West Greenland Shelf Research Articles

Seasonal Variability in Baffin Bay

AbstractThree dominant characteristics and underlying dynamics of the seasonal cycle in Baffin Bay are discussed. The study is based on a regional, high‐resolution coupled sea ice‐ocean numerical model that complements our understanding drawn from observations. Subject to forcing from the atmosphere, sea ice, Greenland, and other ocean basins, the ocean circulation exhibits complex seasonal variations that influence Arctic freshwater storage and export. The basin‐scale barotropic circulation is generally stronger (weaker) in summer (winter). The interior recirculation (∼2 Sv) is primarily driven by oscillating along‐topography surface stress. The volume transport along the Baffin Island coast is also influenced by Arctic inflows (∼0.6 Sv) via Smith Sound and Lancaster Sound with maximum (minimum) in June‐August (October‐December). In addition to the barotropic variation, the Baffin Island Current also has changing vertical structure with the upper‐ocean baroclinicity weakened in winter‐spring. It is due to a cross‐shelf circulation associated with spatially variable ice‐ocean stresses that flattens isopycnals. Greenland runoff and sea ice processes dominate buoyancy forcing to Baffin Bay. Opposite to the runoff that freshens the west Greenland shelf, stronger salinification by ice formation compared to freshening by ice melt enables a net densification in the interior of Baffin Bay. Net sea ice formation in the past 30 years contributes to ∼25% of sea ice export via Davis Strait. The seasonal variability in baroclinicity and water mass transformation changes in recent decades based on the simulation.

Shifting sediment depocenters track ice-margin retreat in Baffin Bay

Reconstructing the depositional history of Baffin Bay allows insights into the deglacial retreat of the Laurentide, Innuitian, and Greenland ice sheets from their maximum extent during the Last Glacial Maximum. Here, we present radiocarbon-controlled sedimentation rates from Baffin Bay based on 79 sediment cores to assess spatio-temporal variabilities in sediment deposition since the Last Glacial Maximum. This comprehensive dataset reveals that until ~15,000 years ago the deep basin and slopes were the dominant active sediment depocenters along most margins of Baffin Bay, suggesting prolonged ice-margin stability near the shelf edge, much longer than previously suggested. Between 13,000-11,000 years ago, most depocenters shifted quickly from the slope to the inner shelf, evidencing a very rapid landward ice-sheet retreat. The sedimentation rate-based mean erosion rates (0.17 and 0.08 millimeters/year) derived from the West Greenland Shelf underscore the high erosion capacity of the western Greenland Ice Sheet draining into Baffin Bay.

Satellite-Derived Lagrangian Transport Pathways in the Labrador Sea

The offshore transport of Greenland coastal waters influenced by freshwater input from ice sheet melting during summer plays an important role in ocean circulation and biological processes in the Labrador Sea. Many previous studies over the last decade have investigated shelfbreak transport processes in the region, primarily using ocean model simulations. Here, we use 27 years of surface geostrophic velocity observations from satellite altimetry, modified to include Ekman dynamics based on atmospheric reanalysis, and virtual particle releases to investigate seasonal and interannual variability in transport of coastal water in the Labrador Sea. Two sets of tracking experiments were pursued, one using geostrophic velocities only, and another using total velocities including the wind effect. Our analysis revealed substantial seasonal variability, even when only geostrophic velocities were considered. Water from coastal southwest Greenland is generally transported northward into Baffin Bay, although westward transport off the west Greenland shelf increases in fall and winter due to winds. Westward offshore transport is increased for water from southeast Greenland so that, in some years, water originating near the east Greenland coast during summer can be transported into the central Labrador Sea and the convection region. When wind forcing is considered, long-term trends suggest decreasing transport of Greenland coastal water during the melting season toward Baffin Bay, and increasing transport into the interior of the Labrador Sea for water originating from southeast Greenland during summer, where it could potentially influence water column stability. Future studies using higher-resolution velocity observations are needed to capture the role of submesoscale variability in transport pathways in the Labrador Sea.

