View source for Andaman Sea

{{Short description|Marginal sea of the northeastern Indian Ocean }}
{{Use dmy dates|date=August 2020}}
{{Infobox sea
| name               = Andaman Sea
| other_name         = Burma Sea
| image              = LocationAndamanSea.png
| caption            = Location of Andaman Sea in the Indian Ocean
| alt                = Location of Andaman Sea in the Indian Ocean
| image_bathymetry   = 
| caption_bathymetry =
| coords             = {{coord|10|N|96|E|type:waterbody_scale:5000000|display=inline, title}}
| type               = Sea
| inflow             =
| outflow            =
| catchment          =
| basin_countries    =
  {{Unbulleted list
  | India
  | Indonesia
  | Malaysia
  | Myanmar
  | Thailand
  }}
| length             = {{convert|1202|km|mi|0|abbr=on}}
| width              = {{convert|647|km|mi|0|abbr=on}}
| area               = {{convert|797000|km2|sqmi|-2|abbr=on}}
| depth              = {{convert|1096|m|ft|0|abbr=on}}
| max-depth          = {{convert|4198|m|ft|0|abbr=on}}
| volume             = {{convert|660000|km3|cumi|-3|abbr=on}}
<!--      Map      -->
| pushpin_map             = Indian Ocean
| pushpin_label_position  = bottom
| reference          = <ref name=bse>[http://bse.sci-lib.com/article057639.html Andaman Sea], [[Great Soviet Encyclopedia]] (in Russian)</ref><ref name=brit>[https://www.britannica.com/EBchecked/topic/23505/Andaman-Sea Andaman Sea], Encyclopædia Britannica on-line</ref><ref name="indjst.org"/>
}}
{{Infobox Chinese
| my = ကပ္ပလီပင်လယ်
| bi = Kappali Pinlae
| msa = Laut Andaman
| ind = Laut Andaman
| tha = ทะเลอันดามัน 
| rtgs = Thale Andaman
| ben = আন্দামান সাগর
| hin = अंडमान सागर
| tam = அந்தமான் கடல்
| order = st
| ci = 
| altname = 
}}

The '''Andaman Sea''' (historically also known as the '''Burma Sea''')<ref name="IHO" /> is a [[marginal sea]] of the northeastern [[Indian Ocean]] bounded by the coastlines of [[Myanmar]] and [[Thailand]] along the [[Gulf of Martaban]] and the west side of the [[Malay Peninsula]], and separated from the [[Bay of Bengal]] to its west by the [[Andaman Islands]] and the [[Nicobar Islands]].  Its southern end is at [[Breueh Island]] just north of [[Sumatra]], with the [[Strait of Malacca]] further southeast.

Traditionally, the sea has been used for fishery and transportation of goods between the coastal countries and its [[coral reef]]s and islands, which are popular tourist destinations.  The fishery and tourist infrastructure was severely damaged by the December [[2004 Indian Ocean earthquake and tsunami]].

==Geography==

===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 [[Bay of Bengal|the Bay of Bengal]] by the [[Andaman Islands|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 {{convert|3|km}} wide and {{convert|37|m}} deep.

===Extent===
{{anchor| Extent}}
The [[International Hydrographic Organization]] defines the limits of the "Andaman or Burma Sea" as follows:<ref name="IHO">{{cite web |url=https://iho.int/uploads/user/pubs/standards/s-23/S-23_Ed3_1953_EN.pdf |title=Limits of Oceans and Seas, 3rd edition |year=1953 |publisher=International Hydrographic Organization |access-date=28 December 2020 |archive-url=https://web.archive.org/web/20111008191433/http://www.iho.int/iho_pubs/standard/S-23/S-23_Ed3_1953_EN.pdf |archive-date=8 October 2011 }}</ref>{{RP|p.21}}

<blockquote>''On the Southwest.'' A line running from ''"[[Point Raja|Oedjong Raja]]"'' <nowiki>[</nowiki>''"Ujung Raja" or "Point Raja"''] ({{coord|5|32|N|95|12|E|display=inline}}) in [[Sumatra]] to [[Poeloe Bras]] (Breuëh) and on through the Western Islands of the [[Nicobar Islands|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 <nowiki>[</nowiki>Myanmar] through the larger islands of the [[Andaman Islands|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 <nowiki>[</nowiki>Thailand], and [[Point Batee|Pedropunt]] (5°40'N) in Sumatra.</blockquote>

