Saba Bank National Park

Note: The data were entered in the language of the country of origin (English, French or Spanish) and there is no translation available yet.

Chapter 3. SITE DESCRIPTION

a - General features of the site

Terrestrial surface under sovereignty, excluding wetlands:

0 sq. km

Wetland surface:

0 ha

Marine surface:

2679 sq. km

Global comment for the 3 previous fields (optional):

This is exclusively a marine area situated far from land. The closest land is the island of Saba at a distance of about 5 nautical miles, and separated by a channel of more than 500 m deep.

b - Physical features

Brief description of the main physical characteristics in the area:

The Saba Bank is an undersea elevation with a flattened top, a bank, 3 - 5 km Southwest of the island of Saba and 25 km west of St. Eustatius. It is raised about 1000m above the general depths of the surrounding sea floor and its shape is approximately square or slightly elliptical, the long axis trending ENE-WSW. With a length of 60 to 65 km and a width of 30 to 40 km, the total surface area is approximately 2200 km2 (measured to the 200 m isobath). The platform is somewhat tilted with the north-western part of the surface being deeper than the south-eastern part. The largest part of the bank is between 20 and 50 m depth, but a substantial eastern part (app. 225 km2) is between 10 and 20 m depth. On its western rim depths are around 50 m, while on the eastern and south-eastern edges, where a prominent coral ridge system (55 km long) runs along the platform, depths vary between 7 and 15 m (Van der Land 1974, MacIntyre et al. 1975).

Geology:

The Saba Bank is located at the intersection of three different types of geological activity. It is near the eastern end of the tectonically active Greater Antilles island chain, at the north end of the Aves Ridge and just to the west of the north end of the volcanic island arc chain near the north-eastern boundary of the Caribbean Sea. The Saba Bank has intrigued many scientists dating back to the beginning of the century. Spencer (1904; p. 357) considered the Bank to be "a remnant of the coastal plains on the mountainous backbone of the Antillean ridge". He concludes that the Bank "has been levelled by coral growth and the sands derived from them". Vaughan (1919) viewed the Bank as a submarine plateau, levelled by planation agencies, which almost certainly were both subaerial and submarine, which has been submerged in recent geologic time. Vaughan already indicated that the Bank essentially duplicates the atolls in the Pacific. This was later verified by Van der Land (1977) who considers the Bank to be an actively growing atoll, although it is completely submerged, and ranks it among the largest atolls in the world. Davis (1926) viewed the Bank as "an atoll lagoon floor, deprived of its original reef and probably somewhat planed down by low-level abrasion in the post glacial epoch" (Davis 1926, p. 138). Differences of opinion on the formation of Banks such as the Saba Bank have caused heated debate. Vaughan stated that infilling behind barrier reefs could never be the reason for the existence of the Bank, whereas Davis thought this was an essential process.

Soil:

N.A.

Topography:

On the Saba Bank the reef zonation pattern follows a sequence from shelf edge to central Bank. On the eastern portion of the Bank, known as Overall Bank, reef zones occur in the following sequence as one moves from east (windward, open ocean) to west (leeward, towards central Saba Bank): seaward slope, fore reef (with one or more “front reefs”), reef flat, backreef slope (“escarpment”), lagoon, and patch reef (located within the lagoon). The fore reef zone is a steeply sloping and topologically variable region. Van der Land (1977) observed a “front reef” rising from a “reef terrace” at 30-40 m depth. High-resolution bathymetry confirmed the presence of at least one front reef feature at Overall Bank. To the west (leeward) of the front reef, an area resembling a spur-and-groove reef is found. For the purposes of this management plan, these various reef features are considered elements of a single zone - the fore-reef zone.
Westward (leeward) of the fore reef zone, the reef rises to ~ 15 m depth and forms a wide (> 1000 m) level expanse. Van der Land (1977) identified this area as the reef flat and suggested that it comprised an inner and outer zone distinguished by bathymetry. Examination of recent highresolution bathymetry data did not differentiate inner and outer reef flat zones within the area of Overall Bank.
The lagoon zone extends eastward (leeward) from the reef flat and backreef slope zones. Van der Land considered the lagoon a single zone, although he distinguished “patch reef’ formations within it. Bathymetry confirmed the presence of patch reef-like features within the lagoon.

Bathymetry:

see topography

Hydrodynamics:

The Saba Bank and the neighbouring islands are affected by The Antilles Current and possibly the Caribbean current. The Antilles Current flows northward east of the Antilles joining the Florida Current past the outer Bahamas. Its waters are concentrated into a strong northward jet about 80-100 km wide centred at 400 m depth. Mooring studies have indicated that the Antilles Current has mean transport speeds of 3.2 Sv (sverdrup) northwards in the upper 800m of water.

The narrowly spaced chain of islands, Banks, and sills of the Antilles Islands Arc, including Saba and the neighbouring islands, separate the Caribbean from the Atlantic Ocean and act as a sieve for the inflow of Atlantic water to the Caribbean Basin. Water flows into the Caribbean Sea through the narrow
passages between the islands and continues westward as the Caribbean Current, the main surface circulation in the Caribbean Sea.

Waves, known as ground swells, are produced by low pressure weather systems at sea. Waves produced by the wind are generally highest from June to July and from December to March when the wind speeds are highest. The dominant easterly wind drives waves towards the west. During swell wave conditions there is likely considerable impact on the communities on the Bank.

Volcanic formations:

The entire Saba Bank is thought to have a core of volcanic rock, completely capped by fossil reefs. and without volcanic activity. The northwestern part of the Saba Bank is thought to be the result of relatively recent volcanic activity and may still have some remaining activity.

Sand dunes:

N.A.

Underwater formations:

see topography