Plough Marks Research Articles

New evidence for prehistoric ploughing in Europe

For the past four decades, the ‘Secondary Products Revolution’ model, i.e., the exploitation of animal resources that do not involve killing the animal, such as the production of milk and wool and the use of animals for physical labour has been the object of heated discussion between Neolithic scholars. According to this model, the use of animal strength arrived relatively late in Europe—during the socio-economic changes of the Late Neolithic in the 4th millennium BCE. Plough marks are the most convincing direct evidence of the use of animal traction. However, few are preserved making them relatively rare throughout Europe and dating them is difficult and often imprecise. Recent research at the Anciens Arsenaux site in Sion, Valais, Switzerland has revealed the presence of the oldest known plough marks in Europe, dating from the beginning of the 5th millennium BCE. They bear witness to the use of animal traction quite soon after the establishment of an agro-pastoral economy in the Alpine region. This is corroborated by recent archaeozoological studies and suggests that this important innovation could already be part of the Neolithic package introduced into Europe during the 6th millennium BCE.

Physicochemical properties of soot in diesel engine lubricating oil: characterizations and impact on frictional characteristics

The study investigates the effects of the physicochemical properties of engine sump soot on the frictional characteristics of its contaminated engine oils. Moreover, the relationship between soot physicochemical properties and its frictional characteristics was also discussed. The results showed that the properties of the two kinds of lubricating oil (A, B) used in diesel engines affect the properties of engine sump soot (Soot-A, Soot-B), i.e. Soot-A showing smaller aggregate size, larger primary particle diameter, more disordered nanostructure, and higher functional content than those of Soot-B. For both soot particles, as the amount of soot particles added to the formula oil went up from 1 wt.% to 2 wt.%, the wear scar diameter (WSD) and friction coefficient of the wear spot increased. For both soot particles, the main wear form of the steel ball wear area was abrasive wear (more than 90%), accompanied by a small amount of plastic deformation and pitting (less than 2%). With the same amount of soot in lubricating oil, soot with a higher degree of graphitization, low oxygen content and low reactivity may cause smaller WSD and lighter wear. Moreover, a larger soot accumulation would result in deeper plow marks and pits in the abrasion areas.

Modern and Relict Evidence of the Iceberg Scouring at the Bottom of the Barents and Kara Seas

The article systematizes and summarizes published data on the parameters and distribution areas of modern and relict iceberg scours (or plough marks), as well as on the maximum possible sizes and drift areas of modern icebergs in the Barents and Kara Seas. According to the open-source bathymetric data, for the first time the analysis of “throughput” of the waters in front of modern glaciers was carried out. Based on summarized and established facts, areas of the most likely distribution of modern iceberg effects on the bottom are determined by the method of expert assessment. This work is relevant both from a fundamental point of view and for determining the current depths limits of iceberg scouring at the bottom of the Barents and Kara Seas, which is important for ensuring the geoecological safety of all kinds of activities on the sea shelf.

Comparative study on the impact-sliding wear behaviour of CAD/CAM resin-ceramic materials and tooth enamel.

To compare the impact-sliding wear of different CAD/CAM resin-ceramic materials and tooth enamel, and explore the corresponding wear damage mechanism. Human tooth enamel (EN), Vita ENAMIC (Vita, VE), Lava Ultimate (3M, LU), and GC CERASMART (GC, CS) were used in this study. The hardness, elastic modulus, and roughness values of the samples were measured. Further, impact-sliding wear tests were performed in a ball-on-flat configuration with spherical zirconia antagonists and the coefficients of friction (CoF) were recorded simultaneously. Additionally, a white light interferometer was used to determine the volume losses and scanning electron microscopy was used to observe the wear morphology of the wear scars and the damage feature in the vertical sections to clarify the damage mechanism during the impact-sliding wear test. EN exhibited the highest elastic modulus and CoF, followed by VE, LU, and CS. The hardness and roughness of EN and VE were similar and were higher than those of LU and CS. Throughout the wear tests, VE exhibited the highest volume loss, whereas CS exhibited the lowest. The wear damage characteristics of VE were similar to those of EN, displaying brittle fractures of inorganic substances and plastic deformation of organic substances in the impact part, exhibiting plough marks in the sliding parts. In the case of LU and CS, the entire wear areas displayed plastic deformation of the resin matrix, exfoliation of the filler particles, and plough marks. Enamel and polymer-infiltrated ceramic network materials exhibit similar wear damage modes. Additionally, the high-density nanocomposite resin material is the most resistant to impact-sliding wear from a tribological perspective.

