Continental Slope Off Research Articles

Mesoscale ocean eddies determine dispersal and connectivity of corals at the RMS Titanic wreck site

The sinking of the RMS Titanic on 15 April 1912 remains one of most iconic maritime disasters in history. Today, the wreck site lies in waters 3800 m deep approximately 690 km south southeast of Newfoundland, Atlantic Canada. The wreck and debris field have been colonized by many marine organisms including the octocoral Chrysogorgia agassizii. Because of the rapid deterioration of the Titanic and the vulnerability of natural deep-sea coral populations to environmental changes, it is vital to understand the role the Titanic as well as other such structures could play in connecting ecosystems along the North American slope. Based on Lagrangian experiments with more than one million virtual particles and different scenarios for larval behavior, given the uncertainties around the biology of chrysogorgiids, the dispersal of larvae spawned at the Titanic wreck is studied in a high-resolution numerical ocean model. While the large-scale bathymetry shields the Titanic from a strong mean flow, mesoscale ocean eddies can considerably affect the deep circulation and cause a significant speed up, or also a reversal, of the circulation. As a consequence, the position of upper and mid-ocean eddies in the model largely controls the direction and distance of larval dispersal, with the impact of eddies outweighing the importance of active larval swimming in our experiments. Although dependent on larval buoyancy and longevity, we find that the Titanic could be reached by larvae spawned on the upper slope east of the Grand Banks. Therefore, the Titanic could act as a stepping stone connecting the upper to the deep continental slope off Newfoundland. From the Titanic, larvae then spread into deep Canadian waters and areas beyond national jurisdiction.

First record of the rare tubeshoulder Holtbyrnia anomala Krefft 1980 (Teleostei, Platytroctidae) in the southwest Atlantic.

Holtbyrnia anomala is a bathypelagic platytroctid widely distributed in the Atlantic Ocean. In this contribution, we report, for the first time, the occurrence of this species in the tropical southwest Atlantic. A single specimen was collected in 2000 on the continental slope off Rio de Janeiro, Brazil, at an average depth of 1158 m. This report also represents the first record of Holtbyrnia anomala in the Brazilian Economic Exclusive Zone.

A diversity baseline of benthic macrofauna along the northwestern slope of Cuba (Gulf of Mexico)

The Gulf of Mexico (GoM) is a unique ecosystem due to its physical characteristics, being influenced by the Mississippi River in the north and the Loop Current from the south, resulting in a gradient of organic to carbonate sediment composition from north to south. The continental slope of the northern and southwestern portions of the GoM are generally well studied; however, less is known about the southeastern GoM along the slope of Cuba. To fill this knowledge gap, sediment cores were collected in 2017 at nine stations (974–1580 m depth) to determine abiotic controls on the deep-sea benthic macrofauna community. Oceanographic data indicated a stratified water column typical of an oligotrophic ocean and no evidence of hypoxia. Sediment texture and composition indicated a west-east gradient likely determined by downslope transport of terrigenous material in the eastern part with a high proportion of carbonate in the west. Heavy metals (Cu, Hg, Pb, and Zn) at concentrations known to cause adverse benthic effects were present in the east near the city of Havana, with the macrofauna community showing characteristics indicative of environmental stress. Overall, this region supported a diverse community of macrofauna families of low abundance, typically only 1–2 animals, and high variability among replicates within stations. Rarefaction curves revealed higher biodiversity per number of individuals in the samples from Cuba compared to those from the nGoM at similar depths, though more samples would be needed to better reveal the true diversity. The major factors influencing macrofauna communities in the continental slope off northwestern Cuba are most likely the lack of organic-rich sediment and low sediment deposition rates, both of which can be attributed to the strong currents and lack of major terrigenous input, along with the regular natural disturbances which prevents domination.

New report of the rare Sciadonus alphacrucis Melo et al., 2022 (Teleostei, Ophidiiformes, Bythitidae), DNA barcoding, and range extension in the western South Atlantic.

Sciadonus alphacrucis Melo, Gomes, Møller & Nielsen, 2022 is a rare deep-sea species, previously known from only two specimens collected off São Paulo State, southeastern Brazil, in the western South Atlantic. Herein, we report a new specimen of S. alphacrucis collected on the continental slope off Santa Catarina State, southern Brazil, thereby extending its known distribution by 420 km. Additionally, we provide the new meristic and morphometric data, the molecular identification using sequences of the cytochrome c oxidase subunit I (COI), an updated distribution map, and a discussion of troglomorphic traits.

