Adjacent Slope Research Articles

Features of the natural bitumen distribution in the Kazan deposits on the territory of the Melekess depression in Tatarstan

This article presents the distribution of natural bitumen in the sediments of the Kazan tier of the middle Permian. Natural bitumens, concentrated in the Permian sediments of the Republic of Tatarstan, occur at shallow depths and are heavy, highly viscous, hypergenically converted oils. In the tectonic relation, the area of maximum Kazan bitumen occurrence is confined to the Melekess depression and the adjacent slope of the South Tatar arch.

Compositional changes in deglacial red mud event beds off the Laurentian Channel reveal source mixing, grain-size partitioning and ice retreat

Between 22 and 17 cal ka BP, five large meltwater events from within the Laurentian Channel Ice Stream deposited mud beds meters thick across a large area of the Laurentian Fan and adjacent continental slopes. This study determines the sources of these event beds and relates them to the glaciological evolution of the retreating Laurentian Ice Stream. We analyzed major element and magnetic mineral contents of these event beds and compare them with a new collection of 80 source reference samples from the Gulf of St. Lawrence area. Element ratios suggest a steady compositional change from older to younger outburst event beds, while element-specific offsets from reference sample compositions indicate grain-size and mineral/element partitioning during suspension transport. Their magnetic properties place event beds on the source mixing trend of four reference samples groups, which represent two magnetite-rich sources (Canadian Shield and/or Southern Newfoundland) and two hematite-rich sources (Appalachian red beds). Using a deterministic linear source mixing model based on IRM100mT, HIRM and Ca%, we find that the earlier two outburst events had higher contributions from granitic and calcareous sources than the later three events. Combining materials, timing and scenarios of the outburst events with ice-sheet retreat and ice-stream dynamics, we argue that the subglacial sediment depocenter of the earlier two event beds was located in the lower Laurentian Channel while that of the later three events was upstream from Cabot Strait.

Evidence of trawling-induced resuspension events in the generation of nepheloid layers in the Foix submarine canyon (NW Mediterranean)

Abstract The temporal evolution of water column turbidity was studied on a submarine canyon on the Barcelona continental margin. From April to June 2014, an instrumented mooring array equipped with an autonomous hydrographic profiler with a CTD and a turbidimeter was deployed in the Foix canyon axis at 870 m depth. The instruments were programmed to collect hydrographic profiles once per day to provide a view of the temporal evolution of water column characteristics from 200 to 800 m water depth. The results illustrate a well-defined water turbidity structure of particulate matter distributed in intermediate nepheloid layers (INLs) developed between 300 and 500 m water depth and above the canyon rims, and INLs and near-bottom nepheloid layers (BNLs) confined inside the canyon between 650 and 800 m water depth. Data from fishing vessels activity at the time of the deployment was obtained from Vessel Monitoring System (VMS). The presence and location of the fishing vessels in the study area suggested a relationship between trawling activity and the generation of such layers. Nepheloid layers were absent during the first part of the deployment, when there was no fishing activity within the Foix Canyon axis or at the adjacent continental slope. Later, with the beginning of trawling activity on the fishing grounds close to the canyon, both INLs and BNLs were observed in the profiling casts, suggesting a causative relationship with fishing activities. Additionally, the hydrodynamic conditions within the canyon also seem to favour particle retention and to increase water turbidity in thick BNLs when water circulation is directed up-canyon. Bottom trawling appears to act as a main sediment resuspension mechanism in the Barcelona continental slope regions, increasing suspended sediment concentration at specific water depths where fishing grounds are located. Suspended particles are then advected and propagate along and across-margin by ambient currents via nepheloid layers.