''Oedjong'' means "[[Cape (geography)|cape]]" and ''Lem'' means "point in the Dutch language on maps of the [[Dutch East Indies|Netherlands East Indies]] (Indonesia).<ref name=oedjong1>[https://books.google.com/books?id=OIAsAAAAIAAJ&dq=Oedjong+meaning&pg=PA115 Glossary of Terms Appearing on Maps of the Netherlands East Indies], United States Army Map Service, page 115, 93.</ref> Lem Voalan [Phromthep Cape] is the southern extremity of Goh Puket ([[Phuket Island]]).<ref>{{cite book|url=http://epic.awi.de/29772/1/IHO1953a.pdf|title=Limits of Oceans and Seas|edition= 3rd|year=1953|publisher=International Hydrographic Organization|page=23|access-date=3 December 2018}}</ref>

===Exclusive economic zone===
[[Exclusive economic zones]] in Andaman Sea:<ref>{{Cite web|url=http://www.seaaroundus.org/data/#/eez|title = Sea Around Us &#124; Fisheries, Ecosystems and Biodiversity}}</ref>

{| class="wikitable" style="font-size:100%"
|-
!width=75|Number
!width=300|Country
!width=100|Area (Km<sup>2</sup>)
|-
| align=center|1 || '''{{IND}}''' - [[Andaman and Nicobar Islands]] || align=center|659,590
|-
| align=center|2 || '''{{MYA}}''' - [[Mainland]] || align=center|511,389
|-
| align=center|3 || '''{{THA}}''' - Andaman Sea || align=center|118,714
|-
| align=center|4 || '''{{IDN}}''' - Northeast [[Aceh]] || align=center|76,500
|- style="background:#9acdff;"
!Total
|'''Andaman Sea''' || align=center|'''-'''
|}

===Channels===

See [[Coastal_India#Channels|Channels in Bay of Bengal, Laccadive Sea, and Arabian Sea]].

==Geology==
[[File:AndamanSeaNASA1.jpg|thumb|left|upright|Satellite image of the Andaman Sea showing the [[green algae]] 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 {{convert|200|km}} (marked by {{convert|300|m}} [[isobath]]). About 45 percent of the basin area is shallower (less than {{convert|500|m}} 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 {{convert|3,000|m}} within a short horizontal distance of a degree. Isobaths corresponding to {{convert|900 and 2000|m}} 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 {{convert|2,500|m}}.<ref name="indjst.org">S. R. Kiran (2017) [http://www.indjst.org/index.php/indjst/article/view/115764 General Circulation and Principal Wave Modes in Andaman Sea from Observations], Indian Journal of Science and Technology {{ISSN|0974-5645}}</ref>

[[File:The Bathymetry (in metres) of A-SEA in 2D and 3D (sectioned along 95E).png|thumb|The bathymetry (in metres) of the Andaman Sea in 2D and 3D (sectioned along 95°E)<ref name="indjst.org"/>]]
[[File:Percentage of total area of A-SEA corresponding to diferent ranges of depth.png|thumb|Percentage of the total area of Andaman Sea corresponding to different depth ranges<ref name="indjst.org"/>]]

The northern and eastern parts are shallower than {{convert|180|m|ft|abbr=off|sp=us}} due to the [[silt]] deposited by the [[Irrawaddy River]]. This major river flows into the sea from the north through Myanmar. The western and central areas are {{convert|900|–|3,000|m|ft|sp=us}} deep. Less than 5% of the sea is deeper than {{convert|3000|m|ft|abbr=off|sp=us}}, and in a system of submarine valleys east of the Andaman-Nicobar Ridge, the depth exceeds {{convert|4000|m|ft|abbr=off|sp=us}}.<ref name=brit/> The sea floor is covered with pebbles, gravel, and sand.<ref name=bse/>