A new Loriciferan, Scaberiloricus samba gen. et sp. nov., links the Higgins larva and the aberrant Shira larva

A new genus and species of Loricifera, Scaberiloricus samba gen. et sp. nov., is described from the continental shelf and slope off Rio de Janeiro, Brazil. Adult morphology remains unknown for the new entity, but information is available from three different Higgins larval instars. The Higgins larva of the new species is characterised by a bulbous head and a slender, elongate trunk, separated by a constriction behind the head. The cuticle of the thorax and the posterior part of the head is characterised by numerous longitudinal zigzag folds. The new species and genus shows greatest morphological resemblance with Wataloricus japonicus, and a phylogenetic analysis based on Higgins larval morphological characters suggests that Scaberiloricus gen. nov., Wataloricus, Tenuiloricus, and Patuloricus form a monophyletic group within Pliciloricidae. The analysis furthermore suggests that the Higgins larvae of Scaberiloricus gen. nov. and Wataloricus represent transitional, evolutionary stages towards the highly aberrant Shira larvae, found in species of Tenuiloricus and Patuloricus.

Basin-scale interaction between post-LGM faulting and morpho-sedimentary processes in the S. Eufemia Gulf (Southern Tyrrhenian Sea)

The integrated interpretation of high-resolution multibeam bathymetry, seismic profiles and backscatter data in the S. Eufemia Gulf (SEG; Calabro-Tyrrhenian continental margin, south-eastern Tyrrhenian Sea) documents the relationship between postglacial fault activity and morpho-sedimentary processes. Three systems of active normal faults that affect the seafloor or the shallow subsurface, have been identified: 1) the S. Eufemia fault system located on the continental shelf with fault planes mainly oriented N26E-N40E; 2) the offshore fault system that lies on the continental slope off Capo Suvero with fault planes mainly oriented N28E-N60E; 3) the Angitola Canyon fault system located on the seafloor adjacent to the canyon having fault planes oriented N60E-N85E. The faults produce a belt of linear escarpments with vertical displacement varying from a few decimeters to about 12 m. One of the most prominent active structures is the fault F1 with the highest fault length (about 9.5 km). Two main segments of this fault are identified: a segment characterised by seafloor deformation with metric slip affecting Holocene deposits; a segment characterised by folding of the seafloor. A combined tectono-stratigraphic model of an extensional fault propagation fold is proposed here to explain such different deformation.In addition to the seabed escarpments produced by fault deformation, in the SEG, a strong control of fault activity on recent sedimentary processes is clearly observed. For example, canyons and channels frequently change their course in response to their interaction with main tectonic structures. Moreover, the upper branch of the Angitola Canyon shows straight flanks determined by fault scarps. Tectonics also determined different sediment accumulation rates and types of sedimentation (e.g., the accumulation of hanging wall turbidite deposits and the development of contourite deposits around the Maida Ridge). Furthermore, the distribution of landslides is often connected to main fault scarps and fluids are locally confined in the hanging wall side of faults and can escape at the seabed, generating pockmarks aligned along their footwall.

El Niño‐Related Stratification Anomalies Over the Continental Slope Off Oregon in Summer 2014 and 2015: The Potential Vorticity Advection Mechanism

AbstractOver the continental slope off Oregon at the US West Coast, at 44.6°N, vertical stratification is found to be anomalously weak in July–August of 2014 and 2015 both in a regional ocean circulation model and conductivity–temperature–depth (CTD) profile observations. To understand the responsible mechanism, we focus on the layer between the isopycnal surfaces σθ = 26.5 and 26.25 kg m−3 that is found between depths 100 and 300 m and represents material properties characteristic of the slope poleward undercurrent and shelf‐slope exchange. This layer thickness, about 50 m on average, can be twice as large during the above‐mentioned periods. In the 2009–2018 model analysis, this anomaly is revealed over the continental slope only in summers 2014 and 2015 and only off the Oregon and Washington coasts (40°–47°N). The stratification anomaly is explained as the effect of advection of the seasonal along‐slope potential vorticity (PV) gradient by an anomalously strong poleward slope current. In the annual cycle, the zone of strong along‐slope PV gradient is found between 40° and 47°N, supported by the local upwelling that results in the injection of the large PV in the bottom boundary layer over the shelf followed by its offshore transport in the slope region. The positive along‐slope current anomaly propagates to Oregon with coastally trapped waves as part of the El Niño oceanic response and can be up to 0.1 m s−1. Advection by this anomalous poleward current results in transporting the seasonal PV gradient earlier in the season than on average.

