Seafloor Research Articles

Trawling-induced change in benthic effect trait composition – A multiple case study

IntroductionThe importance of the response-effect trait dichotomy in marine benthic ecology has garnered recent attention. Response traits, characterising species responses to environmental variations, have been a dominant focus in the development of ecological indicators for ecosystem health assessment. In contrast, effect traits, expressing effects of organism activities on the ecosystem, still do not benefit from an equal interest in spite of the complementary facet that they provide to complete our understanding of functional diversity and ecosystem vulnerability. In this study, we explore the consequences of disturbance by bottom trawl fisheries on benthic effect trait composition.MethodsTo this end, we used different contexts of environmental and trawling conditions from thirteen case studies in European waters and apply the same analytical procedure to derive a gradient that solely account for trawling-induced disturbance (Partial RLQ analysis).ResultsBottom trawling was found to be a selective force of benthic effect trait composition in a majority of case studies. In general, tube-dwelling species were more typical of low trawling frequencies, whereas deep burrowing species were more resistant at high trawling frequencies. Although we report significantly deleterious effects of trawling on benthic ecosystem functions, the effect trait pattern along the gradient was never related to life span, a key response trait generally assumed to express recoverability following disturbance. Furthermore, we show that trends in species multi-functionality and community functional diversity can be negative or positive along the trawling intensity gradient.DiscussionWe discuss the relevance of these results in light of recent developments in the framework of response and effect trait dichotomy, and provide guidelines of trait data analysis in the context of trawl fisheries impact on the sea floor. Our findings emphasize the importance of fundamental concepts from functional ecology in this context and represent a first step toward an assessment of trawling effect more oriented on benthos-mediated biogeochemical processes.

The early history of the Neotethys archived in the ophiolitic mélange of northwestern Croatia

Ophiolite exposures in NW Croatia have been attributed to the Western Vardar Ophiolitic Unit and interpreted as derived from the Meliata–Maliac–Vardar branch of the Neotethys Ocean. Blocks within the ophiolitic mélange on Mt Ivanščica were investigated to determine the petrological and geochemical characteristics of the effusive rocks and to carry out radiolarian dating of the associated pelagic sedimentary rocks. The analysed effusive basic rocks represent chemostratigraphically uniform subalkaline high-Ti massive tholeiitic basalts characterized by an enriched composition typical of incompatible element-enriched mid-ocean ridge basalt (E-MORB). These basalts are compatible with c. 9–11% of partial melting of an enriched mantle source transitional between primitive and depleted MORB-type mantle and were formed in the non-subduction geotectonic setting of E-MORB-type rocks. This reflects an initial succession of oceanic protocrust formation and the onset of ocean spreading. Radiolarians from the chert and shale successions associated with the basalts indicate a Late Anisian–Early Ladinian age of initial ocean floor spreading, which continued into the Langobardian. The obtained data are correlative with reported blocks interpreted as remnants of the Triassic Neotethys crust from the ophiolitic mélange of the Western Vardar Ophiolitic Unit and reaffirm a common origin from a single ocean basin located east of the Adria microplate. Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists

Digestive System Anatomy and Feeding Mechanism of Quatuoralisia malakhovi (Hemichordata, Torquaratoridae)

The digestive system was anatomically studied in the deep-sea enteropneust Quatuoralisia mala-khovi. It was shown that lateral collar lips are twisted in such a way that they form a ciliary groove that leads to an internal channel, through which collected detritus particles are transferred to peripheral pharyngeal channels. The size of the selected particles ranges from 1–6 to 100–200 μm, which corresponds to feeding on the remains of planktonic diatoms. A fecal cord was observed to act as an anchor that holds the heavily watered jelly-like body of Torquaratoridae at the sea floor during feeding.