The western boundary of the Andaman Sea is marked by islands and sea mounts, with straits or passages of variable depths that control the entry and exit of water to the [[Bay of Bengal]]. There is a drastic change in water depth over a short distance of {{convert|200|km}}, as one moves from the [[Bay of Bengal]] (around {{convert|3,500|m}} deep) to the vicinity of islands (up to {{convert|1,000|m}} depth) and further into the Andaman Sea. Water is exchanged between the Andaman Sea and the Bay of Bengal through the straits between the Andaman and Nicobar Islands. Out of these, the most important straits (in terms of width and depth) are [[Preparis Channel]] (PC), [[Ten Degree Channel]] (TDC), and [[Great Channel]] (GC). PC is the widest but shallowest ({{convert|250|m}}) of the three and separates south Myanmar from north Andaman. TDC is {{convert|600|m}} deep and lies between [[Little Andaman]] and [[Car Nicobar]]. GC is {{convert|1,500|m}} deep and separates [[Great Nicobar]] from [[Banda Aceh]].

===Ocean floor tectonics===
[[File:Neic slav fig72narrow.jpg|thumb|left|The Andaman Sea, showing [[tectonic plate]] boundaries]]
[[File:Tectonics Sumatra quake.gif|thumb|[[Tectonic setting]] of Sumatra earthquake (2004)]]

Running in a rough north–south line on the seabed of the Andaman Sea is the boundary between two [[tectonic plate]]s, the [[Burma Plate]] and the [[Sunda Plate]]. These plates (or microplates) are believed to have formerly been part of the larger [[Eurasian Plate]], but were formed when [[transform fault]] activity intensified as the [[Indian Plate]] began its substantive collision with the Eurasian [[continent]]. As a result, a [[back-arc basin]] center was created, which began to form the marginal [[Oceanic basin|basin]] which would become the Andaman Sea, the current stages of which commenced approximately 3–4&nbsp;million years ago ([[annum|Ma]]).<ref>{{cite web| author=J.R. Curray| title=2002 Chapman Conference on Continent – Ocean Interactions within the East Asian Marginal Seas| work=Tectonics and History of the Andaman Sea Region (abstract)| url=http://www.agu.org/meetings/cc02cabstracts/curray-p.pdf| access-date=20 September 2010| archive-date=23 March 2005| archive-url=https://web.archive.org/web/20050323100450/http://www.agu.org/meetings/cc02cabstracts/curray-p.pdf}}</ref>

The boundary between two major tectonic plates results in high seismic activity in the region (see [[List of earthquakes in Indonesia]]). Numerous earthquakes have been recorded, and at least six, in 1797, 1833, 1861, [[2004 Indian Ocean earthquake and tsunami|2004]], 2005, and [[September 2007 Sumatra earthquakes|2007]], had a [[Moment magnitude scale|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 and tsunami|2004 Indian Ocean earthquake]]. This [[megathrust earthquake]] had a magnitude of 9.3. Between {{convert|1300|and|1600|km}} of the boundary underwent [[thrust fault]]ing and shifted by about {{convert|20|m}}, with the sea floor being uplifted several meters.<ref>{{cite journal|url=https://walrus.wr.usgs.gov/reports/reprints/Geist_BSSA_97.pdf |doi=10.1785/0120050619|title=Implications of the 26 December 2004 Sumatra–Andaman Earthquake on Tsunami Forecast and Assessment Models for Great Subduction-Zone Earthquakes|journal=Bulletin of the Seismological Society of America|year=2007|volume=97|issue=1A|pages=S249–S270|last1=Geist|first1=E. L.|last2=Titov|first2=V. V.|last3=Arcas|first3=D.|last4=Pollitz|first4=F. F.|last5=Bilek|first5=S. L.|bibcode=2007BuSSA..97S.249G}}</ref> This rise in the sea floor generated a massive [[tsunami]] with an estimated height of {{convert|28|m|ft|abbr=off|sp=us}}<ref>Tom Paulson (7 February 2005) [https://web.archive.org/web/20101205010745/http://www.seattlepi.com/local/211012_tsunamiscience07.html New findings super-size our tsunami threat. 80-foot waves blasted Indonesia, scientists now say], ''Seattle Post-Intelligencer''</ref> that killed approximately 280,000 people along the coast of the Indian Ocean.<ref>[https://news.bbc.co.uk/2/hi/asia-pacific/4204385.stm Indonesia quake toll jumps again], BBC, 25 January 2005</ref> 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.<ref name=Panjarat>{{cite web|last1=Panjarat|first1=Sampan|title=Sustainable Fisheries in the Andaman Sea Coast of Thailand| url=https://www.un.org/depts/los/nippon/unnff_programme_home/fellows_pages/fellows_papers/panjarat_0708_thailand_PPT.pdf|publisher=United Nations|year=2008|access-date=16 May 2015}}</ref>{{RP|40–42}}