ОЦІНКА СТІЙКОСТІ СХИЛУ ТА ГІДРОГЕОЛОГІЧНОГО РЕЖИМУ НА ПЕРІОД БУДІВНИЦТВА ТА ЕКСПЛУАТАЦІЇ АДМІНІСТРАТИВНО-ГРОМАДСЬКОГО КОМПЛЕКСУ ПО ВУЛ. І. МАЗЕПИ, 1 В М. КИЄВІ

Ущільнення забудови сучасних мегаполісів примушує здійснювати будівництво на територіях зі складними рельєфом, інженерно-геологічними умовами і небезпечними геологічними процесами.На прикладі проектування адміністративно-громадського комплексу виконана оцінка стійкості схилу прилеглої території в період будівництва та впливу гідрогеологічного режиму на комплекс після завершення будівництва, а також визначено приток води в котлован та фільтраційні параметри підземного потоку на майданчику будівництва.Оцінка стійкості схилу виконувалась з урахуван-ням будівництва адміністративно-громадського комплексу для природного стану ґрунтів та при повному їх водонасиченні.Розрахунок притоку води в котлован заснований на теорії фільтрації, що розроблена Н.Н. Павловським.Фільтраційна міцність ґрунту при виході ґрунтових вод в котлован оцінюється на основі розрахунків та експериментальних досліджень ґрунтів при діючих на майданчику будівництва градієнтах напору та особливостей конструкцій.З ціллю аналізу впливу комплексу після закінчення будівництва на гідрогеологічний режим виконано чисельне моделювання руху підземних вод. Моделювання виконувалосьза допомогою обчислювальної програми, що розраховує тримірний фільтраційний потік, баланс водних мас, масоперенос та дозволяє визначити всі необхідні параметри ґрунтового потоку, а також побудувати карту гідроізогіпс для існуючих рівнів ґрунтових вод та їх прогнозованого підйому на 1,5 м та візуалізувати отримані результати. Ці розрахунки дозволяють оцінити можливість підтоплення існуючих будівель на прилеглій території в результаті виникнення «баражного ефекту», що викликаний заглибленням підземної частини комплексу нижче рівня ґрунтових вод.Представлені результати досліджень можуть бути використані при прийнятті технічних рішень щодо підвищення стійкості схилу з урахуванням будівництва, а також вибору конструктивних методів захисту від фільтраційного випору ґрунту в котловані при будівництві та захисту фундаментів і підземних конструкцій від підтоплення підземними водами в результаті зміни гідрогеологічного режиму.

A New Rapid Method to Assess the Durability of Shale

Shale is the most abundant sedimentary rock worldwide and is often used as a construction material in many civil engineering applications. However, this material is easily deteriorated when it is exposed to cyclic wetting and drying processes. Deterioration of shale used for highway construction applications may lead to bearing capacity failure of highway embankments and instability of the adjacent slopes. The susceptibility of shale to deterioration is typically quantified by durability. In this context, durability is a measure of the rate and magnitude of deterioration and is used to describe the susceptibility of a material to environmental factors such as mechanical and chemical weathering. The Jar Slake test is a visual observation-based immersion test used to qualitatively assess the durability of shale. Although the test is relatively rapid and easy to perform, the results are very subjective. This paper presents a new method that utilizes the immersion aspect of the Jar Slake test, which simulates water-induced deterioration of shale. However, the proposed method eliminates the subjectivity associated with the Jar Slake test. The proposed method quantifies the durability of shale using time dependent changes in electrical conductivity measurements of a shale-water solution. In this method, there is only need to monitor the electrical conductivity of the shale-water solution for up to 60 min and predict the durability of the shale by a simple model developed from this study. The results of the proposed method were found to compare well with other more rigorous methods to assess durability.

Urbanization-induced acid rain causes leaching loss of calcium from limestone-derived soil in South China

Acid rain events in Yuebei, a region of northern Guangdong Province, China, have been increasing due to rapid urbanization in recent years. A three-year study was conducted to assess the effect of rainfall on losses of dissolved calcium (Ca2+) from limestone soils in a karst area in Yuebei. Soil leachate was collected from 61 events that produced more than 100 ml leachate per event during a 3-year period. Each rainfall event caused on average a loss of 8.5 × 10−4 g Ca2+ kg−1 soil with a Ca2+ loss of 2.16 × 10−5 g kg−1 per mm of rain. Cumulative net Ca2+ loss from the soil for the 61 events monitored was 0.05 g kg−1. In terms of Ca-loss per mm rain, the largest net Ca2+ loss from the soil occurred with mild acid rain (pH 4.5–5.6), followed by non-acid rain (pH 5.6–6.29) and severe acid rain (pH < 4.5). Net Ca2+ losses through natural rainfall were significantly larger than those induced by simulated rainfall with distilled water (control) or rainwater from the karst depression area of an adjacent talus slope. Total water soluble Ca2+ content in the soil continuously decreased due to acid rain, with a total reduction of 0.36 g kg−1 during the three-year experimental period. Net Ca2+ losses from the soil were positively correlated with leachate Ca2+ concentration and rainfall and negatively correlated with rainwater pH. The losses of Ca2+ from the soil can increase the risk of acidifying soils in the flat karst area in Yuebei, which may also affect the adjacent regions through changing the chemistry of groundwater and surface water.

