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Organic carbon (OC) burial in river-dominated ocean margins plays a pivotal role in the global carbon cycle, impacting atmospheric CO 2 levels over the long term. Despite its significance, uncertainties persist regarding the influence of external environmental factors and intrinsic properties on sedimentary OC. In this study, we conducted a comprehensive analysis of surface sediments from the East China Sea, examining geochemical properties (including total OC content [TOC], Δ14C, δ13C, and C/N ratio), terrestrial biomarkers (n -alkanes), and mineral properties (such as specific surface area, Al/Si ratio, and mineral composition). Our aim was to shed light on the fate of sedimentary OC. The surface sediment's Δ14C values displayed significant spatial heterogeneity, delineating four distinct sub-regions. Strong positive correlations (all p < 0.01) were found between the ∆14C values and fine-grained sediments, specific surface area, and clay minerals, suggesting the potentially pivotal role of mineral protection in shaping the fate of sedimentary OC. The proportion of terrestrial OC gradually decreased towards the south, while marine OC proportion increased, corresponding to the enrichment of Δ14C. The co-variation of Δ14C values, mineral properties, and OC source proportions suggests that terrestrial OC may undergo progressive replacement by marine OC during southward transport. Temporal variations in ∆14C values indicated that seabed erosion led to a significant increase in ∆14C values (p < 0.01) in the coastal mud belt, a phenomenon likely common in river-dominated ocean margins globally due to the new sediment cycle during the Anthropocene. • The aging of sedimentary organic carbon is influenced by hydrodynamics and mineral protection. • River damming is likely responsible for the younger of sedimentary organic carbon in the coastal mud belt. • The loss and replacement of terrestrial organic carbon with marine organic carbon may determine the Δ14C values. [ABSTRACT FROM AUTHOR]

High-resolution seabed sediment information is critical for a range of marine spatial planning applications in multi-use shelf environments. To establish this information for the Bay of Fundy, Canada, legacy seabed sediment measurements were obtained from regional data compilations, and eight parameters describing the grain size were modelled across the extent of the bay using high resolution acoustic seafloor mapping and oceanographic datasets. This was achieved using a purpose-made convolutional neural network configured for geospatial modelling of multivariate grain size parameters. Shared information between the response parameters enabled model training with partially complete observations from the varied legacy data sources, and an explicit multiscale model architecture ensured that environmental predictors were implemented at appropriate scales for modelling each parameter. This avoids typical exhaustive exploration and selection of scale-specific predictor sets that often precede model building. Compositional grain size parameters were additionally accommodated using appropriate output activation functions, providing an efficient alternative to compositional data transformation and imputation. Results agreed well with our current understanding of the surficial geology of the bay, and cross-validation was used to quantitatively evaluate map predictions. Of the eight predicted parameters, the mean grain size and mud (clay and silt) fractions were predicted with high accuracy (> 50% variance explained); the accuracy of grain size skewness was comparatively low (24% variance explained). Exploration of variable importance suggested that compiled acoustic backscatter was the most important environmental variable for predicting the grain size, but that geographic information describing the latitude and longitude within the bay was also highly useful. We hypothesize an interaction between these variables that enables location-specific prediction. Data layers of predicted grain size parameter values are made available for further sedimentological and ecological exploration, and for marine spatial planning activities within the bay. • Seabed sediment dataset compiled from legacy sources in the Bay of Fundy. • Remote sensing data describe morphology and oceanography of the bay. • Grain size parameters modelled spatially using remote sensing data. • Multivariate convolutional neural networks enable efficient geospatial modelling. • Model architecture accommodates compositional data and missing observations. [ABSTRACT FROM AUTHOR]

Based on experiments, a trawling-induced erosion dynamics was included in a 3D realistic and pre-validated hydro-sedimentary model so as to assess its contribution to the overall regional sediment dynamics in the specific case of the Bay of Biscay continental shelf. The effect of trawling was investigated throughout a 5-year period in terms of horizontal/vertical fluxes and changes in seabed mud content, and compared to the natural variability of sediment fluxes at different spatio-temporal scales. Trawling is shown in the model to significantly contribute to sediment re-suspension, and changes in the seabed at the scale of the shelf. The contribution of trawling to re-suspension is >80% during the high fishing season at many locations on the outer shelf and over the Grande-Vasière area (a large and intensively trawled muddy zone located in the middle of the shelf). The contribution of trawling is significantly weaker in winter and at annual scale, particularly over zones with (muddy-) sand facies (between 1‰ and 1%), but remains high, and reaches 20% of the annual erosion over muddy areas (e.g. northern part of the Grande-Vasière). This significant trawling-induced erosion dynamics results in high sediment fluxes which increase natural poleward dynamics from a few percent up to 40%, and contributes to the natural offshore export of sediment on the outer shelf (e.g. +35% of mud fluxes along the 130 m isobath). It is noteworthy that trawling-induced fluxes are larger in winter although the corresponding re-suspension is lower than in summer: this is due to stronger near-bottom flows occurring at this period (largely influenced by energetic wind conditions). In contrast, on the inner shelf, trawling-induced sediment fluxes are rather oriented towards the coast. Finally, simulation results reveal a trawling signature on changes in the seabed. A significant decrease (between 10% and >50%) in mud content is simulated over trawling hotspots, especially over the internal part of the Grande-Vasière and on mud patches located in front of the Gironde estuary. Conversely, trawling causes or intensifies mud deposition on both sides of these preferentially trawled areas. • Trawling-induced sediment dynamics is significant over mid and outer shelf regions. • Trawling increases natural off-shelf export of fine sediment by 30%. • Trawling induces seabed nature changes over and around fishing zones. [ABSTRACT FROM AUTHOR]

Changing sediment provenance and related paleoenvironmental evolution since marine isotope stages (MIS) 3 have been investigated based on accelerator mass spectrometry (AMS) 14C and optically stimulated luminescence (OSL) dating of core CSDP-01, recovered from the western South Yellow Sea (SYS). Based on our results, sea level fluctuations and monsoonal climate variations are identified as the principal factors driving these changes. Sea level fluctuations determined the accommodation space in the shelf area, while the monsoonal climate controlled the sediment supply capacity from river to sea. Mineral and Sr Nd isotopic records reveal the major contribution of the paleo-Changjiang River (Yangtze River) to the study core area during the early-mid MIS 3, which likely defined the northern limit of the paleo-Changjiang delta at that time. High sediment supply and limited accommodation space led to the development of sediment-fed systems on the SYS shelf, resulting in a high preservation potential for thick-stacking and overlapping deltaic sediments. Along with deltaic progradation, core sediment provenance gradually transformed from the paleo-Changjiang River to the paleo-Huanghe River (Yellow River) near the late MIS 3, implying that the paleo-Huanghe River likely emptied into the SYS and built a large delta during the MIS 3 interval. A strong summer monsoon during the early MIS 1 interval was favorable for the Changjiang to deliver abundant sediments to the study core area. A weak summer monsoon during the mid-late MIS 1 when the coastline had retreated to nearly its present-day position decreased the Changjiang and Huanghe supply to the study area. Low sediment supply and sufficient accommodation space gave rise to the development of sediment-starved systems during this period. ɛNd values fluctuated between the Changjiang and Huanghe sources at that time, suggesting that sea bed erosion materials are the main sediment contribution to the study area. In general, sedimentary evolution in the western SYS since MIS 3 is a good example of river-sea interaction in the marginal seas of Southeast Asia, in which sea level and monsoonal climate changes should play an important role. • We present mineral and Sr Nd isotopic records of core CSDP-01 since MIS 3. • Paleo-Changjiang delta built during MIS 3 distributed over a broad area. • Paleo-Huanghe River emptied into the SYS and built a large delta during MIS 3. • Sediment-starved systems have developed in the SYS during the mid-late MIS 1. • Sea level and monsoonal climate play an important role in the river-sea interaction. [ABSTRACT FROM AUTHOR]

The benthic plume generated by nodule mining operations has garnered significant attention due to its intricate environmental impact and the limitations of existing plume control techniques. Prior research has suggested that temperature effects can facilitate the aggregation of suspended sediments; however, a more detailed understanding is needed. In this study, a series of experiments were conducted to examine the sedimentation behavior of the benthic plume and the influence of temperature on its sedimentation process. Suspension concentrations of the plume were monitored over an hour, while flocs characteristics were investigated at 30 and 60-min intervals. A novel function describing the relationship between temperature effects and concentration changes was developed. Results indicate that higher temperatures can accelerate the deposition process by approximately 3–6 times, emphasizing the necessity to consider low water temperatures in laboratory studies of benthic plumes. Moreover, the integration of temperature effects and micro-eddies in plume aggregation research may offer new opportunities for developing advanced plume control and separation methods. • Carried out a series of tests on different seabed under different water jet velocity and water temperature conditions. • •Explored the influence of temperature effect and initial concentration on flocs aggregation and plume sedimentation. • •Proposed function for plume sedimentation considering temperature effect, initial concentration and water jet impact. • •Developed method for benthic plume aggregation and separation via the design of thermal vortex generator and slot array. [ABSTRACT FROM AUTHOR]

Although many studies have been performed in the northern Gulf of Mexico, there have been a paucity of high-resolution sediment data collected from seabed. New multicores were collected repeatedly at 4 fixed stations in the inner Louisiana shelf on March 12, 2021, July 7, 2021, November 20, 2021, and March 5, 2022, respectively, to study detailed spatial and temporal variations of surficial sediment. Being a very high sediment accumulation zone, Raccoon Island dredge pit and its nearby shelf were selected as our study area and additional six vibracores were collected inside and outside the pit for comparison. This study area is about 140 km west of the modern Mississippi Delta and 70 km southeast of the Atchafalaya Delta. A total of 624 samples from both vibracores and multicores were analyzed for this study. Spatially, our results show that sediment near Ship Shoal was the coarsest and sediment deposited in the pit was the finest. The organic matter was highest inside the pit and lowest near Ship Shoal. The carbonate content was the lowest near Ship Shoal. Temporally, surficial sediments were generally coarser in July and November of 2021 and finer in March of 2021 and March of 2022. Although the Mississippi and Atchafalaya Rivers supply a large amount of sediment during spring season, it takes time for the river-derived sediment to be delivered into the study area. Hurricanes Delta, Zeta and Ida passed this area and greatly impacted sediment transport in the years 2021 and 2022. The comparatively coarser sediment in July and November of 2021 were likely related to the resuspension of some coarse sediment by these hurricane events. Besides the river supply, Ship Shoal and barrier islands are nearby localized sandy sources and inner Louisiana shelf is a widespread mud source. This spatial heterogeneity of surficial sediment interplays with the timing of Mississippi and Atchafalaya River flood season and hurricanes and together dictates the sediment texture. This research on a filled-up dredge pit can benefit future evaluation of the safety of existing oil infrastructure and the feasibility of building new pipelines and platforms after dredging activities. Our results also shed light on the study of river- and hurricane-impacted sediment transport in muddy and mixed-texture passive continental margins around the world. • Pit sediment hasn't reached an equilibrium with ambient environment yet. • Surficial sediments were coarser in July and November and finer in March. • Sediment grain size spatial variations were categorized into four groups. • This research will benefit future coastal restoration and sediment management. [ABSTRACT FROM AUTHOR]

