“…The assemblages observed in this study showed similarities to others described in areas characterized by iceberg reworking of the seabed (Gutt et al 1996, Gutt & Piepenburg 2003, Jones et al 2007a. During the Quaternary Period, the majority of the western and southern flanks of Rockall Bank were left covered in scours averaging 2 to 2.3 km in length, ranging between 50 and 200 m in width and up to 8 m in depth (Sacchetti et al 2012). As found in other areas of the northwest European continental margin (Freiwald et al 1999, Wheeler et al 2007, iceberg debris provided hard ground for cold-water coral colonies to establish.…”
Section: Megafaunal Distribution and Biodiversitymentioning
confidence: 97%
“…The shallower areas of the western bank have a heterogeneous seabed, including partly buried rock outcrops, boulder and cobble fields as well as large areas of carbonate sand cover (Roberts 1975). The deeper western and southern flanks (250 to 450 m water depth) are incised with deep scours (< 8 m) from iceberg keels having ploughed the seabed during pe riods of Quaternary low sea levels (Sacchetti et al 2012). Over time, soft sediment filled the centre of the ploughmarks while coarse debris remained at the scar edges.…”
Species distributions are influenced by spatial structure in environmental factors, but the scales at which these dependencies occur and the effect of habitat patch diversity, connectivity and spatial arrangement have rarely been investigated in deep-sea settings. In this study, spatially limited photographic transects collected from Rockall Bank, NE Atlantic, were combined with sidescan and multibeam sonar maps to model spatial patterns in species distribution and biodiversity. Sediment interpretation maps were created and canonical ordination techniques were used to examine relationships between fine-scale sediment characteristics extracted from the digital stills as well as landscape metrics describing the patch mosaic structure of the surrounding areas. Fine-scale sediment characteristics explained 45.1 and 63.8% of the variation in species composition and biodiversity, respectively. This survey effectively captured variation in species distribution resulting from iceberg ploughmarks, occurring at a scale of < 50 m -which would normally go undetected by traditional ship-based studies. Our study suggests that fine-scale environmental information is required to capture the spatial heterogeneity of complex seafloor areas in sufficient detail to model species distributions and biodiversity.
“…The assemblages observed in this study showed similarities to others described in areas characterized by iceberg reworking of the seabed (Gutt et al 1996, Gutt & Piepenburg 2003, Jones et al 2007a. During the Quaternary Period, the majority of the western and southern flanks of Rockall Bank were left covered in scours averaging 2 to 2.3 km in length, ranging between 50 and 200 m in width and up to 8 m in depth (Sacchetti et al 2012). As found in other areas of the northwest European continental margin (Freiwald et al 1999, Wheeler et al 2007, iceberg debris provided hard ground for cold-water coral colonies to establish.…”
Section: Megafaunal Distribution and Biodiversitymentioning
confidence: 97%
“…The shallower areas of the western bank have a heterogeneous seabed, including partly buried rock outcrops, boulder and cobble fields as well as large areas of carbonate sand cover (Roberts 1975). The deeper western and southern flanks (250 to 450 m water depth) are incised with deep scours (< 8 m) from iceberg keels having ploughed the seabed during pe riods of Quaternary low sea levels (Sacchetti et al 2012). Over time, soft sediment filled the centre of the ploughmarks while coarse debris remained at the scar edges.…”
Species distributions are influenced by spatial structure in environmental factors, but the scales at which these dependencies occur and the effect of habitat patch diversity, connectivity and spatial arrangement have rarely been investigated in deep-sea settings. In this study, spatially limited photographic transects collected from Rockall Bank, NE Atlantic, were combined with sidescan and multibeam sonar maps to model spatial patterns in species distribution and biodiversity. Sediment interpretation maps were created and canonical ordination techniques were used to examine relationships between fine-scale sediment characteristics extracted from the digital stills as well as landscape metrics describing the patch mosaic structure of the surrounding areas. Fine-scale sediment characteristics explained 45.1 and 63.8% of the variation in species composition and biodiversity, respectively. This survey effectively captured variation in species distribution resulting from iceberg ploughmarks, occurring at a scale of < 50 m -which would normally go undetected by traditional ship-based studies. Our study suggests that fine-scale environmental information is required to capture the spatial heterogeneity of complex seafloor areas in sufficient detail to model species distributions and biodiversity.
