The threat posed by plastic pollution to marine ecosystems and human health is under increasing scrutiny. Much of the macro- and microplastic in the ocean ends up on the seafloor, with some of the ...highest concentrations reported in submarine canyons that intersect the continental shelf and directly connect to terrestrial plastic sources. Gravity-driven avalanches, known as turbidity currents, are the primary process for delivering terrestrial sediment and organic carbon to the deep sea through submarine canyons. However, the ability of turbidity currents to transport and bury plastics is essentially unstudied. Using flume experiments, we investigate how turbidity currents transport microplastics, and their role in differential burial of microplastic fragments and fibers. We show that microplastic fragments become relatively concentrated within the base of turbidity currents, whereas fibers are more homogeneously distributed throughout the flow. Surprisingly, the resultant deposits show an opposing trend, as they are enriched with fibers, rather than fragments. We explain this apparent contradiction by a depositional mechanism whereby fibers are preferentially removed from suspension and buried in the deposits as they are trapped between settling sand-grains. Our results suggest that turbidity currents potentially distribute and bury large quantities of microplastics in seafloor sediments.
While microplastics are known to pervade the global seafloor, the processes that control their dispersal and concentration in the deep sea remain largely unknown. Here we show that ...thermohaline-driven currents, which build extensive seafloor sediment accumulations, can control the distribution of microplastics and create hotspots of up to 1.9 million pieces m
This is the highest reported value for any seafloor setting, globally. Previous studies propose that microplastics are transported to the seafloor by vertical settling from surface accumulations; here we demonstrate that the spatial distribution and ultimate fate of microplastics is strongly controlled by near-bed thermohaline currents (bottom currents). These currents are known to supply oxygen and nutrients to deep sea benthos, suggesting that deep sea biodiversity hotspots are also likely to be microplastic hotspots.
Abstract
The impacts of large terrestrial volcanic eruptions are apparent from satellite monitoring and direct observations. However, more than three quarters of all volcanic outputs worldwide lie ...submerged beneath the ocean, and the risks they pose to people, infrastructure, and benthic ecosystems remain poorly understood due to inaccessibility and a lack of detailed observations before and after eruptions. Here, comparing data acquired between 2015 - 2017 and 3 months after the January 2022 eruption of Hunga Volcano, we document the far-reaching and diverse impacts of one of the most explosive volcanic eruptions ever recorded. Almost 10 km
3
of seafloor material was removed during the eruption, most of which we conclude was redeposited within 20 km of the caldera by long run-out seafloor density currents. These powerful currents damaged seafloor cables over a length of >100 km, reshaped the seafloor, and caused mass-mortality of seafloor life. Biological (mega-epifaunal invertebrate) seafloor communities only survived the eruption where local topography provided a physical barrier to density currents (e.g., on nearby seamounts). While the longer-term consequences of such a large eruption for human, ecological and climatic systems are emerging, we expect that these previously-undocumented refugia will play a key role in longer-term ecosystem recovery.
Seafloor sediment flows (turbidity currents) are among the volumetrically most important yet least documented sediment transport processes on Earth. A scarcity of direct observations means that basic ...characteristics, such as whether flows are entirely dilute or driven by a dense basal layer, remain equivocal. Here we present the most detailed direct observations yet from oceanic turbidity currents. These powerful events in Monterey Canyon have frontal speeds of up to 7.2 m s
, and carry heavy (800 kg) objects at speeds of ≥4 m s
. We infer they consist of fast and dense near-bed layers, caused by remobilization of the seafloor, overlain by dilute clouds that outrun the dense layer. Seabed remobilization probably results from disturbance and liquefaction of loose-packed canyon-floor sand. Surprisingly, not all flows correlate with major perturbations such as storms, floods or earthquakes. We therefore provide a new view of sediment transport through submarine canyons into the deep-sea.