===Volcanic activity===
[[File:Ile Barren, 1995.jpg|thumb|Eruption of the [[Barren Island (Andaman Islands)|Barren Island]] 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 (Andaman Islands)|Barren Island]], the only currently [[active volcano]] associated with the [[South Asia|Indian subcontinent]]. This island volcano is {{convert|3|km|0|abbr=on}} in diameter and rises {{convert|354|m}} above sea level. Its recent activity resumed in 1991 after a quiet period of almost 200 years.<ref>D. Chandrasekharam, Jochen Bundschuh (2002) [https://books.google.com/books?id=aRkBJRLV8AwC&pg=PA408 Geothermal energy resources for developing countries], Taylor & Francis {{ISBN|90-5809-522-3}} p. 408</ref> 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.<ref>[http://www.volcano.si.edu/world/volcano.cfm?vnum=0600-01=&volpage=erupt Barren Island] {{Webarchive|url=https://web.archive.org/web/20201202213229/https://volcano.si.edu/world/volcano.cfm?vnum=0600-01=&volpage=erupt |date=2 December 2020 }}, Smithsonian National Museum of Natural History</ref> The volcanic island of [[Narcondam Island|Narcondam]], which lies further north, was also formed by this process. No records exist of its activity.<ref>[http://www.volcano.si.edu/world/volcano.cfm?vnum=0600-001 Narcondum] {{Webarchive|url=https://web.archive.org/web/20210405015451/http://www.volcano.si.edu/world/volcano.cfm?vnum=0600-001 |date=5 April 2021 }}, Smithsonian National Museum of Natural History</ref>

===Sediments to the Sea===
Collectively, the modern Ayeyarwady (Irrawaddy) and Thanlwin (Salween) rivers deliver >600 Mt/yr of sediment to the sea.<ref name="sciencedirect2020">{{cite journal  |title=Liu, J.P., Kuehl, S.A., Pierce, A.C., Williams, J., Blair, N.E., Harris, C., Aung, D.W., Aye, Y.Y., 2020. Fate of Ayeyarwady and Thanlwin Rivers Sediments in the Andaman Sea and Bay of Bengal. Marine Geology, 106137. |journal=Marine Geology |year=2020|volume=423 |article-number=106137 |doi=10.1016/j.margeo.2020.106137|doi-access=free|last1=Liu |first1=J. Paul |last2=Kuehl |first2=Steven A. |last3=Pierce |first3=Austin C. |last4=Williams |first4=Joshua |last5=Blair |first5=Neal E. |last6=Harris |first6=Courtney |last7=Aung |first7=Day Wa |last8=Aye |first8=Yin Yin }}</ref> 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 {{convert|60|m}} in thickness, has been deposited seaward in the Gulf of Martaban, extending to approximately {{convert|130|m}} 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 {{convert|20|m}} nearshore and gradually thins to the slope at {{convert|−300|m}} water depth, and likely escapes into the deep Andaman Trench; 4) The estimated total amount of Holocene sediments deposited offshore is approximately {{convert|1290 × 109|t}}. 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 {{convert|215|Mt}} 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.<ref name="sciencedirect2020" />

==Climate==
[[File:Monthly averaged ASCAT winds in ANDAMAN SEA for the year 2011, expressed in mps.png|thumb|Monthly averaged winds in the Andaman Sea for the year 2011, expressed in mps<ref name="indjst.org"/>]]
The climate of the Andaman Sea is determined by the [[Monsoon#South Asian monsoon|monsoons of southeast Asia]],<ref name="indjst.org"/> as the prevailing winds reverse with the start of either season. The region experiences north-easterlies with an average windspeed of {{convert|5|m/s|km/h|abbr=on}} 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 {{convert|8|m/s|km/h|abbr=on}} 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.
[[File:Monthly averaged Ekman Pumping velocity (in m per day) for June and December.png|thumb|Monthly averaged Ekman pumping velocity (in m per day) for June and December<ref name="indjst.org"/>]]

