Pacific Coastal Biome
423
Sunda-Arafura Shelves Province (SUND)
Extent of the Province
The SUND province comprises all the Asiatic continental shelves from Burma to Hainan
and the archipelagic shelves south to the coast of Australia and New Guinea, at the Gulf
of Papua. This is the shallow-water counterpart of the ARCH province that comprises
the deep basins within the archipelagic region to the north of Australia; the logic of this
partition has been discussed previously (see ARCH).
This province comprises both minor shelf areas and also large regions of continuous
shallow water. The deep water of the Flores and Banda Seas separates the western from
the eastern shelf areas, these seas being continuous with the deep basins lying farther
north of the Celebes, Flores, and Sulu Seas. The many islands, large and small, and island
arcs that inhabit these deep basins all have a coastal fringe of shallow water, and these
shallow areas are included in this, the SUND province.
As will become very clear, this province could readily be subdivided into four or five
logical subunits; unfortunately, we currently lack the information on which to base such
a logical partitioning of this complex and beautiful region, which remains so poorly
explored scientifically.
Continental Shelf Topography and Tidal and Shelf-Edge Fronts
These are the largest continental shelves anywhere in the ocean, the scale of which is
not often appreciated. The Arafura and Sunda shelves are together equivalent in area to
about 10 Grand Banks of Newfoundland and the total extent of shelf area in this province
(about 45 × 10
6 km
2 ) is about 18–20% of the total shelf area of all oceans. There are
three major blocks of shelf topography, each representing recently drowned coastlines
(Ben-Avraham and Emery, 1973): (i) the shallow shelves fringing continental Southeast
Asia (Gulf of Tonkin, Vietnam, Gulf of Thailand, eastern South China Sea, Malacca
Straits, and the Andaman Sea) and (ii) the shelves of the western part of the archipelago
(western South China Sea, Sunda Shelf, and the Java Sea), which are separated by deep
water from (iii) the shelves of the eastern archipelago and Australia-New Guinea (Arafura
Sea, Timor Sea, and the Gulf of Carpentaria). Obviously, this is a region ripe for further
logical subdivision, for which these three sub-regions might be a useful start.
This shallow water province is unique in other ways than mere dimension: the unusually shallow shelf that nevertheless has great width, the complex tidal dynamics due to
the interaction of the tides of two adjacent oceans, and the sediment input from rivers
(72 × 10
9 tons annually) all combine to make this a most unusual area. For instance,
the central parts of the Sunda Shelf are less than 100 m, and the southern parts between
Borneo and Sumatra are only 10–40 m deep; many submerged valleys of the rivers that
previously drained the shelf area still exist, and some have been deepened by tidal flows.
Some of the passes between the islands have opened only during the historical era and
are still very shallow indeed.
Soft muddy deposits dominate the eastern complex of shelves more frequently than the
western regions where strong tidal streams are the rule. The Torres Strait is such a case,
because the Arafura and Coral Seas force different tides, such that there are fluctuations
of up to 6 m in difference in sea level on each side of the strait between the two seas. Tidal
streams (>5 knots) in and across the straits are controlled by sea-level slope, bottom
friction, and acceleration (Wolanski et al., 1988). Such tidal streams generate sufficient
bottom friction in many places to overcome water-column stability and, in such places,
we may expect to observe tidal fronts and associated biological enhancement. The Malacca
Strait and the Arafura Sea/Gulf of Carpentaria region have been identified as potentially
productive of such features; the area between Australia and the Lesser Sunda Islands
423
Sunda-Arafura Shelves Province (SUND)
Extent of the Province
The SUND province comprises all the Asiatic continental shelves from Burma to Hainan
and the archipelagic shelves south to the coast of Australia and New Guinea, at the Gulf
of Papua. This is the shallow-water counterpart of the ARCH province that comprises
the deep basins within the archipelagic region to the north of Australia; the logic of this
partition has been discussed previously (see ARCH).
This province comprises both minor shelf areas and also large regions of continuous
shallow water. The deep water of the Flores and Banda Seas separates the western from
the eastern shelf areas, these seas being continuous with the deep basins lying farther
north of the Celebes, Flores, and Sulu Seas. The many islands, large and small, and island
arcs that inhabit these deep basins all have a coastal fringe of shallow water, and these
shallow areas are included in this, the SUND province.
As will become very clear, this province could readily be subdivided into four or five
logical subunits; unfortunately, we currently lack the information on which to base such
a logical partitioning of this complex and beautiful region, which remains so poorly
explored scientifically.
Continental Shelf Topography and Tidal and Shelf-Edge Fronts
These are the largest continental shelves anywhere in the ocean, the scale of which is
not often appreciated. The Arafura and Sunda shelves are together equivalent in area to
about 10 Grand Banks of Newfoundland and the total extent of shelf area in this province
(about 45 × 10
6 km
2 ) is about 18–20% of the total shelf area of all oceans. There are
three major blocks of shelf topography, each representing recently drowned coastlines
(Ben-Avraham and Emery, 1973): (i) the shallow shelves fringing continental Southeast
Asia (Gulf of Tonkin, Vietnam, Gulf of Thailand, eastern South China Sea, Malacca
Straits, and the Andaman Sea) and (ii) the shelves of the western part of the archipelago
(western South China Sea, Sunda Shelf, and the Java Sea), which are separated by deep
water from (iii) the shelves of the eastern archipelago and Australia-New Guinea (Arafura
Sea, Timor Sea, and the Gulf of Carpentaria). Obviously, this is a region ripe for further
logical subdivision, for which these three sub-regions might be a useful start.
This shallow water province is unique in other ways than mere dimension: the unusually shallow shelf that nevertheless has great width, the complex tidal dynamics due to
the interaction of the tides of two adjacent oceans, and the sediment input from rivers
(72 × 10
9 tons annually) all combine to make this a most unusual area. For instance,
the central parts of the Sunda Shelf are less than 100 m, and the southern parts between
Borneo and Sumatra are only 10–40 m deep; many submerged valleys of the rivers that
previously drained the shelf area still exist, and some have been deepened by tidal flows.
Some of the passes between the islands have opened only during the historical era and
are still very shallow indeed.
Soft muddy deposits dominate the eastern complex of shelves more frequently than the
western regions where strong tidal streams are the rule. The Torres Strait is such a case,
because the Arafura and Coral Seas force different tides, such that there are fluctuations
of up to 6 m in difference in sea level on each side of the strait between the two seas. Tidal
streams (>5 knots) in and across the straits are controlled by sea-level slope, bottom
friction, and acceleration (Wolanski et al., 1988). Such tidal streams generate sufficient
bottom friction in many places to overcome water-column stability and, in such places,
we may expect to observe tidal fronts and associated biological enhancement. The Malacca
Strait and the Arafura Sea/Gulf of Carpentaria region have been identified as potentially
productive of such features; the area between Australia and the Lesser Sunda Islands