Nature and Origin of a Massive Sulfide Occurrence in the Karrat Group: Evidence for Paleoproterozoic VMS Mineralization in Central West Greenland

Abstract Mafic volcanic rocks of the Kangilleq Formation of the Paleoproterozoic Karrat Group host volcanogenic massive sulfide (VMS) mineralization in the area of central Kangiusap Kuua, central West Greenland. The mafic volcanic rocks display evidence of subaqueous, effusive eruption and redeposition by mass debris flows generated along fault scarps on the sea floor. A zone of semiconformable quartz alteration and disconformable chlorite alteration within hydrothermal breccias and mafic tuff breccias near the top of the volcanic sequence is interpreted to reflect a synvolcanic hydrothermal system. Conformable, massive to semimassive, and discordant, stringer-style sulfide mineralization is hosted within the quartz- and chlorite-altered volcanic rocks. The massive to semimassive sulfide mineralization is ~10 m thick and crops out along strike for ~2,000 m. The stringer zone is ≤10 m thick with individual sulfide stringers ranging in width from 5 to 90 cm. All sulfide zones are dominated by coarse pyrrhotite and pyrite, with trace amounts of sphalerite and chalcopyrite. The pillow lavas are subalkaline with geochemical characteristics typical of modern transitional to tholeiitic mid-ocean ridge or back-arc basin basalt. Trace element and Nd isotope data suggest that these lavas erupted in an epicratonic, back-arc basin. Characteristics of the host rocks indicate a period of localized rifting, volcanism, and VMS formation during genesis of the Karrat Group, which is dominated by siliciclastic rocks.

Horizontal and vertical motion at the surface of seawater-gas hydrate bearing sediment-seabed under obliquely incident P waves

This study extends the seismic dynamics of two-phase/three-phase poroelastic sediments in coupled ocean-sediment-substrate systems to gas hydrate-bearing sediments. The ocean sediment floor is described as a finite-thickness porous medium with two solids and a compressible viscous fluid (porous skeleton, gas hydrate, and fluid), which sits on an elastic seabed. In the coupled system of seawater, gas hydrate-bearing sediment layer and seabed, analytical solutions for the P wave reflection and transmission coefficients are derived. Two key factors are derived: displacement amplitude and magnification factor. The relationship among two key factors with incident angle, frequency, sediment thickness, cementation parameter, contact parameter, temperature and saturation in the sedimentary layer containing gas hydrate is analyzed. The research shows that when the P wave is vertically incident (θip = 0°), the incident frequency has a greater influence on the vertical displacement amplitude, and when the P wave is grazing incident (θip = 90°), the influence is not observed. The displacement of the sedimentary layer fluctuates in different degrees with the increase of the layer thickness. When the temperature increases, the saturation is higher, that is, the hydrate content is lower, and the influence of the contact parameters gradually disappears.

Impact of hydrological changes and vertical motions on Pleistocene marine environments of the eastern coast of the island of Rhodes (Greece)

The island of Rhodes in the eastern Mediterranean Sea is situated in an area affected by an ongoing plate convergence, and its Pleistocene marine environments were influenced by recurring hypoxia and changes in organic matter fluxes. This makes the island an important site to study the influence of orbital-driven climate changes and tectonic-induced vertical motions on the marine benthic ecosystems in near-coastal areas at local and regional scales. We investigated the Early and Late Pleistocene sediment sections at Agathi Beach and Lardos, located on the middle-eastern coast of the island. Our results show variations in oxygen and food levels at the sea floor, including transient phases of enhanced fresh-water and nutrient input to near-coastal environments. These phases occurred at times of Northern Hemisphere summer insolation maxima, simultaneously to the formation of sapropels in the deep-sea basins of the eastern Mediterranean Sea. The application of a benthic foraminiferal transfer function revealed that both sections were influenced by tectonic-driven long-term and short-term vertical motions with higher rates than expected on the island of Rhodes. While Agathi Beach underwent two short-term cycles of uplift and subsidence, Lardos indicates at least three cycles with average rates of vertical motion as high as 8.6 mm/a.

