Iceberg Scouring Research Articles

The Paleozoic Hydrocarbon System in the Gotland Basin (Central Baltic Sea) Leaks

AbstractThe Baltic Basin is known for its numerous Paleozoic hydrocarbon reservoirs. There is published evidence that hydrocarbons are leaking from the seafloor, however, little is known about the hydrocarbon migration pathways from Paleozoic source and reservoir rocks toward the seafloor and their escape structures. To investigate these processes, we utilize a new set of multibeam, parametric sediment sub‐bottom profiler and 2D seismic reflection data. The integrated analysis of seismic profiles, diffraction imaging and bathymetric maps allow to identify a hydrocarbon migration system within Silurian and Devonian strata that consists of layer parallel and updip migration beneath sealing layers, migration across seals along faults, and seafloor escape structures in form of elongated depressions. The general migration trend is directed updip, from the Paleozoic reservoirs below the southeastern Baltic Sea toward the Gotland Depression in the northwest. The locations of the hydrocarbon escape structures at the seafloor and their elongated shape are mainly controlled by the regional geological setting of outcropping Paleozoic layers. In addition, iceberg scouring may have facilitated hydrocarbon migration through the Quaternary deposits. The description of this hydrocarbon migration system fills the gap between the known reservoirs and the observed hydrocarbon accumulations and seepages. With regard to potential Carbon Capture and Storage projects, the identification of this hydrocarbon migration system is of great importance, as potential storage sites may be leaking.

Reassessing a glacial landscape developed during terminal glaciation of the Late Paleozoic Ice Age in Uruguay

Whalebacks, roche moutonnées, and S-forms carved on Ediacaran granitoids near Cerro de las Cuentas, Uruguay, along with overlying diamictites, siltstones, and sandstones displaying soft-sediment grooved and striated surfaces in the Pennsylvanian San Gregorio Formation, record the glacial to post-glacial transition in the linked Norte, southern Paraná and Chaco-Paraná basins of Uruguay, Brazil, and Argentina respectively. Early authors reported these features resulted from subglacial abrasion and deposition as lodgement tills and glaciotectonites. Our re-examination reveals a nuanced setting with changing ice thicknesses, subglacial kinematics, and ice proximal glaciomarine dynamics associated with advance and retreat of an ice stream, or multiple advances of the Uruguayan Ice lobe, during glaciation of the Late Paleozoic Ice Age (LPIA) in these basins. The preserved landforms indicate temperate glacial conditions. Whalebacks formed under 1.6 to 2.5 km-thick ice and likely formed when the lobe extended across the Uruguayan and Rio Grande do Sul shields into the adjacent Paraná Basin. Previously unidentified m-scale roches moutonnées cut into one whaleback developed under thinner ice where reduced basal pressure allowed for the opening of air and water-filled cavities, thus facilitating quarrying on the lee side of basement bumps. S-forms provide additional evidence for the occurrence of subglacial waters, indicating that the basal ice was at or above its pressure melting point. The lower meter of the overlying strata consists of interstratified trace fossil-bearing, laminated siltstones; thin-bedded diamictites; and current-rippled sandstones. Trace fossils belonging to the Mermia ichnofacies within the basal siltstones, as well as acritarchs in the overlying siltstones, suggest that these sediments were deposited in ice-proximal subaqueous settings with contributions from meltwater discharge. Graded siltstone laminae suggest settling from suspension likely from meltwater plumes, while thin-bedded diamictites were deposited either as debris flows or as two-component sedimentation with fines settling from suspension and coarser particles introduce as iceberg-rafted dropstones. Current-rippled sandstones indicate the occurrence of underflow currents. Soft-sediment troughs, grooves, and striations cutting these sediments display curved and sinuous paths with some features oriented perpendicular, and one oriented opposite to the overall trend. They contain marginal and terminal berms typical of iceberg scour marks suggesting transit across the area by icebergs calving from a tidewater ice front located to the SE.