Due to burning of fossil fuels, carbon dioxide is being absorbed by the ocean where its chemical conversion to carbonic acid has already caused the surface ocean to become more acidic than it has been for at least the last 2 million years. Global ocean modeling suggests that the carbonate compensation depth (CCD) has already risen by nearly 100 m on average since pre-industrial times and will likely rise further by several hundred meters more this century. Potentially millions of square kilometres of ocean floor will undergo a rapid transition in terms of the overlying water chemistry whereby calcareous sediment will become unstable causing the carbonate "snow line" to rise. We carried out a spatial analysis of seafloor geomorphology to assess the area newly submerged below the rising CCD. We found that shoaling of the CCD since the industrial revolution has submerged 12,432,096 km2 of ocean floor (3.60% of total ocean area) below the CCD. Further hypothetical shoaling of the CCD by 100 m increments illustrated that the surface area of seafloor submerged below the CCD has risen by 14% with 300 m of shoaling, such that 51% of the ocean area will be below the CCD. All categories of geomorphic feature mapped in one global database intersect the lysocline and will be (or already are) submerged below the CCD with much regional variation since the rise in CCD depth during the last 150 years varies significantly between different ocean regions. For seamounts, the highest percentages of increase in area submerged below the CCD occurred in the Southern Indian Ocean and the South West Atlantic regions (6.3% and 5.9%, respectively). For submarine canyons we found the South West Atlantic increased from 3.9% in pre-industrial times to 8.0% at the present time, the highest percentage of canyons found below the CCD in any ocean region. We also carried out a relative risk assessment for future submergence of ocean floor below the CCD in 17 ocean regions. In our assessment we assumed that the change in CCD from pre-industrial times to the present is an indicator of the likelihood and the change in percentage of seafloor submerged below the CCD due to a hypothetical 300 m rise in the CCD is an indicator of the consequences. We found that the western equatorial Atlantic is at high risk and 9 other Ocean Regions are at moderate risk. Overall, geomorphic features in the Atlantic Ocean and southern Indian Ocean are at greater risk of impact from a rising CCD than Pacific and other Indian Ocean regions. A separate analysis of the Arctic Ocean points to the possible submergence of glacial troughs incised on the continental shelf within a mid-depth (400–800 m) acidified water mass. We also found that the area of national Exclusive Economic Zones submerged below the rising CCD exhibits extreme variability; with 300 m of CCD shoaling we found a > 12% increase in area submerged below the CCD for 23 national EEZs, whereas there was virtually no change for other countries. • Ocean acidification has caused the carbonate compensation depth (CCD) to rise by ∼98 m. • Seafloor area below the CCD has increased by 3.6% in the last 200 years. • Risk of impact of rising CCD is greatest in the western equatorial Atlantic Ocean. • Different geomorphic features impacted by rising CCD in different ocean areas. [ABSTRACT FROM AUTHOR]

The burial of organic carbon (OC) in marine sediments is a considerable sink for carbon, removing OC from the active ocean-atmosphere system. Both the total OC buried, and the proportion of OC retained in sediments after burial, varies by location, with some areas of the ocean floor known to be 'hotspots' of OC sequestration. Two potential such hotspots may be sediments containing high proportions of tephra (the unconsolidated products of explosive volcanism), and locations of turbidite deposition, but knowledge of specific burial regimes in such locations remains poorly constrained. To fully investigate these processes, we performed a holistic (organic and inorganic) geochemical analysis of samples from the Aegir Ridge, which contain both tephra layers and material from the Storegga Slide, a large turbidite. We show sediments found between the Storegga Slide and the tephra are a location of high OC preservation, linked to reducing conditions caused by the rapidly deposited slide layer sealing the sediments from overlying water column O 2. We see little evidence for tephra positively affecting OC preservation at our site, but this is likely a feature of specific burial conditions, with the responsible mechanisms depending highly on the nature of the tephra. Our findings demonstrate how even in locations proposed as OC burial hotpots, the processes controlling this burial are highly complex, and that levels of sedimentary OC burial must be assessed on a case-by-case basis. • Study of organic carbon (OC) burial processes offshore Iceland. • Sediments between turbidite sediments and tephra show highest OC preservation. • Sediments located between the Storegga slide and a tephra layer display oxygen depleted conditions • OC burial and preservation processes are complex, and must be investigated on a case by case basis. [ABSTRACT FROM AUTHOR]

Abstract Coral mounds formed by framework-forming cold-water corals pierce the seabed along most continental margins of the Atlantic Ocean and new sites are continuously being discovered. Here, we describe an extremely high accumulation of coral mounds at the NW Moroccan Atlantic margin between 35°N and 35.5°N. Within an area of only 1440 km2, >3400 mounds were found exposed at the seabed. The coral mounds are nowadays characterized by an almost complete lack of living cold-water corals. In addition, numerous buried mounds were identified in hydroacoustic sub-bottom profiles, and are estimated to be ~3.7 times more frequent than the exposed mounds. Consequently, a total of ~16,000 buried and exposed mounds is estimated for the entire study area. The exposed mounds are rather small with a mean height of 18 m and show a conspicuous arrangement in two slope-parallel belts that centre in water depths between 720 and 870 m and 890–980 m, respectively, putting them among the deepest mound occurrences discovered so far in the Atlantic. The mostly elongated mounds largely stretch downslope pointing to a significant influence of internal waves in the mound formation process. Moreover, based on their average dimensions, the entire coral mound volume can be estimated as 1.3 km3, which means the mounds store a considerable amount of coral carbonate highlighting their potentially important role as regional carbonate factories. In combination with further occurrences of coral mounds along the Moroccan margin, both in the Mediterranean and in the Atlantic Ocean, these new findings underline Morocco's role as a hotspot for the occurrence of cold-water coral mounds. Highlights • Just 1440 km2 of the Atlantic continental margin off Morocco host ~16,000 exposed and buried cold-water coral mounds. • The exposed coral mounds are predominantly arranged in two slope-parallel belts – a peculiar feature also observed in other coral mound provinces. • Downslope-directed elongated coral mounds point to internal waves as important forcing factors. • The skeletal coral carbonate preserved in these mounds potentially plays a very important role in the regional carbonate budget. [ABSTRACT FROM AUTHOR]

Abstract An integrated analysis of multibeam bathymetry and single- and multichannel seismic records were used to image the morpho-stratigraphy of the Alentejo Margin (Southwest Portuguese Continental Margin). The complex interaction of several alongslope and downslope processes in the area leads to the formation of various bottom current driven depositional and erosive features (moat) as well as gravity-driven features (gullies and landslides) in the Alentejo Margin. These processes feed each other contributing for the active sedimentary pattern on the area. Sines Contourite Drift (SCD) is a ~2311 km2 sedimentary feature with a perimeter of 303.9 km, 98 km length and 35 km width. Landslides occur either on steep and on gentle slopes between ~200 and 3200 mwd (meters water depth) in the study area, which has a total extent of ~85 km × 82 km. Scar concentration is higher in the middle- and lower-slope, whereas the thickest debris deposits are found in the slope basin area - Lebre Basin (LB). Translational landslides, with planar failure planes parallel to the slope surface are the main landslide typology verified in the study area. Several triggering and pre-conditioning factors, resulting from the interaction of alongslope and downslope processes, contribute for varied landslides scar concentration. Steep-slope and high sedimentation rates favour sediments under-consolidation, promoting excess pore water pressure and weak layers formation. In this paper, we show that the interaction of bottom currents with pre-existing tectonic structures promotes the complex interaction of both alongslope and downslope processes thus promoting an active and diversified geomorphological evolution and generalised slope instability. Highlights • Complex morphology from interaction of along- and downslope sedimentary processes • Sines contourite drift results from interplay of MOW and pre-existing structure • High contouritic deposition over irregular structure creates cluster of landslides. • Interplay of MOW, tectonic uplift and seismicity creates multi scale landslides. • Wide slide scars on gentle slopes and contiguous, narrow scars on steep slopes [ABSTRACT FROM AUTHOR]

Abstract Predicting seabed mobility is hampered by the limited accuracy of sediment transport models when the bed is composed of mixed sediments. The hiding-exposure (HE) effect modifies the threshold of motion of individual grain classes in sediment mixtures and its strength is dependent on the grain size distribution. However, an appropriate method of predicting this effect for bimodal sediment mixtures remains to be developed. The prototypical example of a bimodal mixture is that consisting of a well-sorted sand and gravel for the fine and coarse fractions respectively. Through a comprehensive series of laboratory experiments, the HE effect has been quantified for a full range of sand-gravel mixtures from pure sand to pure gravel, the choice of which has been underpinned by an integrated study of offshore geophysical and sedimentological data found in coastal and shelf seas. In the sand–gravel mixtures used in the present study the critical shear stress needed to mobilise the sand and gravel fractions increased by up to 75% and decreased by up to 64%, respectively, compared to that needed to mobilise well-sorted sediment of similar size. The HE effect was found to be dependent on the percentage of gravel (coarse mode) present in the bimodal mixture, whereby the effect for the mixture is the weighted sum of the HE effect for the fine and coarse modes. Highlights • Mobility of bimodal sediment is unpredictable due to Hiding-Exposure (HE) effects • HE effect increases the threshold of motion of sand fractions by up to 75% • HE effect decreases the threshold of motion of gravel fractions by up to 64% • Strength of HE effect can be predicted using the proportion of coarse sediment [ABSTRACT FROM AUTHOR]