Shallow Water Acoustic Vector Sensor Array AutoNomous System (SVAAN) for Coastal Surveillance Applications

Abstract Shallow Water Acoustic Vector Sensor Array AutoNomous System (SVAAN) is a passive acoustic monitoring system using vector sensors. Acoustic vector sensors measure acoustic pressure and particle velocity, and an array of such sensors are very useful in underwater source localization. SVAAN is thus developed for surveillance applications in coastal waters and designed for a 100-m depth rating. The main objective of this work is to present SVAAN that is developed as a sea bed mounted system, consisting of two vector sensors and four hydrophones. In addition, an inertial sensor has been included to measure the system orientation when deployed. This was deployed as a bottom mounted unit in the shallow waters of South-West Bay of Bengal to measure the noise from boats/ships and localize the source. The acoustic data are analyzed, Direction of Arrival is estimated using Multiple Signal Classification for source localization, and the performance of SVAAN is studied. In addition to that, the tracking of boat noise has been estimated from the experiment data. Results and further enhancement of the system are discussed.

Tornado In The Sea: A Media Transposition of the Barracuda Series Painting into a Musical Composition

This work is the manifestation of the transformation of Zaimie bin Sahibil’s painting, Barracuda Series, into musical form. The Barracuda Series painting presents the beauty and richness of the ocean bed as a utopian paradigm of the maritime ecology of the coastal community of Sabah, Malaysia. The composer was inspired by his own aesthetic experience when appreciating the painting. This aesthetic experience became the material object that was treated with the concept of media transposition and turned into a musical composition. The media transposition was implemented through the interpretation and transformation of the external and internal structural levels of the Barracuda Series painting. These elements were adapted to create musical elements as a form of innovation in the way the composition was created. the creation of this work involved a number of work stages that were implemented constructively through a method of creation. These stages included: an analysis of data sources, experimentation, contemplation, composition, and formation. The work process utilized the results of extra-aesthetic interpretation and intra-aesthetic transformation to create an innovative musical text. The musical composition Tornado in the Sea uses the instrumentation of piano, violin, and kalimba. The stages of creation included an analysis of data sources, experimentation, contemplation, arrangement, formation, and execution.

Phylogenetic diversity of functional genes in deep-sea cold seeps: a novel perspective on metagenomics

BackgroundLeakages of cold, methane-rich fluids from subsurface reservoirs to the sea floor are termed cold seeps. Recent exploration of the deep sea has shed new light on the microbial communities in cold seeps. However, conventional metagenomic methods largely rely on reference databases and neglect the phylogeny of functional genes.ResultsIn this study, we developed the REMIRGE program to retrieve the full-length functional genes from shotgun metagenomic reads and fully explored the phylogenetic diversity in cold seep sediments. The abundance and diversity of functional genes involved in the methane, sulfur, and nitrogen cycles differed in the non-seep site and five cold seep sites. In one Haima cold seep site, the divergence of functional groups was observed at the centimeter scale of sediment depths, with the surface layer potentially acting as a reservoir of microbial species and functions. Additionally, positive correlations were found between specific gene sequence clusters of relevant genes, indicating coupling occurred within specific functional groups.ConclusionREMIRGE revealed divergent phylogenetic diversity of functional groups and functional pathway preferences in a deep-sea cold seep at finer scales, which could not be detected by conventional methods. Our work highlights that phylogenetic information is conducive to more comprehensive functional profiles, and REMIRGE has the potential to uncover more new insights from shotgun metagenomic data.8PNdJCR5n5eFCnFqsf6X4UVideo

IMAGE FEATURE EXTRACTION METHODS FOR STRUCTURE DETECTION FROM UNDERWATER IMAGERY

Abstract. The use of autonomous underwater vehicles (AUVs) for surveying underwater infrastructure presents a potential cost saving in comparison to remotely operated vehicles (ROVs). One of the challenges when processing images of underwater structures captured by an AUV, is that vast number of images captured during the mission usually do not show the structure. For instance, images captured during the dive to the structure or of the sea floor, or of the deep sea facing away from the structure. Too many images captured, without relevant information for a 3D reconstruction of the structure, leads to increased processing time and issues during the reconstruction process. There are two solutions to reduce the images to only images showing the structure. Firstly, only images of the structure are captured in the first place or remove images that are not useful after the capture and before further processing. This study developed and evaluated techniques that would enable the first strategy to be applied in an AUV. To apply this strategy in an AUV, would require an on-board structure detection system to ensure that they are correctly orientated for capturing useful footage during a survey mission. However, the marine environment poses several challenges to image-based object detection. Furthermore, small AUVs have limited power and computational resources available while deployed on a mission. To investigate the suitability of creating a lightweight structure detection model for the purpose of image evaluation, three computationally efficient image feature extraction methods (colour moments, local binary patterns (LBP), and Haar wavelet decomposition) were evaluated for their ability to distinguish underwater structures from background areas using unsupervised k-means models. LBP was found to be an effective method for identifying underwater structures in open water conditions. For identifying a structure against the seabed, colour moments were identified as the most effective method.

