Sable Island Bank Research Articles

The inner shelf geology of Atlantic Canada compared with the North Sea and Atlantic United States: Insights for Atlantic Canadian offshore wind energy

The Quaternary history of the Atlantic Canadian inner shelf shares some similarities with the North Sea and northern United States of America (US) Atlantic coast, with the influence of large-scale glaciation and subsequent sea level transgression being the main drivers of seafloor morphology, sedimentology, and uppermost stratigraphy. The geology of the inner shelf, generally confined to 100 m water depth for this study, is an important constraint on the development of offshore renewables, in particular wind energy. Offshore wind has seen rapid growth, particularly in Europe and Asia, where the industry has now experienced decades of production. In the US, one small-scale production farm and many hundreds of MW are in the production pipeline. In contrast, offshore wind in Canada, despite onshore installed wind capacity that ranks highly globally, lacks any operating turbines and there are no plans for development in the wind resource-rich Atlantic Canadian region. In this study, the geological constraints on offshore wind in Atlantic Canada are explored. Generally, the available offshore wind resource is high, and thus the main geophysical constraint on the development of offshore wind energy converters is the inner shelf geology. Several sites with available high-resolution geophysical data are selected for in-depth analysis and comparison with production and planned offshore wind farm sites found elsewhere. In general, a lack of sufficiently thick Quaternary sedimentation—necessary for the most common bottom-fixed foundations for wind turbines—will make developing offshore wind in Atlantic Canada challenging when compared with North Sea and US Atlantic Coast locations. A few locations may be suitable geologically, such as Sable Island Bank in Nova Scotia (thick package of sands), Northumberland Strait between Prince Edward Island and Nova Scotia (shallow firm seabed and sandbanks), Baie des Chaleurs in New Brunswick/Québec (thick, low relief fine sediments), and St. George's Bay, Newfoundland (shallow, postglacially modified moraine).

Influence of Benthic Macrofauna as a Spatial Structuring Agent for Juvenile Haddock (Melanogrammus aeglefinus) on the Eastern Scotian Shelf, Atlantic Canada.

We examined the habitat of juvenile haddock on the eastern Scotian Shelf (off Nova Scotia, Canada) in relation to grab-sampled benthic macrofaunal invertebrate species assemblages in order to determine whether there were significant differences in benthic macrofauna between areas of historically persistent high and low juvenile haddock abundance. Our analyses were conducted over two spatial scales in each of two years: among banks (Emerald, Western and Sable Island), approximately 60 km distant from each other, and between areas of high and low juvenile haddock abundance at distances of 10 to 30 km–all in an area that had not experienced groundfishing in the decade prior to sampling. We also examined fine-scale (10s of metres) within-site variability in the macrofauna and used surficial sediment characteristics, along with hydrographic variables, to identify environmental correlates. PERMANOVA identified statistically significant differences in biomass, density and composition of the benthos associated with juvenile haddock abundance; however it was difficult to determine whether the results had biological relevance. Post hoc tests showed that these differences occurred only on Sable Island Bank where both fish and benthos may have been independently responding to sediment type which was most different there (100% sand in the area of low haddock abundance vs. 22% gravel in the area of high haddock abundance). In total, 383 benthic taxa representing 13 phyla were identified. Annelida was the most specious phylum (36.29% of taxa, representing 33 families), followed by Arthropoda (with Crustaceans, mostly Amphipoda, accounting for 25.07% of the total number of taxa). The strongest pattern in the macrofauna was expressed at the largest scale, between banks, accounting for approximately 25% of the variation in the data. Emerald Bank, deeper, warmer and saltier than the Western and Sable Island Banks, had a distinctive fauna.

Numerical study of three-dimensional shelf circulation on the Scotian Shelf using a shelf circulation model

