Andaman Sea

Location The Andaman Sea, which extends over 92°E to 100°E and 4°N to 20°N, occupies a very significant position in the Indian Ocean, yet remained unexplored for a long period. To the south of Myanmar, west of Thailand, and north of Indonesia, this sea is separated from the Bay of Bengal by the Andaman and Nicobar Islands and an associated chain of sea mounts along the Indo-Burmese plate boundary. The Strait of Malacca (between the Malay Peninsula and Sumatra) forms the southern exitway of the basin, which is wide and deep. Extent The International Hydrographic Organization defines the limits of the "Andaman or Burma Sea" as follows: On the Southwest. A line running from "Oedjong Raja" ["Ujung Raja" or "Point Raja"] () in Sumatra to Poeloe Bras (Breuëh) and on through the Western Islands of the Nicobar Group to Sandy Point in Little Andaman Island, in such a way that all the narrow waters appertain to the Burma Sea. On the Northwest. The Eastern limit of the Bay of Bengal [A line running from Cape Negrais (16°03'N) in Burma [Myanmar] through the larger islands of the Andaman group, in such a way that all the narrow waters between the islands lie to the Eastward of the line and are excluded from the Bay of Bengal, as far as a point in Little Andaman Island in latitude 10°48'N, longitude 92°24'E]. On the Southeast. A line joining Lem Voalan (7°47'N) in Siam [Thailand], and Pedropunt (5°40'N) in Sumatra. Oedjong means "cape" and Lem means "point in the Dutch language on maps of the Netherlands East Indies (Indonesia). Lem Voalan [Phromthep Cape] is the southern extremity of Goh Puket (Phuket Island). Exclusive economic zone Exclusive economic zones in Andaman Sea: Channels See Channels in Bay of Bengal, Laccadive Sea, and Arabian Sea. ==Geology==

and silt deposits due to the Irrawaddy River in its northern part The northern and eastern side of the basin is shallow, as the continental shelf off the coast of Myanmar and Thailand extends over (marked by isobath). About 45 percent of the basin area is shallower (less than depth), which is the direct consequence of the presence of the wider shelf. The continental slope which follows the eastern shelf is quite steep between 9°N and 14°N. Here, the perspective view of the submarine topography sectioned along 95°E exposes the abrupt rise in depth of sea by about within a short horizontal distance of a degree. Isobaths corresponding to are also shown in the figure to emphasize the steepness of the slope. Further, it may be noted that the deep ocean is also not free from sea mounts; hence only around 15 percent of the total area is deeper than . ). Numerous earthquakes have been recorded, and at least six, in 1797, 1833, 1861, 2004, 2005, and 2007, had a magnitude of 8.4 or higher. On 26 December 2004, a large portion of the boundary between the Burma plate and the Indo-Australian plate slipped, causing the 2004 Indian Ocean earthquake. This megathrust earthquake had a magnitude of 9.3. Between of the boundary underwent thrust faulting and shifted by about , with the sea floor being uplifted several meters. This rise in the sea floor generated a massive tsunami with an estimated height of that killed approximately 280,000 people along the coast of the Indian Ocean. The initial quake was followed by a series of aftershocks along the arc of the Andaman and Nicobar Islands. The entire event severely damaged the fishing infrastructure. Volcanic activity volcano in 1995. Andaman Islands (on top) are c. 90 km distant Within the sea, to the east of the main Great Andaman island group, lies Barren Island, the only currently active volcano associated with the Indian subcontinent. This island volcano is in diameter and rises above sea level. Its recent activity resumed in 1991 after a quiet period of almost 200 years. It is caused by the ongoing subduction of the India plate beneath the Andaman island arc, which forces magma to rise in this location of the Burma plate. The last eruption started on 13 May 2008 and continues. The volcanic island of Narcondam, which lies further north, was also formed by this process. No records exist of its activity. Sediments to the Sea Collectively, the modern Ayeyarwady (Irrawaddy) and Thanlwin (Salween) rivers deliver >600 Mt/yr of sediment to the sea. Most recent studies show: 1) There is little modern sediment accumulating on the shelf immediately off the Ayeyarwady River mouths. In contrast, a major mud wedge with a distal depocenter, up to in thickness, has been deposited seaward in the Gulf of Martaban, extending to approximately water depth into the Martaban Depression. Further, 2) There is no evidence showing that modern sediment has accumulated or is transported into the Martaban Canyon; 3) a mud drape/blanket is wrapping around the narrow western Myanmar Shelf in the eastern Bay of Bengal. The thickness of the mud deposit is up to nearshore and gradually thins to the slope at water depth, and likely escapes into the deep Andaman Trench; 4) The estimated total amount of Holocene sediments deposited offshore is approximately . If we assume this has mainly accumulated since the middle Holocene highstand (~6000 yr BP) like other major deltas, the historical annual mean depositional flux on the shelf would be per year, which is equivalent to ~35% of the modern Ayeyarwady-Thanlwin rivers derived sediments; 5) Unlike other large river systems in Asia, such as the Yangtze and Mekong, this study indicates a bi-directional transport and depositional pattern controlled by the local currents that are influenced by tides, and seasonally varying monsoons winds and waves. ==Climate==