Revisiting the relationship between the pore water carbon isotope gradient and bottom water oxygen concentrations

Reconstructing the oxygen content at the ocean floor provides insight into ocean circulation, ventilation, and carbon storage in the deep sea. The microbial breakdown of organic carbon within marine sediment through aerobic respiration consumes oxygen in the pore fluid and releases dissolved inorganic carbon. The offset in the carbon isotopic composition, δ13C, of epifaunal and infaunal foraminifera, Δδ13C, is considered to reflect the aerobic respiration of organic carbon and can be used to reconstruct the oxygen content of the bottom water. Previous work provided an empirical calibration that was suggested to be valid for oxygen reconstructions between 55 and 235 μmol kg−1. In this study, we apply a biogeochemical reactive transport model (RTM) to extend and update this calibration, allowing for the reconstruction of oxygen concentrations ([O2]) up to ∼300 μmol kg−1. Using the RTM and new bottom water [O2] and pore fluid measurements from Iberian Margin sediment cores, we also demonstrate that the calibration between the Δδ13C and bottom water [O2] must account for the coupled changes in the carbon system due to the respiration of organic carbon in the overlying ocean including the concentration and carbon isotopic composition of the dissolved inorganic carbon, and the δ13C of the organic carbon within the sediment column. We apply the improved calibration to reconstruct the changes in oxygen content at International Ocean Discovery Program (IODP) Site U1385 in the deep North Atlantic over the past 1.5 Myr.

Changes in sea floor productivity are crucial to understanding the impact of climate change in temperate coastal ecosystems according to a new size-based model

The multifaceted effects of climate change on physical and biogeochemical processes are rapidly altering marine ecosystems but often are considered in isolation, leaving our understanding of interactions between these drivers of ecosystem change relatively poor. This is particularly true for shallow coastal ecosystems, which are fuelled by a combination of distinct pelagic and benthic energy pathways that may respond to climate change in fundamentally distinct ways. The fish production supported by these systems is likely to be impacted by climate change differently to those of offshore and shelf ecosystems, which have relatively simpler food webs and mostly lack benthic primary production sources. We developed a novel, multispecies size spectrum model for shallow coastal reefs, specifically designed to simulate potential interactive outcomes of changing benthic and pelagic energy inputs and temperatures and calculate the relative importance of these variables for the fish community. Our model, calibrated using field data from an extensive temperate reef monitoring program, predicts that changes in resource levels will have much stronger impacts on fish biomass and yields than changes driven by physiological responses to temperature. Under increased plankton abundance, species in all fish trophic groups were predicted to increase in biomass, average size, and yields. By contrast, changes in benthic resources produced variable responses across fish trophic groups. Increased benthic resources led to increasing benthivorous and piscivorous fish biomasses, yields, and mean body sizes, but biomass decreases among herbivore and planktivore species. When resource changes were combined with warming seas, physiological responses generally decreased species’ biomass and yields. Our results suggest that understanding changes in benthic production and its implications for coastal fisheries should be a priority research area. Our modified size spectrum model provides a framework for further study of benthic and pelagic energy pathways that can be easily adapted to other ecosystems.