Patterns and drivers of meiofaunal assemblages in the canyons Polcevera and Bisagno of the Ligurian Sea (NW Mediterranean Sea)

Meiofaunal abundance, assemblage structure and richness of higher taxa were investigated for the first time in two submarine canyons (Polcevera and Bisagno) of the Ligurian Sea and along the adjacent open slope, in relation with the quantity and quality of sedimentary organic matter and other environmental variables, including grain size. Meiofaunal abundance and richness of higher taxa decreased with increasing water depth (from ca. 200 down to ca. 2000-m depth) in the open slope and Polcevera canyon, whereas the highest values were observed at 500 m depth in the Bisagno canyon. The comparison between canyons and the adjacent open slope, showed the lack of significant differences in meiofaunal abundance, at the same depth except for samples collected at 200 and 2000-m depth. Overall the biodiversity was higher in canyons than in the open slope. Phytopigments, utilised as a proxy of the input of primary organic matter, were up to 3 times higher in canyon than in slope sediments and, along with grain size, explained a large portion of the variability in all meiofaunal variables. Canyon and slope showed a high beta diversity (83%), mostly due to the presence of a high portion of rare taxa in the canyons. Some taxa, such as Cladocera, Cumacea, Gastrotricha, Nemertina were exclusively encountered in canyon sediments, whereas Tardigrada were encountered only in the adjacent slope. Results reported here indicated that, differences in meiofaunal assemblages between canyons and slopes are primarily driven by quantity and quality of the available food resources and by the presence of specific topographic features.

Food web structure and trophodynamics of deep-sea plankton from the Bari Canyon and adjacent slope (Southern Adriatic, central Mediterranean Sea)

Zooplankton represent a key component of deep-sea ecosystems, linking Particulate Organic Matter (POM) to higher trophic levels through both vertical migrations from the photic zone and being prey of several megafaunal species, including demersal and benthopelagic organisms. Nevertheless, this key group in deep-sea ecosystems is far to be well known, especially concerning trophic aspects. In this study, we aimed to depict the trophic web structure of deep-sea zooplankton collected in sediment traps from the Southern Adriatic, central Mediterranean Sea, and adjacent slope from 600 to 1200 m, and its trophodynamics. To achieve these objectives, we considered a long time-series set of samples, from March 2010 to October 2012 and we used stable isotope analysis of nitrogen and carbon. The area is characterised by cascading events of dense shelf waters, and the possible influence of this periodic phenomenon on seasonal changes in the isotopic composition of deep-sea zooplanktonic species was also analysed. Our results evidenced a complex structure for the deep-sea zooplankton food web with taxa organized in three trophic levels from POM feeders to ultra-specialized carnivores. Temporal changes in the isotopic signatures of deep-sea zooplankton species were observed, although the influence of cascading events was not so clear. The high swimming capability of deep-sea zooplankton and their ability to perform vertical migrations may be the cause of such unclear relationship, with species more relying on vertical fluxes from surface primary production than on lateral advective transport of organic particles.

Vertical distribution of microbial communities abundance and biomass in two NW Mediterranean Sea submarine canyons