Deep-Water Glacial Plow Marks in the Western Margin of the Barents Sea

Deep-Water Glacial Plow Marks in the Western Margin of the Barents Sea

Lost in the North Sea-Geophysical and geoarchaeological prospection of the Rungholt medieval dyke system (North Frisia, Germany).

We performed geophysical and geoarchaeological investigations in the Wadden Sea off North Frisia (Schleswig-Holstein, Germany) to map the remains and to determine the state of preservation of the medieval settlement of Rungholt, especially its southern dyke segment, called the Niedam dyke. Based on archaeological finds and historical maps, Rungholt is assumed to be located in the wadden sea area around the island Hallig Südfall. During medieval and early modern times, extreme storm events caused major land losses, turning cultivated marshland into tidal flats. Especially the 1st Grote Mandrenke (or St. Marcellus' flood), an extreme storm surge event in 1362 AD, is addressed as the major event that flooded and destroyed most of the Rungholt cultural landscape. Cultural traces like remains of dykes, drainage ditches, tidal gates, dwelling mounds or even plough marks were randomly surveyed and mapped in the tidal flats by several authors at the beginning of the 20th century. Due to the tidal flat dynamics with frequently shifting tidal creeks and sand bars, the distribution of cultural remains visible at the surface is rapidly changing, making it hard to create a comprehensive map of the cultural landscape by surveying. Today, the Niedam dyke area is fully covered by tidal flat sediments, depriving any remains from further archaeological investigation. Since little is known about the precise location or state of preservation of these remains, our investigation aimed at the rediscovery of the medieval dyke system and associated structure with modern and accurate geophysical, geodetical and geoarchaeological methods. Magnetic gradiometry revealed a large part of the medieval dyke, confirming two tidal gates and several terps connected inland with the dyke, providing a detailed example of a Frisian medieval dyke system. Based on our results, the so far inaccurate and incomplete maps of this part of Rungholt can now be specified and completed. Beyond that, seismic reflection profiles give a first depth resolving insight in the remains of the dyke system, revealing a severe threat to the medieval remains by erosion. The site is exemplary for the entire North Frisian coast, that was influenced by multiple flood events in the middle ages to modern times.

Timing of iceberg scours and massive ice-rafting events in the subtropical North Atlantic

High resolution seafloor mapping shows extraordinary evidence that massive (>300 m thick) icebergs once drifted >5,000 km south along the eastern United States, with >700 iceberg scours now identified south of Cape Hatteras. Here we report on sediment cores collected from several buried scours that show multiple plow marks align with Heinrich Event 3 (H3), ~31,000 years ago. Numerical glacial iceberg simulations indicate that the transport of icebergs to these sites occurs during massive, but short-lived, periods of elevated meltwater discharge. Transport of icebergs to the subtropics, away from deep water formation sites, may explain why H3 was associated with only a modest increase in ice-rafting across the subpolar North Atlantic, and implies a complex relationship between freshwater forcing and climate change. Stratigraphy from subbottom data across the scour marks shows there are additional features that are both older and younger, and may align with other periods of elevated meltwater discharge.