Air temperature is stable over the year at {{convert|26|C}} in February and {{convert|27|C}} in August. Precipitation is as high as {{convert|3,000|mm}}/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 {{convert|26–28|C}} in February and {{convert|29|C}} in May. The water temperature is constant at {{convert|4.8|C}} at the depths of {{convert|1,600|m}} 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]]. [[Tide|Tides]] are semidiurnal with an amplitude of up to {{convert|7.2|m}}.<ref name=bse/>

The effect of wind stress on the ocean surface can be explained by [[Sverdrup balance|wind stress curl]]. The net divergence of water in the ocean mixed layer results in [[Ekman transport|Ekman pumping]].<ref name="indjst.org"/> The contrast between the two seasons elicits a very strong negative pumping velocity of more than {{convert|5|m|abbr=on}} 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 {{convert|3|m|abbr=on}} per day at the mouth of GC in winter (here, December).

==Current and wave fluid dynamics==
[[File:Monthly averaged OSCAR surface currents in January, April, June and October, expressed in cmps.png|thumb|Monthly averaged OSCAR surface currents in January, April, June, and October, expressed in cm/s<ref name="indjst.org"/>]]

Generally, currents are found to be stronger in the south than any other part of the basin.<ref name="indjst.org"/> An intense surface outflux through GC, of the order of {{convert|40|cm/s|abbr=on}}, occurs during summers and winters. While this flow is directed westwards in winter, it is southwards along the west coast of Indonesia in summer. On the other hand, the TDC has strong surface influx in summer, which weakens by October. This is followed by a sturdy outflux in winter, which wanes by the month of April. Although the surface flow through PC is generally inward during summer monsoon, the preceding and succeeding months experience outflow (strong outflow in October, but weak outflow in April). During April and October, when the effects of local winds are minimal, Andaman Sea experiences the intensification of meridional surface currents in the poleward direction along the continental slope on the eastern side of the basin. This is characteristic of the propagation of Kelvin Waves.<ref name="indjst.org"/><ref name="kiransr1991.blogspot.in">{{Cite web |url=https://kiransr1991.blogspot.in/2017/11/read-about-andaman-sea-and-its-dynamics.html |title=My Reflections, Official Webpage of S. R. Kiran(2017) |access-date=11 November 2017 |archive-url=https://web.archive.org/web/20171111151901/https://kiransr1991.blogspot.in/2017/11/read-about-andaman-sea-and-its-dynamics.html |archive-date=11 November 2017 }}</ref>

[[File:Temporal variations of the basin Rainfall, River Influx and Sea Surface Height Anomaly, expressed in volume of water.png|thumb|Temporal variations of the basin rainfall, river influx, and sea surface height anomaly, expressed in volume of water<ref name="indjst.org"/>]]

It is observed that the water level rises in the basin between April and November with the maximum rate of piling up of water during April and October (marked by the steep slope of the curve).<ref name="indjst.org"/> The rise in sea surface height (SSH) is attributed to rainfall, fresh water influx from rivers, and inflow of water through the three major straits. The first two of these are quantifiable and are hence expressed in volumes of water for comparison. From this, the expected influx through the straits (= SSH anomaly – Rainfall – River Influx) could be deduced. A possible fourth factor, evaporative losses, is negligible in comparison. (Previous studies<ref>Baumgartner A, Riechel E. The World Water Balance, Mean Annual Global, Continental and Maritime Precipitation, Evaporation and Runoff, Elsevier. 1975; 1−179pp</ref> show that the annual mean freshwater gain (precipitation minus evaporation) of the Andaman Sea is {{convert|120|cm}} per year.) It is found that the SSH of the basin is primarily determined by the transport of water through the straits. The contributions from rainfall and rivers become substantial only during summer. Hence, a net inward flow occurs through the straits between April and November, followed by a net outward transport until March.<ref name="kiransr1991.blogspot.in"/>