The aim of the present study was to investigate the microbial community along the Ligurian coast corresponding to two marine canyons. The study considered pico-, nano- and micro-planktonic fractions, their abundances and composition. Temperature and salinity profiles along the water column showed the same trend at all stations and no significant difference was found among stations of the canyons’ profiles and those of the adjacent slope. A similar trend for abundances and biomasses was observed at all stations: higher values were generally measured at surface and decreased with increasing depth; significant linear regression was highlighted in each of the three transects. Results of the distribution of all microbial heterotrophs from the surface down to 2500 m indicate that prey abundance was generally higher than the feeding threshold of predators; this evidence suggests that the interaction between different size classes is bottom-up regulated in the study area.The slight decrease of the ratio Heterotrophic Bacteria (HB) vs. Heterotrophic NanoFlagellates (HNF) and the weak increase of relative abundance of larger HNF size classes should be the sole evidence of the expected “canyon effect”, and can be ascribed to the major input at the bottom of the canyon of particulate organic matter (POC) that can be used by heterotrophic nanoflagellates directly as a food source. Our results highlighted that the main pattern regulating community composition is depth, and that, in the aphotic layer, the different water masses (WM) present along the column, play a pivotal role in shaping the planktonic assemblage.

Microbial Community Structure and Functionality in the Deep Sea Floor: Evaluating the Causes of Spatial Heterogeneity in a Submarine Canyon System (NW Mediterranean, Spain)

Understanding community assembly and processes driving diversity in deep-sea environments is a major challenge in marine microbial ecology. The deep sea represents the largest ecosystem on Earth, but its remoteness makes the microbial community composition and functionality largely unknown. Moreover, microbial-focused studies comparing different deep-sea habitats like dynamic submarine canyons and slope ecosystems altogether are rare. The present work aims to study the deep-sea seafloor microbial communities (Bacteria and Archaea) of the Blanes Canyon and its adjacent western open slope (NW Mediterranean) at ca. 1500 m deep, in autumn and spring, and along the vertical sediment profile. Microbial assemblages were studied in terms of abundance, diversity (α and β), community structure and functional potential through 16S rRNA tag-sequencing to assess their adaptations to the canyon’s idiosyncrasy. Furthermore, the relationships of microbes with environmental variables and a potential predator (nematodes) were also assessed. We observed overall marked differences between canyon and open slope microbial assemblages, although their phyla composition was similar. Both the dominant and richest phyla showed significant differences in proportion between canyon and slope. Bacterial diversity was higher in the canyon than in the open slope, together with nematode abundances. Microbial assemblages were more heterogeneous and showed a higher temporal variability in the canyon than in the open slope. Microbial abundances along the vertical sediment profile showed high heterogeneity in the canyon while on the slope consistently decreased with depth. Nematode and microbial abundances were correlated in the more stable slope environments, while in the canyon phytodetritics inputs (Chl a and Chl a: phaeo) and organic carbon seem to play a role in controlling microbial diversity and abundance. Grain size was correlated with microbial abundances and explained part of the variability in the community structure. Predicted functional profiles differed per habitat and sediment layer, and specific metabolisms appear to be distinctively enhanced, such as aerobic pathways in the most superficial sediment layers in the canyon. Overall, we observed specific patterns of nutrient inputs, microbial composition, and predicted functionality, which may affect higher trophic levels (i.e, Meiofaunal nematodes). This study highlights the importance of canyon heterogeneity in shaping microbial communities.

An analytical model of wave overtopping flow velocities on dike crests and landward slopes

An accurate description of the maximum flow velocity across flood-protective structures is necessary in order to determine the stability of the landward slope and the amount of cover erosion. In this paper, two new formulas are derived to describe the change in the maximum overtopping flow velocity along the dike crest and the adjacent landward slope. These formulas are coupled in an effort to accurately predict the velocities in wave overtopping events. This analytical model is validated using 244 data points from flume tests and 300 data points from field tests on river dikes in the Netherlands. The modelled flow velocity shows good agreement with the measured flow velocity, with a Nash-Sutcliffe efficiency factor varying from 0.49 to 0.87. Also, the derived formulas are compared with existing formulas for wave overtopping flow velocities and overall showed a better performance for a wide range of geometries and covers.