Scars in the abyss: reconstructing sequence, location and temporal change of the 78 plough tracks of the 1989 DISCOL deep-sea disturbance experiment in the Peru Basin

Abstract. High-resolution optical and hydro-acoustic sea floor data acquired in 2015 enabled the reconstruction and exact localization of disturbance tracks of a past deep-sea recolonization experiment (DISCOL) that was conducted in 1989 in the Peru Basin during a German environmental impact study associated with manganese-nodule mining. Based on this information, the disturbance level of the experiment regarding the direct plough impact and distribution and redeposition of sediment from the evolving sediment plume was assessed qualitatively. The compilation of all available optical and acoustic data sets available from the DISCOL Experimental Area (DEA) and the derived accurate positions of the different plough marks facilitate the analysis of the sedimentary evolution over the last 26 years for a sub-set of the 78 disturbance tracks. The results highlight the remarkable difference between natural sedimentation in the deep sea and sedimentation of a resettled sediment plume; most of the blanketing of the plough tracks happened through the resettling of plume sediment from plough tracks created later. Generally sediment plumes are seen as one of the important impacts associated with potential Mn-nodule mining. For enabling a better evaluation and interpretation of particularly geochemical and microbiological data, a relative age sequence of single plough marks and groups of them was derived and is presented here. This is important as the thickness of resettled sediment differs distinctly between plough marks created earlier and later. Problems in data processing became eminent for data from the late 1980s, at a time when GPS was just invented and underwater navigation was in an infant stage. However, even today the uncertainties of underwater navigation need to be considered if a variety of acoustical and optical sensors with different resolution should be merged to correlate accurately with the absolute geographic position. In this study, the ship-based bathymetric map was used as the absolute geographic reference layer and a workflow was applied for geo-referencing all the other data sets of the DISCOL Experimental Area until the end of 2015. New high-resolution field data were mainly acquired with sensors attached to GEOMAR's AUV Abyss and the 0.5∘ × 1∘ EM122 multibeam system of RV Sonne during cruise SO242-1. Legacy data from the 1980s and 1990s first needed to be found and compiled before they could be digitized and properly geo-referenced for our joined analyses.

Detection of Boulders in Side Scan Sonar Mosaics by a Neural Network

Boulders provide ecologically important hard grounds in shelf seas, and form protected habitats under the European Habitats Directive. Boulders on the seafloor can usually be recognized in backscatter mosaics due to a characteristic pattern of high backscatter intensity followed by an acoustic shadow. The manual identification of boulders on mosaics is tedious and subjective, and thus could benefit from automation. In this study, we train an object detection framework, RetinaNet, based on a neural network backbone, ResNet, to detect boulders in backscatter mosaics derived from a sidescan-sonar operating at 384 kHz. A training dataset comprising 4617 boulders and 2005 negative examples similar to boulders was used to train RetinaNet. The trained model was applied to a test area located in the Kriegers Flak area (Baltic Sea), and the results compared to mosaic interpretation by expert analysis. Some misclassification of water column noise and boundaries of artificial plough marks occurs, but the results of the trained model are comparable to the human interpretation. While the trained model correctly identified a higher number of boulders, the human interpreter had an advantage at recognizing smaller objects comprising a bounding box of less than 7 × 7 pixels. Almost identical performance between the best model and expert analysis was found when classifying boulder density into three classes (0, 1–5, more than 5) over 10,000 m2 areas, with the best performing model reaching an agreement with the human interpretation of 90%.

Geoarchaeological evidence of marshland destruction in the area of Rungholt, present-day Wadden Sea around Hallig Südfall (North Frisia, Germany), by the Grote Mandrenke in 1362 AD

Geophysical and geoarchaeological investigations were carried out in the Wadden Sea of North Frisia (Schleswig-Holstein, Germany) to elucidate major environmental changes that considerably altered the coastal landscape since medieval times. Between the 12th and 14th cent. AD, the present-day tidal flats around the marsh island Hallig Südfall belonged to the historical Edomsharde district and its main settlement Rungholt. For North Frisia, it is well known that during medieval and early modern times, extreme storm surges caused major land losses associated with a massive landward shift of the coastline. Today, cultural traces like remains of dikes, drainage ditches, terps or even plough marks are still visible in the Wadden Sea and provide evidence of the once cultivated marshland.Based on a multi-proxy analysis of sediment cores retrieved from the tidal flat zone around Hallig Südfall and from the Hallig itself, we identified a late medieval paleosol associated with the formerly cultivated marshland most probably belonging to the Edomsharde and local trade centre of Rungholt. Around Hallig Südfall, remains of medieval marsh deposits were found partly eroded and covered by a coarse-grained high-energy deposit including abundant shell debris and artefacts. Based on sedimentological, micropaleontological, geochemical and geochronological data, we conclude that these deposits are associated with the 1st Grote Mandrenke (or St. Marcellus’ flood), an extreme storm surge event in 1362 AD. Our results, for the first time, provide geological evidence of this 1362 AD storm surge for the Wadden Sea of North Frisia. Moreover, marshland on Hallig Südfall dating to the 17th-18th cent. AD was found covered by a thick layer of storm surge sand and shell debris which seems to be associated with one of the major storm event that hit the German North Sea coast in modern times, e.g. the 2nd Grote Mandrenke (or Burchardi flood) in 1634 AD or the Christmas flood in 1717 AD.

