Geology | Landscape Development | Climate | Fresh Water Soils | Plants | Animals | Scenic Quality Cultural Environment | Topics & Habitats

Geology
Sable Island is an elongated sand island which lies 300 km east of Halifax. It is oriented east-west and measures 42 km by 1.4 km at low tide. Shallow bars extending underwater at either end give it an overall length of 80 km. The island is the emergent part of a very large sand deposit on Sable Island Bank which occupies an area measuring 250 km by 115 km on the Scotian Shelf. Beneath the sand is a wedge of Cretaceous and Tertiary sediments which thickens seaward and is being actively surveyed and drilled for hydrocarbon deposits.

"Shipwreck", Sable Island Click to enlarge

The sand was deposited in a sand and gravel mixture as an outwash fan from a late Wisconsinan ice front which approached but never covered Sable Island Bank. As glacial ice melted and sea levels rose, the sand was winnowed out. Tides and wind-driven currents now keep it in continuous motion within a circulating "sand cell." The sand moves around the island, removing and replacing sand on the emergent part of Sable Island.

Landscape Development
Sable Island has the shape of a shallow crescent which is concave northwards. It consists of two lines of high dunes which were originally separated by a tidal gap. The southern range has now disappeared, leaving a wide beach area. The form of the island changes constantly as strong winds and frequent storms shift the sand around the island and back and forth from offshore. The beach profile undergoes normal seasonal changes; it is steeply inclined in winter and gently inclined in summer.

Sable Island (aerial view) Click to enlarge

Records and maps for the past 200 years or so show that though the island has changed its form, it has more or less maintained the same position and overall size. The eastern half, though more stable than the western half, has decreased in altitude from 50 m to 24 m at its highest elevation. The violent storms which have caused considerable changes in morphology on the island seem to be counterbalanced by a slow rebuilding process during quieter periods when sand is added from offshore.

Climate
The climate of Sable Island is characteristically maritime with a narrow range of temperature and high winds. Sable Island is warmer in winter and cooler in summer than the neighbouring mainland. Fogs are frequent during the summer.

Mean daily temperatures in January hover around 0°C, in April they rise to approximately 4°C, and by July mean daily temperatures are around 15°C. In comparison to the mainland, the temperature regime on Sable Island shows a slightly lower annual mean maximum and a much higher annual mean minimum.

The total annual precipitation is similar to that of Halifax. Only a very small proportion falls as snow because of the mild winter temperatures. The snow that does fall does not linger.

Cloud or fog cover over Sable Island is frequent; the mean number of hours of sunshine is substantially lower than on the mainland. The incidence of foggy days increases between April and August. July is the foggiest month; fog occurs on average 21 days of the month. Average monthly windspeeds are significantly higher, as strong winds blow more of the time and Sable Island is more exposed than the mainland.

The main features of the climate are mild temperatures, constant high winds, and high humidity.

Fresh Water
Several small freshwater ponds are located within the dunes in the vegetated areas, and some larger brackish ponds and lakes are found on the southern beach. Rainwater filtering through the sand collects to form a freshwater lens which, by displacing seawater, appears as pools in depressions. The pH of most of these freshwater pools varies from 5.0-5.7. Brackish ponds receive seawater during storm surges, and both their size and water chemistry can change dramatically. The major brackish pond is Wallace Lake, which can vary in size throughout the year from two or three small ponds to an area up to 14 km long.

The physical and chemical characteristics of pools on Sable Island may be influenced by fluctuating water levels, the grazing and trampling of horses, and nutrient enrichment from colonies of gulls and terns.

Soils
On the beaches, there is no soil development (i.e., no identifiable soil horizon) because of the constant shifting of the sandy substrate. In more sheltered areas in the central part of the island some peat has formed. But the soil is of poor nutritive quality and contains only small amounts of organic material. Podzolization occurred in the past when the sands were more stable, but only remnants remain.

Plants
The main influences on the regional vegetation are the high winds, salt spray, sandblasting, lack of nutrients, and effects of grazing by the Sable Island horses. The variety of plants found on the island has been increased by numerous introductions, both deliberate and accidental. A total of 154 native and 69 introduced vascular plants have been recorded.

Trees cannot survive the effects of wind and salt damage. In 1901, in a massive attempt to stabilize the dunes, over 80,000 trees were transplanted. Almost all died immediately, and by 1981 only one, a maple, could be found. Two pine trees planted in the early 1970s are barely surviving.

In a botanical study completed in 1981, plant communities were divided into several categories: Sandwort, Dense Marram, Sparse Marram, Marram-Fescue, Shrub Heath, Cranberry Heath, and Pond-edge Herbaceous. The first three communities are marked by a relatively low species diversity, which increases through the remaining communities. The greatest diversity is found at the edges of the freshwater ponds.

In the Sandwort community, nearly all the cover is provided by Sea-beach Sandwort. The most important species in the Dense Marram community are American Beach-grass, Beach-pea, and Yarrow. American Beach-grass is the most important species in the Sparse Marram community, with Beach-pea and Seaside Goldenrod. In the Marram-Fescue community, American Beach-grass is joined by Red Fescue and a number of other species.