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.

Mapping intertidal macrophytes in fjords in Southwest Greenland using Sentinel-2 imagery

Changes in the distribution of coastal macrophytes in Greenland, and elsewhere in the Arctic are difficult to quantify as the region remains challenging to access and monitor. Satellite imagery, in particular Sentinel-2 (S2), may enable large-scale monitoring of coastal areas in Greenland but its use is impacted by the optically complex environments and the scarcity of supporting data in the region. Additionally, the canopies of the dominant macrophyte species in Greenland do not extend to the sea surface, limiting the use of indices that exploit the reflection of near-infrared radiation by vegetation due to its absorption by seawater. Three hypotheses are tested: I) 10-m S2 imagery and commonly used detection methods can identify intertidal macrophytes that are exposed at low tide in an optically complex fjord system in Greenland impacted by marine and land terminating glaciers; II) detached and floating macrophytes accumulate in patches that are sufficiently large to be detected by 10-m S2 images; III) iceberg scour and/or turbid meltwater runoff shape the spatial distribution of intertidal macroalgae in fjord systems with marine-terminating glaciers. The NDVI produced the best results in optically complex fjord systems in Greenland. 12 km2 of exposed intertidal macrophytes were identified in the study area at low tide. Floating mats of macrophytes ranged in area from 400 m2 to 326,800 m2 and were most common at the mouth of the fjord. Icebergs and turbidity appear to play a role in structuring the distribution of intertidal macrophytes and the retreat of marine terminating glaciers could allow macrophytes cover to expand. The challenges and solutions presented here apply to most fjords in Greenland and, therefore, the methodology may be extended to produce a Greenland-wide estimate of intertidal macrophytes.

Stratigraphic and palaeo-geomorphological evidence for the glacial-deglacial history of the last British-Irish Ice Sheet in the north-western Irish Sea

During its maximum extent around 25–23 ka BP, the British-Irish Ice Sheet extended to near the present-day shelf break with a large ice stream, the Irish Sea Ice Stream, occupied much of the present-day Celtic and Irish Seas. The different episodes of advance and retreat of the ice sheet have been extensively constrained onshore, with models based on feature characterisation and dating helping to understand the retreat pattern of the ice sheet. Offshore, glacial geomorphologies in the Irish Sea have been mostly recognised on the United Kingdom side but remains poorly constrained on the Irish side. In this paper, based on the analysis of an extensive seismic dataset, an update of the stratigraphic model of the northern Irish Sea, with new sub-units, is proposed with a mapping of newly discovered buried geomorphology. Characterisation of the geomorphology, including megascale glacial lineations, subglacial meltwater channels, moraines, and iceberg scours, has been used to extend the constraints on ice sheet retreat offshore. The transition from late glacial to marine setting has been constrained based on the mapping of marine sediment subunits and their terminations. This paper brings new constraints offshore, in a previously understudied area, and synthesises all the results into an updated conceptual model highlighting stratigraphic units succession and associated processes linked to geomorphology, within the context of a rapidly retreating ice stream.

Northeast Greenland: ice‐free shelf edge at 79.4°N around the Last Glacial Maximum 25.5–17.5 ka