The climate of the Andaman Sea is determined by the monsoons of southeast Asia, as the prevailing winds reverse with the start of either season. The region experiences north-easterlies with an average windspeed of from November to February. During these months, the western part of the domain experiences maximum wind intensity. It weakens by March–April and reverses to strong south-westerlies from May to September, with mean wind speeds touching in June, July, and August, distributed near-uniformly over the entire basin. Wind speeds plummet by October and switch back to north-easterlies from November. Air temperature is stable over the year at in February and in August. Precipitation is as high as /year and mostly occurs in summer. Sea currents are south-easterly and easterly in winter and south-westerly and westerly in summer. The average surface water temperature is in February and in May. The water temperature is constant at at the depths of and below. Salinity is 31.5–32.5‰ (parts per thousand) in summer and 30.0–33.0‰ in winter in the southern part. In the northern part, it decreases to 20–25‰ due to the inflow of freshwater from the Irrawaddy River. Tides are semidiurnal with an amplitude of up to . The effect of wind stress on the ocean surface can be explained by wind stress curl. The net divergence of water in the ocean mixed layer results in Ekman pumping. The contrast between the two seasons elicits a very strong negative pumping velocity of more than per day along the north coast of Indonesia from May to September (shown here, June). This may signify coastal downwelling in the summer. It is also observed that the region develops a weak but positive pumping velocity of less than per day at the mouth of GC in winter (here, December). ==Current and wave fluid dynamics==

The basin has a very high rate of transport of water through the straits in April and October. This is a period of equatorial Wyrtki jets, which hit the coast of Sumatra and reflect back as Rossby waves and coastal Kelvin waves. These Kelvin waves are guided along the eastern boundary of Indian Ocean, and a part of this signal propagates into the Andaman Sea. The northern coast of Sumatra is the first to be affected. The isotherm which deepens during the same period is suggestive of the downwelling nature of Kelvin waves. The waves further propagate along the eastern boundary of the Andaman Sea, which is confirmed by the differential deepening of the 20-degree isotherm along longitudes 94°E and 97°E (averaged over latitudes 8°N and 13°N). These longitudes are chosen so that one represents the western part of the basin (94°E) and the other along the steep continental slope on the eastern side of the basin (97°E). It is observed that both these longitudes experience deepening of the isotherms in April and October, but the effect is more pronounced at 97°E (isotherms deepen by in April and in October). This is a concrete signature of downwelling in the basin and is definitely not forced locally as the winds are weaker during this period. This confirms unequivocally that the sudden burst of water into the basin through the straits, the intensification of eastern boundary currents and the coincidental deepening of isotherms in April and October are the direct consequence of the propagation of downwelling Kelvin waves in the Andaman Sea, remotely forced by equatorial Wyrtki jets. The evolution of vorticity in the basin is suggestive of strong shear in the flow during different times of the year, and further indicates the presence of low frequency geophysical waves (such as westward propagating Rossby waves) and other transient eddies. ==Ecology==

Flora The coastal areas of the Andaman Sea are characterized by mangrove forests and seagrass meadows. Mangroves cover between more than of the Thai shores of Malay Peninsula whereas seagrass meadows occupy an area of . ==Human activities==

The sea has long been used for fishing and transportation of goods between the coastal countries. Fishing Thailand alone harvested about of fish in 2005 and about in 2000. Of those , are accounted for by trawling (1,017 vessels), by purse seine (415 vessels), and about by gillnets. Of Thailand's total marine catch, 41% is caught in the Gulf of Thailand and 19% in the Andaman Sea. 40% is caught in waters outside Thailand's EEZ. Production numbers are significantly smaller for Malaysia and are comparable, or higher, for Myanmar. Competition for fish resulted in numerous conflicts between Myanmar and Thailand. In 1998 and 1999, they resulted in fatalities on both sides and nearly escalated into a military conflict. In both cases, the Thai navy intervened when Burmese vessels tried to intercept Thai fishing boats in the contested sea areas, and Thai fighter aircraft were thought to be deployed by the National Security Council. Thai fishing boats were also frequently confronted by the Malaysian navy to the extent that the Thai government had to caution its own fishers against fishing without license in foreign waters. The 2004 marine production in Thailand was composed of: pelagic fish 33 percent, demersal fish 18 percent, cephalopod 7.5 percent, crustaceans 4.5 percent, trash fish 30 percent and others 7 percent. The nearby coast also has numerous marine national parks – 16 only in Thailand, and four of them are candidates for inclusion into UNESCO World Heritage Sites. However, the journey is extremely risky: in 2024 alone, hundreds died or went missing, with estimates suggesting that nearly one in every 13 people on these routes did not survive. The situation has continued into 2025 and 2026, with more than 800 deaths reported in a single year across the region. Tragic incidents still occur, such as a boat capsizing in the Andaman Sea in April 2026 that left around 250 migrants missing. ==See also==