[[File:Temporal variation of depth of 20 degree isotherm (95 E to 96 E averaged) in metres.png|thumb|Temporal variation of depth of 20-degree isotherm (95°E to 96°E averaged) in metres]]
[[File:Evolution of vorticity in Andaman sea.gif|thumb|upright=.8|Evolution of relative vorticity in Andaman Sea]]

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 wave]]s and coastal [[Kelvin wave]]s. 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 {{convert|20|C}} isotherm which deepens<ref name="indjst.org"/> 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 {{convert|30|m}} in April and {{convert|10|m}} in October). This is a concrete signature of downwelling in the basin and is definitely not forced<ref name="indjst.org"/> 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.<ref name="indjst.org"/> 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===
[[File:Andaman Islands, Neil, Mangrove trees.jpg|thumb|Mangrove trees on the coast, Neil Island, Andaman and Nicobar Islands]]

The coastal areas of the Andaman Sea are characterized by [[mangrove]] forests and [[seagrass meadow]]s. Mangroves cover between more than {{convert|600|km2|0|abbr=on}} of the Thai shores of Malay Peninsula whereas seagrass meadows occupy an area of {{convert|79|km2|0|abbr=on}}.<ref name=Panjarat />{{rp|25–26}} Mangroves are largely responsible for the high productivity of the coastal waters – their roots trap soil and sediment and provide shelter from predators and nursery for fish and small aquatic organisms. Their body protects the shore from the wind and waves, and their [[detritus]] are a part of the aquatic food chain. A significant part of the Thai mangrove forests in the Andaman Sea was removed during the extensive [[Palaemonetes|brackish water shrimp]] farming in 1980s{{citation needed|date=November 2018}}. Mangroves were also significantly damaged by the 2004 tsunami. They were partly replanted after that, but their area is still gradually decreasing due to human activities.<ref name=Panjarat />{{RP|6–7}}

Other important sources of nutrients in the Andaman Sea are seagrass and the mud bottoms of lagoons and coastal areas. They also create a habitat or temporal shelter for many burrowing and benthic organisms. Many aquatic species migrate from and to seagrass either daily or at certain stages of their life cycle. The human activities which damage seagrass beds include waste water discharge from coastal industry, shrimp farms and other forms of coastal development, as well as trawling and the use of push nets and dragnets. The 2004 tsunami affected 3.5% of seagrass areas along the Andaman Sea via [[siltation]] and sand sedimentation and 1.5% suffered total habitat loss.<ref name=Panjarat />{{RP|7}}

===Fauna===
[[File:Phantom Bannerfish - Heniochus pleurotaenia.jpg|thumb|[[Heniochus pleurotaenia|Phantom bannerfish]] (''Heniochus pleurotaenia''), [[Similan Islands]], Thailand]]
[[File:Dugong Marsa Alam.jpg|thumb|Dugong]]
[[File:Phuket fauna.jpg|thumb|Starfish, Andaman Sea]]

The sea waters along the [[Malay Peninsula]] favor molluscan growth, and there are about 280 edible fish species belonging to 75 families. Of those, 232 species (69 families) are found in mangroves and 149 species (51 families) reside in seagrass; so 101 species are common to both habitats.<ref name=Panjarat />{{RP|26}} The sea also hosts many vulnerable fauna species, including [[dugong]] (''Dugong dugon''), several dolphin species, such as [[Irrawaddy dolphin]] (''Orcaella brevirostris'') and four species of sea turtles: critically endangered [[leatherback turtle]] (''Dermochelys coriacea'') and [[hawksbill turtle]] (Eletmochelys imbricata) and threatened [[green turtle]] (''Chelonia mydas'') and [[olive ridley]] turtle (''Lepidochelys olivacea''). There are only about 150 dugongs in the Andaman Sea, scattered between [[Ranong Province|Ranong]] and [[Satun Province]]s. These species are sensitive to the degradation of seagrass meadows.<ref name=Panjarat />{{RP|8}}

Coral reefs are estimated to occupy 73,364 [[rai (area)|rai]] (117&nbsp;km<sup>2</sup>) in the Andaman Sea with only 6.4 percent in ideal condition.<ref>{{cite news|last1=Wipatayotin|first1=Apinya|title=Rising sea temps bring coral bleaching to Gulf|url=http://www.bangkokpost.com/news/general/919989/rising-sea-temps-bring-coral-bleaching-to-gulf|access-date=4 April 2016|work=Bangkok Post|date=4 April 2016}}</ref>

==Human activities==
The sea has long been used for fishing and transportation of goods between the coastal countries.