The size of the last glacial ice sheet on the Northeast (NE) Greenland shelf and its interaction with ocean circulation have been the subject of debate. Here we provide insights into the extent of the ice sheet around the Last Glacial Maximum (LGM) and investigate timing and strength of changes in the flow of Atlantic Water. The study is based on a multiproxy investigation of a marine sediment core, gravity core DA17‐NG‐ST01‐019G, from 323‐m water depth at the NE Greenland shelf edge at 79.4°N. We present benthic and planktic foraminiferal distribution data, AMS‐14C dates, sedimentological (ice‐rafted debris (IRD) and grain sizes), and geochemical (XRF) data in combination with geophysical (sub‐bottom profiler) data. The oldest sediments at the study site are dated to 25.5–17.5 ka, encompassing the time frame from the beginning of the LGM to the early deglaciation. This part is overlain by sediments from the late deglaciation and Holocene. The deposits dating from the LGM are very rich in both planktic and benthic foraminifera and macrofossils of excellent preservation. The faunas show that the site generally was affected by a strong flow of relatively warm subsurface Atlantic Water during the LGM and Early Holocene. Conditions turned more polar with cold bottom water flow in the Middle–Late Holocene (c. 7.5 ka to Recent) with presence of mainly agglutinated benthic foraminiferal species. Our data from the LGM also indicate that the deposits were mixed by iceberg scouring, confirmed by the geophysical data showing extensive ploughing of the sediments on the outer shelf area. The results further indicate that the Greenland Ice Sheet did not reach to the edge of the NE Greenland shelf at 79.4°N during the LGM 24–18 ka.

Morphological variation of kelps (Alaria esculenta, cf. Laminaria digitata, and Saccharina latissima) in an Arctic glacial fjord

Kelp forests supply many important ecosystem services that often are dependent on kelp morphological characteristics. Understanding the relationship between environmental factors and the morphological response of macroalgae is essential. The main aim of this study was to investigate the impact of factors associated with glacial activity and depth on the variability of dominant kelp species in the Arctic fjord, Hornsund. A total of 347 individuals of three kelp species (Alaria esculenta, cf. Laminaria digitata, Saccharina latissima) were collected in July 2003 at three sites located at different distances from glacier outflows (two sites under the influence of active tidewater glaciers and one site without any glacial impact) and at two depths (5 and 10 m). The length and wet weight of the thallus, blade and stipe were measured. The morphological response to environmental conditions was complex and species-specific. At one glacier-proximal site, light limitations due to seasonally increasing mineral particle flux did not affect kelp morphology, while iceberg scouring could have caused a reduction in kelp size and biomass at another site. Depth had a significant effect on the morphological traits of A. esculenta and S. latissima, which tended to have longer and heavier stipes at greater depths, most likely to improve light capture. No effect of depth on morphological traits of cf. L. digitata was noted. Regression models between thallus biomass and length, constructed for the kelp species that were studied, can be used in non-destructive kelp biomass estimations.

The macro-and megabenthic fauna on the continental shelf of Prydz Bay, east Antarctica

Ten triangle trawls in Prydz Bay were collected from 97 m to 638 m. A total of 206 species of macro- and mega-benthos were identified, belonging to 9 phyla and 118 families, of which pycnogonids (41 species), gammarid amphipods (38 species) and echinoderms (36 species) were the most dominant groups. The species richness per station varied from 1 to 92. The abundance of macro- and mega-benthos (1 × 10−3-0.24 Ind./m2) was low, compared to that in the southeastern Weddell Sea (131–1.28 × 103 Ind./m2) and South Shetland waters (160–4.38 × 103 Ind./m2). The results were similar to the Amundsen Sea abundances (1.10 × 10−3-0.40 Ind./m2) at comparable depths and in the Antarctic deep sea. The macrobenthic community had 2 types, Sessile Suspension Feeders with Associated fauna - dominated by sponges (SSFA-SPO) and mobile deposit feeders, infauna and grazers - epifauna dominated (MOIN-EPI). The macrobenthic community in Prydz Bay showed a dispersed patchy distribution pattern which may result from the Antarctic water mass and iceberg scouring.

Response to concerns regarding the role of Antarctic blue carbon habitats in a global context

We address Hunter (2021) concerns regarding our recent contribution to Global Change Biology on the quantification of blue carbon pathways contributing to negative feedback on climate change following glacier retreat in West Antarctic fjords (Zwerschke et al 2021).