Response of the benthic biomass-size structure to a high-energy submarine canyon

IntroductionBody size regulates all biological processes, including growth, reproduction, metabolism, trophic interactions, etc., and is the master trait across organisms, populations, and communities. Despite a rich literature on the impacts of human and natural disturbances on body size, a clear knowledge gap is the effect of the submarine canyons on the benthic size structures in the deep sea, hindering our understanding of the ecological processes of these dominant ecosystems on the continental margin.MethodsTherefore, we conducted repeated sediment sampling to compare meiofauna and macrofauna biomass body-size spectrum, growth, metabolism, and size composition from a high-energy submarine canyon, Gaoping Submarine Canyon (GPSC), and the adjacent continental slope off SW Taiwan. The GPSC is a dynamic ecosystem connected to a high sediment-yield small mountain river subjected to strong internal-tide energy, swift bottom currents, frequent mass wasting events, and high terrestrial sediment inputs.ResultsWe found that the meiofauna and macrofauna were characterized by relatively larger individuals dominating on the slope to smaller ones dominating in the canyon. As a result, the community biomass, secondary production, and respiration were depressed with distinctive biomass-size composition in the canyon compared to the non-canyon slope. The environmental factors related to internal tide disturbance (i.e., bottom current velocity, duration of sediment erosion, or low light transmission) substantially influence the body size composition of the canyon benthos, while food supplies (i.e., TOC and C/N ratio) and sediment characters (i.e., grain size and porosity) correlated closely with the slope communities.DiscussionWe concluded that the disturbed condition in the GPSC may have wiped out or depressed the local benthic assemblages, and only the smaller, more resilient species could persist. Our results also highlight that the alterations of the canyon benthic community could be a reference to deep-sea ecosystems under anthropogenic disturbances or global climate change.

Blue shark (Prionace glauca) occurrence and relative abundance in the western South Atlantic Ocean influenced by spatiotemporal variability, environmental variables, and oceanographic processes

The aim of this study was to evaluate spatiotemporal patterns in the distribution and relative abundance of blue sharks and their relationship with environmental variables and oceanographic processes in the southwestern Atlantic Ocean. We modeled data on catch records from the Brazilian pelagic tuna longline fleet using generalized additive models (GAMs). The distribution of Prionace glauca was influenced by salinity, chlorophyll-a and temperature. Our models showed that both the catch per unit of fishing effort (CPUE) and the probability of presence increased mainly between March and August. The CPUE was also influenced by ocean depth and sea surface height, and the probability of occurrence by ocean fronts and slope. The highest CPUE values and probability of occurrence of blue sharks tended to occur mainly in parts of the continental slope off Brazil and at the Rio Grande Rise, characterized by the presence of seamounts. Such hotspots for P. glauca could potentially be considered in fisheries management plans.

Deep-sea bottom-water environment change caused by sediment resuspension on the continental slope off Sanriku, Japan, before and after the 2011 Tohoku Earthquake