A numerical shelf circulation model was developed for the Scotian Shelf, using a nested-grid setup consisting of a three-dimensional baroclinic inner model embedded inside a two-dimensional barotropic outer model. The shelf circulation model is based on the Princeton Ocean Model and driven by three-hourly atmospheric forcing provided by a numerical weather forecast model and by tidal forcing specified at the inner model's open boundaries based on pre-calculated tidal harmonic constants. The outer model simulates the depth-mean circulation forced by wind and atmospheric pressure fields over the northwest Atlantic Ocean with a horizontal resolution of 1/12°. The inner model simulates the three-dimensional circulation over the Gulf of St. Lawrence, the Scotian Shelf, and the adjacent slope with a horizontal resolution of 1/16°. The performance of the shelf circulation model is assessed by comparing model results with oceanographic observations made along the Atlantic coast of Nova Scotia and in the vicinity of Sable Island (on the Scotian Shelf) during two periods: October 2000–March 2001 and April–June 2002. Analysis of model results on Sable Island Bank indicates that tidal currents account for as much as ∼80% of the total variance of near-bottom currents, and currents driven by local winds account for ∼30% of the variance of the non-tidal near-bottom currents. Shelf waves generated remotely by winds and propagating into the region also play an important role in the near-bottom circulation on the bank.

Multibeam bathymetric investigations of the morphology of sand ridges and associated bedforms and their relation to storm processes, Sable Island Bank, Scotian Shelf

Storm-formed sand ridges are important morphologic features occurring on many continental shelves of the world. Our understanding of the morphology, migration, and the controlling processes over this type of sand ridges under different environmental settings is still limited. In the present study, an integrated approach of combining multibeam bathymetry survey, seabed sampling, sidescan/seismic surveys and seabed instrumentation measurements was used to characterize the surficial geology and morphology of offshore sand ridges on Sable Island Bank, Scotian Shelf, and to evaluate the relationship between sand ridge morphology, migration and the storm processes on this storm-dominated outer shelf bank. Multibeam data obtained at selected sites demonstrated the series of NE–SW oriented sand ridges with an average height of 4.3 m and wavelength of 1.5 km. Sand ridges attain maximum spacing, height and steepness in the intermediate depths. Sand ridge size and steepness also decrease from west to east and this decrease is correlated with decreasing dynamic condition, sediment grain size, and depth. Sand ridge profiles show weak easterly asymmetry. This morphological asymmetry augments the sediment texture and grain size asymmetry to suggest eastward long-term sand ridge migration and net sediment transport in the study area. Sand ridge asymmetry also shows strong local variation and the number of sand ridges asymmetric to the west is nearly equal to that asymmetric to the east. The likely cause is the nearly equal number of major storms passing to the south versus to the north of the Island so that the westerly and easterly peak storm-driven currents associated with these storm path scenarios affect equally the sand ridges on Sable Island Bank. A suite of smaller bedforms were found superimposed on the sand ridges: sand waves widely superimposed on both flanks of sand ridges, mixed 2D and 3D megaripples commonly occurring in the sand ridge troughs and on the lower western flanks, and large-wave ripples ubiquitously found in the troughs of all megaripples. Surficial sediment is coarsest (coarse sand with shell fragments) in the sand ridge trough and becomes progressively finer eastward toward the sand ridge crest and down the eastern flank, while best sorting occurs near the sand ridge crest. Box cores collected across sand ridges reveal characteristic storm event bed structure that reflects the development and migration of bedforms with the evolution of storms.

Use of parasite and genetic markers in delineating populations of winter flounder from the central and south‐west Scotian Shelf and north‐east Gulf of Maine

Discriminant function analyses of infection parameters of parasitic helminths revealed that abundances of seven helminth species contributed significantly to the delineation of four host populations of winter flounder Pleuronectes americanus from the central and south‐west Scotian Shelf and the north‐east Gulf of Maine (NAFO subdivision 4WX‐5Z). These were adult digeneans, Derogenes varicus, Genolinea laticauda, Steganoderma formosum and Steringophorus furciger, metacercariae of the digenean, Stephanostomum baccatum, and larval nematodes, Anisakis simplex and Hysterothylacium aduncum. The correct classification rate was 84% overall, with Georges Bank (5Z) and Sable Island Bank (4W) winter flounder being the most accurately classified samples at 98 and 88%, respectively. Winter flounder from south‐west Nova Scotia (4X), an inshore sample from St Marys Bay and offshore fish from Browns Bank, had the lowest rates of correct classification (76 and 71%, respectively) due, primarily, to cross‐misclassification between the two samples. Winter pairwise comparisons of four microsatellite markers identified significant genetic differences between all populations sampled with the Georges Bank population being the most genetically distinct overall, and St Marys Bay and Browns Bank fish being the least dissimilar.