Intermediate ice scour disturbance is key to maintaining a peak in biodiversity within the shallows of the Western Antarctic Peninsula

Climate-related disturbance regimes are changing rapidly with profound consequences for ecosystems. Disturbance is often perceived as detrimental to biodiversity; however, the literature is divided on how they influence each other. Disturbance events in nature are diverse, occurring across numerous interacting trophic levels and multiple spatial and temporal scales, leading to divergence between empirical and theoretical studies. The shallow Antarctic seafloor has one of the largest disturbance gradients on earth, due to iceberg scouring. Scour rates are changing rapidly along the Western Antarctic Peninsula because of climate change and with further changes predicted, the Antarctic benthos will likely undergo dramatic shifts in diversity. We investigated benthic macro and megafaunal richness across 10–100 m depth range, much of which, 40–100 m, has rarely been sampled. Macro and megafauna species richness peaked at 50–60 m depth, a depth dominated by a diverse range of sessile suspension feeders, with an intermediate level of iceberg disturbance. Our results show that a broad range of disturbance values are required to detect the predicted peak in biodiversity that is consistent with the Intermediate Disturbance Hypothesis, suggesting ice scour is key to maintaining high biodiversity in Antarctica’s shallows.

Late Pleistocene iceberg scouring in the north-eastern Baltic Sea, west of Estonia

During the last glacial period, the western sea area of Estonia in the northern Baltic Sea was covered by the Fennoscandian continental ice sheet. High-resolution multibeam bathymetric images of the seafloor reveal widespread linear and curved depressions, interpreted as iceberg scours (ploughmarks) that were produced by ploughing and grounding icebergs during and soon after the final ice retreat from the area. Two main populations (A and B) of scours are identified, formed either on top of the acoustic substratum (bedrock or coarse-grained glacial deposits) or on top of the superimposed glaciolacustrine and post-glacial sediments that are exposed on the seafloor. Both populations have similar characteristics, being on average 780 m long, 54 m wide and 1.6 m deep. Most of the scours are linear, with an average NE-SW orientation for Population A, and an average ENE-WSW orientation for Population B. The scour patterns indicate a partially grounded ice sheet in the shallower parts of the study area. We suggest that the period of most intensive iceberg calving and scouring lasted for approximately 1100 years, from 13.2 to 12.3 kyr BP.

Responses of Southern Ocean Seafloor Habitats and Communities to Global and Local Drivers of Change

Knowledge of life on the Southern Ocean seafloor has substantially grown since the beginning of this century with increasing ship-based surveys and regular monitoring sites, new technologies and greatly enhanced data sharing. However, seafloor habitats and their communities exhibit high spatial variability and heterogeneity that challenges the way in which we assess the state of the Southern Ocean benthos on larger scales. The Antarctic shelf is rich in diversity compared with deeper water areas, important for storing carbon (“blue carbon”) and provides habitat for commercial fish species. In this paper, we focus on the seafloor habitats of the Antarctic shelf, which are vulnerable to drivers of change including increasing ocean temperatures, iceberg scour, sea ice melt, ocean acidification, fishing pressures, pollution and non-indigenous species. Some of the most vulnerable areas include the West Antarctic Peninsula, which is experiencing rapid regional warming and increased iceberg-scouring, subantarctic islands and tourist destinations where human activities and environmental conditions increase the potential for the establishment of non-indigenous species and active fishing areas around South Georgia, Heard and MacDonald Islands. Vulnerable species include those in areas of regional warming with low thermal tolerance, calcifying species susceptible to increasing ocean acidity as well as slow-growing habitat-forming species that can be damaged by fishing gears e.g., sponges, bryozoan, and coral species. Management regimes can protect seafloor habitats and key species from fishing activities; some areas will need more protection than others, accounting for specific traits that make species vulnerable, slow growing and long-lived species, restricted locations with optimum physiological conditions and available food, and restricted distributions of rare species. Ecosystem-based management practices and long-term, highly protected areas may be the most effective tools in the preservation of vulnerable seafloor habitats. Here, we focus on outlining seafloor responses to drivers of change observed to date and projections for the future. We discuss the need for action to preserve seafloor habitats under climate change, fishing pressures and other anthropogenic impacts.