Abstract The northeastern margin of the South China Sea experienced continental rifting followed by magmatism in the Cenozoic. This evolution has strongly influenced the heterogeneity of its crustal structure. To gain insights into the spatial variation in crustal structure, data from 30 ocean bottom seismometers were used to forward model ten P -wave velocity models along both dip and strike directions. The Cenozoic strata (1.7–3.5 km/s), the Mesozoic strata (3.5–5.5 km/s), the crystalline crust (5.5–7.5 km/s) and high velocity lower crust (7.0–7.5 km/s) were identified based on P -wave velocities. Overall, the crust thins from ~25 km on the continental shelf to ~15 km on the slope, with thicker crust underneath the Dongsha Basin (a Mesozoic basin) but thinner crust underneath the pre-Cenozoic NW-trending fault zones. This difference in thickness is possibly controlled by different strength of inherited structures, i.e., the Dongsha Basin and the fault zones. Furthermore, a widespread high velocity lower crust layer, which resulted from the intrusion of a mafic sill complex, was observed over the shelf to slope. Mafic intrusions within the lower crust have uplifted the caprock on the shelf, and magma eruptions have formed many post-rift seamounts on the slope. The evidence suggests that post-rift magmatism overprinted the vertical crustal structure. We therefore propose that the heterogeneous crustal structures in this passive margin are an integrated result of segmental extension followed by magmatic overprinting. Highlights • Ten 2-D crustal models constrained by wide-angle seismic data are presented. • Pre-rift inherited structures controlled the lateral variation of crustal structure. • Post-rift magmatism overprinted the initial crustal structure and rifted features. [ABSTRACT FROM AUTHOR]

Abstract A joint study and mapping of the morphological features and architecture of the Galicia margin based on high-resolution multibeam bathymetry data and multichannel seismic profiles, provides new insights of the margin morphostructure. Tectonic processes are the major control of the margin's morphology, where the imprint of the North Atlantic rifting and opening and later subduction of the Bay of Biscay and compressional events are still well preserved. The West Galicia margin, which is up to 350 km wide, is composed from east to the west of inner, transitional and outer sectors. The inner sector shows a graded upper slope strongly dissected by a system of submarine canyons and valleys that flow into the 170 km long and 40–60 km wide NW-SE Valle Inclán Valley. The transitional sector, which is up to 75 km wide, displays a smooth relief dominated by landslides and giant craters. Finally, the outer sector is characterised by several banks, N-S sub-parallel ridges and elongated valleys that project seaward over 200 km (i.e., Galicia Bank, Half-Graben, Deep Galicia margin and Peridotite Ridge domains). The North Galicia margin is characterised by a system of terraces up to 30 km wide, that form a stepped slope followed by an abrupt lower slope affected by large-scale rotational failures. The Galicia margin constitutes an exceptional area within the Atlantic margins for identifying different morphostructure styles that characterised the main stages of the margin's evolution along the Wilson cycle. The Galicia margin hosts the transition between two end-members of continental margin styles: a western hyperextended rifted margin (being the conjugate with the Newfoundland margin during the Late Jurassic) and a northern convergent margin (now fossilised) associated with the partial subduction of the southern sector of the Bay of Biscay underneath the North Iberian margin, which occurred in Paleocene-Eocene times. Thus, the morphostructure of the West Galicia margin still reflects the detached fault systems and tilted blocks that resulted from the Mesozoic North Atlantic rifting. Furthermore, the Coruña and Jean Charcot seamounts, which are adjacent to the Galicia margin, correspond to spreading ridges formed by the simultaneous opening of North Atlantic Ocean and the Bay of Biscay in the Upper Cretaceous. The rest of the terraced morphology of the North Galicia margin is derived from extensional faults caused by an overriding of the Iberian plate in relation to the subduction of the Bay of Biscay oceanic crust during Cenozoic times. Since the late Neogene, compressional tectonics resulting from the reorganisation of the Eurasia/Iberia and Africa plates is also reflected on the present-day morphology as the following: (i) an elevation of the Biscay Abyssal Plain up to 150 m over the Iberia Abyssal Plain; (ii) deep-seated landslides associated with an uplift of the Galicia Bank; and (iii) an orientation of submarine canyons along NW-SE strike slip faults. Graphical abstract Unlabelled Image Highlights • Multibeam bathymetry and seismic allow mapping morphostructure of the Galicia margin. • Galicia margin hosts transition between two end-members of continental margin stages. • Western margin related to the Mesozoic hyperextended rift margin • Northern margin related the Cenozoic subduction active margin • Morphostructure styles characterise main stages of the margin's evolution along the Wilson cycle. [ABSTRACT FROM AUTHOR]

Recent developments in seismic acquisition systems and seismic data visualization have contributed to improve the imaging of seismic geomorphologies over a broad range of topics. This study focuses on a new high-resolution P-Cable 3D seismic cube located in the Hoop area in the SW Barents Sea. The scientific motivations of the study are (1) to document glacial landforms on a meter-scale, (2) to study the link of these landforms with the subsurface, and (3) to understand ice-stream dynamics by detailed interpretation of main horizons, including the seabed, intra-glacial horizons, and Upper Regional Unconformity (URU). The horizons are assessed using the concept of seismic geomorphology, and compared with interpretations derived from conventional 3D seismic and state-of-the-art multibeam echosounder technologies to discuss the benefits and limitations of the different geophysical technologies. A well-defined intra-glacial seismic reflection is imaged in the eastern part of the P-Cable cube. This reflection has an overall NE-trending ridge-shaped morphology, which is up to 50 m high and 5–10 km wide, and interpreted as a shear margin moraine. The top of the moraine displays well-defined iceberg ploughmarks and clear slope failure events along its eastern flank. The seabed geomorphology, which has been directly shaped by glacial processes related to multiple phases of ice streaming, appears to be influenced by the buried shear margin moraine. Mega-scale glacial lineations (MSGLs) indicative of fast-flowing ice streams characterize the seabed west of the moraine. Infilled MSGLs and different sets of iceberg ploughmarks with large berms dominate the seabed geomorphology above the moraine. The seabed east of the moraine, characterized by a smooth morphology and few pockmarks, is inferred to reflect more slowly-moving ice. Not resolved by other geophysical techniques, seismic attribute maps of P-Cable 3D allowed the identification of smaller ploughmarks and corrugated ridges related to paleo tides. Eroded by the larger iceberg ploughmarks, these small ploughmarks are suggested to be linked to an earlier rapid disintegration of the Barents Sea Ice Stream. The new high-resolution 3D seismic data have led to the development of a revised ice-stream model of the Barents Sea, linking the glacial deposits to different ice stream events. [ABSTRACT FROM AUTHOR]

The near-bottom nepheloid layer in the western margin of the Southern Adriatic Sea was monitored for 8-years by measurements acquired at two mooring sites. The two moorings, equipped with CTD probes and ADCPs, are located in the Bari Canyon and in an open slope sector along the Southern Adriatic Margin. These regions are of interest because affected by episodic dense shelf water cascading events whose dynamic has direct implications on deepwater morpho-dynamic, biogeochemical cycles and trophic networks. In this work, the sedimentation flux and its interdecadal dynamic is analysed examining in detail the sedimentary processes triggered by dense water flow through the analysis of the echo records of ADCPs. The integration of hydrodynamic, turbidity and particle grain-size data provided estimates of the sediment flux, separating phases when the flow actively erodes the seabed from phases when particles are transported to the mooring location through density flows. The frequency and velocity of dense-water cascading currents vary in time and space reflecting the capacity of sediment transport. Data analysis demonstrated that the hydrodynamic event that mostly accounts for sediment transfer to the deep basin is represented by current pulses induced by the passage of dense waters. The average annual sediment flux has been quantified and the Bari canyon shows transport more than five time larger than in the open slope sector, confirming that the canyon is the dominant pathway of sediment transfer to the deep basin. In contrast, in the open slope, albeit a minor lateral sediment advection, is impacted by currents that are able to trigger intense resuspension of seabed sediments, which can contribute over 80% of the total solid load. This study allows unravelling the role of cascading in the sediment resuspension and transport processes and is essential to support deciphering the sedimentary records in the study area. The long temporal extent of the dataset used for quantification provides a reliable contribution to the Quaternary sediment budget determination. • The integrated approach proposed in the study made it possible to determine sediment flux during dense water cascade events. • This study allows unravelling the role of cascading in the sediment resuspension and transport processes • The characterization of short-lived events can improve the high-resolution interpretation of the stratigraphic records. • The large temporal extension of the dataset used provides a reliable contribution to the Quaternary sediment budget [ABSTRACT FROM AUTHOR]

The inlet channel of the Tagus River estuary is located in the biggest urban area of Portugal and connects the river estuary basin to the Atlantic Ocean. Hence, it is a region with extreme economic importance, attested by the presence of the Lisbon port. For this reason, a large amount of resources is invested in acoustic surveys to update nautical charts and monitor the bottom modifications induced by the high hydrodynamics of this river. The use of acoustic remote characterization allows mapping the seafloor, including discrimination of different seafloor types. In this study, we used the Angular Range Analysis (ARA) technique to analyze the backscatter data from four distinct surveys acquired by different multibeam echo sounders systems to estimate the mean grain size of the bottom sediments. The correlation between the mean grain size provided by the ARA and laboratory results present in most cases a moderate to a strong linear relationship between them and the standard deviation of the residuals of the mean grain size between the ARA and the laboratory results varied between 0.52 and 1.01 ϕ. The higher residuals could be explained by regions with poor sediment sorting; changes in the seabed that occurred during the time interval between the hydrographic and sediment sampling surveys; solid input from tributary rivers; dumping of dredged material; positional inaccuracy of the samples; insufficient signal penetration of the multibeam echo sounders system to represent the vertical variation of the samples; and sediment mixing of vertical sedimentary structures during sampling. Therefore, we show that it is possible to apply acoustic remote characterization to highly hydrodynamic areas such as the Tagus River channel. [ABSTRACT FROM AUTHOR]

The 2011 Great East Japan Tsunami caused severe morphological changes along the affected coastline on the northeast part of Japan. This study investigates the recovery of river mouths and breaching of sandy coast at the place used to be river mouth in Miyagi Prefecture, Japan after severe erosion induced by the tsunami through analyzing aerial photograph and investigating field data. After several years since the tsunami took place, the morphology of some river mouths has mostly recovered while others still have some damage. Results on the analysis of aerial photograph clearly indicate that the total length of sandy coast on both sides of river mouth plays important role in the recovery process. Moreover, the relevant phenomenon occurring during the morphological recovery process is also investigated. The findings demonstrated the intrusion of sand spit into river mouths due to the tsunami having scoured river mouth deeper than the depth of closure. Interestingly, the intrusion distance was found to be positively correlated with the width of river mouth. In addition, there is an important finding on the practical problem which is related to the intrusion upstream of sand spit. That intrusion shifts the boundary of fresh-sea water upstream, therefore external wave forces must be considered when implementing the design of river structures. [ABSTRACT FROM AUTHOR]

