1100 km long submarine canyonchannel. They show that erosion was predominantly (94 %) along the canyon-channel axis, with only 6 % from failures along canyon or channel flanks. However, erosion along the canyon-channel floor was very patchy; some areas were eroded to depths of 10-20 m, whilst intervening areas showed no significant change. Knickpoints with up-slope migrating headscarps account for 22 % of the total eroded volume. One knickpoint in the deep-sea channel migrated by 21 km in one year, making it the fastest moving submarine knickpoint yet documented. Most (62 %) eroded sediment was in zones extending across the canyon or channel floor, without distinct headscarps as is the case for knickpoints. Erosion restricted to outer bends only comprised 10 % of the total, suggesting processes of erosion differ significantly from meandering rivers in which outer bend erosion is more important. Patchy seabed erosion appears to be mainly due to flow-bed processes (e.g. knickpoints), but spatial variations in seabed sediment properties may also play a role. The irregular seabed erosion occurs despite near-uniform flow speeds observed between moorings and submarine cable breaks with spacing of tens to hundreds of kilometers. Patchy and localised erosion has important implications for assessing hazards to seabed telecommunication cables, which are more likely to break in areas of deep erosion, and for creating appropriate numerical models of seabed erosion and turbidity current behaviour, or how to interpretate ancient submarine canyons and channels in rock outcrops.

Submarine canyons and channels are globally important pathways for sediment, organic carbon, nutrients and pollutants to the deep sea, and they form the largest sediment accumulations on Earth. However, studying these remote submarine systems comprehensively remains a challenge. In this study, we used the only complete-coverage and repeated bathymetric surveys yet for a very large submarine system, which is the Congo Fan off West Africa. Our aim is to understand channel-modifying features such as subaqueous landslides, meander-bend evolution, knickpoints and avulsions by analyzing their morphometric characteristics. We used a new approach to identify these channel-modifying features via morphometric fingerprints, which allows a systematic and efficient search in low-resolution bathymetry data. These observations have led us to identify three morphodynamic reaches within the Congo Canyon-Channel. The upper reach of the system is characterized by landslides that can locally block the channel, storing material for extended periods and re-excavating material through a new incised channel. The middle reach of the system is dominated by the sweep and swing of meander bends, although their importance depends on the channel’s age, and the time since the last up-channel avulsion. In the distal and youngest part of the system, an upstream migrating knickpoint is present, which causes multi-stage sediment transport and overspill through an underdeveloped channel with shallow depths. These findings complement previous less-detailed morphometric analyses of the Congo Canyon-Channel, offering a clearer understanding of how submarine canyon-channels can store sediment (due to channel-damming landslides, meander point bars, levee building due to overspill), re-excavate that sediment (via thalweg incision, meander propagation, knickpoint migration) and finally transport it to the deep sea. This improved understanding of the morphodynamics of the Congo Canyon-Channel may help to understand the evolution of other submarine canyon-channels, and assessment of hazards faced by seabed infrastructure such as telecommunication cables.

Burial of organic carbon in marine sediments is a long-term sink of atmospheric CO2, and submarine turbidity currents are volumetrically the most important sediment transport process on Earth. Yet the processes, amounts, and efficiency of organic carbon transfer by turbidity currents through submarine canyons to the deep sea are poorly documented and understood. We present an organic carbon budget for the submarine Congo Canyon, offshore West Africa, constrained with time-lapse bathymetry, sediment cores, and flow monitoring, including the effects of two >1000-km-runout canyon-flushing turbidity currents. In one year, flows eroded an estimated 6.09 +/- 2.70 Mt of previously buried terrestrial organic carbon in the canyon, primarily from fine-grained and vegetation-rich muddy sand facies with high organic carbon contents (as high as 11%). The age and composition of organic carbon in the Congo Canyon is comparable to those in the Congo River, indicating that transfer is efficient. Over the whole canyon-channel system, we extrapolate that 43 +/- 15 Mt of organic carbon was eroded and transported to the deep (>5 km) sea, equivalent to 22% of the annual global particulate organic carbon export from rivers to oceans and 54%-108% of the predicted annual terrestrial organic carbon burial in the oceans. Canyon-flushing turbidity currents carried a globally significant mass of terrestrial organic carbon down just one submarine canyon in a single year, indicating their importance for redistribution and delivery of organic carbon to the deep sea.

Abstract Turbidity currents carve the deepest canyons on Earth, deposit its largest sediment accumulations, and break seabed telecommunication cables. Powerful canyon‐flushing turbidity currents break sensors placed in their path, making them notoriously challenging to measure, and thus poorly understood. This study provides the first remote measurements of canyon‐flushing flows, using ocean‐bottom seismographs located outside the flow's destructive path, revolutionizing flow monitoring. We recorded the internal dynamics of the longest sediment flows yet monitored on Earth, which traveled >1,000 km down the Congo Canyon‐Channel at 3.7–7.6 m s−1 and lasted >3 weeks. These observations allow us to test fundamental models for turbidity current behavior and reveal that flows contain dense and fast frontal‐zones up to ∼400 km in length. These frontal‐zones developed near‐uniform durations and speeds for hundreds of kilometres despite substantial seabed erosion, enabling flows to rapidly transport prodigious volumes of organic carbon, sediment, and warm water to the deep‐sea.

Submarine channels are conduits for sediment-laden flows called turbidity currents, which play a globally significant role in the offshore transport of sediment and organic carbon and pose a hazard to critical seafloor infrastructure. Time-lapse repeat surveys of active submarine channels have recently shown that upstream-migrating knickpoints can dominate channel evolution. This finding contrasts with many studies of ancient outcrops and subsurface geophysical data that inferred channel bends migrate laterally, as occurs in meandering rivers. Here, we aim to test these two contrasting views by analysing two high-resolution repeat seafloor surveys acquired 13 years apart across the entirety of an active submarine channel in Knight Inlet, British Columbia. We find that two main mechanisms control channel evolution, with the normalised channel radius of curvature (specifically, R* - channel radius of curvature normalised to channel width) explaining which of these mechanisms dominate. Pronounced outer bend migration only occurs at tight bends (R*<1.5). In contrast, at broader bends and straighter sections (R*>1.5), erosion is focused within the channel axis, where upstream-migrating knickpoints dominate. High centrifugal accelerations at tight bends promote super-elevation of flows on the outer channel flank, thus, enhancing outer bend erosion. At R*>1.5, flow is focused within the channel axis, promoting knickpoints that migrate upstream at an order of magnitude faster than the rate of outer bend erosion at tight bends. Despite the dominance of knickpoints in eroding the channel axis, their stratigraphic preservation is very low. In contrast, the lateral migration of channel bends results in much higher preservation via lateral accretion of deposits on the inner bend. We conclude that multiple mechanisms can control evolution at different channel reaches and that the role of knickpoints has been underestimated from past studies that focused on deposits due to their low preservation potential.

Volcanic eruptions on land create hot and fast pyroclastic density currents, triggering tsunamis or surges that travel over water where they reach the ocean. However, no field study has documented what happens when large volumes of erupted volcanic material are instead delivered directly into the ocean. We show how the rapid emplacement of large volumes of erupted material onto steep submerged slopes triggered extremely fast (122 kilometers per hour) and long-runout (>100 kilometers) seafloor currents. These density currents were faster than those triggered by earthquakes, floods, or storms, and they broke seafloor cables, cutting off a nation from the rest of the world. The deep scours excavated by these currents are similar to those around many submerged volcanoes, providing evidence of large eruptions at other sites worldwide.