The 2011 off the Pacific coast of Tohoku Earthquake occurred off southern Sanriku, Japan, on March 11 and generated strong shaking and huge tsunami along the entire eastern coast of Tohoku. The mainshock and numerous large aftershocks caused mass-wasting sedimentation events on the continental shelf, slope, and trench bottom. To investigate the impacts of the 2011 Tohoku Earthquake on the deep-sea bottom-water environment off Sanriku, we conducted shipboard surveys up to ~ 2000 dbar during 2011–2018 and long-term monitoring of the seafloor on the continental slope using a deep-sea station (~ 1000 dbar) off Otsuchi Bay during 2012–2018. The high turbidity (maximum ~ 6%) was observed for the bottom water deeper than 500 dbar on the continental slope of the entire area off Sanriku during 2012–2018. This high turbidity was caused by sporadic sediment resuspension induced by frequent large aftershocks. Furthermore, dissolved oxygen concentrations in the bottom layer from 1000 to 1500 dbar dropped significantly by about 10% after the earthquake, while nutrients and dissolved inorganic carbon showed no significant changes but exhibited wide variations. The high turbidity was associated with the increase in the concentrations of phosphate, dissolved inorganic carbon, and methane, as well as the decrease in those of dissolved oxygen and nitrate. This suggests that remineralization of suspended organic matter resulting from the respiration and denitrification of microbial communities after the earthquake caused the chemical properties of the deep-sea bottom-water. The deep-sea bottom-water environment change was maintained by sporadic sediment resuspension due to continued large aftershocks and was likely caused by variations in dissolved inorganic carbon and phosphate. There are two peaks in the concentration and carbon isotope ratio of methane on the deeper slope from 1000 to 2000 dbar near the hypocenter, which were advected along isopycnal surfaces of 27.38σθ (1000 dbar) and 27.56σθ (1500 dbar). The source of the shallower peak of chemical input is considered to be the sediment resuspension from the shallow sediment on the continental slope induced by the mainshock and large aftershocks.Graphical abstract

Rissoidae gastropods of the outer continental shelf and slope off Galicia (NW Spain)

More than 5000 shells (more than half of them with soft tissues) belonging to the caenogastropod family Rissoidae have been found in samples from several expeditions carried out in the outer continental shelf and slope off Galicia (Northwest Spain) in the depth range 100-2700 m. They belong to 9 genera and 23 species, two of them described as new for science: Alvania candasae sp. nov. and Alvania xelae sp. nov. The most abundant species in the samples were Obtusella macilenta (Monterosato, 1880) and Alvania testae (Aradas & Maggiore, 1844), followed by Alvania cimicoides (Forbes, 1844), Alvania jeffreysi (Waller, 1864) and Gofasia thalassae (Bouchet & Warén, 1993) comb. nov., which is proposed to be assigned to the genus Gofasia instead of Frigidoalvania. Five of the species are typically from upper shelf of which only few empty shells were found (Alvania cancellata, Crisilla semistriata, Manzonia crassa, Onoba semicostata) and their presence in the samples studied was considered accidental. Taxonomic complexity involving the species Alvania electa (Monterosato, 1874), Pseudosetia amydralox Bouchet & Warén, 1993 and Pusillina inconspicua (Alder, 1844) are highlighted.

Evidence for an extensive ice shelf in northern Baffin Bay during the Last Glacial Maximum

The glaciological significance of ice shelves is relatively well established for the stability of modern ice sheets of Antarctica. Past ice shelves of the Arctic, however, are poorly documented while their role for the stability of former ice sheets remains mostly unknown. Here we present swath bathymetry data and seismostratigraphic profiles that reveal a large moraine system extending along the continental slope off Baffin Island, demonstrating that a 500-m thick ice shelf covered northern Baffin Bay during the last glacial episode. We suggest that this ice shelf had a profound impact on the stability of a series of major ice streams that drained the interior of the Laurentide, Innuitian and Greenland ice sheets. Climate warming and global sea-level rise in the early stage of deglaciation possibly contributed to a large-scale break-up of the ice shelf, which led to the destabilisation and reorganisation of tributary ice streams from these three ice sheets.

First in situ observations of the benthic-demersal fauna on the upper continental slope off Punta Pichalo (19°36'S), northern Chile

An autonomous lander equipped with a video camera (dropcam) was used for in situ observations of the bento-demersal macrofauna on the upper continental slope off Punta Pichalo in northern Chile, an area of permanent coastal upwelling processes, located ~70 km north of Iquique. The lander was deployed at nine stations and between 227 and 798 m of depth. According to morphological characteristics, 34 operational taxonomic units (OTUs) were identified to the lowest taxonomic level; 24 belonged to macroinvertebrates and 10 to fishes. Macroinvertebrates comprised 9 OTUs of crustaceans, seven cnidarians, and six echinoderms. Fishes included 3 OTUs of the order Chondrichthyes, 3 belonging to macrourid. Perciformes, Anguilliformes, and Alepocephaliformes were represented by one OTU each. Also, we observed one species of lanternfish (Myctophidae). Apart from the brachyuran decapod Lophorochinia parabranchia Garth, 1969 and euphausiids, all species were observed at depths greater than 560 m. The presence of one individual identified as the granulate dogfish Centroscyllium granulatum Günther, 1887 extended the known distribution range of this species about 1000 km to the north. Images taken at 795 m showed Bathyraja peruana McEachran & Miyake, 1984. Our study suggests that the upper continental slope of northern Chile harbors nearly undiscovered biodiversity, worth to be studied more intensively to complete the comparable sparse knowledge about marine biodiversity and species distribution at the continental margin in front of Chile.

