Andaman Sea

• Category: Marine and Oceanic Biomes.
• Geographic Location: Southeast Asia.
• Summary: The Andaman Sea is a reef- and coastal seagrass-rich basin that connects the South China Sea with the Indian Ocean via the Straits of Malacca.

The Andaman or Burma Sea is a marginal sea adjoining Sumatra, Thailand, and Burma; it is situated in the eastern Indian Ocean and transitions southward into the Straits of Malacca (between Sumatra and the Malay Peninsula). The Andaman Sea borders the western margin of the Sunda continental shelf (6 to 16 degrees north, 93 to 98 degrees east). It has more or less an elliptical shape, covering the equivalent of approximately 308,882 square miles (approximately 800,000 square kilometers), with its longest axis oriented approximately north-south. Further adjacencies include the deltaic plain of the Irrawaddy River to the north and the Andaman and Nicobar Islands to the west.

The Andaman combines scarcely known oceanographic and ecological patterns with an unfortunately all-too-well-known, highly active tectonic location—it was heavily affected by the 2004 Indian Ocean seaquake and tsunami. The Andaman also boasts a strategic position for shipping trade routes. The name Andaman probably originated from Handuman, the Malay form of Hanumān, a Hindu apelike deity. This name possibly refers to the aboriginal people of the Andaman Islands, a unique and ancient human lineage that migrated from Africa more than 50,000 years ago and is now almost completely extinct.

Geology and Recent Seismic Activity

The Andaman Sea is a back-arc marginal basin that originated along the oblique Sunda subduction zone in the Miocene. Several transform faults oriented north-south and an active oceanic ridge separate the Burma microplate to the west from the Sunda plate to the east. Barren Island in the Andaman is an active volcano.

This tectonic scenario was the stage for the 2004 event, which featured a catastrophic 9.2 magnitude quake with the epicenter in the southern portion of the Burma microplate, about 62 miles (100 kilometers) off the northwest Sumatran coast. This massive tsunami killed some 200,000 people from Thailand and Indonesia to Sri Lanka and India. Large slip earthquakes of this type, although relatively rare and usually not associated with tsunamis, continue to occur in this active seismic area.

Oceanography and Meteorology

The average depth of the Andaman Sea is about 3,609 feet (1,100 meters). A depression 6,562 to 13,123 feet (2,000 to 4,000 meters) deep, 62 to 186 miles (100 to 300 kilometers) wide, and 466 miles (750 kilometers) long is oriented north-south along the oceanic ridge.

The seasonal patterns of the rainforest climate that is prevalent along its shores is dominated by the South Asian monsoon, with a dry winter or northeastern monsoon in December through February and a rainy summer or southwestern monsoon season during May through September. The northeastern monsoon is much weaker and less persistent. During transitional periods, in spring and fall, weather is more unpredictable, with lower average wind speeds and occasional extreme winds. Along the mainland coast, the average annual rainfall is the equivalent of 138 inches (3,500 millimeters).

The distribution and fluctuations of sea surface temperatures directly influence the effects of global climate cycles such as the El Niño Southern Oscillation and the Indian Ocean Dipole on neighboring continental areas. Such patterns are influenced by river discharge, strong tidal mixing and internal waves, and the exchange of surface and deep water from the Bay of Bengal.

Coastal Systems and Continental Shelf

To the north, the Irrawaddy, Sittang, and Thanlwin (or Salween) Rivers discharge, on average more than 144 cubic miles (600 cubic kilometers) of freshwater and more than 386 million tons (350 million metric tons) of sediments per year, resulting in the progradation, or outgrowth, of the eastern portion of this delta, and deeply affecting the seasonal hydrological patterns and habitat suitability of the northern basin. South of the Gulf of Martaban, the Burmese Tanintharyi coast includes the Mergui Archipelago. Due to the influence of freshwater inputs along the coast, nearshore systems here are often characterized by mangrove forests and seagrass beds, while fringing and patch coral reefs colonize offshore islands.

Moving southward along the Thai Andaman Sea coast, the shoreline is more regular, with limited river inputs and abundant coral reefs fringing both near-shore and offshore islands. On the west side of the basin, the Andaman and Nicobar Islands—territories of India—are also fringed by mangrove formations and seagrass beds, being characterized by 2,510 square miles (6,500 kilometers) of coral reefs. This body of reefs constitutes 88 percent of all India's coral reefs.

Anthropogenic Impact

The Andaman Sea fisheries are exploited by four countries whose Exclusive Economic Zones (EEZs) extend over this basin: Thailand; Burma; India, through its Andaman and Nicobar Island populations; and Indonesia, through the island of Sumatra. All these countries are known to fish to some degree in others' EEZs, generating harsh economic and legal disputes.

On both the west and east sides of the basin, coral reefs and seagrass beds are increasingly affected by illegal and destructive fishing practices, including blast fishing, poisoning, trawling, push-netting, and long-line fishing. The Thai coastal ecosystems are also affected by habitat destruction and silting-up from land erosion, coastal and inland deforestation, damming, and rapid development due to the infrastructure needs of the growing tourism industry.

Global warming threatens the sea. The predicted rise in sea temperatures could exacerbate coral bleaching, as well as create drastic and unstable weather in the region.

Bibliography

Hall, Robert, and Jeremy D. Holloway, editors. Biogeography and Geological Evolution of SE Asia. Backhuys, 1998.

Jacob, Ashish P., et al. "Investigating the Biological Diversity and Ecological Dynamics of Oceanic Fishery Resources in the Andaman Sea, Indian Ocean." Discover Environment, vol. 2, no. 1, Aug. 2024, pp. 1-15. EBSCOhost, doi.org/10.1007/s44274-024-00125-2. Accessed 30 Oct. 2024.

Jithin, A. K., and P. A. Francis. "Rate of Internal Tide Mixing in Keeping the Deep Andaman Sea." Scientific Reports, vol. 10, 20 July 2020, www.nature.com/articles/s41598-020-68708-6. Accessed 30 Oct. 2024.

Ramasamy, V., et al. "Tidal Influence on Suspended Sediment Distribution and Dispersal in the Northern Andaman Sea and Gulf of Martaban." Marine Geology, vol. 208, no. 1, 2004, pp. 33-42.

Shankar, D., et al. "The Monsoon Currents in the North Indian Ocean." Progress in Oceanography, vol. 52, no. 1, 2002, pp. 63-120.

Temple, R. C. Imperial Gazetteer of India Provincial Series: Andaman and Nicobar Islands. Superintendent of Government Printing, 1909.

Varkey, M. J., et al. "Physical Oceanography of the Bay of Bengal and Andaman Sea." Oceanography and Marine Biology, vol. 34, no. 1, 1996, pp. 1-70.