Fringing reefs are rare on the mid-shelf of the central Great Barrier Reef, with Holocene development histories established for a few examples. The paucity of reef growth records from mid-shelf fringing reefs has limited opportunities for comparisons with inshore fringing reef growth records to better understand the influence of changes in environmental conditions on reef growth with distance offshore. The long-term development of the mid-shelf fringing reef at Holbourne Island was reconstructed using nine percussion and drill cores that captured the entire Holocene period of reef growth. The cores were chronologically constrained by 16 high-precision 230 Th ages. A weathered, Pleistocene reef substrate was U-Th dated as last interglacial (open system age of 131,100 ± 1000 cal yBP) and this provides the underlying foundation upon which the Holocene reef initiated prior to ~7520 ± 20 cal yBP. The last interglacial reef was encountered 5.9 m below the present reef surface and is the shallowest confirmed last interglacial reef in the central GBR region to date. Most of the Holocene reef structure was emplaced within 1000 years of initiation. The chronostratigraphy and contemporary geomorphology of the fringing reef at Holbourne Island preserve evidence of re-working and stripping of the reef structure by cyclones. This evidence includes: 1) an age hiatus in core data of ~3500 years (6238 ± 18 to 2683 ± 10 cal yBP); 2) the abundance of detrital branching coral rubble material within the core facies; 3) the surface elevations and ages of fossil microatolls, which reveal that storm-induced ponding of water during low tidal stages up to 55 cm deep has been active (but intermittent) across the reef flat for at least 600 years and is still active today; and 4) long-standing shingle ridges onshore and modern shingle ridges on the reef flat. [ABSTRACT FROM AUTHOR]

This study confirms that the fine sand-sized detritus in the central-northern Yellow Sea is chiefly derived by the Yellow River and explains the Holocene Yellow River dispersal system and the preservation of transgressive deposits by heavy-mineral and grain-size analyses. Micas, which are sensitive to hydraulic sorting, offer an effective key for identifying the dispersal of Holocene Yellow River-derived fine-grained sediments. The heavy-mineral compositional changes are attributed to hydraulic sorting by different marine dynamics and various mixing with additional local transgressive deposits of miscellaneous provenance. The effects of hydraulic sorting are dominated by Holocene tidal currents and by foreshore waves during the rapid transgression, respectively. The former results in obvious enrichments of garnet and common stable species such as Ti oxides, tourmaline, and titanite, whereas the latter seems more remarkable for the compositional changes, with further depletion of epidote, actinolite/tremolite and zoisite/clinozoisite. The central Yellow Sea mud deposit and the alongshore muddy zone off the southern Liaodong Peninsula are opposite to each other as a pair of structurally symmetric coalesced terminal lobes far away from the high-energy strait between Cape Chengshan and Changsan-got. The Haiyang subaqueous clinoform as another terminal lobe is revealed by a heavy-mineral index, which represents an extremity of deposits accumulated by the modern Yellow River-derived sediments off the southwestern Shandong coast. A small mud patch is revealed, roughly corresponding to the central regime of the amphidromic system of principal M 2 constituent. The tidal current-dominated depositional pattern proposed here emphasizes the importance of time–velocity asymmetry of tidal currents. Such a dynamic mechanism is primarily responsible for the dispersal of the modern Yellow River-derived sediments when they are entrained from the Bohai Sea to the South Yellow Sea through the Bohai Strait and the strait between Cape Chengshan and Changsan-got. [ABSTRACT FROM AUTHOR]

A high-resolution multibeam echosounder (MBES) dataset covering over 279,000 km 2 was acquired in the southeastern Indian Ocean to assist the search for Malaysia Airlines Flight 370 (MH370) that disappeared on 8 March 2014. The data provided an essential geospatial framework for the search and is the first large-scale coverage of MBES data in this region. Here we report on geomorphic analyses of the new MBES data, including a comparison with the Global Seafloor Geomorphic Features Map (GSFM) that is based on coarser resolution satellite altimetry data, and the insights the new data provide into geological processes that have formed and are currently shaping this remote deepsea area. Our comparison between the new MBES bathymetric model and the latest global topographic/bathymetric model (SRTM15_plus) reveals that 62% of the satellite-derived data points for the study area are comparable with MBES measurements within the estimated vertical uncertainty of the SRTM15_plus model (± 100 m). However, > 38% of the SRTM15_plus depth estimates disagree with the MBES data by > 100 m, in places by up to 1900 m. The new MBES data show that abyssal plains and basins in the study area are significantly more rugged than their representation in the GSFM, with a 20% increase in the extent of hills and mountains. The new model also reveals four times more seamounts than presented in the GSFM, suggesting more of these features than previously estimated for the broader region. This is important considering the ecological significance of high-relief structures on the seabed, such as hosting high levels of biodiversity. Analyses of the new data also enabled sea knolls, fans, valleys, canyons, troughs, and holes to be identified, doubling the number of discrete features mapped. Importantly, mapping the study area using MBES data improves our understanding of the geological evolution of the region and reveals a range of modern sedimentary processes. For example, a large series of ridges extending over approximately 20% of the mapped area, in places capped by sea knolls, highlight the preserved seafloor spreading fabric and provide valuable insights into Southeast Indian Ridge seafloor spreading processes, especially volcanism. Rifting is also recorded along the Broken Ridge – Diamantina Escarpment, with rift blocks and well-bedded sedimentary bedrock outcrops discernible down to 2400 m water depth. Modern ocean floor sedimentary processes are documented by sediment mass transport features, especially along the northern margin of Broken Ridge, and in pockmarks (the finest-scale features mapped), which are numerous south of Diamantina Trench and appear to record gas and/or fluid discharge from underlying marine sediments. The new MBES data highlight the complexity of the search area and serve to demonstrate how little we know about the vast areas of the ocean that have not been mapped with MBES. The availability of high-resolution and accurate maps of the ocean floor can clearly provide new insights into the Earth's geological evolution, modern ocean floor processes, and the location of sites that are likely to have relatively high biodiversity. [ABSTRACT FROM AUTHOR]

Seafloor morphology beyond nine tidewater glaciers terminating in open-marine settings in eastern Svalbard has been investigated using multibeam swath-bathymetry. Historical information on tidewater glacier fluctuations over the past century or so shows that the seafloor offshore has been exposed only recently. Most glaciers have been observed to surge or have looped surface moraines indicating past surges. During these ice advances and subsequent retreat, a well-preserved submarine landform assemblage has been produced. (a) Subglacial landforms include: overridden moraine ridges, mega-scale glacial lineations (MSGLs), other streamlined lineations, elongate drumlins and medial moraines, small ridges forming a complex boxwork or rhombohedral pattern, and meltwater-related eskers and channels. (b) Ice-marginal landforms include: large terminal moraines with debris flow lobes on their outer flanks and indentations on their inner sides, small transverse retreat moraines, and crater-like kettle holes. (c) Glacimarine features include: iceberg ploughmarks and an otherwise relatively smooth sedimentary seafloor produced by fine-grained debris rain-out. A schematic plan-view landform assemblage model for tidewater glaciers advancing into open-marine settings is developed. Arcuate terminal moraines marking the ice-advance limit provide a distinctive component. Submarine basin(s) exposed inside these moraine ridges when ice retreats contain suites of individual landforms, produced subglacially and ice-marginally, with a consistent order of timing of deposition and stratigraphic superposition. The new schematic model is compared with earlier models based on submarine landforms associated with surges in the more topographically constrained setting of Spitsbergen fjords. Differences include: (i) the overall arcuate shape of the open-marine assemblage; (ii) the indented ice-proximal sides of terminal moraine ridges; (iii) the fan-shaped pattern of streamlined lineations; (iv) crater-like kettle holes at the inner lateral margins of many submarine basins; (v) prominent systems of eskers and channels. Modern glaciological analogues from ongoing surges of ice caps in eastern Svalbard and Severnaya Zemlya provide contemporary observations of ice advance into open-marine settings, including heavily crevassed ice lobes with finger-like termini. [ABSTRACT FROM AUTHOR]

Ontong Java and Nukumanu atolls sit atop Earth's largest oceanic plateau – the Ontong Java Plateau – in the western equatorial Pacific Ocean. In 2014, scientists aboard the Schmidt Ocean Institute's RV Falkor mapped the seafloor surrounding Ontong Java Atoll (Solomon Islands) and Nukumanu Atoll (Papua New Guinea) for the first time using multibeam acoustic systems. These and pre-existing data help reveal the evolution of the atolls, which has involved volcanism, erosion, deposition, and carbonate growth. We use the new multibeam bathymetry and backscatter data, together with legacy seismic reflection data, to: (i) qualitatively characterise the submarine flanks of the atolls; (ii) identify broad and fine scale geomorphological features and classify the seafloor environment; (iii) investigate how submarine processes have influenced the morphological evolution of the atolls over geological timescales; and (iv) provide evidence that these atolls have fed sediment downslope to Kroenke Canyon that incises the NE flank of the Ontong Java Plateau. Submarine erosion is widespread on both atolls, and submarine landslides control, at least in part, the dynamic geomorphology and hence development of both atolls. Channels and gullies are abundant on the flanks of both atolls. Scarps are common on the upper flanks of both atolls, whereas undulating bedforms and crescent shaped bedforms are more common at the foot of the atolls' slopes. The Ontong Java Atoll coastline has widespread bights that appear to be linked to submarine debris deposits downslope. The overall shape of Ontong Java Atoll could result from one or more extensive edifice failure(s), or multiple smaller cones amalgamating to form one island. Active erosion of Nukumanu Atoll is manifested by crescent shaped bedforms, although compared to Ontong Java, Nukumanu has a much less sinuous coastline and more subdued mass wasting. We estimate ~ 1500 km 3 of volcaniclastic sediment has been eroded and transported from Ontong Java and Nukumanu atolls, some of which has likely fed Kroenke Canyon downslope. [ABSTRACT FROM AUTHOR]

The interpretation of sedimentary records in terms of glacial-interglacial changes in particle flux in the eastern equatorial Pacific (EEP) has been controversial. Here, we analyze disaggregated inorganic grain size (DIGS) distributions of three marine sediment cores from this region, focusing on the last 21 ka, to investigate evidence of sediment redistribution on the sea floor. Grain size sorting coefficients show that sediments in the EEP are moderately to well sorted, indicating sediment reworking in this region due to bottom currents. Furthermore, a systematic correlation between focusing factors and sorting coefficients at two sites shows that more focused sediments are also better sorted. We conclude that grain size based sedimentary records are consistent with the 230 Th-based evidence of lateral sediment redistribution on the sea floor in the EEP. [ABSTRACT FROM AUTHOR]