Conoidean gastropods of the outer continental shelf and slope off Galicia (NW Iberian Peninsula)

Conoidean gastropods of the outer continental shelf and slope off Galicia (NW Iberian Peninsula)

A new octocoral species of Swiftia (Holaxonia, Plexauridae) from the upper bathyal off Mauritania (NE Atlantic).

Three species of the genus Swiftia are known for the NE Atlantic Ocean and Mediterranean Sea. Remotely-operated vehicle (ROV) surveys and sampling on board RV Maria S. Merian during cruise MSM 16/3 'PHAETON' in 2010 provided footage and specimens of octocorals off Mauritania. Micro-computed tomography (micro-CT) reveals, for the first time in taxonomy of octocorals, the three-dimensional arrangement of the sclerites in a polyp. Swiftiaphaeton sp. nov. is described for the continental slope off Mauritania. This azooxanthellate octocoral is distinctive from NE Atlantic and Mediterranean congenerics by the dark red colour of the colonies (including the polyps), the presence of a layer of rod sclerites on top of the polyp mounds, and different sizes of polyps and sclerites. Using micro-CT has allowed the observation and imaging of a layer of sclerites that is distinct from other species of the same genus. ROV images revealed live records of S.phaeton sp. nov. in submarine canyons and on cold-water coral mounds in the upper-bathyal off Mauritania (396-639 m depth), mainly attached to dead coral, coral rubble, or rocks. The new species represents an extension of the genus distribution to the tropical latitudes (17°07'N and 20°14'N) of the NE Atlantic Ocean.

Interannual Bottom-Intensified Current Thickening Observed on the Continental Slope Off the Southeastern Coast of Hokkaido, Japan

By rotary empirical orthogonal function and coastal-trapped wave mode analyses, we analyzed current velocity data, collected from 2001 to 2016. The data were obtained by an acoustic Doppler current profiler, deployed upward at a location of 41°39.909′ N, 144°20.695′ E, on a 2630-m deep continental slope seabed off the southeastern coast of Hokkaido, Japan. The results indicate that the current intensifies toward the bottom and is directed nearly toward the shore, reaching an average speed of ~2.5 cm s−1 just above the bottom. The thickness of the along-slope northward component of the bottom-intensified current varied within the range of 50–350 m. We found that the current thickness change was caused by oceanic barotropic disturbances, produced by the intensification of the Aleutian Low, largely related to the El Niño–Southern Oscillation and modified through the excitation of bottom-trapped modes of coastal-trapped waves. This finding improves the prediction accuracy of the the bottom-intensified current change, being beneficial for suspended sediment studies, construction and maintenance of marine structures, planning of deep drilling, and so on.

Influence of Natural Processes and Bottom Trawling in the Nepheloid Layer Structure Off Vancouver Island (British Columbia, Canada, NE Pacific)