Role of spatial scales and environmental drivers in shaping nematode communities in the Blanes Canyon and its adjacent slope

Understanding community assembly and processes driving diversity in deep-sea environments is a major challenge in marine ecosystems. In this paper, we investigated the importance of environmental gradients at different spatial scales in structuring deep-sea canyon and continental slope meiobenthic nematode communities in the NW Mediterranean Sea. Three scales were investigated 1) Ecosystem: Blanes Canyon vs. adjacent open slope; 2) Water-depth within each ecosystem: 1500, 1750 and 2000 m; and 3) Vertical profile (three layers within the first 5 cm of sediment). Nematode communities were analysed in terms of density, biomass, diversity and community structure. Grain size, Chl a, Chl a: phaeopigments, CPE, organic carbon and total nitrogen were measured to assess the relationships with nematode assemblages. Blanes Canyon harbours more abundant and diverse assemblages than the slope, particularly at 1750 m and 2000 m depth respectively. The higher canyon values may be related to the higher food availability there, which can be a consequence of the so-called “canyon effect”. Slope assemblages were overall more uniform than those in the canyon, where there were greater bathymetrical differences in community structure. Densities in the canyon peaked at 1750 m depth, which did not correspond with the bathymetric gradient in food availability. The deepest canyon station was the most similar to the slope stations in terms of both environmental conditions and nematode communities, suggesting it lie outside the canyon influence. The higher habitat heterogeneity of the canyon (indicated by its greater vertical sediment and water depth differences) played a key role in structuring nematode spatial distribution. Independently of the ecosystem, however, the vertical sediment profile was the most determinative factor for density, community structure, and diversity.

Living foraminiferal assemblages in two submarine canyons (Polcevera and Bisagno) of the Ligurian basin (Mediterranean Sea)

Living (Rose-Bengal stained) benthic foraminifera were investigated in eleven stations sampled along transects following a depth gradient from Polcevera and Bisagno canyons and the adjacent open slope (Ligurian Sea), in a depth interval ranging from 200 to 2000 m. In order to understand which environmental factors influence the abundance and taxonomical composition of the foraminiferal assemblages in these two domains (canyon and open slope), qualitative and quantitative foraminiferal data were correlated to the sediment biochemical composition (in terms of phytopigments, proteins, lipids, carbohydrates and biopolymeric carbon), grain size and the main hydrological characteristics (salinity, temperature, dissolved oxygen). The Cluster Analysis and Canonical Correspondence Analysis allowed us to detect two sectors (coastal and offshore) characterized by contrasting trophic conditions. The coastal sector reflects spread meso-eutrophic conditions in both physiographic domains being possibly more impacted by the river inputs and sediment transport processes from land. In fact, the narrow continental shelf of the Ligurian Sea favors the deposition of sediment transported by riverine processes on the immediately adjacent coastal areas. As a result homogenization of sea-bottom conditions occurs, leading to an unclear differentiation between open slope and canyon foraminiferal assemblages. Conversely, the offshore sector is less affected by physical disturbance due to the sedimentary flows decreasing in relation to the larger distance from the coastline. Consequently, the lower organic matter content and lower food quality (expressed in terms of contribution of the primary material to the biopolymeric carbon pool) lead to a more oligotrophic condition, which favors the development of peculiar assemblages dominated by Glomospira charoides, Ammolagena clavata and epifaunal taxa. The first finding ever of a warm tropical species (Amphistegina lessonii) in the Ligurian Sea sediments at 500-m depth can be considered the first evidence of upward expansion of tropical species to the Northern portion of the Mediterranean Sea, which is experiencing an evident water warming linked to the ongoing global climate change.

Molecular and Isotopic Composition of Hydrate-Bound, Dissolved and Free Gases in the Amazon Deep-Sea Fan and Slope Sediments, Brazil

In this work, we investigated the molecular stable isotope compositions of hydrate-bound and dissolved gases in sediments of the Amazon deep-sea fan and adjacent continental slope, Foz do Amazonas Basin, Brazil. Some cores were obtained in places with active gas venting on the seafloor and, in one of the locations, the venting gas is probably associated with the dissociation of hydrates near the edge of their stability zone. Results of the methane stable isotopes (δ13C and δD) of hydrate-bound and dissolved gases in sediments for the Amazon fan indicated the dominant microbial origin of methane via carbon dioxide reduction, in which 13C and deuterium isotopes were highly depleted (δ13C and δD of −102.2% to −74.2% V-PDB and −190 to −150% V-SMOW, respectively). The combination of C1/(C2+C3) versus δ13C plot also suggested a biogenic origin for methane in all analysed samples (commonly &gt;1000). However, a mixture of thermogenic and microbial gases was suggested for the hydrate-bound and dissolved gases in the continental slope adjacent to the Amazon fan, in which the combination of chemical and isotopic gas compositions in the C1/(C2+C3) versus δ13C plot were &lt;100 in one of the recovered cores. Moreover, the δ13C-ethane of −30.0% indicates a thermogenic origin.