Can Antarctica's shallow zoobenthos 'bounce back' from iceberg scouring impacts driven by climate change?

All coastal systems experience disturbances and many across the planet are under unprecedented threat from an intensification of a variety of stressors. The West Antarctic Peninsula is a hotspot of physical climate change and has experienced a dramatic loss of sea-ice and glaciers in recent years. Among other things, sea-ice immobilizes icebergs, reducing collisions between icebergs and the seabed, thus decreasing ice-scouring. Ice disturbance drives patchiness in successional stages across seabed assemblages in Antarctica's shallows, making this an ideal system to understand the ecosystem resilience to increasing disturbance with climate change. We monitored a shallow benthic ecosystem before, during and after a 3-year pulse of catastrophic ice-scouring events and show that such systems can return, or bounce back, to previous states within 10years. Our long-term data series show that recovery can happen more rapidly than expected, when disturbances abate, even in highly sensitive cold, polar environments.

Iceberg disturbance to benthic communities in McMurdo Sound, Antarctica

Abstract On the continental shelf of the Antarctic the major disturbance to benthic ecosystems is from iceberg scouring; however, this is based on observations from the Peninsula region. We combine observation and experimentation in the McMurdo Sound region of the Ross Sea to determine if community recovery patterns there are similar to those in better-studied Antarctic regions, and if local immigration is an important factor in recovery dynamics. We found that regardless of habitat differences in depth, substrate, and oceanographic setting, iceberg disturbance strongly impacted benthic communities in McMurdo Sound. Notably, in shallow water (<30 m) where anchor ice is an annual disturbance, both the benthic communities and recovery processes were more variable than at deeper locations. A manipulative experiment performed in a shallow area indicated that recruitment might be more important than immigration to infaunal community recovery. We conclude that whilst disturbance frequency influences dominant epifauna, recovery from iceberg disturbance is a slow ecological progression that is dependent on the extremely inconsistent recruitment processes of the high Antarctic benthic ecosystem.

Spatial and temporal dynamics of Antarctic shallow soft-bottom benthic communities: ecological drivers under climate change

BackgroundMarine soft sediments are some of the most widespread habitats in the ocean, playing a vital role in global carbon cycling, but are amongst the least studied with regard to species composition and ecosystem functioning. This is particularly true of the Polar Regions, which are currently undergoing rapid climate change, the impacts of which are poorly understood. Compared to other latitudes, Polar sediment habitats also experience additional environmental drivers of strong seasonality and intense disturbance from iceberg scouring, which are major structural forces for hard substratum communities. This study compared sediment assemblages from two coves, near Rothera Point, Antarctic Peninsula, 67°S in order to understand the principal drivers of community structure, for the first time, evaluating composition across all size classes from mega- to micro-fauna.ResultsMorpho-taxonomy identified 77 macrofaunal species with densities of 464–16,084 individuals m−2. eDNA metabarcoding of microfauna, in summer only, identified a higher diversity, 189 metazoan amplicon sequence variants (ASVs) using the 18S ribosomal RNA and 249 metazoan ASVs using the mitochondrial COI gene. Both techniques recorded a greater taxonomic diversity in South Cove than Hangar Cove, with differences in communities between the coves, although the main taxonomic drivers varied between techniques. Morphotaxonomy identified the main differences between coves as the mollusc, Altenaeum charcoti, the cnidarian Edwardsia sp. and the polychaetes from the family cirratulidae. Metabarcoding identified greater numbers of species of nematodes, crustaceans and Platyhelminthes in South Cove, but more bivalve species in Hangar Cove. There were no detectable differences in community composition, measured through morphotaxonomy, between seasons, years or due to iceberg disturbance.ConclusionsThis study found that unlike hard substratum communities the diversity of Antarctic soft sediment communities is correlated with the same factors as other latitudes. Diversity was significantly correlated with grain size and organic content, not iceberg scour. The increase in glacial sediment input as glaciers melt, may therefore be more important than increased iceberg disturbance.

