320
Chapter 10: The Indian Ocean
productivity and chlorophyll accumulation: the former responds to the seasonal irradiance cycle, whereas phytoplankton biomass is apparently maximal in austral winter.
This apparently anomalous situation results from the dynamic upwelling events that were
described earlier.
Australia-Indonesia Coastal Province (AUSW)
Extent of the Province
Like EAFR, the extent of this coastal boundary province is largely a matter of convenience
to avoid excessive subdivision in this work. As defined here, it extends from northern
Sumatra to southern Australia. Like EAFR, it could readily and logically be subdivided
into several primary entities. A logical first cut would be the following: (i) the tropical
southern coasts of Sumatra, Java, and the Lesser Sunda Islands; (ii) the subtropical
western coast of Australia from Cape Bougainville (14
N) in the southeastern Timor Sea
down to Cape Leeuwin at 34
S; and (iii) from Cape Leeuwin to the Bass Strait along the
temperate coast of the Great Australian Bight.
The offshore boundary is identified in the usual manner, where limits of coastal flow
can be identified (Colborn: coastal parts of 22, 23, 25, 26, and 34).
Continental Shelf Topography and Tidal and Shelf-Edge Fronts
The southern islands of the Indonesian archipelago have a very narrow continental shelf,
except off central to northern Sumatra where the chain of the Mentawai Islands 100–
200 km offshore encloses a significant area of shallow water. The shallow shelf of the Timor
Sea, not part of this province, is continuous with the wide Sahul shelf off northwestern
Australia. The Sahul shelf extends from Cape Talbot (13
S) southwest to Northwest Cape
(22
S), the shelf edge lying parallel to the coast and about 150–250 km offshore. Further
south, from Northwest Cape to Cape Leeuwin (34
S), the shelf is narrower (50–100 km),
especially off Perth, and the coastline lies almost directly toward the south. In the Great
Australian Bight, on the south coast of Australia, there is a further region of significant
shelf, reaching 150 km at about the center of the bight, south of the flatlands of the
Nullabor Plains.
The tidal range on the northwest coast of Australia increases progressively northward
so that at Broome (17
S) the spring tidal range is > 6 m; there are no reports, however,
of thermal fronts between stratified and tidally mixed water on this wide section of the
shelf. Instead, we should note that tropical cyclones are important in forcing storm surges
that propagate southward as coastally trapped Kelvin waves.
Defining Characteristics of Regional Oceanography
It will be convenient to deal with these three subregions individually, emphasizing that
there is a fundamental difference in atmospheric forcing between northern and southern
parts of this coastal province, corresponding to oceanic regions north and south of
the tropical convergence at about 20
S. From the coast of Indonesia south to ∼25
S,
alternating seasonal monsoons dominate the wind regime, whereas further to the south
the high-latitude westerly winds dominate. From ∼25
S, therefore, a summer thermocline
regime is appropriate, this feature forming each year in spring at ∼40 m and subsequently
deepening to ∼100 m in autumn, above a permanent thermocline that lies at ∼250 m.
South Coast of Sumatra and Java The Java Coastal Current is reversed by the seasonal changes in orientation of boreal summer monsoon winds, and salinity is modified
by rainfall on the highlands of the southern Indonesian archipelago at the same period,
Chapter 10: The Indian Ocean
productivity and chlorophyll accumulation: the former responds to the seasonal irradiance cycle, whereas phytoplankton biomass is apparently maximal in austral winter.
This apparently anomalous situation results from the dynamic upwelling events that were
described earlier.
Australia-Indonesia Coastal Province (AUSW)
Extent of the Province
Like EAFR, the extent of this coastal boundary province is largely a matter of convenience
to avoid excessive subdivision in this work. As defined here, it extends from northern
Sumatra to southern Australia. Like EAFR, it could readily and logically be subdivided
into several primary entities. A logical first cut would be the following: (i) the tropical
southern coasts of Sumatra, Java, and the Lesser Sunda Islands; (ii) the subtropical
western coast of Australia from Cape Bougainville (14
N) in the southeastern Timor Sea
down to Cape Leeuwin at 34
S; and (iii) from Cape Leeuwin to the Bass Strait along the
temperate coast of the Great Australian Bight.
The offshore boundary is identified in the usual manner, where limits of coastal flow
can be identified (Colborn: coastal parts of 22, 23, 25, 26, and 34).
Continental Shelf Topography and Tidal and Shelf-Edge Fronts
The southern islands of the Indonesian archipelago have a very narrow continental shelf,
except off central to northern Sumatra where the chain of the Mentawai Islands 100–
200 km offshore encloses a significant area of shallow water. The shallow shelf of the Timor
Sea, not part of this province, is continuous with the wide Sahul shelf off northwestern
Australia. The Sahul shelf extends from Cape Talbot (13
S) southwest to Northwest Cape
(22
S), the shelf edge lying parallel to the coast and about 150–250 km offshore. Further
south, from Northwest Cape to Cape Leeuwin (34
S), the shelf is narrower (50–100 km),
especially off Perth, and the coastline lies almost directly toward the south. In the Great
Australian Bight, on the south coast of Australia, there is a further region of significant
shelf, reaching 150 km at about the center of the bight, south of the flatlands of the
Nullabor Plains.
The tidal range on the northwest coast of Australia increases progressively northward
so that at Broome (17
S) the spring tidal range is > 6 m; there are no reports, however,
of thermal fronts between stratified and tidally mixed water on this wide section of the
shelf. Instead, we should note that tropical cyclones are important in forcing storm surges
that propagate southward as coastally trapped Kelvin waves.
Defining Characteristics of Regional Oceanography
It will be convenient to deal with these three subregions individually, emphasizing that
there is a fundamental difference in atmospheric forcing between northern and southern
parts of this coastal province, corresponding to oceanic regions north and south of
the tropical convergence at about 20
S. From the coast of Indonesia south to ∼25
S,
alternating seasonal monsoons dominate the wind regime, whereas further to the south
the high-latitude westerly winds dominate. From ∼25
S, therefore, a summer thermocline
regime is appropriate, this feature forming each year in spring at ∼40 m and subsequently
deepening to ∼100 m in autumn, above a permanent thermocline that lies at ∼250 m.
South Coast of Sumatra and Java The Java Coastal Current is reversed by the seasonal changes in orientation of boreal summer monsoon winds, and salinity is modified
by rainfall on the highlands of the southern Indonesian archipelago at the same period,