Evidence of marine ice-cliff instability in Pine Island Bay from iceberg-keel plough marks.

Marine ice-cliff instability (MICI) processes could accelerate future retreat of the Antarctic Ice Sheet if ice shelves that buttress grounding lines more than 800 metres below sea level are lost. The present-day grounding zones of the Pine Island and Thwaites glaciers in West Antarctica need to retreat only short distances before they reach extensive retrograde slopes. When grounding zones of glaciers retreat onto such slopes, theoretical considerations and modelling results indicate that the retreat becomes unstable (marine ice-sheet instability) and thus accelerates. It is thought that MICI is triggered when this retreat produces ice cliffs above the water line with heights approaching about 90 metres. However, observational evidence confirming the action of MICI has not previously been reported. Here we present observational evidence that rapid deglacial ice-sheet retreat into Pine Island Bay proceeded in a similar manner to that simulated in a recent modelling study, driven by MICI. Iceberg-keel plough marks on the sea-floor provide geological evidence of past and present iceberg morphology, keel depth and drift direction. From the planform shape and cross-sectional morphologies of iceberg-keel plough marks, we find that iceberg calving during the most recent deglaciation was not characterized by small numbers of large, tabular icebergs as is observed today, which would produce wide, flat-based plough marks or toothcomb-like multi-keeled plough marks. Instead, it was characterized by large numbers of smaller icebergs with V-shaped keels. Geological evidence of the form and water-depth distribution of the plough marks indicates calving-margin thicknesses equivalent to the threshold that is predicted to trigger ice-cliff structural collapse as a result of MICI. We infer rapid and sustained ice-sheet retreat driven by MICI, commencing around 12,300 years ago and terminating before about 11,200 years ago, which produced large numbers of icebergs smaller than the typical tabular icebergs produced today. Our findings demonstrate the effective operation of MICI in the past, and highlight its potential contribution to accelerated future retreat of the Antarctic Ice Sheet.

New geophysical evidence for a revised maximum position of part of the NE sector of the Greenland ice sheet during the last glacial maximum

The extent and dynamics of the north-eastern sector of the Greenland ice sheet (GIS) during the last glacial still remain very uncertain, and maximum ice extents to inner-shelf, mid-shelf and outer-shelf positions have been suggested. Here we argue that the margin of the GIS reached the shelf break along part of its NE sector during the last glacial maximum. Swath-bathymetry and sub-bottom profiler data from the outermost part of the Store Koldewey glacial trough reveal the first documentation of moraine ridges/grounding-zone wedges in this area, supporting ice expansion to the shelf break at ~76°N. A complex pattern of retreat moraines in the outer trough reflects a stepwise early deglaciation. It is suggested that this behavior is not in line with a deglaciation triggered by an abrupt sea level rise. According to established glacial geomorphological models this should have resulted in ice lift-off and a sea floor dominated by landforms formed during full-glacial conditions (streamlined bedforms) and ice disintegrations (iceberg plough marks). Instead, formation of the recessional moraines must have involved other mechanisms resulting in a step-wise ice retreat. This could possibly be related to melting of the grounded ice controlled by a temperature increase of the ocean as inferred for other parts of the Greenland ice sheet. An ice front position at the shelf break instead of at the inner or mid-shelf also implies a larger ice volume for this sector of the GIS during the LGM. It also implies a larger contribution of meltwater from GIS during the deglaciation.