Wave‐current bedform scales, orientation, and migration on Sable Island Bank

Field observations of wave‐current bedforms on Sable Island Bank show that medium to large bedforms were generally aligned with the wave direction, and did not follow the rotating tidal current. Normalized bedform heights and wavelengths were larger than predictions by Nielsen (1992), but agreed well with predictions by Khelifa and Ouellet (2000) which includes current effects. Maximum observed bedform wavelengths of 1.9 m were larger than those predicted for bedforms in wave‐dominated nearshore conditions, but this may be expected as the water depths are larger (20–42 m) and currents are present. Measured bedform migration rates had higher vector correlation amplitudes when compared to significant wave velocity than with current velocity or skewness. Migration rate predictions from three presently available models were not able to predict net migration rate and direction in all cases.

Integrated fate modeling for exposure assessment of produced water on the Sable Island Bank (Scotian Shelf, Canada)

Produced water is the largest waste discharge from the production phase of oil and gas wells. Produced water is a mixture of reservoir formation water and production chemicals from the separation process. This creates a chemical mixture that has several components of toxic concern, ranging from heavy metals to soluble hydrocarbons. Analysis of potential environmental effects from produced water in the Sable Island Bank region (NS, Canada) was conducted using an integrated modeling approach according to the ecological risk assessment framework. A hydrodynamic dispersion model was used to describe the wastewater plume. A second fugacity-based model was used to describe the likely plume partitioning in the local environmental media of water, suspended sediment, biota, and sediment. Results from the integrated modeling showed that the soluble benzene and naphthalene components reach chronic no-effect concentration levels at a distance of 1.0 m from the discharge point. The partition modeling indicated that low persistence was expected because of advection forces caused by tidal currents for the Sable Island Bank system. The exposure assessment for the two soluble hydrocarbon components suggests that the risks of adverse environmental effects from produced water on Sable Island Bank are low.

Surveys of larval sealworm (<i>Pseudoterranova decipiens</i>) infection in various fish species sampled from Nova Scotian waters between 1988 and 1996, with an assessment of examination procedures

Between November 1988 and October 1996, >10,000 fish from the Breton Shelf, Sable Island Bank and the northeastern Gulf of Maine were examined for larval anisakines. Larval sealworm, Pseudoterranova decipiens, occurred in 30 of 39 species surveyed, including 8 new host records, Enchelyopus cimbrius, Lycodes reticulatus, Eumesogrammus praecisus, Lumpenus lumpretaeformis, Lumpenus maculatus, Cryptacanthodes maculatus, Artediellus atlanticus and Triglops murrayi. The parasite was most prevalent and abundant in mature demersal piscivores and benthic consumers. Sealworm densities (nr kg-1 host wt.), however, were greatest in small benthophagous fish including mature E. cimbrius, A. atlanticus, T. murrayi and Aspidophoroides monopterygius, and juvenile Hippoglossoides platessoides. ANOVA revealed that geographical disparities in sealworm prevalence and abundance were highly significant in 14 of 20 species tested, although significant disparities between samples from each of the three areas were evident only in H. platessoides. Almost invariably, infection parameters were greatest in fish from Sable Island Bank. ANOVA also indicated that sealworm prevalence and/or abundance increased significantly in Sable Island Bank populations of Gadus morhua, H. platessoides, and seven other species between 1985-1986 and 1989-1990. Routine examinations, in which host flesh was sliced and candled, proved as efficacious as digestion in warm (35° C) pepsin-HCl for detection of larval sealworm in the flesh of large frozen fish. Procedures employing fresh (iced) samples, digestion at ambient temperature and microscopy are recommended, however, for surveys of small benthic consumers. Many of the sealworm infecting the latter hosts are tiny (2 to 10 mm in length) nematodes, which escape detection by routine inspection, and may not survive in warm pepsin-HCl solution.

Review of experimental and natural invertebrate hosts of sealworm (<i>Pseudoterranova decipiens</i>) and its distribution and abundance in macroinvertebrates in eastern Canada