===Fishing===
Thailand alone harvested about {{convert|943,000|t|lb|abbr=on}} of fish in 2005 and about {{convert|710,000|t|lb|abbr=on}} in 2000.<ref>{{cite book |title=Review of Fisheries in OECD Countries: Policies and Summary Statistics 2005 |date=20 December 2005 |publisher=OECD Publishing |location=Paris |isbn=978-92-64-00904-2 |page=403 |url=https://books.google.com/books?id=o_v8wAEACAAJ |access-date=31 March 2023 |language=en}}</ref> Of those {{convert|710,000|t|lb|abbr=on}}, {{convert|490,000|t|lb|abbr=on}} are accounted for by [[trawling]] (1,017 vessels), {{convert|184,000|t|lb|abbr=on}} by [[Seine fishing|purse seine]] (415 vessels), and about {{convert|30,000|t|lb|abbr=on}} by [[gillnet]]s. 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]].<ref name=GP-2012>{{cite book|title=Oceans in the Balance, Thailand in Focus|date=c. 2012|publisher=Greenpeace Southeast Asia (Thailand)|location=Bangkok|url=http://www.greenpeace.org/seasia/PageFiles/536808/english-singlePages.pdf|access-date=11 July 2017|archive-date=22 September 2015|archive-url=https://web.archive.org/web/20150922104018/http://www.greenpeace.org/seasia/PageFiles/536808/english-singlePages.pdf}}</ref>

Production numbers are significantly smaller for Malaysia and are comparable, or higher, for Myanmar.<ref>{{cite book |last1=De Young |first1=Cassandra |title=Review of the state of world marine capture fisheries management: Indian Ocean |date=2006 |publisher=Food and Agriculture Organization of the United Nations |location=Rome |isbn=978-92-5-105499-4 |pages=39, 178 |url=https://books.google.com/books?id=_7JD1V3PijUC&pg=PA178 |access-date=31 March 2023 |language=en}}</ref> 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.<ref>{{cite book |last1=Dupont |first1=Alan |title=East Asia Imperilled: Transnational Challenges to Security |date=15 October 2001 |publisher=Cambridge University Press |location=Cambridge |isbn=978-0-521-01015-3 |pages=103–105 |url=https://books.google.com/books?id=uGaINo0FofcC&pg=PA103 |access-date=31 March 2023 |language=en}}</ref>

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.<ref name=Panjarat />{{RP|12}} Trash fish refers to non-edible species, edible species of low commercial value and juveniles, which are released to the sea.<ref name=Panjarat />{{RP|16}} Pelagic fishes were distributed between anchovies (''Stolephorus'' spp., 19 percent), Indo-Pacific mackerel (''[[Rastrelliger]] brachysoma'', 18 percent), [[sardinella]]s (''Sardinellars'' spp., 14 percent), [[Decapterus|scad]] (11 percent), longtail tuna (''[[Thunnus tonggol]]'', 9 percent), eastern little tuna (''Euthynnus affinis'', 6 percent), [[Carangidae|trevallies]] (6 percent), [[bigeye scad]] (5 percent), [[Indian mackerel]] (''Rastrelliger kanagurta'', 4 percent), [[king mackerel]] (''Scomberomorus cavalla'', 3 percent), [[torpedo scad]] (''Megalaspis cordyla '', 2 percent), [[wolf herring]]s (1 percent), and others (2 percent).<ref name=Panjarat />{{RP|13}} Demersal fish production was dominated by [[Priacanthidae|purple-spotted bigeye]] (''Priacanthus tayenus''), [[threadfin bream]] (''Nemipterus hexodon''), [[brushtooth lizardfish]] (''Saurida undosquamis''), [[slender lizardfish]] (''Saurida elongata'') and Jinga shrimp (''Metapenaeus affinis''). Most species are [[overfished]] since the 1970s–1990s, except for [[Scomberomorus commerson|Spanish mackerel]] (''Scomberomorus commersoni''), [[carangidae]] and [[torpedo scad]] (''Meggalaspis'' spp.). The overall [[overfishing]] rate was 333 percent for pelagic and 245 percent for demersal species in 1991.<ref name=Panjarat />{{RP|14}} Cephalopods are divided into squid, [[cuttlefish]] and molluscs, where squid and cuttlefish in Thai waters consists of 10 families, 17 genera and over 30 species. The main mollusk species captured in the Andaman Sea are [[scallop]], [[blood cockle]] (''Anadara granosa'') and short-necked clam. Their collection requires bottom dredge gears, which damage the sea floor and the gears themselves and are becoming unpopular. So, the mollusk production has decreased from {{convert|27,374|t|lb|abbr=on}} in 1999 to 318 tonnes in 2004. While crustaceans composed only 4.5 percent of the total marine products in 2004 by volume, they accounted for 21 percent of the total value. They were dominated by [[Indian prawn|banana prawn]], [[Penaeus monodon|tiger prawn]], king prawn, school prawn, bay lobster (''[[Thenus orientalis]]''), mantis shrimp, swimming crabs and [[Scylla paramamosain|mud crabs]]. The total catch in 2004 was {{convert|51,607|t|lb|abbr=on}} for squid and cuttlefish and {{convert|36,071|t|lb|abbr=}} for crustaceans.<ref name=Panjarat />{{RP|18–19}}