Seismic stratigraphy and glacial cycles in the inland passages of the Magallanes Region of Chile, southernmost South America

We present results of a marine geophysical survey that imaged submarine sedimentary and geomorphic features of the main inland channels of the Magallanes Region of Chile, in southernmost South America. This region holds a remarkable terrestrial and marine record of glacial variations in the closest landmass to Antarctica. We report evidence for grounded ice along the main channels associated with two ice lobes that flowed from Cordillera Darwin, part of the Austral Andes, into Central Estrecho de Magallanes and Seno Almirantazgo. Multibeam data show drumlins and glacial lineations in Whiteside Channel the northern continuation of Seno Almirantazgo, and iceberg plough marks in Central Estrecho de Magallanes. Multichannel seismic data show a complex array of seismic facies, interpreted as representing two main types of sedimentary units: glacimarine sediments, corresponding to glacial periods, and pelagic sediments, corresponding to interglacial periods. We find that there are two interglacial-glacial cycles represented in this marine sedimentary record. Chronologically: 1) the youngest glacial unit corresponds to the last regional glaciation (~31–18ka); 2) these passageways deglaciated with the retreat from regional glacial limit ‘D’ (~17–18ka), and 3) there is no marine sedimentary or morphological evidence that the Magallanes glaciers readvanced into the main passageways during the Antarctic Cold Reversal (~14–13ka). These findings suggest that final deglaciation of southernmost South America was driven by the atmospheric and ocean warming that started ~18ka as recorded in Antarctic ice core records and sea surface temperature proxies offshore the Magallanes Region.

Comparative Solid Particle Erosion Characterization of Conventional and Nanostructured Al<sub>2</sub>O<sub>3</sub>-13wt.%TiO<sub>2</sub> Ceramic Coatings Fabricated by Plasma Spraying Process

Abstract. In this work, conventional and nanostructured Al2O3-13wt.%TiO2 coatings were deposited by the plasma spraying technique. The microstructures of the two types of coatings were analyzed, and the solid particle erosion behaviors of the two coatings were comparatively researched in an erosion tester. Meanwhile, the erosion failure mechanisms of the coatings were discussed. The results show that the traditional coating has laminated structure and some pores. However, the nanostructured coating possesses a denser structure and not obviously lamellar-like structure, and exhibits a bimodal microstructure consisted of fully melted regions and partially melted regions. Owing to the compact microstructure and remained nano-particles, the nanostructured coating had a better erosion wear resistance than the conventional coating. Eroded morphology analysis indicates the main erosion mass loss of the coatings is attributed to lamellar spalling of the sprayed splats and fracture of brittle ceramic particles. In addition, the nanostructued coating has some impact craters and plough marks. In terms of the erosion mechanism, the conventional ceramic coating is dominated by brittle erosion, while the nanostructured ceramic coating is dominated by brittle erosion as well as ductile erosion to some extent.

Reconstruction of Holocene environmental changes in two archaeological sites of Calabria (Southern Italy) using an integrated pedological and anthracological approach

This paper focuses on the reconstruction of Holocene climatic and environmental changes in two archaeological sites of southwestern and north-central Calabria (southern Italy). It is based on a comparison of geoarchaeological, pedological and pedoanthracological data from soil profiles in the coastal hilly and inland mountainous surroundings of Palmi and Cecita Lake, respectively. At the Palmi site, the representative soil profile includes settlements and artefacts ranging from late Neolithic to late early Bronze Age and undifferentiated historical epochs. The archaeological record of soils at Cecita spans from late Neolithic/early Eneolithic to Roman ages. At both sites, surface A horizons are affected by repeated plough marks. All soils display some Andisol-like features, related to some volcanic input during soil formation originating from late Pleistocene to Holocene explosive eruptions of the Aeolian Islands. The occurrence of clay coatings, their relict nature and overall dominant phyllosilicate clay minerals in the Neolithic soil horizons of both sites, suggest warm climate conditions with high moisture availability and some seasonal contrast, during the late early-middle Holocene climatic optimum. The post-Neolithic soils show comparable or more abundant amounts of short-range order minerals than phyllosilicates, and no to scarce clay coatings. These features indicate a transition towards (probably cooler) prolonged humid conditions, intercalated by one or more drought episodes. Severe land degradation is recorded between these major climatic phases, indicated by human impact (deforestation and agriculture) and soil erosion. Soil charcoal analysis from Cecita soils provide evidence of these anthropogenic environmental changes, as indicated by the dominance of deciduous oak forest in Neolithic soils, followed by a transition to a mountain pine forest recorded in the Roman soils. A deciduous oak forest characterizes the vegetation at Palmi from the Neolithic onward.