Experimental and natural invertebrate intermediate hosts of sealworm (Pseudoterranova decipiens) as well as transmission experiments of sealworm from invertebrates to fish are reviewed and summarized. Experimental hosts include copepods, mysids, cumaceans, isopods, amphipods, decapods, annelids, and molluscs. Invertebrates collected from eastern Canada between 1989 and 1995 were checked for nematode infections by microscopic examination of dissected animals or enzymatic digestion of bulk samples. Third-stage larval sealworm were found in mysids (Neomysis americana, Mysis stenolepis) from Passamaquoddy Bay, the Bras d’Or Lakes, inshore Cape Breton, Sable Island and Sable Island Bank. Infected amphipods (Amphiporeia virginiana, Americorchestia megalophthalma, Gammarus spp.) were found only on Sable Island. Typical infection rates in macroinvertebrates were 1-4/1000. No sealworm infections were found in approximately 18,000 amphipods examined from Sable Island Bank, the site of the most heavily infected fishes in eastern Canada. In Wallace Lake, a brackish pond on Sable Island, infection rates were much higher in mysids than in amphipods. Estimates of rates of transmission of sealworm from invertebrates to fish were derived from infection levels in Wallace Lake and feeding experiments involving sticklebacks and invertebrate prey. It is concluded that mysids may be much more important than amphipods in transmitting sealworm to fish hosts.

Seasonal Circulation on the Western and Central Scotian Shelf*

A realistic representation of 3D seasonal circulation and hydrography on the western and central Scotian Shelf has been obtained from historical observations and a combination of diagnostic and prognostic numerical models with forcing by tides, wind stress, and baroclinic and barotropic pressure gradients. The major current features—the southwestward Nova Scotian and shelf-edge currents, and partial gyres around Browns and Sable Island Banks—are found to persist year-round but with significant seasonal changes. Comparison with current meter observations shows good agreement for the Browns Bank, southwest Nova Scotia, and inner-shelf regions, and poorer agreement in the Sable Island Bank and shelf-edge regions where current and density observations are sparser and tidal influences weaker. There is significant spatial structure in the seasonal circulation and hydrography, and in the underlying dynamical processes. On the shelf scale there are substantial changes in stratification, potential energy, and alongshelf throughflow between the central and western areas, related to topography, different tidal regimes, and proximity to major water mass sources. The baroclinic pressure field is the predominant shelf-scale forcing, but there are important cross-shelf meanders of the throughflows associated with topography. The partial bank gyres are connected to the throughflows and have multiple, and in some cases, opposing forcings. Tidal rectification and baroclinic flow dominate on Browns Bank, with a relatively small wind influence on the climatology, while baroclinic flow and barotropic inflow from the shelf edge are important on Sable Island (including Western) Bank. The flows are generally clockwise (counterclockwise) over the shallow (deep) area, but have substantial vertical shear. The combination of spatial structure, multiple forcings, and other flow components provides the potential for strong sensitivity of drift to location and time.

Wisconsinan glacial and sea-level history of Maritime Canada and the adjacent continental shelf: A correlation of land and sea events

The Wisconsinan glacial history of Maritime Canada records the interaction of land-based glaciers with the sea, which dissects the region along the deep embayments of the Bay of Fundy and the Laurentian Channel. Ice centers, collectively termed the Appalachian ice complex, shifted in a clockwise manner across the varied bedrock terranes of the region, producing cross-striated bedrock outcrops and compositionally distinct till sheets on land. Offshore glacial sediments can be correlated to their terrestrial counterparts on the basis of provenance, thus establishing crucial land-sea links in the glacial record. Five glacier flow events have been recognized. During the Caledonia phase in early to middle Wisconsinan time, ice from eastern Appalachian upland sources crossed Nova Scotia and extended to the continental shelf edge, where a calving margin was established. Slumping at this margin produced proximal wedge-shaped bodies of diamicton that interfinger with glaciomarine sediments. The Caledonia phase glacier retreated during middle Wisconsinan time to the inner Scotian Shelf. During the Escuminac phase in late Wisconsinan time (22–19 ka), an ice center formed over the Magdalen Shelf (Escuminac ice center) and transported large quantities of local red-bed material southward to the outer shelf-slope margin. This glacier retreated about 18 ka to a tidewater margin at Sable Island Bank and Banquereau. Sea level during this time was falling as a result of isostatic recovery from earlier Escuminac phase maximum ice loads. Just after 18 ka, ice wasted back across the midshelf basins to the tidewater margin of the Scotian Shelf end moraine complex and was stabilized by falling sea levels. Escuminac ice was reorganized into the Scotian ice divide (Scotian phase) over mainland Nova Scotia and the continental shelf south of Cape Breton Island. Between 15 and 13 ka another period of glacier retreat ensued, and the margin settled close to the present-day land areas. Between 13 and 12.5 ka an ice margin was established from local terrestrial ice centers in northern Nova Scotia (Chignecto phase) into the Bay of Fundy and just beyond the present-day Atlantic coast. Responding to increasing climatic warming, these smaller glaciers dissipated and their margins retreated landward. A sea-level lowstand of −65 m on the inner shelf occurred ca. 11.7 ka. Isolated terrestrial remnants of Chignecto phase glaciers were reactivated as a result of cooling during the Collins Pond phase (Younger Dryas) ca. 10.8 ka. Enhanced ice rafting, evident in the North Atlantic deep oceanic record, appears to correlate with periods of glacier retreat in the Appalachian ice complex. During melting and sea-level rise, both the quantity and thickness of icebergs increased due to grounding-line retreat within the Magdalen Shelf, thereby increasing the net flux of hematite-stained quartz to the North Atlantic.

