380
Chapter 11: The Pacific Ocean
partly isolated from the SW Pacific behind island arcs, whereas the South China Sea has
a major deep-water connection to the Pacific between Taiwan and Luzon and extensive
shallow connections to the southwest with the Indian Ocean.
Defining Characteristics of Regional Oceanography
The circulation of the shelves and deep basins comprising the Indo-Pacific Archipelago
and Coral Sea are treated as a single, complex hydrographic and atmospheric system,
the Southeast Asian Waters, in the Naga Report of 1961. Nevertheless, it will be useful
here to distinguish three components: the South China Sea, the archipelagic seas, and
the Coral Sea. The discussion that follows of circulation through the archipelago and
adjacent basins is intended to have relevance for the ecology of both the coastal (SUND)
and oceanic (ARCH) provinces.
The regional oceanography of this region, of which the most complete description
remains that of Wyrtki, is unique. Because of a small sea-level difference, in the absence
of wind forcing, flow would be through the archipelago toward the Indian Ocean, but
the near-surface flow, in which we shall be most interested, is in fact dominated by the
effect of the reversing monsoon winds. Satellite imagery confirms the dynamic nature of
the flows through passages between islands. Though apparently not described, it would
not be surprising to find examples of barrier layers (shallow halocline above a deeper
thermocline) here, as is typical of the WARM Province.
The East Asian monsoon system is the classical model of such seasonal patterns; the
intertropical convergence zone (ITCZ) between the easterly winds of the northern and
southern hemisphere lies seasonally on each side of the equator, following the sun between
23
N and S. In boreal winter, then, the Indonesian archipelago lies below the northerly
trade winds that are first felt in October in the East China Sea, and then progressively
strengthen as the ITCZ passes south of the equator; the northwest monsoon brings moist
air, causing heavy rainfall and rapid discharge of freshwater from the short rivers in the
archipelago. In May, the northerly monsoon collapses as the ITCZ moves north, so that
southerly trades (Beaufort force 4 over the open sea) develop over the whole archipelago,
and by August the monsoon of boreal summer is fully developed. This is a significantly
drier season and in the archipelagic region the southeast trades are strongly zonal, so
forcing a westward component in resultant flows. This seasonal near-reversal of wind
stress induces reversing current systems through the channels of the archipelago and
is associated with a great diversity of hydrographic processes likely to have biological
consequences, usefully summarized in the review by Wyrtki (1961).
The strongest reversing flow is in the South China Sea, because of western intensification along the coast of Vietnam, and is usually associated with a countercurrent offshore.
Thus, in February, at the peak of the Northeast Monsoon, a strong surface flow of cool
water passes south as a western boundary current along the coasts of southern China and
Vietnam, continuing on to the southeast around the southern side of the South China
Sea, and then through the Java Sea to join Pacific water originating in the Molucca Sea.
This combined stream then passes east through the Banda Sea to rejoin the Pacific Ocean
around New Guinea. In boreal summer, this flow is reversed.
In August, the onset of the Southeast Monsoon reverses the circulation in the South
China Sea, and flow is now forced to the northwest through the Java Sea and to the
west through the Banda Sea by the westward component of the Southeast Monsoon
winds north of Australia. Part of the water entrained from the Pacific around Mindanao
returns to that ocean along the north coast of Celebes, while some passes through the
Straits of Macassar. Here, flow is persistently to the south with maximum velocities in
February–March into the Flores Sea and July–September into the Java Sea.
The deep basin of the Banda Sea, especially toward the east, experiences regional
upwelling during the Southeast Monsoon, and downwelling during the northerly
Chapter 11: The Pacific Ocean
partly isolated from the SW Pacific behind island arcs, whereas the South China Sea has
a major deep-water connection to the Pacific between Taiwan and Luzon and extensive
shallow connections to the southwest with the Indian Ocean.
Defining Characteristics of Regional Oceanography
The circulation of the shelves and deep basins comprising the Indo-Pacific Archipelago
and Coral Sea are treated as a single, complex hydrographic and atmospheric system,
the Southeast Asian Waters, in the Naga Report of 1961. Nevertheless, it will be useful
here to distinguish three components: the South China Sea, the archipelagic seas, and
the Coral Sea. The discussion that follows of circulation through the archipelago and
adjacent basins is intended to have relevance for the ecology of both the coastal (SUND)
and oceanic (ARCH) provinces.
The regional oceanography of this region, of which the most complete description
remains that of Wyrtki, is unique. Because of a small sea-level difference, in the absence
of wind forcing, flow would be through the archipelago toward the Indian Ocean, but
the near-surface flow, in which we shall be most interested, is in fact dominated by the
effect of the reversing monsoon winds. Satellite imagery confirms the dynamic nature of
the flows through passages between islands. Though apparently not described, it would
not be surprising to find examples of barrier layers (shallow halocline above a deeper
thermocline) here, as is typical of the WARM Province.
The East Asian monsoon system is the classical model of such seasonal patterns; the
intertropical convergence zone (ITCZ) between the easterly winds of the northern and
southern hemisphere lies seasonally on each side of the equator, following the sun between
23
N and S. In boreal winter, then, the Indonesian archipelago lies below the northerly
trade winds that are first felt in October in the East China Sea, and then progressively
strengthen as the ITCZ passes south of the equator; the northwest monsoon brings moist
air, causing heavy rainfall and rapid discharge of freshwater from the short rivers in the
archipelago. In May, the northerly monsoon collapses as the ITCZ moves north, so that
southerly trades (Beaufort force 4 over the open sea) develop over the whole archipelago,
and by August the monsoon of boreal summer is fully developed. This is a significantly
drier season and in the archipelagic region the southeast trades are strongly zonal, so
forcing a westward component in resultant flows. This seasonal near-reversal of wind
stress induces reversing current systems through the channels of the archipelago and
is associated with a great diversity of hydrographic processes likely to have biological
consequences, usefully summarized in the review by Wyrtki (1961).
The strongest reversing flow is in the South China Sea, because of western intensification along the coast of Vietnam, and is usually associated with a countercurrent offshore.
Thus, in February, at the peak of the Northeast Monsoon, a strong surface flow of cool
water passes south as a western boundary current along the coasts of southern China and
Vietnam, continuing on to the southeast around the southern side of the South China
Sea, and then through the Java Sea to join Pacific water originating in the Molucca Sea.
This combined stream then passes east through the Banda Sea to rejoin the Pacific Ocean
around New Guinea. In boreal summer, this flow is reversed.
In August, the onset of the Southeast Monsoon reverses the circulation in the South
China Sea, and flow is now forced to the northwest through the Java Sea and to the
west through the Banda Sea by the westward component of the Southeast Monsoon
winds north of Australia. Part of the water entrained from the Pacific around Mindanao
returns to that ocean along the north coast of Celebes, while some passes through the
Straits of Macassar. Here, flow is persistently to the south with maximum velocities in
February–March into the Flores Sea and July–September into the Java Sea.
The deep basin of the Banda Sea, especially toward the east, experiences regional
upwelling during the Southeast Monsoon, and downwelling during the northerly