===Mineral resources===
[[File:Andaman Sea, Andaman Islands.jpg|thumb|right|Andaman Sea off [[Havelock Island]]]]
The sea's mineral resources include [[tin]] deposits off the coasts of Malaysia and Thailand. Major ports are [[Port Blair]] in India; [[Dawei]], [[Mawlamyine]] and [[Thilawa Port|Yangon]] in Myanmar; [[Port Authority of Thailand|Ranong port]] in Thailand; [[George Town, Penang|George Town]] and [[Penang]] in Malaysia; and [[Belawan]] in Indonesia.<ref name=brit/>

===Tourism===
The Andaman Sea, particularly the western coast of the [[Malay Peninsula]], and the [[Andaman Islands|Andaman]] and [[Nicobar Islands]] of India and Myanmar are rich in [[coral reef]]s and offshore islands with spectacular topography. Despite having been damaged by the 2004 Sumatra earthquake and tsunami, they remain popular tourist destinations.<ref>{{cite book |title=World and Its Peoples: Eastern and Southern Asia |date=2007 |publisher=Marshall Cavendish |location=New York |isbn=978-0-7614-7638-2 |page=585 |url=https://books.google.com/books?id=CiTAx3unBkYC |access-date=31 March 2023 |language=en}}</ref> 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 Site]]s.<ref name=Panjarat />{{RP|7–8}}

==See also==
* [[Countries of the Bay of Bengal]]
* [[History of Indian influence on Southeast Asia]]
* [[Kra Isthmus]]
* [[Maritime Silk Road]]
* [[Mergui Archipelago]]
* [[Moscos Islands]]

==References==
{{Reflist}}

== External links ==
* {{Commons category-inline|Andaman Sea}}
* [https://web.archive.org/web/20170305113754/http://marine.myanmarbiodiversity.org/ Myanmar Marine Biodiversity Atlas Online]
* {{Wikivoyage-inline}}

{{List of Indonesian seas}}
{{List of seas}}
{{Authority control}}

[[Category:Andaman Sea| ]]
[[Category:Marginal seas of the Indian Ocean]]
[[Category:Maritime Southeast Asia]]
[[Category:Bay of Bengal]]
[[Category:Seas of Asia]]
[[Category:Bodies of water of Myanmar]]
[[Category:Seas of Malaysia]]
[[Category:Seas of Indonesia]]
[[Category:Seas of India]]
[[Category:Seas of Thailand]]
[[Category:Seas of Myanmar]]
[[Category:Geography of the Andaman and Nicobar Islands]]
[[Category:Geography of Sumatra]]
[[Category:Back-arc basins]]
[[Category:Malay Peninsula]]
[[Category:Malaysia–Thailand border]]
[[Category:India–Myanmar border]]
[[Category:Myanmar–Thailand border]]
[[Category:Indonesia–Thailand border]]
[[Category:Ecoregions of Asia]]
[[Category:Marine ecoregions]]