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An Introduction to Sea-Level Change in Malaysia
Sea level is changing and affecting coastal zones around the world. This, however,
is not the first time it has happened. The last approximately 2 million years of
Earth’s history, the Quaternary Period, is defined by expanding and contracting
polar ice sheets and corresponding low and high sea levels. The last major glacial
interval was at its maximum about 20,000 years ago. Since then, the polar continental ice sheets have been melting causing sea level to rise and flood continental
shelves around the world. What were once inland hills became islands. Some islands
and low-lying land connections between islands became submerged. Shorelines
evolved and backstepped as seas rose ~120 m to modern levels.
Since all of the Earth’s oceanic basins are connected, one would think that the
melting ice would cause sea level to rise everywhere. Indeed, the land is sinking in
some places causing a greater rate of sea-level rise, but at other locations, the land
is rising, sometimes faster than the rate of rise caused by the addition of water to
oceanic basins. The result is that sea-level changes, in relation to the land, are variable around the world.
The country of Malaysia is composed of two parts (Fig. 5.1). Peninsular Malaysia
is a contiguous part of the Asian continent and occupies the southern end of a peninsula extending south from Thailand and Myanmar. The peninsula is bounded on
the west by the Straits of Malacca and on the east by the southern South China Sea.
The other part of Malaysia lies over 600 km to the east, across the South China Sea
on the northwestern side of the island of Borneo.
The South China Sea separating Peninsular Malaysia from Borneo is shallow,
with an average water depth of ~70 m. This submerged area is known as the Sunda
Shelf (Fig. 5.1) and is the second largest continental shelf in the world. The waters
of the Straits of Malacca are even shallower than those of the southern South
China Sea.
Around 20,000 years ago, when polar glaciation was at its maximum and global
sea level was ~120 m lower than it is now, the Straits of Malacca and the Sunda
Shelf part of the South China Sea were dry land. Thus, the islands of Sumatra, Java
and Borneo were connected by land to the Asian continent. The connection had a
profound influence on the terrestrial biology of the region.
Subsequently, as high latitude continental ice sheets melted, seas rose rapidly
until 8000–7000 years ago, inundating the Straits of Malacca and the Sunda Shelf.
Sea level in this region then rose at a much slower rate for at least 1000 more years
to ~3 m above current sea level, after which it fell to the present level.
It is this period, between approximately 8000 years ago and present, that most
influenced the character of the Malaysia coastal zone as we see it today. The main
phenomenon responsible for this higher-than-present mid-Holocene sea level (the
Holocene encompasses the last 11,700 years) was a process called continental levering, the vertical movement of land in response to weight added by increased seawater on the continental shelf. Parts of the world far from the direct influence of
P. R. Parham
An Introduction to Sea-Level Change in Malaysia
Sea level is changing and affecting coastal zones around the world. This, however,
is not the first time it has happened. The last approximately 2 million years of
Earth’s history, the Quaternary Period, is defined by expanding and contracting
polar ice sheets and corresponding low and high sea levels. The last major glacial
interval was at its maximum about 20,000 years ago. Since then, the polar continental ice sheets have been melting causing sea level to rise and flood continental
shelves around the world. What were once inland hills became islands. Some islands
and low-lying land connections between islands became submerged. Shorelines
evolved and backstepped as seas rose ~120 m to modern levels.
Since all of the Earth’s oceanic basins are connected, one would think that the
melting ice would cause sea level to rise everywhere. Indeed, the land is sinking in
some places causing a greater rate of sea-level rise, but at other locations, the land
is rising, sometimes faster than the rate of rise caused by the addition of water to
oceanic basins. The result is that sea-level changes, in relation to the land, are variable around the world.
The country of Malaysia is composed of two parts (Fig. 5.1). Peninsular Malaysia
is a contiguous part of the Asian continent and occupies the southern end of a peninsula extending south from Thailand and Myanmar. The peninsula is bounded on
the west by the Straits of Malacca and on the east by the southern South China Sea.
The other part of Malaysia lies over 600 km to the east, across the South China Sea
on the northwestern side of the island of Borneo.
The South China Sea separating Peninsular Malaysia from Borneo is shallow,
with an average water depth of ~70 m. This submerged area is known as the Sunda
Shelf (Fig. 5.1) and is the second largest continental shelf in the world. The waters
of the Straits of Malacca are even shallower than those of the southern South
China Sea.
Around 20,000 years ago, when polar glaciation was at its maximum and global
sea level was ~120 m lower than it is now, the Straits of Malacca and the Sunda
Shelf part of the South China Sea were dry land. Thus, the islands of Sumatra, Java
and Borneo were connected by land to the Asian continent. The connection had a
profound influence on the terrestrial biology of the region.
Subsequently, as high latitude continental ice sheets melted, seas rose rapidly
until 8000–7000 years ago, inundating the Straits of Malacca and the Sunda Shelf.
Sea level in this region then rose at a much slower rate for at least 1000 more years
to ~3 m above current sea level, after which it fell to the present level.
It is this period, between approximately 8000 years ago and present, that most
influenced the character of the Malaysia coastal zone as we see it today. The main
phenomenon responsible for this higher-than-present mid-Holocene sea level (the
Holocene encompasses the last 11,700 years) was a process called continental levering, the vertical movement of land in response to weight added by increased seawater on the continental shelf. Parts of the world far from the direct influence of
P. R. Parham