Characterization of the Mitochondrial Genome, Ecological Distribution, and Morphological Features of the Marine Gastropod Mollusc Lophocochlias parvissimus (Gastropoda, Tornidae)

The larvae of the marine gastropod Lophocochlias parvissimus are meroplankton that spend part of their lives as plankton that disperse and drift in the water column before settling on the sea floor. Two individuals of L. parvissimus larvae were sampled by the Multiple Opening/Closing Net and Environmental Sensing System (MOCNESS) from the Central Indian Ridge of the southwestern Indian Ocean in 2018 and 2019. We generated the first mitochondrial sequences for L. parvissimus, which will provide valuable genetic insight into the evolution of these organisms. In this study, we have determined that the mitogenome of L. parvissimus was 13,575 bp in length, consisting of 13 protein-coding genes, 18 tRNAs, and two rRNAs. Our work provides a new insight into the dispersal of L. parvissimus and previously missing components to the general understanding of the evolution of Truncatelloidea (Subclass Caenogastropoda).

The upper Cambrian SPICE carbon isotope excursion from the Alborz Ranges, northeastern Iran

Seawater chemistry has been highly variable during Earth's history. Whereas variations in the ratio of organic relative to inorganic carbon burial in oceanic basins are considered to trigger positive shifts in global seawater δ13C values, those in δ18O are related to Earth's climate fluctuations. Positive shifts in the carbon isotope record known from Cambrian marine carbonates on a global scale have provided invaluable stratigraphic insights. Carbon and oxygen isotope data from Middle-Upper Cambrian shallow marine carbonates of the Mila Formation, eastern Alborz Ranges, Iran are presented herein. Accordingly, the Furongian SPICE (Steptoean Positive Carbon Isotope Excursion) event is documented from the Qol-Qol Member of the Mila Formation at two stratigraphic exposures where this prominent and globally recorded isotopic event is detected in micrites/skeletal limestone with a maximum δ13C value of +4‰ at both localities. The positive shift initiates at the base, reaches the climax in the middle, and then declines in upper part of the Qol-Qol Member. Therefore, the base of the latter denotes the base of Furongian Series/Paibian Stage in the Alborz Ranges. The event occurred in the Palaeadotes–Torifera and Prochuangia trilobite Zones but detailed biostratigraphic studies are yet to be undertaken. The occurrence of glauconite and abundant benthic fauna in some intervals within the rock unit can be interpreted as recurring slightly-reduced and oxygenated sea floor circumstances during deposition of the Qol-Qol Member of the Mila Formation.

Localization of seismic waves with submarine fiber optics using polarization-only measurements

Monitoring seismic activity on the ocean floor is a critical yet challenging task, largely due to the difficulties of physical deployment and maintenance of sensors in these remote areas. Optical fiber sensing techniques are well-suited for this task, given the presence of existing transoceanic telecommunication cables. However, current techniques capable of interrogating the entire length of transoceanic fibers are either incompatible with conventional telecommunication lasers or are limited in their ability to identify the position of the seismic wave. In this work, we propose and demonstrate a method to measure and localize seismic waves in transoceanic cables using only conventional polarization optics, by launching pulses of changing polarization. We demonstrate our technique by measuring and localizing seismic waves from a magnitude Mw 6.0 earthquake (Guerrero, Mexico) using a submarine cable connecting Los Angeles, California and Valparaiso, Chile. Our approach introduces a cost-effective and practical solution that can potentially increase the density of geophysical measurements in hard-to-reach regions, improving disaster preparedness and response, with minimal additional demands on existing infrastructure.

Spatial distribution of pteropods from North Andaman Sea: Insights into aragonite supply and deposition in low saline, delta shelf regimes

Pteropods are important components of the marine zooplankton. Not only are they crucial parts of the pelagic ecosystem but are also key contributors to the global carbon budget. Their shells sink to the ocean floor contributing to the inorganic carbon supply to the ocean floor. Being aragonitic, they easily dissolve in oceans receiving fresh water. They also dissolve as they sink beyond the Aragonite Saturation Zone, that is, within the top 500 m of the water column, releasing the trapped CO2 into the surrounding waters. Their taxonomic and quantitative distribution on the modern ocean floor can help strengthen estimates of inorganic carbon supply in shallow oceans, which are also susceptible to climate-induced dissolution. The present study, for the first time, reports 18 pteropod taxa, their abundances and spatial distribution from the surface sediments of the Ayeyarwady Delta Shelf in the North Andaman Sea, characterised by a very high influx of riverine water and sediments.