Efficient Edge-Based Image Interpolation Method Using Neighboring Slope Information

This paper presents an image interpolation method that provides superior performance with low complexity. Applying a simple linear method achieves time-efficient interpolation, but often produces artifacts; however, applying other complex methods reduce unwanted artifacts at the cost of high computation time. The proposed interpolation scheme is based on the improvement of an algorithm called “Edge Slope Tracing (EST)” that predicts the slope based on the information of the adjacent slopes. Predicted slopes are used in slope-based line averaging to perform the interpolation. Slope-based line averaging is followed by post-processing of an interpolated image using two-way interpolation and thin edge correction to avoid the production of unwanted artifacts at the cost of low complexity. The proposed algorithm is very simple and simulation results indicate that it provides better or nearly equal results compared to conventional state-of-the-art algorithms and that it also reduces complexity to a great extent compared to conventional methods.

Productivity controls macrofauna diversity in the deep northern Gulf of Mexico

The α-diversity in two large-scale, systematic macrobenthos surveys (1983–1985 and 2000–2001) in the deep northern Gulf of Mexico (GoM) has been compared under strong vertical and horizontal productivity gradients to examine underlying factors that control the distribution of deep-sea diversity. We calculated the effective numbers of equally abundant species (Hill numbers) from 100 randomly selected individuals to examine spatial patterns of species richness and evenness. Macrofauna α-diversity was a negative parabolic function of depth; the minima occurred at high export POC flux on the upper continental slope and on the abyssal plain with extremely low input of POC; the maximum occurred at intermediate levels of macrofauna biomass and input of POC. The overall parabolic pattern of α-diversity was stable over the 20-year period and not statistically different between meso-scale depressions (e.g., basins and canyons) and their adjacent slope habitats; however, the diversity was significantly higher in the NE than the NW slope habitats. The observed Mid-Depth-Maximum (MDM) in α-diversity, we suggest, was likely a result of dynamic equilibrium between productivity and competitive exclusion. The higher diversity and productivity in the NE than the NW GoM at similar depth ranges suggests that, for the first time, the productivity-diversity relationship was observed independent of other depth-related factors. The findings provide a foundation for predicting the possible responses of diversity to climate change and anthropogenic impacts in the deep sea.

High diversity of benthic bacterial and archaeal assemblages in deep-Mediterranean canyons and adjacent slopes

Submarine canyons and slopes increase the topographic heterogeneity of continental margins and enhance mass and energy transfer from the shelf to the deeper basins, profoundly influencing the biodiversity and functioning of deep-sea ecosystems. However, information on the distribution and diversity of microbial assemblages in such habitats is extremely scant. In the present study, for the first time, we investigated abundances of benthic prokaryotes and their diversity (i.e., bacterial and archaeal) in two of the largest canyons of the Mediterranean Sea (Bisagno and Polcevera Canyons, in the Ligurian Margin) and their adjacent open slope along a water-depth gradient from 200 to 2000 m. We found that prokaryotic abundance and the richness of Operational Taxonomic Units (OTUs) varied within a narrow range despite the high variability of thermohaline and trophic conditions in the habitats investigated. Conversely, the taxonomic composition (in terms of OTUs) was highly variable among the different habitats and depths investigated. The largest fraction of OTUs (representing >80% of the total OTUs identified) were unique of each sampling site, indicating a high prokaryotic β-diversity among the investigated systems. Thermo-haline and trophic conditions and water depth only partially influenced the composition of the prokaryotic assemblages suggesting that other factors, potentially related to physical forcing typically occurring in margin ecosystems, could promote a high diversification of benthic bacterial and archaeal assemblages. This study provides new insights into the benthic prokaryotic diversity of Ligurian canyons and suggests that microbial assemblages thriving in continental margins can largely contribute to the whole diversity of Mediterranean deep-sea ecosystems.