Soil erosion induced by land use changes as determined by plough marks and field evidence in the Aksum area (Ethiopia)

The aim of the research presented here was to analyse soil erosion in response to changes in agricultural and soil conservation practices throughout history. The Aksum area (Tigray, northern Ethiopia) presents favourable conditions for the development of a long-term approach for assessing soil conservation techniques that have been applied for centuries (i.e., since the Aksumite kingdom, 400 BC to 800 AD). These techniques have been maintained until the present day, and parts of the terraced systems of the area are still in use. During the 1970s, social and political events led to a remarkable change in land use patterns, and large arable areas were converted into grazing land, resulting in a significant increase in soil loss. The rates of soil erosion were evaluated based on analyses of the deep scratches (plough marks) left on stones in the soil by the maresha, the ard plough pulled by oxen used in agricultural practices of the area, and the patinas, varnishes and weathering rinds exposed by soil loss after the abandonment of the fields. The study results show average rates of soil erosion of 2.8 t ha −1 y −1 and 65.8 t ha −1 y −1 for the soil conservation conditions under traditional agriculture (long-term observations) and accelerated erosion after abandonment (short-term observations), respectively. A comparison using recently calibrated erosion evaluation techniques conducted to support the field measurements revealed a close correlation between the calculated and recorded data.

Ice sheet grounding and iceberg plow marks on the northern and central Yermak Plateau revealed by geophysical data

We present new evidence for a grounded ice sheet and subsequent erosion by large fields of coherent icebergs for the central and northern Yermak Plateau (80.6°N to 82.2°N). Sediment echosounder and swath bathymetry data were combined with seismic reflection profiles and reveal at least three different glacial events marked by erosional unconformities: (i) An erosional unconformity was observed at ∼70–90 m below seafloor down to depths of more than 850 m present water depth, extending to ∼82°N. The erosional unconformity is overlain by an acoustically chaotic layer of ∼50 m thickness interpreted as a diamicton originating from a grounded ice sheet. The erosional unconformity and the overlying diamicton can be correlated to the overconsolidated sediments found at ODP Site 910 at a sediment depth between ∼19 and 70–95 m. The oldest sediments just above the overconsolidated sediments are of late Early Pleistocene age (MIS19/20) and provide a minimum age for the grounding event. (ii) Parallel to sub-parallel mega-scale lineations are observed on large parts of the plateau west and northeast of the Sverdrup Bank at water depths between 725 and 850 m. These lineations are mainly oriented NNE-SSW and were quite likely formed by the keels of deep-draft, mega-scale tabular icebergs entrapped in a coherent mass of icebergs and sea ice. The lineations are of late Middle Pleistocene age. (iii) Smaller-scale curvilinear plow marks were found in the southernmost part of our study area at water depths between 640 and 775 m. These were possibly caused by single icebergs and are of Late Pleistocene age. Iceberg scours are also found on three basement heights on the Yermak Plateau. These, however, cannot be assigned to specific events; they might as well originate from additional glacial phases. The western (at >850 m water depth) and eastern (at >1000–1200 m water depth) flanks of the Yermak Plateau are relatively featureless, and indicate the maximum depth of a grounded ice sheet and of iceberg armadas probably entrapped in sea ice.