In this paper we describe a numerical modelling study carried out to investigate the prevailing sediment dynamics of two large sandbanks located at a site designated for future development of tidal stream energy extraction, in the Inner Sound Channel of Pentland Firth, Scotland, UK. A calibrated and validated 3D Delft3D hydrodynamic model covering Pentland Firth channel was combined with a morphodynamic model. The sea bed changes occurring around the sandbanks during a period of two spring-neap tidal cycles are described and discussed in detail. It was found that both sandbanks, which are located in a deep shelf region (depths > 18 m), are morphodynamically active and their existence and integrity are strongly linked with the existing hydrodynamic regime. [ABSTRACT FROM AUTHOR]

An integrated geology and geophysics investigation has been carried out to study the late Quaternary deepwater depositional system in the Gulf of Papua (NSF-MARGINS focus area) focusing on two contrasting depocentres, Pandora and Moresby troughs. The studies incorporate multi-beam bathymetry, sub-bottom sonar, and core data in order to define and map acoustic and lithofacies; and relate depositional processes, sediment routing, timing and geomorphic products that have developed since Marine Isotope Stage (MIS) 3, ca. 40 cal ka. 3D seafloor visualisation is used to infer sedimentary processes responsible for observed morphology, which are then placed into a chronostratigraphic framework using recently published age models of sediment cores. The peak depositional period in Pandora Trough occurred during MIS 2. At that time a large deep-sea channel network linked the Pandora and Moresby troughs, allowing long-distance sediment transport by large turbidity currents from the Papuan mainland to the Coral Sea Basin. Near the LGM, shelf-edge failure led to emplacement of mass-transport deposits on the floor of the Pandora Trough, blocking this pathway for large turbidity currents. Intermittent turbidity currents continued to feed minibasins upslope of the MTD complex until early MIS 1 (earliest Holocene). Along the shelf edge of the Papuan Peninsula, substantial sediment delivery by turbidity currents continued until middle Holocene and perhaps later; combined with bottom currents, these flows contributed to the formation of large sediment waves of Moresby Fan. However, this Holocene turbidite sedimentation does not extend much farther into the Moresby Trough, based on negligible Holocene sediment accumulation deeper in the basin. This study has shown that sediment delivery from fluvial sources to deep basins in the GoP is controlled by a complex interplay of changing sea level, evolving basin bathymetry (influenced by depositional and tectonic processes), and oceanic transport of sediment from shelf to slope. These conditions have created highly localised conduits for shelf to slope sediment delivery that respond both to global forcing (eustatic sea level) as well as local conditions (shelf gradient, mass wasting, currents, and source proximity), resulting in a complex network of deep-sea depositional morphologies active from the Last Glacial Maximum to Holocene time. [ABSTRACT FROM AUTHOR]

The seabed morphology, type of sediments, and dominant benthic species on eleven mud volcanoes and diapirs located on the northern sector of the Gulf of Cádiz continental slope have been studied. The morphological characteristics were grouped as: (i) fluid-escape-related features, (ii) bottom current features, (iii) mass movement features, (iv) tectonic features and (v) biogenic-related features. The dominant benthic species associated with fluid escape, hard substrates or soft bottoms, have also been mapped. A bottom current velocity analysis allowed, the morphological features to be correlated with the benthic habitats and the different sedimentary and oceanographic characteristics. The major factors controlling these features and the benthic habitats are mud flows and fluid-escape-related processes, as well as the interaction of deep water masses with the seafloor topography. Mud volcano eruptions give rise to mud flows and/or aqueous fluid seepage. These processes sustain chemosynthesis-based communities, closely associated with fluid seepage. Large depressions in the nearby area are influenced by collapse-related phenomena, where active fluid escape and the erosive effect of bottom currents have been identified. When the extrusion activity of the mud volcano is low and the seepage is diffuse, authigenic carbonates form within the edifice sediments. The bottom current sweeps the seafloor from the SE to the NW. When the velocity is moderate, sedimentary contourite processes take place on both sides of the edifices. At high velocities, the authigenic carbonates may be exhumed and colonised by species associated with hard substrates. Small carbonate mounds are found at the summits of some volcanoes and diapirs. Living corals have been found on the tops of the shallowest mud volcanoes, revealing different oceanographic conditions and strong bottom currents that favour the availability of nutrients and organic particles. The edifices affected by very high current velocities are located in the channels where erosive processes dominate. [ABSTRACT FROM AUTHOR]

Seabed acoustic data (e.g. deep-tow side scan sonar) together with information from seabed photography is presented for estimating near-bottom current speed maxima in North Atlantic contourite environments. These include the southern Iceland–Faroe Ridge flank, the southeast and southwest Greenland Margin, and the Greater Antilles Outer Ridge in the southwestern part of the North Atlantic. Geomorphological response to North Atlantic deep water circulation is expressed in a variety of dynamic bedforms and other current-controlled seabed features. Various types of dynamic bedforms reflect different hydraulic energy levels. Maximum near-bottom flow speed of almost 1.0 m/s, or more, is illustrated by ‘infinite’ sand ribbons found on lag sediment, while a much lower maximum of near-bottom water flow speed (< 0.5 m/s) can be inferred for fine-grained sediment environments where small erosional furrows and small-scale ripple marks occur. These various dynamic bedforms notably are indicators of (past) extreme current events often not captured by current measurements, which is due to decadal-scale variability in deep-ocean circulation. The results from our study demonstrate that at (multi)decadal time scale near-bottom current speed may in some areas reach values well in excess of what is known from current measurements. [ABSTRACT FROM AUTHOR]

Wave and current supported gravity flows (WCSGFs) carry substantial fine-grained sediment across gently sloping seabeds of coastal and shelf waters, representing a primary mechanism of sediment transport. An existing buoyancy-friction model, which considers the important parameters of drag coefficient (C D) and bulk Richardson number (Ri b), has been widely used to analyze WCSGF dynamics. However, an improved validation of the two parameters on the basis of in situ measurements is still outstanding. Here, we analyze 23 short-lived WCSGF events that were recorded at the shallow sea floor of a muddy open coast to quantify the parameters. The C D values, as defined in the buoyancy-friction model, were found to be around 0.02 and 0.01 for early flood and ebb phases of the tide, respectively, which are significantly larger than the range of 0.001–0.006 reported elsewhere from in situ observations, numerical simulations and laboratory experiments. The calculations of Ri b from our WCSGF observations were all close to the critical value of 0.25, which supports the use of such a value in WCSGF models. Large C D values of our observed WCSGFs imply that strong currents can dilute the high-concentration layer and slow down the movement of WCSGFs, which reveals a remarkable difference between WCSGFs and gravity flows supported by waves alone. • An existing buoyancy-friction model is used to determine the drag coefficient (C D). • Strong currents dilute the high-concentration layer to enhance the C D. • The critical bulk Richardson number is close to 0.25. [ABSTRACT FROM AUTHOR]

The amount of suspended fines in the southern North Sea strongly depends on their exchange with the sandy seabed. This exchange is governed by resuspension of fines during storms, followed by burial in the week thereafter. Despite its importance for fine sediment dynamics, the burial of fines into a sandy seabed is currently not well understood. This paper presents a mechanistic conceptual model, explaining how the interaction of migrating small ripples and larger megaripples can bury fine sediment in a sandy seabed shortly after storms. The burial process consists of four phases forming a dynamic cycle. A storm stirs up the bed, remobilising fines, while forming megaripples. After the storm, fines can settle again depositing atop the sandy seabed. Interaction between bedforms of different scales is then crucial to bury fines 1–2 dm within the seabed. Megaripples formed during storms gradually adjust to calmer conditions in the waning of storms. During this adjustment period, fines are buried by current-induced ripples in the troughs of the former megaripples. Field measurements collected in 2017 corroborate this conceptual model, showing fines in distinct patches, both horizontally and vertically. Furthermore, fines are found up to 10–15 cm in the seabed shortly after storms. The data further reveal how fine sediment occurrences on and within the seabed vary strongly over multiple length scales. They both vary on the mega-scale (kilometres) and on the micro-scale (metres-centimetres). As the micro-scale is multiple orders of magnitude smaller than the scale on which hydro-morphological models operate, parameterisations are required to aggregate the effect of burial in numerical models. • Novel conceptual model explains how small-scale bedforms can bury fine sediment in a sandy seabed shortly after storms. • The interaction between ripples and megaripples is crucial for this burial. • Field data support this conceptual model, showing how presence of fines varies strongly on multiple spatial scales. [ABSTRACT FROM AUTHOR]

The processes of continental breakup, reassembling of landmasses, and huge deltaic sediment depositions contribute to reconfiguring the Earth's surface. Here, we show a classic example of contiguous structures of paleo-continental margin on the eastern Indian Shield and an ancient fragment of the oceanic lithosphere beneath Bangladesh. In the present work, we collated gravity data from Bangladesh and adjoined parts of the Indian shield and the northern Bay of Bengal to decipher rocks' nature and long-term behavior. The gravity map illustrates N-S oriented alternate bands of ∼150 km wide positive and negative anomalies in the Bangladesh region, besides showing signatures of prominent geomorphic features such as the Shillong Plateau, Sylhet Trough, Burmese Arc, etc. The crustal models reveal the presence of paleo-continental margin segments on the eastern edge of the Singhbhum craton and south of the Shillong Plateau, ∼150 km wide folded oceanic crust beneath Bangladesh, and a low slab dip of the subducting Indian plate beneath the Burma platelet. The inferred continental margin evolved after the breakup occurred between the Rajmahal-Sylhet Line and continental fragments (Elan Bank and southern parts of the Kerguelen Plateau) at about 120 Ma. Subsequently, the sediments carried by two great Himalayan river systems were excessively deposited on the margin and over an older fragment of the oceanic lithosphere, resulting in the progradation of the Bengal delta towards the ocean. The oceanic crust beneath Bangladesh was folded with approximately 150 km wavelength as the compressive stress regime is locally operative due to the eastward moment of the Indian plate and westward propagation of the Indo-Burman Wedge. • Gravity data of NE India reveal paleo-continental margin east of Singhbhum craton and oceanic crust beneath Bangladesh. • Margin segments evolved after continental breakup at 120 Ma. Then, sediments bury the margin segments and old ocean floor. • The crust beneath Bangladesh folded as stress regime is operative with moments of the Indian plate and Indo-Burman Wedge. [ABSTRACT FROM AUTHOR]

