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Near-seabed (<50 m) sediments were studied throughout the Irish sector of the Rockall Trough (ca. 123,000 km) based on a combined analysis of shallow seismic (3.5 kHz) and multibeam swath data acquired by the Irish National Seabed Survey and reprocessed here at higher resolution. The detailed identification of seven acoustic facies served to classify the Rockall Trough into six main sedimentary provinces, incorporating the well-known Feni Drift, Donegal-Barra Fan and Rockall Bank mass flow. In the northern part of the study area, extensive mass transport deposits from both flanks of the trough are the dominant depositional features. Debris flow deposits formed by ice streaming of the British-Irish ice sheet characterise most of the Donegal-Barra Fan, whereas turbidite deposition occurs towards the toe of the fan. On the western margin of the trough, the post-glacial Rockall Bank mass flow deposit displays a rough topography with no acoustic penetration. Several failure scarps are visible on the flank of the bank where the mass flow originated, and pass downslope into large sediment lobes and smaller debris flow deposits. Smaller-scale mass transport deposits were also discovered close to some canyons indenting the eastern slope. High seismic penetration characterises the Feni contourite drift deposit, and precise mapping of its geographical extent shows that it is considerably wider than previously reported. The sediment waves that drape this drift are interpreted as predominantly relict features, and their varied geometry suggests a complex oceanographic regime. In the deeper part of the trough, the data reveal novel evidence of the widespread occurrence (about 12,000 km) of distinct seismic and backscatter signatures indicating the possible presence of fluid escape structures within fine-grained sediments of mixed contouritic, hemipelagic and turbiditic origin. Sediment overloading and increased pore pressure resulting from extensive mass wasting to the north of the area is a likely cause of dewatering-rooted fluid migration towards the seabed, but further investigations are required to confirm the nature and origin of such fluids in the Rockall Trough. [ABSTRACT FROM AUTHOR]

The Irish Shelf Seabed Geomorphological Map (ISSGM) (v2023) presented here, is the first high-resolution geomorphological map of the entire Irish continental shelf. This large-scale mapping exercise took advantage of the vast INFOMAR multibeam echosounder dataset, and used a protocol of semi-automated mapping techniques to accurately and rapidly extract seabed features. All previous mapping efforts and existing literature on the Irish shallow shelf geomorphology have also been collated and integrated in the map, critically evaluating the previous interpretations. An internationally standardised classification scheme was adopted, aligning the ISSGM (v2023) to other international geomorphological work. At a national level, this detailed geomorphological digital map is intended primarily as a resource to better inform multiple offshore activities and management of the marine environment. The map also acts as a baseline for future studies in marine geomorphology, as it identifies gaps in the knowledge and highlights areas of contentious interpretation that require further work. The map is available online on the Irish Marine Atlas. [ABSTRACT FROM AUTHOR]

Please clickhereto download the map associated with this article. Multibeam echosounder data collected by the Irish National Seabed Survey (INSS) between 2000 and 2001 in the Rockall Trough have been used by many projects to analyze the geomorphology and the sedimentary processes of the margins of the Trough. However, due to the low spatial resolution of 150–250 m and the amount of artefacts still embedded in the publicly available data, many geomorphological features have been overlooked. This paper shows that the same multibeam dataset can provide more detailed information on seabed processes when the latest hydrographic and backscatter post-processing techniques are used to reduce data artefacts and improve data quality and spatial resolution. The resulting map, presented here at a scale of 1:450,000, is based on a semi-automatic and manual interpretation of geomorphological features highlighted using a new and improved 30 m bathymetric grid and a multibeam backscatter mosaic obtained using the GEOCODER post-processing algorithm. Overall, the map shows a complex sedimentological scenario where the Rockall Bank Mass Flow failure, the Donegal-Barra trough-mouth fan, along slope structures such as the Feni Contourite Drift and the Porcupine moat dominate the Rockall Trough flanks and basin floor. Smaller features such as canyon and gully systems, escarpments, coral mounds, volcanic mounds and iceberg scours have also been mapped in detail. In addition, the interpretation of the backscatter mosaic allows for the first time the identification of depositional lobes generated by downslope mass transport and canyon drainage systems, particularly where these features completely lose their bathymetric expression. [ABSTRACT FROM PUBLISHER]

