Sediment resuspension due to internal solitary waves of elevation in the Messina Strait (Mediterranean Sea).

By combining real-field observations and theoretical predictions, we describe role and relationships among north-propagating internal solitary waves (ISWs) generated by tidal currents in the Messina Strait (Mediterranean Sea), buoyancy deformation, sediment resuspension, and mixing effects. In particular, our results show that the presence of ISWs traveling along the Gioia Basin (north of the Strait) is not strictly related to seasonality. During winter, when the remote observation of ISWs from satellite is particularly rare due to the weak water column stratification, we observe elevation-type ISWs from hydrographic data. This finding reveals a different scenario with respect to the summer one, when the high stratified water column gives rise to depression-type north-propagating ISWs and the subsequent sea surface manifestations, detectable from satellite imagery. Moreover, our beam transmission observations and theoretical predictions of the induced near-bottom horizontal velocity suggest that these elevation-type ISWs induce sediment resuspension over the seafloor, as well as mixing effects as they break on the frontal slope nearby Capo Vaticano.

Plastic burial by flash-flood deposits in a prodelta environment (Gulf of Patti, Southern Tyrrhenian Sea).

Plastic pollution affects all oceans and sequestration of plastics in sediments is considered its ultimate sink. We report evidence of macroplastic burial retrieved within a sediment core collected at 38 m depth at the mouth of the Mazzarrà River, a torrential river able to carry a large amount of sediment during seasonal flash-floods. Two macroplastic items were found at 68 and 255 cm below the core top (corresponding to the seafloor). Their association with terrestrial vegetal debris and their inclusion in decimetre-thick sandy/silty intervals showing coarsening- and fining-upward trends, suggest that they were deposited by hyperpycnal flows possibly triggered by flood events. These findings testify the potential of sedimentary flows in burying macroplastic at depth below the seafloor, especially in nearshore prodelta environments. Furthermore they raise the quest on the magnitude of macroplastic storage in the subsurface and on the lack of specific devices and strategies for their reckoning.

Spatial distribution of microplastics in volcanic lake water and sediments: Relationships with depth and sediment grain size.

Microplastics (plastics <5 mm) are globally widespread pollutants of aquatic ecosystems. As microplastics contaminate both water and sediments, research on their spatial distribution in these different environmental matrices has increased. However, fresh waters are poorly studied and even less so are lentic ecosystems. To contribute filling this knowledge gap, this study analyses the distribution of microplastics in the water column and surface sediments of a volcanic lake, namely Lake Bracciano. Furthermore, it analyses in more detail the relationship between the concentration of microplastics in sediments, its grain size and the sampling depth (i.e. nearshore or deep). Water and sediment sampling was carried out in different sectors of the lake (northern, eastern, southern, western) using a plankton net and a van Veen grab sampler, respectively. Two sediment samples were collected at each station in order to analyse the abundance of microplastic and to perform grain size analysis. Results show a mean concentration of 2.4 items m-3 in water and 42 items kg-1 in sediments. The distribution of microplastics is uneven between the different sampling stations, with the northern sector being the most contaminated in both matrices. The chemical composition and shape of microplastics vary between water and sediment. In particular, polyethylene terephthalate and polyvinyl chloride are the most abundant polymers in water and sediments, respectively. Fibres are the main shape of microplastics in water while fragments are more abundant in sediments. In-depth analysis of sediment shows that sediments from deep stations are more contaminated than nearshore samples and have more fragment-shaped microplastics than fibre-shaped ones. Furthermore, there is a significant positive correlation between the concentration of microplastics and the abundance of silt, confirming data emerging from the scientific literature on marine and lotic ecosystems.

Plastics, (bio)polymers and their apparent biogeochemical cycle: An infrared spectroscopy study on foraminifera.

To understand the fate of plastic in oceans and the interaction with marine organisms, we investigated the incorporation of (bio)polymers and microplastics in selected benthic foraminiferal species by applying FTIR (Fourier Transform Infrared) microscopy. This experimental methodology has been applied to cultured benthic foraminifera Rosalina globularis, and to in situ foraminifera collected in a plastic remain found buried into superficial sediment in the Mediterranean seafloor, Rosalina bradyi, Textularia bocki and Cibicidoides lobatulus. In vitro foraminifera were treated with bis-(2-ethylhexyl) phthalate (DEHP) molecule to explore its internalization in the cytoplasm. Benthic foraminifera are marine microbial eukaryotes, sediment-dwelling, commonly short-lived and with reproductive cycles which play a central role in global biogeochemical cycles of inorganic and organic compounds. Despite the recent advances and investigations into the occurrence, distribution, and abundance of plastics, including microplastics, in marine environments, there remain relevant knowledge gaps, particularly on their effects on the benthic protists. No study, to our knowledge, has documented the molecular scale effect of plastics on foraminifera. Our analyses revealed three possible ways through which plastic-related molecules and plastic debris can enter a biogeochemical cycle and may affect the ecosystems: 1) foraminifera in situ can grow on plastic remains, namely C. lobatulus, R. bradyi and T. bocki, showing signals of oxidative stress and protein aggregation in comparison with R. globularis cultured in negative control; 2) DEHP can be incorporated in the cytoplasm of calcareous foraminifera, as observed in R. globularis; 3) microplastic debris, identified as epoxy resin, can be found in the cytoplasm and the agglutinated shell of T. bocki. We hypothesize that plastic waste and their associated additives may produce modifications related to the biomineralization process in foraminifera. This effect would be added to those induced by ocean acidification with negative consequences on the foraminiferal biogenic carbon (C) storage capacity.

Massive benthic litter funnelled to deep sea by flash-flood generated hyperpycnal flows.

Marine litter is an emerging environmental threat affecting all world's oceans including the deep seafloor, where the extent of the phenomenon is still largely unknown. We report the spatial patterns of macro-litter distribution within the Messina Strait's channels (Central Mediterranean), focusing on the transfer mechanisms responsible for its emplacement, a key information to better understand litter distribution. Litter is patchy but pervasive on all surveyed channels, reaching densities up to ~200 items/10 m, the highest reported for the deep sea until now. Litter is often arranged in large accumulations formed by hundreds of land-sourced items, mixed to vegetal and coarse-grained debris, indicating an emplacement from sedimentary gravity flows. Such impressive amount of litter can be explained by the superposition of a very efficient source-to-sink sedimentary transport and a strong urbanization of the coastal area. These findings point out that macro-benthic litter pollution is a major, often overlooked, threat for deep-sea ecosystems. Further explorations are thus required in similar marine settings to fully understand the magnitude of the problem, since they may represent the largest litter hotspots in the deep-sea.