The pattern of sediment dispersal and the location of sediment depocentres on continental margins can be very complex in both space and time. We aim at investigating how significantly external and internal factors, such as river runoff, bottom current and sliding can deviate the sediment dispersal from a simplistic fully sea-level controlled spreading. In this study we examined the sedimentation at two transects across the Mozambique-Zambezi slope between 17°20S-20°S, where multibeam bathymetry, sub-bottom profiler data and sediment cores were acquired. The period investigated spans the last 40 cal ka BP with a focus on the contrast between the last glacial (lowstand) and the Holocene (highstand) periods. Results show contrasting patterns of sediment dispersal, deposition and preservation. Sea level fluctuation remains the main forcing and most of the sediment from the Zambezi River settled on the inner shelf since the last sea level rise. However, we found that two major depocentres have developed on the upper slope during the Holocene consequent to the interaction of bottom currents with seabed morphologies at the shelf edge and at the upper slope. Early Holocene sliding in the north-east and in the south-west upper slope is a secondary but yet major factor of sediment transfer to the deep domain. Identified preconditioning factors for sliding on the slope are related to lowstand sediment loading and fluid circulation on the upper slope, and erosion at the base of slope of a plastered drift. Triggering must be related to margin wide mechanisms such as changes in hydrostatic pressure and reorganisation of sediment dispersal, subsequent to the post-glacial sea level rise, or maybe a period of regional seismicity. Climatic conditions in the Zambezi River watershed during the Bolling-Allerod and Younger Dryas periods are recorded and imprinted on the upper slope in the form of a detrital rich layer and a prominent slope-wide high-amplitude reflector. All over the continental slope, plastering of sediment deposits by bottom currents is pervasive and shows a morphological continuum from erosional scours at the base of slope to sediment waves on the upper slope and a possible interaction between along and across slope transport processes. We conclude that, in addition to sea level, the interplay of external and internal factors such as oceanic circulation and sliding, together with margin morphology, lead to the development of unexpected depocentres on the continental slopes. Thus, the study of modern marine analogues is crucial to avoid misleading interpretation of fossil deposits in terms of paleo sea level and more generally of paleo-environmental conditions. • Early Holocene sliding occurred in contrasting morphological and sedimentary settings • Expanded Holocene deposits on the upper slope related to interaction between bottom current and the morphology of the margin and of the seabed • Continuum of sediment undulations ranging from scours to sediment waves from base of slope to upper slope • Sedimentation contrast between Bolling-Allerod/Younger Dryas and Early Holocene periods visible as a high amplitude reflector [ABSTRACT FROM AUTHOR]

Large (> ~ 1 km 3 ) submarine landslides can potentially generate very destructive tsunamis and damage expensive sea floor infrastructure. It is therefore important to understand their frequency and triggers, and whether their frequency is likely to change significantly due to future climatic and sea level change. It is expensive to both collect seafloor samples and to date landslides accurately; therefore we need to know how many landslides we need to date, and with what precision, to answer whether sea level is a statistically significant control. Previous non-statistical analyses have proposed that there is strong correlation between climate driven changes and landslide frequency. In contrast, a recent statistical analysis by Urlaub et al. (2013) of a global compilation of 41 large (> 1 km 3 ) submarine landslide ages in the last 30 ka concluded that these ages have a temporally random distribution. This would suggest that landslide frequency is not strongly controlled by a single non-random global factor, such as eustatic sea level. However, there are considerable uncertainties surrounding the age of almost all large landslides, as noted by Urlaub et al. (2013). This contribution answers a key question that Urlaub et al. (2013) posed, but could not address — are large submarine landslides in this global record indeed temporally random, or are the uncertainties in landslide ages simply too great to tell? We use simulated age distributions in order to determine the significance of available age constraints from real submarine landslides. First, it is shown that realistic average uncertainties in landslide ages of ± 3 kyr may indeed result in a near-random distribution of ages, even where there are non-random triggers such as sea level. Second, we show how combination of non-random landslide ages from just 3 different settings, can easily produce an apparently random distribution if the landslides from different settings are out of phase. Third, if landslide frequency was directly proportional to sea level, we show that at least 10 to 53 landslides would need to be dated perfectly globally — to show this correlation. We conclude that it is prudent to focus on well-dated landslides from one setting with similar triggers, rather than having a poorly calibrated understanding of ages in multiple settings. [ABSTRACT FROM AUTHOR]

This study reported geochemical and Sr–Nd isotopic variation of fine-grained mineral components in a deep-sea piston core G6-4, south of the Sumba Island, Eastern Indian Ocean. The new data enables us to characterize dust contributions from Australian continent and volcanic eruption history in the adjacent volcanic arc over approximately the last 300,000 years. The geochemical and isotopic features of the fine-grained components (< 20 μm) in Core G6-4 are broadly consistent with mixing between aeolian dusts from the Australian continent and volcanic ashes of the Sunda arcs. Simple two-component modeling shows that the majority of the core samples probably are composed of 50–80% aeolian dusts derived from the Australian continent. Sr–Nd isotopic ratios are fairly uniform for samples older than 180 ka, in contrast with those of the samples younger than 180 ka, which are much more variable with three anomalies characterized by higher 143 Nd/ 144 Nd and lower 87 Sr/ 86 Sr values recognized. We interpret the three anomalies in the last 80 ka as recording episodes of eruptions from nearby volcanoes. Thus, it is likely that volcanism become more active in the last 80 ka. Excluding these anomalies, the average 143 Nd/ 144 Nd was generally lower, and average 87 Sr/ 86 Sr was higher in the post-180 ka section than in the older section, which might be associated with increased Australian continental aridity toward more recent time. [ABSTRACT FROM AUTHOR]

An ability to estimate the large-scale spatial variability of seabed sediment type in the absence of extensive observational data is valuable for many applications. In some physical (e.g., morphodynamic) models, knowledge of seabed sediment type is important for inputting spatially-varying bed roughness, and in biological studies, an ability to estimate the distribution of seabed sediment benefits habitat mapping (e.g., scallop dredging). Although shelf sea sediment motion is complex, driven by a combination of tidal currents, waves, and wind-driven currents, in many tidally energetic seas, such as the Irish Sea, long-term seabed sediment transport is dominated by tidal currents. We compare observations of seabed sediment grain size from 242 Irish Sea seabed samples with simulated tidal-induced bed shear stress from a three-dimensional tidal model (ROMS) to quantitatively define the relationship between observed grain size and simulated bed shear stress. With focus on the median grain size of well-sorted seabed sediment samples, we present predictive maps of the distribution of seabed sediment classes in the Irish Sea, ranging from mud to gravel. When compared with the distribution of well-sorted sediment classifications (mud, sand and gravel) from the British Geological Survey digital seabed sediment map of Irish Sea sediments (DigSBS250), this ‘grain size tidal current proxy’ (GSTCP) correctly estimates the observed seabed sediment classification in over 73% of the area. [ABSTRACT FROM AUTHOR]

Actively growing, dense rhodolith beds are found in the wide channel between the volcanic Jeju and Udo islands in Korea. This shallow area (water depths of up to 25 m) has unique geological features affected by the marine hydraulic regime. Spheroidal and sub-spheroidal, living or dead rhodoliths with the size range from sand to pebble are common (mostly 2–4 cm in diameter), but some of them are actively growing up to over 10 cm. Most sand- to granule-sized sediments are characterized by nonliving fragments, and the pebble-sized sediment beds are a mixture. In order to understand the factors affecting the characteristics (morphology, distribution, the living portion of rhodoliths, etc.) Seabed topography and sedimentary texture associated with hydraulic energy were investigated. We divided the study area into four types based on topographical properties. Among these classifications, the "Flat plain" and "Gentle slope" geomorphic categories have dense rhodolith beds, whereas a low distribution of rhodoliths was identified in areas with uneven topography or extreme high hydraulic energy flux. In addition, rhodolith growth was affected by the size of carbonate grains on the seafloor, and rhodoliths with more spheroidal shapes tend to occur on flatter floors. This study delineates that the substrate with coarse-sized substrate at relatively deeper water depth as well as flatter bottom topography provides favorable conditions for continuous growth of rhodoliths. Our findings will help the understanding of the growth conditions of rhodoliths in other parts of the world. • Factors affecting the distribution and growth density of rhodoliths were identified using water depth and slope. • The physical factors contributing to the growth of rhodoliths are the low slope, soft substrate and normal ocean energy. • The presented method proved the correlation between the growth of rhodoliths and submarine topography. [ABSTRACT FROM AUTHOR]

The key goals to studying submarine landslides and associated tsunamis are to better assess the magnitude information of palaeo-tsunamis and to contribute to assessing future tsunami risks. The numerical modelling of submarine landslides and the tsunamis thus generated comprises important interdisciplinary research that requires knowledge of both geology and numerical modelling. Models are capable of delineating the time evolution of tsunami hydrodynamics, sediment transport, and the resulting morphological changes associated with deposition. To advance towards the ultimate goal of improved tsunami risk assessment, modellers and geologists need to develop an in-depth mutual understanding of the advantages, limitations, and uncertainties in both numerical modelling and geological records. In this work, seafloor features related to former submarine landslides in the Alboran Sea basin have been identified through multibeam bathymetry data and high- to very high-resolution seismic profiles. The mathematical modelling and hindcasting have been performed through numerical simulation of a hypothetical submarine landslide and the associated tsunami that could have originated one of the submarine landslides identified. This system, on the southern Alboran Ridge slope, is currently reworked by turbidite processes, forming a submarine canyon-sedimentary fan system known as the Al-Borani System. The HySEA numerical model simulates the submarine landslide triggering the tsunami and the water mass evolution, wave propagation, and the final penetration of the tsunami waves onto the coast, reproducing initial and subsequent tsunami wave impacts by means of a single coupled numerical model. This numerical model allows an analysis of the influence of basin morphology on the tsunami propagation features, such as shape and propagation patterns, speed or wave amplitude and, finally, its impact on the coast (in this case South Iberia and North Africa). This model can also be used as a prediction tool for the simulation of potential landslides, many of which generate tsunamis. Monitoring of critical areas, where landslides are more probable, and modelling their consequences will allow a choice of the appropriate mitigation strategies. Therefore, monitoring and modelling are areas of key scientific and socio-economic interests. [ABSTRACT FROM AUTHOR]