Asexual reproduction and heterozygote selection in an Antarctic demosponge (Stylocordyla chupachus, Suberitida)

Antarctic bottoms harbor stable, benthic communities, subjected to low temperatures. Environmental stability may promote the asexual (clonal) reproduction of sponges to maintain adapted genotypes to those particular conditions. Stylocordyla chupachups forms patchy populations across the Antarctic continental shelf. Individuals are mostly similar in size without distinct cohorts, which indicates fast growth of the new recruits. Settlement of incubated (clonal?) functional sponges may accelerate sponge growth and success at early colonization phases. To analyze the weight of clonal reproduction in the species, a genetic study was performed on three close populations using eight polymorphic microsatellite loci that were designed from massive sequencing. The three study populations showed a relatively low genetic diversity and low loci polymorphism (from 2 to 6 alleles). The estimators of genetic structure, the Analysis of the Molecular Variance (AMOVA), and the presence of private alleles indicated low but significant structure between the populations. A relatively high rate of asexual reproduction (ca. 25% of the individuals) was detected. The program MLGsim found five identical multilocus genotypes (MLGs) with an asexual origin. An excess of heterozygotes (in five out of the eight loci genotyped) was found, which suggests a positive selection mechanism for heterozygotes. The relatively high rates of asexual reproduction may be the result of adaptation to the environmental stability, while heterozygote selection would help maintain some genetic diversity in the populations. S. chupachups has been reported to be one of the first sponge species recolonizing bare areas resulting from iceberg scouring, which indicates a high species fitness and adaptation to Antarctic bottoms. Two out of the three study populations showed bottleneck, which may indicate a recent founder effect and supports the pioneer nature of this species.

Rapid Quaternary subsidence in the northwestern German North Sea

3D and 2D seismic data reveal the base-reflection of the Quaternary in the northwestern German North Sea locally at depths of more than 1000 m. This indicates extremely fast subsidence, with a rate of up to 480 m/Ma during the Quaternary, resulting in a NNW-SSE oriented sedimentary depocentre. Distinct iceberg scour marks, identified in 3D seismic data are used to calibrate quantitative subsidence analysis and to document shallow marine conditions during the Quaternary interglacials. Previously, a number of mechanisms have been proposed to explain the Quaternary subsidence. Here we show that compaction and load-induced subsidence alone explain about 75% of the observed Quaternary subsidence. However, a certain portion of the subsidence needs additional processes to be invoked. The extensive seismic dataset interpreted here makes it possible to exclude a phase of renewed tectonic activity as the origin of the subsidence anomaly. From the orientation and extent of the depocentre, lithosphere buckling and subsidence due to salt movement are considered unlikely. Possibly a post-glacial collapse after the retreat of glaciers in the North Sea Basin, local lower crustal flow, or dynamic topography or a combination of these processes contributed to the residual subsidence.

Element concentrations of environmental concern in surface sediment samples from a broad marine area of 25 de Mayo (King George) Island, South Shetland Islands

Western Antarctica (WA) constitutes the area with the highest human presence in the white continent and also the region where the effects of global warming are more evident worldwide. Such human presence represents a potential risk of pollution with both, organic and inorganic contaminants. Global warming also could modify dynamics and transport of the pollutants, increasing summer water runoff, ice melting and iceberg scouring. Under this fast-changing scenario, knowledge about the concentration of contaminants is essential to evaluate the environmental status of this ecologically relevant area. In this work, we performed the first regional-scale monitoring of 9 trace elements (Cr, Co, Ni, Cu, Zn, As, Pb, Cd and Hg), as well as Fe and Mn, in surface sediment from 64 sites comprising six different areas in Maxwell Bay, 25 de Mayo (King George) Island. Target elements were quantified in surface sediment samples (20–30 m depth) obtained during two summer Antarctic expeditions: 2010/11 and 2011/12 by inductively coupled plasma linked to a quadrupole mass spectrometer (ICP-MS). Based on the average values observed for the reference areas, baseline values were defined for the studied region. A regional enrichment in Cu (compared with the global mean upper crust) was observed and related to the widespread mineralization of volcanic rocks. The most anthropized area (South Fildes) mainly showed sediment class 3 (moderately polluted) for Pb, Cd and Hg with a number samples revealing some highly contaminated hot spots. Although elemental contamination in some samples close to scientific stations or sites where logistic operations were evidenced, a pollution pattern was not clearly identified. The present work represents the first regional-scale attempt to define the baseline values and the anthropic impacts in this region of the WA and also provides the first data about Hg concentration in surface sediment of the study area.