Moored Observations of the West Greenland Coastal Current along the Southwest Greenland Shelf

Abstract We present the first continuous mooring records of the West Greenland Coastal Current (WGCC), a conduit of fresh, buoyant outflow from the Arctic Ocean and the Greenland Ice Sheet. Nearly two years of temperature, salinity, and velocity data from 2018 to 2020 demonstrate that the WGCC on the southwest Greenland shelf is a well-formed current distinct from the shelfbreak jet but exhibits strong chaotic variability in its lateral position on the shelf, ranging from the coastline to the shelf break (50 km offshore). We calculate the WGCC volume and freshwater transports during the 35% of the time when the mooring array fully bracketed the current. During these periods, the WGCC remains as strong (0.83 ± 0.02 Sverdrups; 1 Sv ≡ 106 m3 s−1) as the East Greenland Coastal Current (EGCC) on the southeast Greenland shelf (0.86 ± 0.05 Sv) but is saltier than the EGCC and thus transports less liquid freshwater (30 × 10−3 Sv in the WGCC vs 42 × 10−3 Sv in the EGCC). These results indicate that a significant portion of the liquid freshwater in the EGCC is diverted from the coastal current as it rounds Cape Farewell. We interpret the dominant spatial variability of the WGCC as an adjustment to upwelling-favorable wind forcing on the West Greenland shelf and a separation from the coastal bathymetric gradient. An analysis of the winds near southern Greenland supports this interpretation, with nonlocal winds on the southeast Greenland shelf impacting the WGCC volume transport more strongly than local winds over the southwest Greenland shelf.

Impact, Responses and Future Prediction of Climate Change on the Phenology of Jellyfish

Climate variation can be devastating to marine life. This essay mainly focuses on how jellyfish cope with changes in ocean temperature and whether they benefit or are also affected by the population's decline. In terms of whether jellyfish benefit from climate change, this paper focuses on two case studies: the mass propagation of jellyfish in the coastal areas of China and the abundance change of jellyfish in the Bering Sea area. The results conclude that jellyfish are increasing because of climate change. However, for the case study on the decrease of the race caused by the influence of jellyfish, this paper only found that it occurred in Humboldt Current, West Greenland Shelf, and Oyashio Current. Through comparative study, this paper demonstrates that jellyfish mainly benefited from climate variation because overfishing significantly reduced their predators. Critical species of the Marine food chain were transformed into flagellates. Flagellates reduce the oxygen content in the ocean. In addition, the paper found that the mortality of individual jellyfish in the study was increased by ocean acidification due to climate change. The increase in mortality rate is because the jellyfish's reproductive and body functions are greatly affected, leading to higher mortality. This discovery proves that there are still a few jellyfish that could be negatively affected by climate change. As a result, jellyfish, with their simple but adaptable bodies, gradually replaced fish as the dominant creatures in the water. Since studies of jellyfish and their corresponding measures are still scarce, researchers will need more attention to these small and unremarkable creatures in the future. Even in the face of human overfishing, their numbers are still more significant than the correct number. To restore the marine ecosystem balance, scientists must do something to reduce the number of jellyfish in the ocean.

Multidecadal Water Mass Dynamics on the West Greenland Shelf

AbstractThe waters on the West Greenland continental shelf and slope play an important role in the global climate system with their link to the subpolar North Atlantic Ocean circulation system and the Greenland Ice Sheet. Lately, low temperature waters on the West Greenland shelf have been observed as far south as ∼64°N and associated with a cold and relatively saline water mass originating north of Davis Strait in Baffin Bay referred to as Baffin Bay Polar Water (BBPW). Here we use long, seasonal hydrographic time series from West Greenland at ∼64°N to study how frequently BBPW is reaching this far south. The analysis covers the period 1950–2018 with a data gap between 1988 and 2005. BBPW was observed frequently and was responsible for the temperature changes observed in the late 1960s–1980s and more intermittently post‐2008. Some of the large temperature changes we observe in the time series have previously been ascribed to “Great Salinity Anomalies” (GSAs) propagating around the subpolar North Atlantic Ocean circulation system. The prevailing view of the propagation of GSAs has been ascribed to advection of anomalies along the large‐scale circulation system. Our study shows that BBPW may play an important role in the interpretation of GSAs and melt of the Greenland Ice Sheet. Large temporal temperature changes at ∼64°N are associated with arrival of BBPW from the north and not advection of anomalies with the large‐scale current system from the south. This advocates for a shift in water masses caused by changes in the position and/or strength of oceanic currents.