Transmission of the sealworm, Pseudoterranova decipiens (Krabbe), from invertebrates to fish in an enclosed brackish pond

The life cycle and transmission dynamics of sealworm, Pseudoterranova decipiens (Krabbe), were studied in Wallace Lake, an enclosed brackish pond on Sable Island, Nova Scotia. Abundance of larval sealworm was determined in amphipods ( Gammarus spp. ), mysids ( Neomysis americana S.L. Smith), and threespine ( Gasterosteus aculeatus Linnaeus) and fourspine ( Apeltes quadracus Mitchill) sticklebacks. Sealworm larvae were more numerous in mysids (0.001–0.004 worms/host) than in amphipods (0–0.0005 worms/host), and P. decipiens abundance in mysids and fourspine stickleback was positively correlated. Amphipods outnumbered mysids in three depth zones in the lake, but density of infected mysids (1.43/m 2) was much higher than that of infected amphipods (0.22/m 2) in the vegetated zone where fish were found. Threespine and fourspine stickleback fed mainly on copepods (98% and 57% of diets, respectively), and less frequently on amphipods (1% and 23% of diets, respectively) and mysids (1% and 19% of diets, respectively). Both sticklebacks fed preferentially on mysids (Murdoch's index of preference=1.49) over amphipods (Murdoch's index=0.67). In separate feeding experiments, fourspine stickleback ingested 1.3 (±1.2) amphipods or 7.7 (±2.0) mysids per day. Calculated transmission rates suggest that these fish acquire sealworm from eating infected mysids at a rate of about 1 per month, compared to 1 every 8 yr from amphipods. Abundance of larval sealworm in N. americana on Sable Island Bank (0.002 worms/host) in January 1995 was similar to that in Wallace Lake. Results of this study demonstrate that mysids are more important than amphipods in transmission of sealworm to small benthophagous fishes in an isolated, landlocked brackish-water environment.

Storm-generated, hummocky stratification on the outer-Scotian Shelf

Hummocky megaripples occur on Sable Island Bank, Scotian Shelf. Submersible observations show that the megaripples form during winter storms and are subsequently obliterated through bioturbation and fair-weather reworking. The megaripples of this study were underlain by a storm bed composed of: (A) a basal scoured and infilled gravel lag facies; (B) low-angle tangential crossbedding in gravel to coarse sand; (C) anisotropic hummocky stratification in medium sand; and (D) wave ripple cross-lamination in medium/fine sand. This sequence forms a tempestite bed created by a winter storm during our sampling program. Numerical simulation of bed conditions during the storm suggests that the hummocky megaripples and hummocky stratification formed together during late stages of storm decay from conditions of sheet flow. Near-bed wave motion during deposition exceeded steady currents by an order of magnitude.

Transmission of Pseudoterranova decipiens (Nematoda: Ascaridoidea) via benthic macrofauna to sympatric flatfishes (Hippoglossoides platessoides, Pleuronectes ferrugineus, P. americanus) on Sable Island Bank, Canada

Larval ascaridoid nematodes were surveyed in three flatfish species, Hippoglossoides platessoides, Pleuronectes ferrugineus, and P. americanus, from Sable Island Bank in February and June 1989. Pseudoterranova decipiens (sealworm) abundances differed significantly with both host species, the heaviest levels being found in H. platessoides, and host length, infections generally increasing with length, but not between February and June samples. Moderate numbers of larvae were found in P. ferrugineus while P. americanus were seldom infected. Two third-stage P. decipiens larvae (L3), 3.2 and 7.0 mm in length, were recovered from the cephalothoraxes of two Mysis mixta in H. platessoides stomachs while five L3's (2.8 to 8.7 mm in length) were found among food (polychaetes, cumaceans, tanaids, amphipods) in the stomach of a P. ferrugineus. Levels of P. decipiens infection appear to be directly related to consumption of suprabenthic prey, which commonly occur in the diet of H. platessoides but are exploited less frequently by P. ferrugineus and rarely by P. americanus.