An estimated 8.3 billion tons of non-biodegradable plastic has been produced over the last 65 years. Much of this is not recycled and is disposed into the natural environment, has a long ...environmental residence time and accumulates in sedimentary systems worldwide, posing a threat to important ecosystems and potentially human health. We synthesize existing knowledge of seafloor microplastic distribution, and integrate this with process-based sedimentological models of particle transport, to provide new insights, and critically, to identify future research challenges. Compilation of published data shows that microplastics pervade the global seafloor, from abyssal plains to submarine canyons and deep-sea trenches (where they are most concentrated). However, few studies relate microplastic accumulation to sediment transport and deposition. Microplastics may enter directly into the sea as marine litter from shipping and fishing, or indirectly via fluvial and aeolian systems from terrestrial environments. The nature of the entry-point is critical to how terrestrially sourced microplastics are transferred to offshore sedimentary systems. We present models for physiographic shelf connection types related to the tectono-sedimentary regime of the margin. Beyond the shelf, the principal agents for microplastic transport are: (i) gravity-driven transport in sediment-laden flows; (ii) settling, or conveyance through biological processes, of material that was formerly floating on the surface or suspended in the water column; (iii) transport by thermohaline currents, either during settling or by reworking of deposited microplastics. We compare microplastic settling velocities to natural sediments to understand how appropriate existing sediment transport models are for explaining microplastic dispersal. Based on this analysis, and the relatively well-known behavior of deep-marine flow types, we explore the expected distribution of microplastic particles, both in individual sedimentary event deposits and within deep-marine depositional systems. Residence time within certain deposit types and depositional environments is anticipated to be variable, which has implications for the likelihood of ingestion and incorporation into the food chain, further transport, or deeper burial. We conclude that the integration of process-based sedimentological and stratigraphic knowledge with insights from modern sedimentary systems, and biological activity within them, will provide essential constraints on the transfer of microplastics to deep-marine environments, their distribution and ultimate fate, and the implications that these have for benthic ecosystems. The dispersal of anthropogenic across the sedimentary systems that cover Earth’s surface has important societal and economic implications. Sedimentologists have a key, but as-yet underplayed, role in addressing, and mitigating this globally significant issue.
Flutes and tool marks are commonly observed sedimentary structures on the bases of sandstones in deep‐water successions. These sole structures are universally used as palaeocurrent indicators but, in ...sharp contrast to most sedimentary structures, they are not used in palaeohydraulic reconstructions or to aid prediction of the spatial distribution of sediments. Since Kuenen's famous 1953 paper, flutes and tool marks in deep‐water systems have been linked to turbidity currents, as reflected in the standard Bouma sequence taught to generations of geologists. Yet, these structures present a series of unaddressed enigmas. Detailed field studies in the 1960s and early 1970s observed that flutes are typically associated with thicker, more proximal beds, whilst tools are generally prevalent in thinner, more distal, beds. Additionally, flutes and tool marks are rarely observed on the same surfaces, and flutes are seen to change downstream from larger wider parabolic to smaller narrower spindle‐shaped forms. No model has been proposed that explains these field‐based observations. This contribution undertakes a radical re‐examination of the formative flow conditions of flutes and tool marks, and demonstrates that they are the products of a wide range of sediment gravity flows, from turbulent flows, through transitional clay‐rich flows, to debris flows. Flutes are not solely the product of turbulent flows, but can continue to form in transitional flows. Grooves are shown to be formed by debris flows, slumps and slides, not turbidity currents, and in many cases the debris flows are linked to the debritic component of hybrid flows. Discontinuous tool marks, including skim (bounce) marks, prod marks and skip marks, are shown to be formed by transitional mud‐rich flows. Consequently, the observed spatial distribution of flutes and tool marks can be explained by a progressive increase in flow cohesivity downstream. This model of flutes and tool marks dovetails with models of hybrid flows that predict such a longitudinal increase in flow cohesivity. However, some deposits show grooves preferentially associated with Bouma TA beds, and these are likely formed by flows transforming from higher to lower cohesion, and are present in basins where hybrid beds are absent or rare. The recognition that sole structures may have no genetic link to the later overlying turbidity current deposits, and can be formed by a wide range of flow types, indicates that the existing pictorial description of the Bouma sequence is incorrect. A modified Bouma sequence is proposed here that addresses these points. In utilizing the advances in fluid dynamics since Kuenen's pioneering research, this study demonstrates that it is possible to use flutes and tool marks to interpret flow type at the point of formation, the nature of flow transformations, and the mechanics of the basal layer. These advances suggest that it is then possible to predict the nature of deposit type down‐dip. This new understanding, in combination with further testing in outcrop of the proposed relationships between sole marks and palaeohydraulics, opens up a wealth of possibilities for improving the understanding of deep‐water clastic environments, with implications for developing more complete facies models, assessing subaqueous geohazards and the resilience of seafloor infrastructure, and advancing our understanding of deep‐water sediments as archives of palaeoenvironmental change.