Circulation Over the South‐East Greenland Shelf and Potential for Liquid Freshwater Export: A Drifter Study

AbstractFreshwater input into deep convection regions could affect the overturning circulation. With a set of 15 Consortium for Advanced Research for the Transport of Hydrocarbon in the Environment (CARTHE) drifters and 15 Surface Velocity Program (SVP) drifters, we investigate the circulation over the south‐east Greenland shelf and the potential for off‐shelf freshwater export. Part of the East Greenland Current flow is steered into the East Greenland Coastal Current immediately upstream of Sermilik Trough. Between the trough and Cape Farewell, two separate cores are visible. Just past Cape Farewell drifters are redistributed into a shelfbreak core and a slow eddying shelf flow. A coastal core is reestablished downstream. Exchanges between the shelfbreak and coastal flows take place both on the east and west Greenland shelf, allowing fresher water to be diverted away from the coast. Five of 15 shallower CARTHE drifters were exported, mainly at Cape Farewell. CARTHE motion shows a higher correlation with local winds, which are more favorable for off‐shelf transport in this area.

Atlantic water inflow to Labrador Sea and its interaction with ice sheet dynamics during the Holocene

The hydrodynamics of the Labrador Sea, controlled by the complex interplay of oceanographic, atmospheric and ice-sheet processes, play a crucial role for the Atlantic Meridional Overturning Circulation (AMOC). An improved understanding of the hydrodynamics and its forcing in the past could therefore hold a key to understanding its future behaviour. At present, there is a remarkable temporal mismatch, in that the largely microfossil-based reconstructions of Holocene Atlantic-water inflow/influence in the Labrador Sea and Baffin Bay appear to lag grain size-based current strength reconstructions from the adjacent North Atlantic by > 2ka. Here, we present the first current strength record from the West Greenland shelf off Nuuk to reconstruct Atlantic Water (AW)-inflow to the Labrador Sea via the West Greenland Current. Our data show that the Holocene AW-inflow into Labrador Sea is well aligned with the Holocene Speed Maximum documented in the North Atlantic (McCave and Andrews, 2019; Quat. Sci. Rev. 223), suggesting a close coupling with the AMOC. The observed lag between the microfossil-based records and the Holocene Speed Maximum can be explained when considering the presence of an extended meltwater lens that prevented the shoaling of the inflowing Atlantic waters. Once the meltwater discharge waned after the cessation of large-scale melting of the surrounding ice sheets, the AW could influence the surface waters, independently of the strength of its inflow. Only then was an effective ocean-atmosphere heat transfer enabled, triggering the comparably late onset of the regional Holocene Thermal Maximum. Furthermore, sediment geochemical analyses show that short term cooling events, such as the 8.2 ka event related to the final drainage of glacial Lake Agassiz, lead to glacier advances of the Greenland Ice Sheet. Since the grain size data show that these events had no influence on the AW-inflow to the north eastern Labrador Sea, these advances must have been caused by atmospheric cooling. Consequently, we argue that (i) in this region, surface water-based proxies register AW influence rather than inflow (ii) the AW inflow into the Labrador Sea is controlled by the AMOC, but (iii) its impact on an effective ocean-atmosphere heat transfer was hindered by a prevailing meltwater lens in the early Holocene, i.e. until the cessation of large-scale melting of the surrounding ice sheets.

Baffin Bay/Nares Strait surface (seafloor) sediment mineralogy: further investigations and methods to elucidate spatial variations in provenance

The goal of the paper is to ascertain whether there are significant regional variations in sediment mineral composition that might be used to elucidate ice sheet histories. The weight percentages of nonclay and clay minerals were determined by quantitative X-ray diffraction. Cluster analysis, an unsupervised learning approach, is used to group sediment mineralogy of 263 seafloor/core top samples between ∼80°N and 62°N. The optimum number of clusters, based on 30 indexes, was three for the weight percentage data but varied with data transformations. Maps of the distribution of the three mineral clusters or facies indicate a significant difference in weight percentages between samples from the West Greenland and Baffin Island shelves. However, several indexes support a larger number of clusters and similar analyses of the spatial distribution and defining minerals of nine mineral facies indicated a strong association with the original three clusters and with broad geographic designations (i.e., West Greenland shelf, Baffin Island fiords, etc). Classification Decision Tree analysis indicates that this difference is primarily controlled by the percentages of plagioclase feldspars versus alkali feldspars.