A Persistent Norwegian Atlantic Current Through the Pleistocene Glacials

AbstractChanges in ocean‐circulation regimes in the northern North Atlantic and the Nordic Seas may affect not only the Arctic but potentially hemispheric or even global climate. Therefore, unraveling the long‐term evolution of the North Atlantic Current‐Norwegian Atlantic Current system through the Pleistocene glaciations could yield useful information and climatological context for understanding contemporary changes. In this work, ~50,000 km2 of 3‐D seismic reflection data are used to investigate the Pleistocene stratigraphy for evidence of paleo‐oceanographic regimes on the mid‐Norwegian margin since 2.58 Ma. Across 33 semicontinuous regional paleo‐seafloor surfaces ~17,500 iceberg scours have been mapped. This mapping greatly expands our spatiotemporal understanding of currents and iceberg presence in the eastern Nordic Seas. The scours display a dominant southwest‐northeast trend that complements previous sedimentological and numerical modeling studies that suggest northward‐flowing currents in the Norwegian Sea during the Pleistocene. This paleo‐oceanographic study suggests that through many of the Pleistocene glaciations, the location of surface ocean currents in the Norwegian Sea and, by extension, the eastern North Atlantic, were broadly similar to the present.

Bathymetric distribution pattern in Antarctic benthic hydroids

Benthic hydroids are an important component of the Antarctic benthic ecosystem. This is characterised by extreme environmental conditions that undoubtedly affect organism distribution. In some cases, these conditions are related to depth (e.g. anchor ice or iceberg scouring). The Antarctic depth profile has special characteristics that reflect the depression of the continental crust by isostatic loading as well as glacial erosion during ice sheet expansion. Indeed, the Antarctic continental shelf is much deeper than others elsewhere in the world. This fact, along with the dynamic ice formation, affects a priori the bathymetric distribution of Antarctic benthic hydroids. This was first studied by Stepanjants in 1979, and later by Pena Cantero, in 2004, who summarised all available bathymetric information for Antarctic benthic hydroids, and established a series of bathymetric groups according to ecological features. The aim of this study was to review and update the present knowledge of bathymetric distribution of Antarctic benthic hydroids with data gathered in recent years in order to define hydrozoan bathymetric assemblages and depth-indicator species. To this end, all the valid records from the Antarctic (including the Scotia Arc) were compiled. Using similarity matrices (Sorensen coefficient), hierarchical clusters with SIMPROF test were performed. The results of the present study provide the division of the bathymetric profile into three main zones. The first one, which corresponds to the Shelf, extends from 0 to 700 m, and is clearly characterised by Eudendriidae and Campanulinidae. The second one, named Slope, associated with the continental slope, extends from 700 to 1500 m, and is characterised by a few exclusive species, like Halisiphonia prolifica Pena Cantero, 2014. Finally, the third zone, here named Abyss, extends beyond 2000 m, and includes a few species [e.g. Clathrozoella abyssalis Pena Cantero, Vervoort & Watson, 2003 (3083 m)]. The results also indicate a further division of the Shelf into three sub-zones: the anchor ice, the upper shelf and the lower shelf. The results show distinct boundaries between divisions, which could be linked to environmental factors, some of them likely related to the influence of ice.