Diets of sympatric flatfishes, Hippoglossoides platessoides, Pleuronectes ferrugineus, Pleuronectes americanus, from Sable Island Bank, Canada

Prey exploitation was documented for Hippoglossoides platessoides, Pleuronectes ferrugineus, and P. americanus collected from southeast Sable Island Bank in February and June 1989. Diets varied significantly by sample and with fish species and length. Of 239 species consumed by flatfishes, 66 were determined to be principal prey. Crustaceans, particularly amphipods, were the most frequently exploited prey of all three flatfish species. Small H. platessoides fed on suprabenthic fauna, while larger fish exploited epifauna and hyperiid suprafauna. P. ferrugineus exploited epibenthic fauna, consuming crustaceans and tunicates when small and polychaetes when larger. P. americanus preyed on epifauna; smaller fish exploited polychaetes while larger fish usually consumed crustaceans associated with ectoproct colonies. Feeding intensity was dramatically lower in February, food being found in stomachs of only 36% of H. platessoides and 49% of P. ferrugineus, and lacking in the stomachs of P. americanus. In June, stomachs of 86% of H. platessoides, 94% of P. ferrugineus and 96% of P. americanus contained food. Results indicate that prey resources for the three flatfish species are partitioned by specific habitat and prey type preferences.

Diets of sympatric flatfishes, Hippoglossoides platessoides, Pleuronectes ferrugineus, Pleuronectes americanus, from Sable Island Bank, Canada

Prey exploitation was documented for Hippoglossoides platessoides, Pleuronectes ferrugineus, and P. americanus collected from southeast Sable Island Bank in February and June 1989. Diets varied significantly by sample and with fish species and length. Of 239 species consumed by flatfishes, 66 were determined to be principal prey. Crustaceans, particularly amphipods, were the most frequently exploited prey of all three flatfish species. Small H. platessoides fed on suprabenthic fauna, while larger fish exploited epifauna and hyperiid suprafauna. P. ferrugineus exploited epibenthic fauna, consuming crustaceans and tunicates when small and polychaetes when larger. P. americanus preyed on epifauna; smaller fish exploited polychaetes while larger fish usually consumed crustaceans associated with ectoproct colonies. Feeding intensity was dramatically lower in February, food being found in stomachs of only 36% of H. platessoides and 49% of P. ferrugineus, and lacking in the stomachs of P. americanus. In June, stomachs of 86% of H. platessoides, 94% of P. ferrugineus and 96% of P. americanus contained food. Results indicate that prey resources for the three flatfish species are partitioned by specific habitat and prey type preferences.

Interaction of internal waves with the seabed on continental shelves

Large-amplitude internal waves generated by tidal fluctuations at the outer edge of the continental shelf propagate shoreward and interact with seabed sediment. A crude mathematical model describing the propagation of such internal waves is used to predict wave-induced sediment flux and thereby to provide a possible explanation of sand-ridge formation on continental shelves. The ocean over the shelf is modelled as a two-layer system and it is assumed that the internal waves are generated at the shelf edge. Field measurements indicate that the very low frequency tidal fluctuations create a train of internal oscillations of periods between 15 and 20 min. Because of nonlinear effects these wave trains generate differential sediment fluxes and, in the model, this leads to the creation of seabed topography. The predictions of the model are tested against field data collected on the eastern Canadian continental shelf and in particular on Sable Island Bank and the Grand Banks of Newfoundland. The comparisons between predictions and measurements are encouraging especially in light of the fact that the model has no free parameters.