The evolution of light and vertical mixing across a phytoplankton ice-edge bloom

During summer, phytoplankton can bloom in the Arctic Ocean, both in open water and under ice, often strongly linked to the retreating ice edge. There, the surface ocean responds to steep lateral gradients in ice melt, mixing, and light input, shaping the Arctic ecosystem in unique ways not found in other regions of the world ocean. In 2016, we sampled a high-resolution grid of 135 hydrographic stations in Baffin Bay as part of the Green Edge project to study the ice-edge bloom, including turbulent vertical mixing, the under-ice light field, concentrations of inorganic nutrients, and phytoplankton biomass. We found pronounced differences between an Atlantic sector dominated by the warm West Greenland Current and an Arctic sector with surface waters originating from the Canadian archipelago. Winter overturning and thus nutrient replenishment was hampered by strong haline stratification in the Arctic domain, whereas close to the West Greenland shelf, weak stratification permitted winter mixing with high-nitrate Atlantic-derived waters. Using a space-for-time approach, we linked upper ocean dynamics to the phytoplankton bloom trailing the retreating ice edge. In a band of 60 km (or 15 days) around the ice edge, the upper ocean was especially affected by a freshened surface layer. Light climate, as evidenced by deep 0.415 mol m–2 d–1 isolumes, and vertical mixing, as quantified by shallow mixing layer depths, should have permitted significant net phytoplankton growth more than 100 km into the pack ice at ice concentrations close to 100%. Yet, under-ice biomass was relatively low at 20 mg chlorophyll-a m–2 and depth-integrated total chlorophyll-a (0–80 m) peaked at an average value of 75 mg chlorophyll-a m–2 only around 10 days after ice retreat. This phenological peak may hence have been the delayed result of much earlier bloom initiation and demonstrates the importance of temporal dynamics for constraints of Arctic marine primary production.

Evolution of the Freshwater Coastal Current at the Southern Tip of Greenland

AbstractShipboard hydrographic and velocity measurements collected in summer 2014 are used to study the evolution of the freshwater coastal current in southern Greenland as it encounters Cape Farewell. The velocity structure reveals that the coastal current maintains its identity as it flows around the cape and bifurcates such that most of the flow is diverted to the outer west Greenland shelf, while a small portion remains on the inner shelf. Taking into account this inner branch, the volume transport of the coastal current is conserved, but the freshwater transport decreases on the west side of Cape Farewell. A significant amount of freshwater appears to be transported off the shelf where the outer branch flows adjacent to the shelfbreak circulation. It is argued that the offshore transposition of the coastal current is caused by the flow following the isobaths as they bend offshore because of the widening of the shelf on the west side of Cape Farewell. An analysis of the potential vorticity shows that the subsequent seaward flux of freshwater can be enhanced by instabilities of the current. This set of circumstances provides a pathway for the freshest water originating from the Arctic, as well as runoff from the Greenland ice sheet, to be fluxed into the interior Labrador Sea where it could influence convection in the basin.

North Atlantic subpolar gyre along predetermined ship tracks since 1993: a monthly data set of surface temperature, salinity, and density

Abstract. We present a binned product of sea surface temperature, sea surface salinity, and sea surface density data in the North Atlantic subpolar gyre from 1993 to 2017 that resolves seasonal variability along specific ship routes (https://doi.org/10.6096/SSS-BIN-NASG). The characteristics of this product are described and validated through comparisons to other monthly products. Data presented in this work were collected in regions crossed by two predetermined ship transects, between Denmark and western Greenland (AX01) and between Iceland, Newfoundland, and the northeastern USA (AX02). The data were binned along a selected usable transect. The analysis and the strong correlation between successive seasons indicate that in large parts of the subpolar gyre, the binning approach is robust and resolves the seasonal timescales, in particular after 1997 and in regions away from the continental shelf. Prior to 2002, there was no winter sampling over the West Greenland Shelf. Variability in sea surface salinity increases towards Newfoundland south of 54∘ N, as well as in the western Iceland Basin along 59∘ N. Variability in sea surface temperature presents less spatial structure with an increase westward and towards Newfoundland. The contribution of temperature variability to density dominates in the eastern part of the gyre, whereas the contribution of salinity variability dominates in the southwestern part along AX02.

Cascading off the West Greenland Shelf: A numerical perspective

AbstractCascading of dense water from the shelf to deeper layers of the adjacent ocean basin has been observed in several locations around the world. The West Greenland Shelf (WGS), however, is a region where this process has never been documented. In this study, we use a numerical model with a 1/4° resolution to determine (i) if cascading could happen from the WGS; (ii) where and when it could take place; (iii) the forcings that induce or halt this process; and (iv) the path of the dense plume. Results show cascading happening off the WGS at Davis Strait. Dense waters form there due to brine rejection and slide down the slope during spring. Once the dense plume leaves the shelf, it gradually mixes with waters of similar density and moves northward into Baffin Bay. Our simulation showed events happening between 2003–2006 and during 2014; but no plume was observed in the simulation between 2007 and 2013. We suggest that the reason why cascading was halted in this period is related to: the increased freshwater transport from the Arctic Ocean through Fram Strait; the additional sea ice melting in the region; and the reduced presence of Irminger Water at Davis Strait during fall/early winter. Although observations at Davis Strait show that our simulation usually overestimates the seasonal range of temperature and salinity, they agree with the overall variability captured by the model. This suggests that cascades have the potential to develop on the WGS, albeit less dense than the ones estimated by the simulation.