한국 해양국립공원의 동계와 하계 부유퇴적물 특성

The analyzed concentration of suspended sediments in the bottom layer during winter season increased higher than bottom layer during summer season in the marine national parks of Korea. This explains poor correlation between sediment concentration and attenuation coefficient during summer season (r²=0.74) and much high degree of correlation during winter season (r²=0.92). Relatively fine-sized and well-defined, monotonous size distribution may promote the correlation between concentration and attenuation coefficient due to optical homogeneity of particles during winter season. During summer season, the values showed remarkable decrease in mean size which seemed to be associated more with deflocculation. During winter season, the grain size of suspended particles showed characteristic development of floc-sized particles. This finding suggests that tidal currents enhance resuspension and sedimentation near the sea floor.

Venturi nozzles for desalination brine discharges

Seawater desalination is a reliable way to confront the growing challenges of freshwater demands in the world. Brine is the primary by-product of this process and needs to be carefully managed and discharged back into the sea. In coastal desalination plants, the use of submerged outfall as a pipeline laying on the ocean floor is a popular strategy to minimize the environmental impacts of brine discharge. The Venturi nozzle has been proposed as a more efficient method for dispersing brine into the ocean. However, it requires a high exit velocity, which poses limitations for steep nozzle angles in shallow waters. This study aims to investigate the benefits of a lower range of exit velocities in the Venturi nozzles. The 60° inclined dense jet from a Venturi nozzle was explored, numerically and experimentally, and the results were compared to those of a simple dense jet. Comparisons showed that the Venturi nozzle decreases the flow path and diminishes flow dilution at the critical points. However, this reduction can be compensated by increasing the discharge Froude number to reach the same trajectory as a simple jet. It is important to note that this compensation is intricately linked to the discharge velocity, and it makes the use of Venturi nozzles for brine discharge a challenging proposition in both deep and shallow waters.

Collective synchrony of mating signals modulated by ecological cues and social signals in bioluminescent sea fireflies.

Individuals often employ simple rules that can emergently synchronize behaviour. Some collective behaviours are intuitively beneficial, but others like mate signalling in leks occur across taxa despite theoretical individual costs. Whether disparate instances of synchronous signalling are similarly organized is unknown, largely due to challenges observing many individuals simultaneously. Recording field collectives and ex situ playback experiments, we describe principles of synchronous bioluminescent signals produced by marine ostracods (Crustacea; Luxorina) that seem behaviorally convergent with terrestrial fireflies, and with whom they last shared a common ancestor over 500 Mya. Like synchronous fireflies, groups of signalling males use visual cues (intensity and duration of light) to decide when to signal. Individual ostracods also modulate their signal based on the distance to nearest neighbours. During peak darkness, luminescent 'waves' of synchronous displays emerge and ripple across the sea floor approximately every 60 s, but such periodicity decays within and between nights after the full moon. Our data reveal these bioluminescent aggregations are sensitive to both ecological and social light sources. Because the function of collective signals is difficult to dissect, evolutionary convergence, like in the synchronous visual displays of diverse arthropods, provides natural replicates to understand the generalities that produce emergent group behaviour.

Characteristics of iron-manganese nodules containing nickel and cobalt in chromite deposits in Co Dinh, Thanh Hoa province

Along with the chromite ore bodies, very early on, geologists recorded the presence of cobalt (Co) and nickel (Ni) metal. The resource of cobalt and nickel is forecasted with over 3 million tons of Ni and over 260 thousand tons of Co metals. Until now, however, knowledge about the existence form and distribution of Ni and Co in chromite ore bodies is very limited. Researching the sludge in the chromite mines and in comparison with manganese nodules found in the ocean floor helps to detect the presence of particles of iron and manganese (Fe-Mn nodules) in granular sewage sludges and in primary chromite ore bodies. Fe-Mn hydroxides, including todorokite mineral, are believed to be the adsorption medium and forming of Ni and Co in the Co Dinh placer chromite. Determining the existence form and distribution of Ni and Co in chromite placer deposits has scientific and practical significance in sampling orientation, sample processing, geological exploration, and reserve and resource estimations, sorting and recovering technology of Co and Ni metals.