Plough marks as a tool to assess soil erosion rates: A case study in Axum (Ethiopia)

Abstract From the antiquity, the hilly landscape around the city of Axum in northern Ethiopia has been terraced and extensively used for agriculture purposes. Impacts of the “ard” plough on protruding and/or buried boulder at a depth less than the tillage depth produce scratches on their sides or their top. The spatial relationship among plough marks and rock surface orientations gives information on the ploughing direction, whereas the relative height from the present ground surface to the top of the marks and information on the age of cultivation can be used to assess soil loss rates. Parameters to define plough mark orientation were defined and measured in the field on boulders with plough marks within a study terrace located in an archaeological area with an approx of 2040 year age. These parameters are height from the ground, dip, slope and frequency. The measurements also show that the initial terrace slope was steeper than the present one confirming the effectiveness of the traditional terracing practice in soil conservation because of the low soil erosion rates assessed over a so large time interval. For the main time intervals of the Axumite history, corresponding to the rise and fall of the Axumite civilization and to variable conditions of human pressure on the land, the maximum erosion rates inferred are of the order of 3.4 Mg ha − 1 y − 1 . This result is compared with erosion rates calculated with other methods reported in literature (e.g. PSIAC) and field measurement on terraces in the same region leading to values coinciding with those obtained by the plough marks method.

Giant iceberg plow marks at more than 1 km water depth offshore West Greenland

During a recent (2006) cruise of RV ‘Dana’ high resolution side-scan sonar and sub-bottom profiling was carried out on selected shelf and slope transects offshore Disko Bugt, central West Greenland. Available commercial seismic data from the margin indicate here irregular seabed morphology with erosional features locally extending down to c. 1100 m water depth. The newly acquired side-scan sonar data reveal the presence of giant iceberg plow marks extending (sub)parallel to the slope between about 800 and 1085 m water depth. The height difference between bottom of the scours and rim crest is up to 40 m. The largest plow marks are about 750 m wide. To date no observed modern icebergs including those from Antarctica have drafts in excess of c. 500 m. Taking into account maximum glacial sea level lowering of c. 120 m, the paleo-iceberg keel depth was at least 950 m. Due to the presence of the relatively shallow (< 700 m) sill of Davis Strait to the south, calving of these paleo-icebergs is thought to have occurred from an ice margin in the Baffin Bay region (Jakobshavn Isbræ paleo-ice stream?). The depth of occurrence (> 1000 m) and dimensions of the plow marks are concluded to be exceptional, and comparable to glacial scouring features reported from the Arctic Ocean.

Evidence for Late Pleistocene ice stream activity in the Witch Ground Basin, central North Sea, from 3D seismic reflection data

Buried submarine landforms mapped on 3D reflection seismic data sets provide the first glacial geomorphic evidence for glacial occupation of the central North Sea by two palaeo-ice-streams, between 58–59°N and 0–1°E. Streamlined subglacial bedforms (mega-scale glacial lineations) and iceberg plough marks, within the top 80 m of the Quaternary sequence, record the presence and subsequent break-up of fast-flowing grounded ice sheets in the region during the late Pleistocene. The lengths of individual mega-scale glacial lineations vary from ∼5 to ∼20 km and the distance between lineations typically ranges from 100 to 1000 m. The lineations incise to a depth of 10–12 m, with trough widths of ∼100 m. The most extensive and best-preserved set of lineations, is attributed to the action of a late Weichselian ice stream which either drained the NE sector of the British–Irish ice sheet or was sourced from the SW within the Fennoscandian ice sheet. The 30–50 km wide palaeo ice-stream is imaged along its flow direction for 90 km, trending NW–SE. An older set of less well-preserved lineations is interpreted as an earlier Weichselian or Saalian ice-stream, and records ice flow in an SW–NE orientation. Cored sedimentary records, tied to 3D seismic observations, support grounded ice sheet coverage in the central North Sea during the last glaciation and indicate that ice flowed over a muddy substrate that is interpreted as a deformation till. The identification of a late Weichselian ice stream in the Witch Ground area of the North Sea basin provides independent geomorphic evidence in support of ice-sheet reconstructions that favour complete ice coverage of the North Sea between Scotland and Norway during the Last Glacial Maximum.