Evolution of Baffin Bay Water Masses and Transports in a Numerical Sensitivity Experiment under Enhanced Greenland Melt

ABSTRACTWe used a numerical model forced with three different scenarios to analyze Baffin Bay circulation sensitivity to runoff around Baffin Bay, especially the Greenland runoff, for the past (1970–2010) and future (2010–2099). We observed an overall decrease in transport from the Arctic to the North Atlantic for the volume, heat, and freshwater over the time period as well as an augmentation of the freshwater and heat in Baffin Bay. In the early 1990s, the increase in heat in Baffin Bay was consistent with an increase in the West Greenland Irminger Water (WGIW) inflow at Davis Strait while later West Greenland Shelf Water played an important role in the heat import, sustaining the idea that the West Greenland Current might have an impact on the melt of West Greenland tidewater glaciers. The increase in freshwater and later in heat in Baffin Bay leads to changes in the steric height inside Baffin Bay, which leads to changes in the circulation. After 1978, the WGIW reaches the North Water polynya and recirculates into the Baffin Bay gyre where it accumulates over time. In the future experiment, the dynamic changes in Baffin Bay are mainly related to the accumulation of heat inside the gyre.

Mapping and classifying the seabed of the West Greenland continental shelf

Marine benthic habitats support a diversity of marine organisms that are both economically and intrinsically valuable. Our knowledge of the distribution of these habitats is largely incomplete, particularly in deeper water and at higher latitudes. The western continental shelf of Greenland is one example of a deep (more than 500 m) Arctic region with limited information available. This study uses an adaptation of the EUNIS seabed classification scheme to document benthic habitats in the region of the West Greenland shrimp trawl fishery from 60°N to 72°N in depths of 61–725 m. More than 2000 images collected at 224 stations between 2011 and 2015 were grouped into 7 habitat classes. A classification model was developed using environmental proxies to make habitat predictions for the entire western shelf (200–700 m below 72°N). The spatial distribution of habitats correlates with temperature and latitude. Muddy sediments appear in northern and colder areas whereas sandy and rocky areas dominate in the south. Southern regions are also warmer and have stronger currents. The Mud habitat is the most widespread, covering around a third of the study area. There is a general pattern that deep channels and basins are dominated by muddy sediments, many of which are fed by glacial sedimentation and outlets from fjords, while shallow banks and shelf have a mix of more complex habitats. This first habitat classification map of the West Greenland shelf will be a useful tool for researchers, management and conservationists.

The impact of trawling on the epibenthic megafauna of the west Greenland shelf

Benthic habitats are important elements of polar marine environments, but can be vulnerable to anthropogenic influences such as trawling. Bottom trawling can reduce diversity and alter communities, although some habitats show resilience. The shrimp trawl fishery of West Greenland is a significant part of Greenland's economy. It operates along the west coast from the narrow rockier shelf of the south, up to deeper, muddy areas around Disko Bay. Here we use a benthic drop camera to sample 201 sites between latitudes 60–72°N and depths of 61–725m. Linear models examined relationships of taxon abundance and diversity with bottom trawling intensity and environment (depth, temperature, current, iceberg concentration). Trawling intensity is the most important factor determining the overall abundance of benthic organisms, accounting for 12–16% of variance, although environmental conditions also show significant associations. Sessile erect organisms such as corals show a significant negative response to trawling. Soft sediment communities show a higher resilience than rocky areas. On soft sediments significantly lower abundance characterises sites trawled under five years ago. On hard/mixed ground reduced abundance remains characteristic of sites trawled a decade ago. Continued monitoring of benthic habitats is an essential part of evaluating the ongoing impacts of trawl fisheries.

Size differences of Arctic marine protists between two climate periods-using the paleoecological record to assess the importance of within-species trait variation.