“…Identification of ploughmarks was based on their dimensions and the presence of unique morphological characteristics, including their cross-cutting linear and curvilinear character, chaotic distribution and the presence of lateral berms ( e . g ., Belderson et al, 1973 , Woodworth-Lynas et al, 1985 , Ó Cofaigh et al, 2002 , Dowdeswell et al, 2007 , Dowdeswell et al, 2010b , Sacchetti et al, 2012 , Dowdeswell and Ottesen, 2013 ). Fig.…”
Section: Methodsmentioning
confidence: 99%
“…g ., Woodworth-Lynas et al, 1991 , Andreassen et al, 2007 , Dowdeswell and Ottesen, 2013 , Jakobsson, 2016 ). These methods enable the identification of multiple characteristics that are unique to iceberg ploughmarks, such as the presence of lateral berms, the often chaotic pattern of their spatial distribution, grounding pits and surcharges of sediment at the terminations of grooves ( Sacchetti et al, 2012 ). The dimensions of ploughmarks are spatially variable, with features that are typically tens to hundreds of metres wide and a few to tens of metres deep ( e .…”
Over 7500 buried linear and curvilinear depressions interpreted as iceberg ploughmarks were identified within the Quaternary Naust Formation from an extensive three-dimensional seismic dataset that covers ~ 40,000 km2 of the mid-Norwegian continental margin. The morphology and net orientation of ploughmarks were mapped and analysed. These features are up to 28 km long, 700 m wide and are incised up to 31 m deep. On average, ploughmarks are incised 5 m deep, with median width of 185 m and median lengths ranging from 1.2 to 2.7 km for individual palaeo-surfaces. Width to depth ratio ranges from 8:1 to 400:1 and is on average 36:1. The presence of ploughmarks buried deeply within some palaeo-slope surfaces implies the occasional presence of very large icebergs since the middle Quaternary, suggesting that thick ice-sheet margins with fast-flowing ice streams were present in order to calve icebergs of such dimensions into the Norwegian Sea. The wide geographical distribution of ploughmarks suggests unrestricted iceberg drift and an open Norwegian Sea during the periods of iceberg calving since the early Quaternary. Ploughmark trajectory analysis demonstrates that the ocean current circulation, now dominated by the northeasterly flowing Norwegian Atlantic Current (NwAC), has largely persisted throughout the Quaternary. Despite the overall strikingly consistent pattern of iceberg drift, ploughmark mapping also shows evidence for short-lived NwAC reductions possibly related to major phases of iceberg discharge and/or meltwater pulses from the Fennoscandian Ice Sheet during the middle and late Quaternary.
“…These are found in two separate areas ( Figure 4 A and C), possibly indicating two distinct calving margins or different episodes of calving. North of the study area, iceberg scours are commonly found on the Western Irish shelf break in water depths between 230 and 590 m (Belderson et al, 1973;Sacchetti et al, 2012). Whilst the most westerly scour signature off Bantry Bay does occur fairly close to the shelf break adjacent to the Porcupine Seabight, the most easterly ploughmarks are found in shallower water (140 to 150 m water depth), positioned on the flat continental shelf and closer to the current coastline than any examples previously reported for this section of the shelf.…”
'Late Quaternary evolution and sea-level history of a glaciated marine embayment, Bantry Bay, SW Ireland.', Marine geology., 369 . pp. 251-272. Further information on publisher's website:
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AbstractIreland experienced a spatially complex pattern of relative sea-level (RSL) changes and shoreline development caused by the interplay of isostatic and eustatic (ice equivalent sea level) processes since the Last Glacial Maximum (LGM). Using a combination of high-resolution marine geophysical data, vibrocores, foraminiferal analysis and 10 AMS radiocarbon dates, we reconstruct the Late Quaternary evolution and RSL history of Bantry Bay, a large (40 km long, 5-10 km wide) embayment in SW Ireland.The data indicate two infill phases: one before and one after the LGM, separated by glacial and lowstand sediments. The pre-LGM history is not dated and the depositional history is inferred. A large sediment lobe formed at the outer edge of Bantry Bay as a lowstand ice-proximal glacimarine outwash system as the ice retreated after the LGM, at a sea level ca. 80 m lower than present.Iceberg scour immediately west of this location likely relate to the break-up of the local Kerry-Cork Ice Cap. Long curvilinear ridges, seen both offshore and on top of the sediment lobe, probably formed as shoreface ridges under stronger-than-present tidal currents during a period of RSL stability (pre-14.6 ka cal BP). A subsequent infill phase is characterised by a basin-wide erosional (ravinement) surface and the deposition of inter-and sub-tidal estuarine sediments. Although our data support the general trends, our stratigraphic and radiocarbon data suggest a higher sea level between 11 and 13.5 ka cal BP than predicted by existing glacial isostatic adjustment models.
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