Numerous calcium carbonate veins were recovered from the igneous basement of the Early Cretaceous Shatsky Rise during Integrated Ocean Drilling Program (IODP) Expedition 324. The chemical (Sr/Ca, Mg/Ca) and isotopic ( 87 Sr/ 86 Sr, 143 Nd/ 144 Nd, δ 18 O, δ 13 C) compositions of these veins were determined to constrain the timing of vein formation. A dominant control by seawater chemistry on calcite composition is evident for most vein samples with variable contributions from the basaltic basement. Slightly elevated precipitation temperatures (as inferred from oxygen isotope ratios), indicative of hydrothermal vein formation, are only observed at Site U1350 in the central part of Shatsky Rise. The highest 87 Sr/ 86 Sr ratios (least basement influence) of vein samples at each drill site range from 0.70726 to 0.70755 and are believed to reflect the contemporaneous seawater composition during the time of calcite precipitation. In principle, age information can be deduced by correlating these ratios with the global seawater Sr isotope evolution. Since the Sr isotopic composition of seawater has fluctuated three times between the early and mid Cretaceous, no unambiguous precipitation ages can be constrained by this method and vein precipitation could have occurred at any time between ~ 80 and 140 Ma. However, based on combined chemical and isotopic data and correlations of vein composition with formation depth and inferred temperature, we argue for a rather early precipitation of the veins shortly after basement formation at each respective drill site. [ABSTRACT FROM AUTHOR]

The non-clay and clay mineralogies of the < 2 mm sediment fraction from 157 seafloor samples in the western Nordic Seas is calculated by quantitative X-ray diffraction analysis. Our sample coverage includes the Iceland shelf, the ice-impacted East Greenland margin, and the Greenland, Iceland, and Irminger seas. The bedrock geology of source areas includes Precambrian basement rocks, Devonian red beds and younger marine and fluvial sediments, and large outcrops of early tertiary to recent flood basalts and other volcanic facies. Sediment erosion and transport in the area are associated with ice (sea ice and icebergs), and glacial meltwater and fluvial sediment plumes. We use Principal Component Analysis, fuzzy k-means clustering, and Discriminant Function Analysis to reduce the original 31 (minerals) × 157 (sites) matrix to more manageable 5 regional coherent clusters of sites, which are well discriminated by the weight % of six minerals, namely quartz, pyroxene, illites, magnetite and maghemite, amorphous silica (e.g. glass) and muscovite. The close spatial relationship between bedrock geology and discrete cluster membership stresses the importance of this variable and indicates that far-distant sediment transport by sea ice, icebergs, or other mechanisms, although occurring does not radically change the mineral composition of present-day sea-floor sediments. Our improved knowledge of the regional mineral assemblages allows for tracking distinct Eastern Greenland and Icelandic sources. [ABSTRACT FROM AUTHOR]

This study explores the full potential of high-resolution multibeam data for the automated and accurate mapping of complex seabed features under a predictive modelling framework. For an area of seabed on the Carnarvon shelf in Western Australia, morphometric variables and textural measures were derived from multibeam bathymetry and backscatter data. Several feature extraction approaches were applied to backscatter angular response curves to obtain new features. These derivatives and new features were used separately and in combination in the predictions. Despite the complex distribution of various hard substrata within the study area, we achieved a nearly perfect prediction of “hard vs soft” seabed types with an AUC (Area Under Curve) close to 1.0. The predictions were also satisfactory for gravel, sand and mud content, with R 2 values that range from 0.55 to 0.73. This study demonstrates that using a full range of derivatives and new features from both multibeam bathymetry and backscatter data optimises the accuracy of seabed mapping. From the modelled relationships between sediment properties and multibeam data, we confirmed that coarser sediment generally generates stronger backscatter return. Importantly, the results again highlight the advantages of applying proper feature extraction approaches over using original backscatter angular response curves. [ABSTRACT FROM AUTHOR]

Analysis of high resolution sub-bottom profiles, topographical data and sediment samples reveals that the tidal delta system of Qiongzhou Strait is morphologically a "butterfly delta" system consisting of Western Mouth Tidal Delta (WMTD) and Eastern Mouth Tidal Delta (EMTD). WMTD covers an area of about 11,000 km², and is more than two times larger than EMTD (4000 km²). WMTD is fan-shaped with a tributary branch extending southwards along Hainan Island, while EMTD is typically fan-shaped. Seismic architectures of WMTD and EMTD are both characterized by a thick progradational unit overlying a thin transgression unit. Both WMTD and EMTD start to develop at about 8.7 cal ka BP when Qiongzhou Strait completely opened, and have the same three sedimentary facies: tidal delta top, tidal delta slope and tidal delta toe. The formation of WMTD and EMTD is attributed to Qiongzhou Strait's hydrodynamic regime which is dominated by the strong east-west reciprocal-tidal currents and influenced by the year-round westward mean flow modified by the wind-driven seasonal currents. [ABSTRACT FROM AUTHOR]

Newly acquired sediment cores and high-resolution seismic lines were studied in order to constrain the timing and mechanism of pockmark formation in the Loppa High area in the southwestern Barents Sea. The evolution of the pockmarks after their formation was also investigated, together with the possibility that they are currently active features. The cores retrieved within the pockmarks lack a layer of ice-rafted debris and an overlying sequence of laminated glaciomarine sediments that were deposited on the undisturbed seafloor at the inception of the Bølling interstadial (~ 15 cal kyr BP). The pockmarks are suggested to have formed in that period, probably due to climate change-induced destabilisation of methane hydrates and the subsequent release of free gas. The depressions deepened as a result of reduced sedimentation above active seeps. The pockmark cores contain a series of gravel-rich layers, which are attributed to the winnowing of sediment during episodic fluid venting activity. The seismic images reveal little disturbance of the most ancient sediments underneath the pockmarks, indicating that the pockmark chimneys are localised features and were not imaged. The Holocene marine sediment cover in the pockmarks is thinner than on the surrounding seafloor, indicating relatively low sedimentation rates inside the depressions. The gas seepage may thus have been active until the recent past, although no indications of present-day methane flux were found. [ABSTRACT FROM AUTHOR]

High-resolution multibeam data in the central and eastern part of the Aeolian volcanic arc (Southern Tyrrhenian Sea) reveal widespread large-scale waveforms on the submarine flanks of these insular volcanoes. These features show high variability in wave parameters (wavelength of 60-1600 m and wave height of 4-200 m) and morphology (from sinuous to arcuate in plan-view, and from undulating to stepped, with very steep scarps, in cross-section), indicating that different processes, at variable spatial and temporal scale, are responsible for their genesis. By relating the morphological characters of the different waveforms and the local boundary conditions (morphological setting, regional slope gradients, sediment source and dynamics) where these features form, we were able to distinguish bedforms formed by sedimentary gravity flows from bedform-like features due to gravity instability processes. In detail, bedforms have been interpreted as coarse-grained sediment waves according to their wave parameters, geometry and texture. Bedforms are always found where the slope gradients markedly decrease to values < 4°-8°, promoting a hydraulic jump in the sedimentary gravity flow. Hence, we tested if the recognized coarse-grained sediment waves can be generated as cyclic steps by comparing their morphometric characteristics with the results of experimental evidence and numerical modeling proposed in literature. The results show that cyclic step is a reasonable interpretation for these features, and we discuss the effect of flow depth, flow concentration and discharge as governing parameters affecting their wavelength, wave height and shape. [ABSTRACT FROM AUTHOR]

The recognition of peculiar laminated layers atypically rich in a biogenic intrabasinal component in the mudstone intervals from the Messinian (late Miocene) Primary Lower Gypsum unit (5.97-5.60 Ma) of the Piedmont basin (NW Italy) provides information on the palaeoenvironmental evolution at precessional insolation maxima. These cyclic layers consist of irregular alternation of cm-thick grey terrigenous laminae and whitish composite packets; the latter is in turn composed of sub mm-thick wrinkled dolomite-rich laminae that alternate with terrigenous ones. Two types of layers can be distinguished: i) peloidal layers, composed of faecal pellets and irregular diatom-rich aggregates, interpreted as marine snow floccules; and ii) filament bearing layers, composed of interwoven filaments up to 150 μm across, corresponding to remains of Beggiatoa-like giant sulphide-oxidising bacteria. By comparison with present-day settings, the peloidal layers are interpreted as flocculent layers, deposited on anoxic sea bottoms, following episodes of phytoplankton bloom in the upper water column. The filament-bearing layers are considered as chemotrophic microbial mats, growing on dysaerobic sea bottoms. The uncommon preservation of both kinds of layers is the result of extensive dolomite precipitation in the shallow subsurface, induced by bacterial sulphate reduction. The laminated layers are the first reported example of a high frequency climate-driven cyclicity in the non-evaporitic portion of the Primary Lower Gypsum unit. Their stacking pattern within the mudstone intervals reflects the gradual increase of the oxygen content of bottom waters during the humid precessional hemicycle, culminating with gypsum deposition at the onset of the arid phase. [ABSTRACT FROM AUTHOR]

Wave and/or current supported gravity-driven sediment flows (GDSFs) cause substantial sediment movement across the continental shelf, contributing to morphological evolution in many regions worldwide. However, they appear to occur episodically and ephemerally and, therefore, it remains a challenge to document them in detail with in situ measurements. Here we present solid evidence of frequent generation of such flows over the shallow sea floor of a muddy open coast. They were triggered by wave resuspension and/or sediment settling from the overlying water column, maintained by wave- and/or current-induced bed stress, and terminated due to upward spreading of bottom sediment within the high concentration layer. Randomly selected GDSF events were analyzed to realize parameterization with a buoyancy-friction model; the resultant bed drag coefficient for two of the cases is higher than the value of 0.003, which is attributed to the additional drag at the interface between the overlying flow and the moving GDSFs. Although short-lived, the observed GDSF events in the three different seasons indicate that they occur more frequently than previously thought. • Multiple events of short-lived gravity-driven sediment flows (GDSFs) were directly observed. • GDSFs were neatly parameterized with a simple but elegant buoyancy-friction model. • GDSFs may occur more frequently than previously believed. [ABSTRACT FROM AUTHOR]

The combination of oceanographic processes and a negligible fluvial terrestrial sediment contribution makes the Santos Basin margin (southwestern Brazil) a unique environment for studying thew morphological imprint of bottom currents on the seafloor morphology. We divide the seafloor into four domains: outer shelf, upper, middle, and lower slope, based on an analysis of sub-bottom Chirp profiles, multichannel seismic data, hydrographic data, numerical simulation outputs, and a seismic-derived bathymetry map. A clinoform at the outer shelf and upper slope, topped by erosional morphologies, developed below the SW-flowing Brazil Current (BC). At the bottom of the upper slope, a rugged and mounded surface around 600 mbsl coincides with the current flow reversal to the underlying NE-flowing Intermediate Western Boundary Current (IWBC). The smooth middle slope exhibits sheeted contourites interrupted by occasional channel-and-mound complexes. From the middle slope base, salt tectonics becomes a major player in setting the seafloor morphology. The slope-parallel Santos Channel develops above a subsurface diapir and the Cabo Frio Fault. The latter divides between the landward gap in subsurface Albian salt and the basinward rich diapir realm. Hence, the lower slope is reworked by the SW-flowing Deep Western Boundary Current (DWBC); however, salt tectonics dictates its morphology. Our study consists of a unique example for studying the morpho-sedimentary imprint of a counter-current flowing on the continental slope and also for exploring the interaction between bottom flows with a suite of endogenic processes, such as salt tectonics, fluid flows, and mass movements. • Acoustic recognition of contourites generated by opposite flows. • Outer shelf and upper slope dominated by the Brazil Current. • A smooth surface represents the boundary between Brazil Current and Intermediate Western Boundary Current. • Steep middle slope molded by channel-and-mound features. • Santos channel and drift not in equilibrium with present-day hydrodynamics. [ABSTRACT FROM AUTHOR]