In the Shrub Heath community, Black Crowberry, Common Juniper, Bayberry, Wild Rose, blueberry, and Heather (in one area) are common plants. In the Cranberry Heath community, cranberries grow with such plants as Baltic Rush, Bayberry, and aster.

Cranberries on Sable Island Click to enlarge

Freshwater pools are usually fringed by a wide variety of plants, such as bulrushes, irises, Spike-rush, Baltic Rush, and Lance-leaved Violet, usually grading into the Cranberry Heath. In the brackish ponds, Ditch-grass and Sago Pondweed grow, surrounded either by bare sandy margins or salt-tolerant plants. The only vascular plant to grow in very brackish water is Eelgrass.

Animals
Sable Island provides sand-beach, sand-dune, and heathland habitats, with a number of fresh and brackish pools. The fact that the island is the only landfall for 160 km also ensures that it receives many migratory and marine visitors. The only terrestrial mammal now found on the island is the horse.

Horse, Sable Island Click to enlarge

The Sable Island horses were probably deliberately introduced in the eighteenth century. The horse population fluctuates and in recent years has varied between 150 and 350. At one time 500 cattle lived on the island, and pigs roamed wild. Both Grey and Harbour seals whelp on the island, and whales and dolphins are quite regularly washed up on the beaches. A number of other mammals have at one time been introduced to the island, including rats, cats, rabbits, and foxes, but all are now extirpated.

A total of 489 species of insects have been recorded on the island. The pattern of their distribution in North America has given rise to theories that Sable Island may have acted as a coastal-plain refugium during the Pleistocene glaciation. Insects have also been introduced with livestock, vegetation, and shipwrecks. A number of rare and unusual insects occur on Sable Island, and numerous moths appear, different enough to warrant the status of sub-species. More than 100 other invertebrates have been recorded, including the freshwater sponge Heteromyenia macouni.

Five species of fish - Mummichog, American Eel, Black-spotted Stickleback, Ninespine Stickleback, and Fourspine Stickleback - are found in the freshwater and brackish pools. All five species are capable of crossing salt water to reach the island.

Of the 12 species of birds that regularly breed on Sable Island, the most famous is the Ipswich Sparrow, which is an endemic sub-species of the Savannah Sparrow. Other birds include the European Starling, Great Black Back Gull, Herring Gull, Arctic Tern, Common Tern, Roseate Tern, Spotted Sandpiper, Least Sandpiper, Semipalmated Plover, Black Duck, and Red-breasted Merganser. Up to 312 other birds have been recorded as vagrants, strays, or migrants.

Scenic Quality
For those lucky enough to visit, Sable Island presents unique vistas from the higher dunes, which allow the island's shape and size to be seen. Elsewhere the sand beaches and dune systems are notable for their number and size. Sheltered hollows around the interior ponds provide visual relief from the surrounding ocean.

Cultural Environment
For years, Sable Island was the bane of sailing ships, and many were wrecked on its shores. A series of stations here, including a lighthouse, have long been lifesaving navigational aids to ships. In 1901 the Canadian government attempted to forest Sable Island to control shifting sands. More than 80,000 trees and shrubs were planted, and 30 pounds of pine seed were scattered over some parts of the island. Several years later, 2,000 willow transplants from sandy soil in France were sent to Sable Island. The first planting was made with no fencing, and the Sable Island horses soon consumed the entire plantation. A second attempt with this willow was made the next year by planting and fencing about a half acre. But these transplants did not survive either, because the wind-driven sand blasted the young trees. By the 1920s, nothing was left of these efforts except for some fence posts.

Most of the ecological damage on Sable Island resulted from disturbances to the vegetation, leaving loose sand exposed to the wind. Small holes in the sand soon blow out to become big holes and gullies. In the 1970s, snow fences were erected at strategic points, causing the wind to drop sand leeward of the fences and marram grass colonized the dunes. Government approval must be gained to visit the island, which is off limits to most people. Oil exploration has been conducted on the island and current production wells are located offshore. Sable Island has considerable scientific value as a unique ecological environment. It is one of the most intensively studied areas in the province (Catling, 1984; Wright, 1989).

Associated Topics T2.7 Offshore Geology T3.4 Terrestrial Glacial Deposits and Landscape Features T3.5 Offshore Bottom Characteristics T4.1 Post-glacial Climatic Change T6.1 Ocean Currents T7.1 Modifying Forces T7.3 Coastal Landforms T11.1 Factors Influencing Birds T11.8 Land Mammals T11.12 Marine Mammals T11.14 Marine Fishes T11.16 Land and Freshwater Invertebrates T11.18 Rare and Endangered Animals

Associated Habitats H1.1 Offshore Open Water H1.2 Offshore Benthic H2.3 Sandy Shore H2.5 Tidal Marsh H2.6 Dune System Associated Offshore Unit 931e Sable Island Bank