Type 1 diabetes (T1D) is a chronic autoimmune disease leading to immune-mediated destruction of pancreatic beta cells, resulting in the need for insulin therapy. The incidence of T1D is increasing ...worldwide, thus prompting researchers to investigate novel immunomodulatory strategies to halt autoimmunity and modify disease progression. T1D is considered as a multifactorial disease, in which genetic predisposition and environmental factors interact to promote the triggering of autoimmune responses against beta cells. Over the last decades, it has become clear that vitamin D exerts anti-inflammatory and immunomodulatory effects, apart from its well-established role in the regulation of calcium homeostasis and bone metabolism. Importantly, the global incidence of vitamin D deficiency is also dramatically increasing and epidemiologic evidence suggests an involvement of vitamin D deficiency in T1D pathogenesis. Polymorphisms in genes critical for vitamin D metabolism have also been shown to modulate the risk of T1D. Moreover, several studies have investigated the role of vitamin D (in different doses and formulations) as a potential adjuvant immunomodulatory therapy in patients with new-onset and established T1D. This review aims to present the current knowledge on the immunomodulatory effects of vitamin D and summarize the clinical interventional studies investigating its use for prevention or treatment of T1D.
Rivers (on land) and turbidity currents (in the ocean) are the most important sediment transport processes on Earth. Yet how rivers generate turbidity currents as they enter the coastal ocean remains ...poorly understood. The current paradigm, based on laboratory experiments, is that turbidity currents are triggered when river plumes exceed a threshold sediment concentration of ~1 kg/m3. Here we present direct observations of an exceptionally dilute river plume, with sediment concentrations 1 order of magnitude below this threshold (0.07 kg/m3), which generated a fast (1.5 m/s), erosive, short‐lived (6 min) turbidity current. However, no turbidity current occurred during subsequent river plumes. We infer that turbidity currents are generated when fine sediment, accumulating in a tidal turbidity maximum, is released during spring tide. This means that very dilute river plumes can generate turbidity currents more frequently and in a wider range of locations than previously thought.
Key Points
Here we document for the first time how very dilute (up to 0.07 kg/m3) river plumes can generate powerful turbidity currents
Such low sediment concentrations are 20 times lower than those predicted by past theory and experiments
Therefore, turbidity currents are likely to be much more frequent and occur at a far wider range of locations than previously thought
Assessment of risks to seabed habitats from industrial activities is based on the resilience and potential for recovery. Increased sedimentation, a key impact of many offshore industries, results in ...burial and smothering of benthic organisms. Sponges are particularly vulnerable to increases in suspended and deposited sediment, but response and recovery have not been observed in-situ. We quantified the impact of sedimentation from offshore hydrocarbon drilling over ∼5 days on a lamellate demosponge, and its recovery in-situ over ∼40 days using hourly time-lapse photographs with measurements of backscatter (a proxy of suspended sediment) and current speed. Sediment accumulated on the sponge then cleared largely gradually but occasionally sharply, though it did not return to the initial state. This partial recovery likely involved a combination of active and passive removal. We discuss the use of in-situ observing, which is critical to monitoring impacts in remote habitats, and need for calibration to laboratory conditions.
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•We observed a sponge respond to sedimentation from oilfield drilling for 48 days.•Pulses of sedimentation occurred over ∼5 days, with ∼40 days recovery time.•Sediment accumulated on the sponge, then was cleared.•Sponge movement coincided with sediment clearance, changes in currents.
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