Continental margins are transitional areas between the land and the deep ocean where large amounts of particulate matter are supplied, transported, and ultimately deposited in the deep sea. High-energy hydrodynamic processes such as storms, ocean currents, or internal waves and tides, as well as bottom trawling activities contribute to the resuspension and remobilization of these particles. These mechanisms favor their transference from the continental shelf to the continental slope and maintain high concentrations of particulate matter in the water column forming nepheloid layers. The temporal evolution of the hydrographic and nepheloid structure in the upper slope off Vancouver Island (British Columbia, Canada, NE Pacific) was assessed by analyzing 4 months (from mid-August to late-November 2018) of sensor data from Ocean Networks Canada (ONC) NEPTUNE cabled seafloor observatory. The distribution of particulate matter during the study period illustrated a well-defined turbidity structure consisting of surface nepheloid layers (SNLs) at <100 m depth associated to primary and secondary productivity, intermediate nepheloid layers (INLs) between 150 and 300 m depth at the shelf-break and upper slope domain, and bottom nepheloid layers (BNLs) developed at >400 m depth. Moderate storm events occurred during fall when the more intense INLs were recorded at shelf-break depths. However, not all the INLs recorded during this period occurred in coincidence with these storms, indicating that these INL detachments were modulated by a different sediment resuspension mechanism. Analyses of fishing vessel activity during the study period revealed that trawlers operated over the same depth range as these INLs. Our results suggest that, in combination with the regional currents, the presence of continuous fishing along the continental slope off Vancouver Island contributes to the advection of suspended sediment particles, playing a major role in their transfer as nepheloid layers.

Sedimentary Anthropogenic Carbon Signals From the Western Pacific Margin for the Last Century

The declining trend of the δ13C of tropical corals over the last century was about −0.01‰ year−1, according to global coral records. The decrease was attributable to the significant input of anthropogenic CO2 (13C Suess effect) to the atmosphere. Previous studies of δ13C in corals suggested that the signal of the anthropogenic carbon in the Pacific and Indian Oceans were weaker than that in the Atlantic Ocean. However, biases relating to environments in which corals grew caused concerns. To investigate the anthropogenic carbon signal in the Western Pacific, foraminiferal records in a suite of 13 box cores with good age control were obtained from the continental slope off southwestern Taiwan between 2004 and 2006. δ18O values of planktonic foraminifera (Globigerinoides sacculifer or so-called Trilobatus sacculifer) in collected cores were relatively stable at −2.5‰ to −2‰ in the last century, but foraminiferal δ13C had a gradual secular decline after the 1900s. The decline trend of δ13C began to intensify after the 1960s, and its rate was similar to that observed in the Atlantic. Similar decline trends of δ13C were also found in coral records at regions where the human activity is high (Liuqiu) and low (Dongsha). Our findings indicate that the anthropogenic carbon signal in the Western Pacific was not weaker than that recorded in the Atlantic, and the nearshore sediment can supplement the lack of δ13C records in corals, which are deficient when the environment is not suitable to grow.

A new species of the rare deep-sea genus Sciadonus Garman, 1899 (Teleostei, Bythitidae) from off Brazil, with a discussion of the evolution of troglomorphism and miniaturization in the aphyonid clade

A new species of the rare, deep-sea genus Sciadonus Garman, 1899 (Bythitidae) is described based on two specimens obtained by the Brazilian R/V Alpha Crucis on the continental slope off São Paulo State, Southeastern Brazil, western South Atlantic. It differs from its congeners by the combination of the following characters: body pale lacking dark pigmentation except for on female claspers; a pair of dermal tissue flaps anteriorly on lower jaw; pelvic-fin rays present; precaudal vertebrae 39 or 40 and total vertebrae 74 or 75. The key to the species of Sciadonus is updated. A discussion of the presence and differentiation between troglomorphic and miniature characteristics among the species in the aphyonid clade is provided and compared with other bythitids.

Monitoring fin whale calls using Ocean Observatories Initiative Regional Cabled Array

The Ocean Observatory Initiative (OOI) Regional Cable Array (RCA) and the Ocean Networks Canada NEPTUNE cabled observatory provide an opportunity for long-term studies of the distribution and behavior of calling marine mammals. We will present the results of a study to build a database of “20-Hz” fin whale calls that spans from 2015 to present. Fin whale calls were collected by bottom-mounted low-frequency hydrophones and seismometers deployed on the OOI RCA and are detected automatically by spectrogram cross-correlation with a detection kernel that sweeps down linearly from ∼26 Hz to ∼19 Hz with a duration of ∼0.8 s. The kernel is tuned to detect the high amplitude portions of both the high- and low-frequency calls of the doublet calling pattern which is currently the dominant fin whale song in this area. Preliminary results show significant interannual variations at a given site in the distribution of calls during the fall and winter calling season. The onset of calling appears to be significantly earlier near the continental slope off central Oregon than at Axial Seamount, 450 km offshore. There also appears to be a higher overall rate of calling nearer the continental slope.