The study of palaeo‐glacial landforms and sediments can give insights into the nature and dynamics of ice sheets. This is particularly the case with regards to the subglacial record, which is challenging to observe in contemporary glaciated settings and hence remains only partially understood. The subglacial hydrological system is an essential component of ice dynamics, where increased water pressure enhances ice motion and sediment deformation, thus reducing ice‐bed contact. Tunnel valleys are large, sinuous, steep‐sided incisions that, together with smaller scale meltwater channels, indicate subglacial meltwater discharge beneath large ice sheets. Through the use of high‐resolution marine geophysical data, a system of buried and exposed tunnel valleys, possible subglacial or proglacial meltwater channels and palaeo‐fluvial valleys have been identified across the shelf of the Celtic Sea between Ireland and Britain. The presence of steep‐sided and overdeepened tunnel valleys is indicative of a large channelized meltwater drainage system beneath the former Irish Sea Ice Stream, the most extensive ice stream to drain the last British–Irish Ice Sheet. After the rapid ice expansion across the Celtic Sea shelf around 28–26 ka, the tunnel valleys were carved into both bedrock and glacigenic sediments and are associated with rapid ice stream retreat northwards into the Irish Sea Basin between 25.6 and 24.3 ka. The presence of a major subglacial meltwater system on the relatively shallow shelf suggests that significant erosive meltwater discharge occurred during the last deglaciation and highlights the important contribution of meltwater to the retreat of the British–Irish Ice Sheet on the continental shelf. [ABSTRACT FROM AUTHOR]

The Co nfined M orphologies Ma pping (CoMMa) Toolbox, a novel ArcGIS Pro python toolbox expressly created for semi-automated seabed morphological mapping, is presented here. The toolbox includes a selection of tools for the pre-processing, delineation and description of confined features on a digital elevation model (DEM) that are either negative or positive. The CoMMa Toolbox addresses the need for a flexible and multi-faceted solution applicable to different mapping problems, also encapsulating and re-interpreting existing methodologies. This study also evaluates, qualitatively and quantitatively, the performance of CoMMa delineations performed on a synthetic bathymetry DEM with 150 coral mounds of known characteristics against manual digitisations completed by five expert geomorphologists. The results show that the best CoMMa delineation falls within the range of competence demonstrated by the expert manual mappers. Edge evaluation metrics and attribute error scores are comparable or often superior to four of the five human delineations, although the Toolbox never reaches the performance of the best expert. Nevertheless, the semi-automated techniques can be of assistance to any user, providing rapid, visually unbiased and consistent delineations, thus saving time: they can then be optimised manually where desirable. Moreover, while the toolbox was created for marine geomorphometry, it can be applied to any DEM, either marine, terrestrial or extra-terrestrial. The CoMMa Toolbox is available in a public GitHub repository with a thorough user guide. • We present CoMMa, a toolbox that allows users to characterise confined morphologies. • A synthetic seabed DEM was used to gain statistical control on the accuracy of the toolbox. • CoMMa delineations are compared to those done manually by five expert mappers. • The results by CoMMa are as precise or better than those of the manual mappers. • CoMMa is freely available on GitHub with a complete User Guide. [ABSTRACT FROM AUTHOR]

Recent mapping programmes in Irish territorial waters, such as the Irish National Seabed Survey and the Integrated Mapping for the Sustainable Development of Ireland's Marine Resource programme, have generated high resolution multibeam bathymetry, backscatter and sediment sample datasets at an unprecedented resolution and coverage. Building upon previous mapping of glacial landforms on the northwest Irish continental shelf, a 1:225,000 scale map identifying contemporary bedforms has been produced between 54°40′N/56°10′N and 10°2′W/6°45′W. The analysis of bathymetric derivatives and backscatter interpretation has enabled the classification of several types of depositional feature including six sediment wave assemblages. Erosional features have also been identified across the shelf in the form of surface sediment lineations, as well as more spatially confined formations such as furrows. Based on wave asymmetry, sedimentary composition and orientation, in agreement with published modelled hydrodynamic conditions, these bedforms are assumed to be contemporary features. Data interpretation, particularly of backscatter imagery reveals that these sediments mask the acoustic signatures of an underlying glacial architecture and may alter their apparent morphology due to burying. [ABSTRACT FROM AUTHOR]