Mean body size decreases with increasing temperature in a variety of organisms. This size–temperature relationship has generally been tested through space but rarely through time. We analyzed the sedimentary archive of dinoflagellate cysts in a sediment record taken from the West Greenland shelf and show that mean cell size decreased at both intra‐ and interspecific scales in a period of relatively warm temperatures, compared with a period of relatively cold temperatures. We further show that intraspecific changes accounted for more than 70% of the change in community mean size, whereas shifts in species composition only accounted for about 30% of the observed change. Literature values on size ranges and midpoints for individual taxa were in several cases not representative for the measured sizes, although changes in community mean size, calculated from literature values, did capture the direction of change. While the results show that intraspecific variation is necessary to accurately estimate the magnitude of change in protist community mean size, it may be possible to investigate general patterns, that is relative size differences, using interspecific‐level estimates.

Emerging impact of Greenland meltwater on deepwater formation in the North Atlantic Ocean

The Greenland ice sheet has experienced increasing mass loss since the 1990s1, 2. The enhanced freshwater flux due to both surface melt and outlet glacier discharge is assuming an increasingly important role in the changing freshwater budget of the subarctic Atlantic3. The sustained and increasing freshwater fluxes from Greenland to the surface ocean could lead to a suppression of deep winter convection in the Labrador Sea, with potential ramifications for the strength of the Atlantic meridional overturning circulation4, 5, 6. Here we assess the impact of the increases in the freshwater fluxes, reconstructed with full spatial resolution3, using a global ocean circulation model with a grid spacing fine enough to capture the small-scale, eddying transport processes in the subpolar North Atlantic. Our simulations suggest that the invasion of meltwater from the West Greenland shelf has initiated a gradual freshening trend at the surface of the Labrador Sea. Although the freshening is still smaller than the variability associated with the episodic ‘great salinity anomalies’, the accumulation of meltwater may become large enough to progressively dampen the deep winter convection in the coming years. We conclude that the freshwater anomaly has not yet had a significant impact on the Atlantic meridional overturning circulation.

Ice stream retreat following the LGM and onset of the west Greenland current in Uummannaq Trough, west Greenland

The deglacial history and oceanography of Uummannaq Trough, central West Greenland continental shelf, was investigated using foraminiferal, sedimentological, and bathymetric records together with a radiocarbon chronology, providing a timeline for the retreat of glacial ice after the Last Glacial Maximum (LGM). To map ice stream retreat, data were collected from cores from the outer (JR175-VC45 and JR175-VC43) and inner (JR175-VC42) Uummannaq Trough. A large ice stream, fed by confluent glaciers draining the interior of the Greenland Ice Sheet, extended across the outer shelf during the LGM and was in retreat by 15.0 cal kyr BP. Foraminiferal data indicate that the ‘warm’ West Greenland Current (WGC) was established prior to 14.0 cal kyr BP, which is the hitherto earliest record of Atlantic Water found on the West Greenland shelf. For each of the cores, foraminifera indicate that ice sheet retreat was followed quickly by incursion of the WGC, suggesting that the warm water may have enhanced ice retreat. Prior to the Younger Dryas cold event, the radiocarbon chronology indicates that the ice sheet retreated to the mid-shelf, where it subsequently stabilised and formed a large grounding-zone wedge (GZW). After the Younger Dryas, around 11.5 cal kyr BP, the ice retreated rapidly from the GZW and into the fjords.

Grounding-zone wedges on the West Greenland shelf imaged from multibeam and seismic data

Grounding-zone wedges (GZWs) are asymmetrical depocentres built up beneath the grounding zone of marine-terminating ice streams through the delivery of soft, deforming subglacial till from upglacier. They are typically tens of metres thick, tens of kilometres in length and usually form subdued transverse-to-flow ridges across the long axes of fjords and cross-shelf troughs on high-latitude continental shelves (e.g. Dowdeswell & Fugelli 2012; Batchelor & Dowdeswell 2015). The ridges, representing the relatively steeper ice-distal face of the wedge, usually appear as small scarps or steps in multibeam imagery. The wedges thin in an ice-proximal direction, often becoming difficult to identify except by using acoustic-stratigraphic methods. Relatively large sedimentary wedges have been identified in multibeam data from several Greenland cross-shelf troughs (e.g. Dowdeswell et al. 2014). The features generally have a scarp at their ice-distal end, and a subdued, low-gradient ice-proximal slope which makes their termination difficult to pinpoint from bathymetric data. Where a basal reflection can be identified, there is some evidence that the wedges thin progressively over a few tens of kilometres away from the former ice margin and have a characteristic asymmetry along trough axes. A multibeam image of a modern wedge from the outer shelf of …