Abstract: Physical disturbances of the seafloor play a key role in ecosystem function and are postulated to exert control over spatial patterns of biodiversity. This review investigates the role of natural physical sedimentological processes that occur in shelf, slope and abyssal environments that also act as disturbances to benthic ecosystems and which, under certain circumstances, give rise to benthic disturbance regimes. Physical sedimentological processes can cause both press (process that causes a disturbance by acting over a timespan that is intolerable to benthos) and pulse (process that causes a disturbance by exceeding a threshold above which benthos are unable to remain attached to the seabed or are buried under rapidly deposited sediment) types of disturbance. On the continental shelf, pulse-type disturbances are due to temperate and tropical storm events, and press-type of disturbances identified here are due to the migration of bedforms and other sand bodies, and sustained periods of elevated turbidity caused by seasonally reversing wind patterns. On the continental slope and at abyssal depths, pulse-type disturbances are due to slumps, turbidity currents; benthic storms may cause either press or pulse type disturbances. A possible press-type of disturbance identified here is inter-annual changes in abyssal bottom current speed and/or direction. It is concluded that: 1) physical sedimentary disturbance regimes may characterize as much as 10% of the global ocean floor; 2) multidisciplinary research programs that integrate oceanography, sedimentology and benthic ecology to collect time series observational data sets are needed to study disturbance regimes; and 3) predictive habitat suitability modeling must include disturbance regime concepts, along with other biophysical variables that define the fundamental niches of marine species, in order to advance. [Copyright &y& Elsevier]

Abstract: Coarse-grained ripples (CGRs) develop within the seafloor depression–sand ridge systems along the Shimizu coast, in the northwestern part of Suruga Bay facing the Pacific Ocean, central Japan. In this paper, we analyze data from high-resolution bathymetry, seafloor observation by an underwater video camera, and high-resolution seismic surveys and seafloor trenching of shallow strata, obtained between 2005 and 2007, to describe their geomorphological and sedimentological characteristics in detail, and to examine the formative processes and maintenance of the systems. In water depths of 5–30m, CGRs occur in seafloor depressions that are approximately 40–70cm deeper than the surrounding sandy seafloor. In many cases, the ripples develop in depressions between shore-normal sand ridges composed mainly of fine sand (<70cm high, 100–400m long) on a relatively narrow shelf. The alongshore width of the sand ridges is 10–100m, and that of the depressions is 10–150m. The CGRs (wavelength<3.5m, height<30cm) have almost shore-parallel crests with a symmetrical or slightly asymmetrical shape, suggesting wave-generated oscillating flows. The crests of the lager ripples are composed of gravel (maximum long axis: 5–8cm) and the troughs consist of fine to very fine sand. The CGR–depression–sand ridge systems develop widely during the passage of typhoons in the summer–autumn seasons. At the narrower shelf, the surface fine-grained sediments and the surface and subsurface coarse-grained sediments, which form the sand ridges and the CGRs respectively, are repeatedly eroded and redeposited during typhoon-related storms. In contrast, active sediments are currently limited to the surface fine deposits on the wider shelf areas. The sediments that make up the CGRs appear to be derived from both modern beach sediments and relict sediments. We postulate that the CGR–depression–sand ridge system appears to be controlled mainly by both seafloor erosion and offshore-directed sediment transport during storms, and these processes may depend on the shelf width. In fact, the sand ridges (covering the CGRs) that imply significant offshore-directed transport only develop on the narrower shelf. The distribution and seabed expression of the CGRs is constrained by the thickness and distribution of surface-covering sandy sediments, such as the sand ridges. This represents a new interpretation of the distribution of CGRs within seafloor depressions on the shelf of an active margin that receives a large supply of sandy and gravelly fluvial sediments, and differs from the processes seen on the sediment-starved shelves of passive margins. [Copyright &y& Elsevier]

Abstract: Seabed data acquired from the southern Barents Sea continental margin offshore Norway reveal detailed morphology of large sandwave fields. Multibeam echosounder bathymetry and backscatter, shallow seismic, sediment samples and seabed video data collected by the MAREANO program have been used to describe and interpret the morphology, distribution and transport of the sandwaves. The bedforms lie on a slope dominated by relict glacial forms and muddy/sandy/gravelly sediments. Sandwave migration across small gravity mass failures of the glacial mud constrains the field initiation as early post glacial or later. The contour-parallel nature of the fields and crestlines normal to the bathymetry contours and the geostrophic Norwegian Atlantic Current (NwAC) demonstrate that the NNW-flowing oceanographic circulation is the primary driving current. The fields coincide with the depth range at which a transition between warm, saline and underlying cooler, less saline waters fluctuate across the seabed. Statistically rigorous measurements of height, width and various parameters of slope and symmetry confirm a tendency to downstream (NNW) sandwave migration but with significant exceptions. Anomalous bedform symmetry domains within the fields are tuned to meso-scale topography along (relict) glacial debris flow chutes, indicating current focusing. Upstream and upper slope-derived winnowed sand transport eroded from the glacial sediments is the supposed source. Sandwave flank slope values are comparable to the regional slope such that the gravitational vector would have a cumulative downslope migration affect unless balanced by upslope drivers. Perpendicular cross-cutting of stoss face 3-D ripples by linear (2-D) ripples in the sandwave troughs and lee faces is evidence for non-synchronous, episodic current variations. Though deep Ekman transport and internal wave action are unproven here, these could explain chute-related tuning of bedform symmetry through funneling in the debris flow chutes and favor sand recycling, thus contributing to long-term maintenance of the sandwave field. [Copyright &y& Elsevier]

Abstract: The relation between seafloor fault ruptures and the generation of turbidity currents was investigated to better understand the structural growth of tectonic basins with direct implications for earthquake hazard assessment. This study focuses on the Holocene earthquake record of transtensional basins in the Marmara Sea, Turkey, that are associated with the North Anatolian Fault system. The physical and chemical composition of three 10m-long cores recovered from the Central Basin was studied at high-resolution and turbidite–homogenite units were identified. Turbidite–homogenite units (T–H units) are complex deposits that consist of a sharp basal contact and multiple fining upward beds of sand to coarse silt, above. All are capped by a 25cm to 75cm thick layer of medium to fine silt. A chronology developed from radiocarbon and short-lived radioisotopes allowed the correlation of these T–H units to the historical record of earthquakes that in Turkey goes back 2000years. We found that the best location to recover the most complete sedimentation record is in the deepest part of a basin or “depocenter” where T–H units constitute ~80% of the sediments. A very good correlation was established between T–H units in Central Basin and proximal inferred historic epicentres along the central Marmara segment of the North Anatolia Fault that occurred in 1343, 860, 740, and 557AD, and two more distal earthquakes that occurred in 268 and 1963 (or possibly1964). These sedimentation events can then be referred to as “seismo-turbidites”. The results when compared to findings from other transform basins in Marmara Sea reveal a very good correlation between T–H units and historic ruptures. Most importantly, there is a strong correlation between the inferred locations of historical earthquakes and the preservation of turbidite–homogenite units in the basin adjacent to the inferred rupture. The 740AD earthquake correlates with T–H units in Izmit Gulf and Central Basin and could represent a multi-segment rupture of the NAF. Generally, T–H units appear to be clustered through the Holocene sections, suggesting temporal earthquake clustering in the Marmara Sea region. Such clustering may account for the lack of T–H units and hence large ruptures through the Central Basin since 1343. [Copyright &y& Elsevier]

Abstract: The recent marine carbonate world comprises two major compartments: (1) the surface domain of the photozoan carbonates, confined in space by water depth and by the penetration of light, and (2) a deep domain, where heterozoan mound-builder guilds directly forage on fluxes of nutrients, which primarily percolate from the photic zone and/or are generated by in situ benthic processes. Locally, giant cold-water coral mounds tower up to heights of 150 to 250m above the sea floor, in general between 500 and 1300m water depth and within sharply delineated provinces. Some 15years of research on these giant mound provinces conveys a picture of their distribution in space and possibly sheds light on controls, acting in concert. Globally, there is no counterpart for the prolific North Atlantic Mound Basin (NAMB). A chemical control is seen by an overlay of the mound provinces on a map of the aragonite saturation horizon (ASH). An external physical control is inferred from the position of the mound provinces, girdling a vigorous North Atlantic subtropical gyre system and clustering close to the roof of the intermediate to deep water masses of a dynamically stratified ocean. On the eastern boundary of the NAMB, nutrient fluxes are enhanced by mixing processes, driven either by internal waves between Galicia and the Shetlands, or by the vast and heterogeneous Eastern Boundary Upwelling System along the Iberian/African margins down to 10°N. Early diagenesis by carbonate dissolution and re-precipitation driven by convecting or advecting internal fluids can contribute to stabilize such constructions, facilitating an exuberant vertical accretion. It is speculated that in the North Atlantic Ocean, the deep-water carbonate factory outclasses in size the shallow water coral reefs. Giant mound formation is a recurrent play of Life since the dawn of the metazoans (Nama Group, Upper Neoproterozoic), however with actors and plots, varying from act to act. Remarkably, literature reports only three occurrences of deep-water mounds in the Phanerozoic: the modern ocean, possibly the Danian, and the Carboniferous. Some striking parallelisms in the development of the Atlantic and the Paleo-Tethys oceans, combined with the developing insights in the controls on deep-water mounds in the present ocean, invite for a comparative study. This has the potential to eventually shed light on the full circulation pattern of the Paleo-Tethys Ocean, surface and deep. Comparative studies will build upon (1) modeling of ocean circulation constrained by the record of deep-water carbonate systems and supported by advances in tracer and proxy tools, and (2) field studies on representative and accessible continental locations. The mound route that develops in Morocco under the auspices of IOC-UNESCO will provide to multi-disciplinary teams with marine and continental experience opportunities for confronting observations from the modern ocean and on key records of past oceanic basins. It has the potential to eventually qualify for a UNESCO recognition as World Heritage. [Copyright &y& Elsevier]