Abstract: The eastern flank of the Rockall Bank is dominated by the scarps of a large slide complex with unusual low aspect ratio (120km wide and 150km long). With the use of an extensive 2D seismic dataset, re-processed high-resolution multibeam bathymetry, a TOBI mosaic and one piston core we demonstrate that the headwall of the Rockall Bank Slide Complex (previously referred to as the Rockall Bank Mass Flow) may have occurred as a multiphase slope collapse in at least three episodes of instability since 16ka BP, with each of the events generating a slide with a more typical elongate morphology. Reconstructions of the pre-slide seafloor suggest a volume of collapsed sediments in the range265–765km3. Seismic facies investigation indicates that the slope and failed sediments comprise almost exclusively contourites that are prone to failure due to their well sorted character and high water content. A systematic examination of the slope morphology, seismic facies and sub-seafloor structures demonstrates a direct relationship between the RBSC seafloor scarps and the basement morphology. Focused fluid flow along basement-bounding faults, and/or differential compaction across the scarps, are considered to have had an important role in slope failure. This study highlights the importance of deeply-buried structures in the stability of slopes. It also shows how detailed examination of high-resolution data across large areas of slope instability can reveal smaller-scale multiple events. We believe that where contour-swept slopes are steep, the resulting intensification of near-bottom velocities prevents healing slope processes and as a result steep slope gradients remain steep and thus unstable. [Copyright &y& Elsevier]

Shipwrecks are an integral part of our maritime archaeological landscape and are associated with diverse societal and cultural interests, yielding significant management challenges. Coupled hydrodynamic and geomorphological processes significantly impact the effective in situ preservation of these fragile sites. In this study, we assess sediment budget change and hydrodynamic triggers at metal‐hulled shipwrecks lost between 1875 and 1918, all located in the tidally dominated Irish Sea at depths between 26 and 84 m. This is conducted using time‐lapse, multibeam echosounder surveys at multiannual, annual, and weekly time steps, supported by sediment grain‐size analysis, modeled ocean currents, and shallow seismic data. Results indicate significant changes at all time steps for sites located in sand‐dominated environments, whereas the seabed around shipwrecks settled in multimodal sediments shows virtually no change outside of measurement errors (±30 cm). Variability in geomorphic change is attributed to local environmental factors, including bed shear stress, sediment supply, and spatial barriers to scour. We demonstrate that individual wrecks in similar shelf sea regions can be in very different equilibrium states, which has critical implications for the in situ management of underwater cultural heritage. [ABSTRACT FROM AUTHOR]

A combination of multibeam bathymetry and backscatter, LiDAR altimetry and bathymetry, satellite images, and hydrodynamic model outputs were used to map the seafloor and coastline of Galway Bay (western Ireland). This is the first time these multiple datasets have been integrated into a single combined geomorphological and substrate map. The substrate of the bay is predominantly mud and sand with bedrock outcropping extensively around the coastline. The main depositional features are dunes, while the main erosional features are scours and outcropping bedrock. Hydrodynamic model outputs show good correlation between the direction and intensity of prevailing currents and the location and shape of the features in the bay. This indicates that although Galway Bay was shaped glacially through the passage of the British-Irish Ice Sheet across the bay and ensuing glacial and marine sediment deposition, many of the mapped seafloor landforms are modern and current-induced. [ABSTRACT FROM AUTHOR]

Conservation of historic shipwrecks is prohibitively expensive and in situ preservation and recording are the preferred archaeological approaches. Non-destructive high-definition 3D imaging is therefore essential for recording and managing submerged historic shipwrecks. Multibeam echosounders (MBES), the standard tool for hydrographic survey, can produce point clouds to image complex 3D structures. However, wreck imaging is often done using MBES in traditional survey mode optimised for morphological characterisation of the seafloor. This does not necessarily provide high-definition imagery required by archaeologists. This study demonstrates key factors influencing high-definition MBES imaging of wrecks through a controlled field experiment. Results show that optimal high-definition 3D imaging is achieved through maximising the pulse rate, narrowing the angular sector, using the highest frequency and shortest pulse lengths, applied to at least 3 to 5 overlapping centreline-parallel and offset passes with additional perpendicular/oblique lines. Variations in survey design are demonstrated to exert strong controls on sounding density and distribution, with high-density on horizontal and vertical wreck surfaces enabled by a combination of overlapping passes and offset lines. Adoption of this method would result in more widespread high-definition 3D imaging of wrecks to benefit archaeological research and develop effective mitigation strategies to minimise loss of the fragile underwater resource. [ABSTRACT FROM AUTHOR]