High rates of viral lysis stimulate prokaryotic turnover and C recycling in bathypelagic waters of a Ligurian canyon (Mediterranean Sea)

Submarine canyons are able to preferentially channel primary production and shelf export to the deep ocean, thus acting as hotspots of biomass and biogeochemical cycling of organic matter. Despite their global relevance, no information is available about the influence of submarine canyons on deep-sea virus-prokaryote interactions. Here, we show that deep-sea waters overlying the Bisagno Canyon (Ligurian Sea, NW Mediterranean) can sustain up to 4 times higher abundances of bathypelagic prokaryotes and viruses when compared to the waters overlying the adjacent slope. We also report that the bathypelagic waters of the canyon are hotspots of viral infections, with rates of virus-induced prokaryotic mortality and biomass turnover up to 10 times faster compared to the adjacent slope at similar depths. In addition, C released by viral lysis of their prokaryotic hosts in bathypelagic waters of the canyon was up to 40 times higher than in the slope. The prokaryotic distribution in bathypelagic waters of the investigated area of the Ligurian margin was largely influenced by organic C concentrations and temperature. Our results highlight that the peculiar characteristics of the canyons (such as the Bisagno canyon) could contribute to sustain the metabolism of bathypelagic prokaryotes, promoting C cycling through virus-induced prokaryotic mortality. We conclude that submarine canyons could represent hot spots of prokaryotic and viral activities able to support the deep-sea pelagic food webs.

Biodiversity and distribution of meiofauna in the Gioia, Petrace and Dohrn Canyons (Tyrrhenian Sea)

Habitat heterogeneity is a major structuring agent of benthic assemblages promoting high turnover in species composition and ultimately contributing to overall higher diversity. Submarine canyons, a pervasive feature of the continental margins worldwide, increase habitat heterogeneity at multiple spatial scales. In the present study, we test the hypothesis that different topographic structures or/and food sources controlling the abundance, biomass and biodiversity (using meiofauna and nematodes as a model study) in canyon systems. To do so, we compared different topographic structures: canyon edge, thalweg and axis, and the upper shelf and open slope in the Gulf of Gioia (Gioia and Petrace Canyons) and in the Gulf of Naples (Dohrn Canyon) (Tyrrhenian Sea) at different depths. Our results suggest that meiofaunal abundance and biomass are generally higher in the canyon thalwegs than in the canyon edge or adjacent open slopes at regional scale. This pattern is not always confirmed for biodiversity and when thalwegs are compared to different topographic structures within the Gioia Canyon system. In our study, the role of food quantity and quality is preeminent to explain the spatial distribution of meiofaunal variables among different topographic structures at 200-m while habitat heterogeneity become relevant at 500-m and within the Dohrn Canyon. In Gioia and Petrace Canyons we observed a high food availability is associated to specific topographic structures (thalwegs) that influenced the meiofaunal abundance and diversity distribution and nematode diversity and species composition. Each topographic structure shows a high number of exclusive species that contributes to a high species turnover and high overall biodiversity in all canyon systems. Changes in nematode composition determine also differences in the functional diversity (trophic guilds composition) and life strategy of the nematode assemblages. Our findings reveal that the presence of different topographic structures influences the spatial distribution of food quality and quantity that determine the presence of exclusive taxa and species enhancing both local and regional diversity.

Macrofaunal assemblages in canyon and adjacent slope of the NW and Central Mediterranean systems

Macrofaunal assemblages were studied along bathymetric transects in six canyons and four adjacent open slopes of the Mediterranean Sea. The different areas investigated were located approximately along a longitudinal gradient at similar latitudes. Three regions were investigated: the Catalan (from 334 to 1887 m depth), the Ligurian (from 222 to 2005 m depth) and the South Adriatic margins (from 196 to 908 m depth). The analysis of the meso-scale distribution of assemblage structure and biomass showed significant differences among regions, which resulted in high values of δ-diversity. Clear differences in trophic composition were also observed, and a decreasing pattern in the individual body size of macrofaunal organisms moving Eastward. These patterns were apparently linked to changes in food supply, whereas macrofaunal abundance and number of taxa showed a decrease pattern with increasing water depth. When the assemblage structure was compared between canyons and adjacent open slope, a very high β-diversity was observed, indicating that the bottom topography exerted a strong effect on the assemblage characteristics.