Sediment transport on the eastern Canadian continental shelf

A synthesis is presented of the sediment transport pathways resulting from hydrodynamic processes over the eastern Canadian continental shelf. This is based on interpretation of bedform type and orientation, grain size trends, sediment stratigraphy, visual observation and direct measurements. These pathways are then compared with results of numerical simulations of the transport of 0.35 mm (medium) sand for the Grand Banks of Newfoundland, the Scotian Shelf and the Gulf of Maine. The abundance of hydrodynamically reworked sediment increases from north to south. There is no evidence for sediment transport on the Baffin Shelf or Arctic Island Channels due largely to ice cover and deep (200 m) water. Sediment transport on the Labrador Shelf, by contrast, is apparent though restricted to bank tops in depths less than 120 m. This transport is predominantly to the southeast under the influence of strong wind-driven and geostrophic flows. The Grand Banks of Newfoundland is subject to storm-induced sand transport in depths less than 120 m. Transport here is to the south and southeast over much of Grand Bank and Avalon Channel. Above approximately 60 m the seabed is devoid of sand, suggesting scouring; between 60 and 120 m sand transport takes place principally as bedload. The shelf immediately south of Newfoundland is subject to strong easterly sediment transport that has scoured the banktops of all but gravel-sized sediment. The Scotian Shelf and Georges Bank also exhibit storm-induced sediment transport that is tidally-modulated in depths less than 100 m. The predicted and observed sand transport pathways are remarkably consistent. Predicted zones of sand convergence and divergence correspond to known regions of sand accumulation and depletion, respectively. Quantitative predictions are, by contrast, only within an order of magnitude of observations. Percentage exceedence predictions of sand transport for the Hibernia (Grand Banks of Newfoundland) and Venture (Sable Island Bank) discovery sites show strongly linear trends on a Gumbel distribution. These plots show that intense storms (greater than 20 year return interval) dominate net transport at Hibernia, whereas short-term storms (annual or shorter return interval) dominate at Venture.

The origin and stability of sand ridges on Sable Island Bank, Scotian Shelf

Two models are used to predict the evolution of sand ridges on Sable Island Bank: the wave model of Boczar-Karakiewicz and Bona (1986a) and the sediment transport system: SED1DG ( Davidson and Amos, 1985) . The genesis of sand ridges is proposed to be the result of differential potential sediment transport ( i d) induced by 50–80 s period infragravity waves. Sand ridge crests are found where the spatial horizontal derivative of the transport rate ( i d) is negative, and troughs develop where this derivative is positive. These crests and troughs are orthogonal to the propagation direction of the infragravity waves, their consecutive distances vary in repetition length ( L r) in proportion with depth, and near the shelf break they are phase-locked to the shelf edge. Refraction of infragravity waves on Sable Island Bank is minor compared to refraction at the shelf edge. Sand ridge orientation is, therefore, largely determined by the orientation of the shelf edge over which the infragravity waves pass. The time scale for sand ridge generation, the degree of ridge asymmetry and the rate of migration are proposed to be the direct result of the rate and direction of shelf sediment transport which, for Sable Island Bank, is storm controlled and almost independent of the infragravity wave field. We predict that a typical time-scale for ridge formation in 40 m of water is 890 years with a time-averaged migration rate of 1.9 m y −1.

The Quaternary stratigraphy of southwest Sable Island Bank, eastern Canada

Three boreholes, ten vibrocores, and high-resolution seismic reflection records were analyzed to reconstruct the stratigraphy of the topmost 50 m of the sedimentary column of southwest Sable Island Bank. The sequence is complex owing to the effects of two low stands of sea level, two periods of ice influence, and two periods of open water during the past 40,000 yr. A low stand at -98 m occurred at 28,000 to 32,000 yr B.P.; a second low stand occurred at -110 m between 13,000 and 15,000 yr B.P. Ice covered the region prior to 32,000 yr B.P. and from 11,000 to 10,000 yr B.P. Open water prevailed at other times. The sequence of sediments follows the formational subdivision of King and the member subdivision of Amos and Knoll. The Sable Island Sand and Gravel Formation is subdivided into three members: trough-bedded sand, cross-bedded sand, and conformably bedded sand. The conformably bedded sand formed under heavy sea ice and represents the Younger Dryas event. The uppermost two members result from shelf sediment reworking. The Emerald Silt Formation is subdivided into four members: channel gravel, upper stratified sand/fines, barren gravelly/sand, and lower stratified sand/fines and two regional discontinuities, R1 and R2. The coarser-grained facies of the channel gravel and barren gravelly/sand members are the result of reworking during late and mid-Wisconsinan transgressions of Sable Island Bank. The upper stratified sand/fines member is interpreted as an open-water marine deposit formed during the Scotian Stade. The lower stratified sand/fines member is interpreted as a glacio-marine deposit formed during the Digby Stade.