Relict landforms and sediments across former glaciated settings provide information about ice-sheet dynamics and can contribute to the understanding of the behaviour of contemporary ice masses, for which observations are limited in spatial and temporal extent. In this study, we focus on the shelf offshore southwest Ireland, in the Celtic Sea, which was once occupied by the Irish Sea Ice Stream (ISIS), the largest ice stream draining the southern portion of the marine-terminating British-Irish Ice Sheet (BIIS). Newly acquired high-resolution multibeam echosounder, sub-bottom and core data enabled the investigation of the shelf geomorphology and of the sedimentology and chronology of glacial and glacimarine sediments. A suite of drumlins records ice sheet flow from the coastline towards the central part of the shelf in southwest Ireland. Pre-existing highs in the seafloor topography promoted the formation of arcuate and transverse landforms interpreted as a grounding-zone wedge and moraines and they document episodic retreat of the ISIS across this portion of the shelf. Observed lithofacies show consolidated subglacial till and laminated fine muds. The sediments provide evidence of ice grounded ca. 30 km off the south-west Irish coastline with subsequent deglaciation occurring under glacimarine conditions. These new data refine the current reconstructions of the dynamics of the southern BIIS. They reveal for the first time the interplay of marine- and land-based ice and the presence of grounded ice offshore SW Ireland. This study highlights the importance of high-resolution data in revealing palaeo-landscapes as valuable analogues to test possible scenarios of modern ice sheet changes. • We present new marine high-resolution multibeam, sub-bottom and core data from Ireland. • A suite of glacial and glacially-related landforms is mapped on the Celtic Sea shelf. • Evidence shows that ice was grounded ∼30 km offshore of SW Ireland. • Deglaciation occurred under glacimarine conditions. • Dating refines the current reconstructions of the dynamics of the southern BIIS. [ABSTRACT FROM AUTHOR]

The large number of historic metal-hulled shipwrecks on the seabed is a major consideration for the marine environment, heritage management and spatial planning. Their stability is driven by linked hydro- and sediment-dynamics, which in turn influence chemical corrosion and biological encrustation. The dynamism at underwater sites is frequently expressed in elaborate patterns of depositional and erosional features developed due to seabed scour. These settings are complex, due to the variable morphologies of the wrecks, and diverse types of seabed geology and geomorphology. Not only are the flow patterns and geomorphic changes at shipwreck sites not fully understood, but how these influence the wreck structures remains under-researched. Here we combine high-resolution multibeam echosounder, ocean current and sediment data with 3D Computational Fluid Dynamics (CFD) to investigate interrelations between hydro- and sediment-dynamics and the deterioration of two complex, fully submerged tidally-influenced shipwrecks. Intricate patterns of wake and horseshoe vortices are observed, and modelled wall shear stresses predict geomorphic changes recorded in 4-year and one-week interval difference models. Moreover, substantial damage is detected on the wrecks, correlated with areas of elevated wall shear stress and pressure in CFD simulations. The combined approach aids site management and provides analogies for offshore engineering. • The sheer number of metal shipwrecks on the seabed creates perplexing management challenges. • Their structures significantly influence, and are influenced by, the local hydro- and sediment-dynamic settings. • Computational fluid dynamics and difference modelling using bathymetric data provide new insights into wreck deterioration. • Intricate patterns of simulated flows and wall shear stresses correspond to the areas of sediment erosion and deposition. [ABSTRACT FROM AUTHOR]

Cheko, a small lake located in Siberia close to the epicentre of the 1908 Tunguska explosion, might fill a crater left by the impact of a fragment of a Cosmic Body. Sediment cores from the lake's bottom were studied to support or reject this hypothesis. A 175-cm long core, collected near the center of the lake, consists of an upper ~1 m thick sequence of lacustrine deposits overlaying coarser chaotic material. 210Pb and 137Cs indicate that the transition from lower to upper sequence occurred close to the time of the Tunguska Event. Pollen analysis reveals that remains of aquatic plants are abundant in the top post-1908 sequence, but are absent in the lower pre-1908 portion of the core. These results, including organic C, N and δ13C data, suggest that Lake Cheko formed at the time of the Tunguska Event. [ABSTRACT FROM AUTHOR]

The original version of this article was revised: Additional correction in Table 1: please delete (') in the second column heading was incorrectly carried out. It should read "Acquisition settings test"; by this, the author meant only to delete the apostrophe symbol, not the entire second column heading. [ABSTRACT FROM AUTHOR]