Gulf of Thailand

The Gulf of Thailand or Gulf of Siam is located in the Pacific Ocean, bathing the coasts of Malaysia, Thailand, Cambodia and Vietnam; and borders in a southeasterly direction with the South China Sea.

In Thai it is called: อ่าวไทย (RTGS: Ao Thai, Thai pronunciation: [ʔàːw tʰaj]). The Malays call it Teluk Siam, and the Cambodians Boeung Tonle Siem, which literally means 'Gulf of Siam'.

At the northern end of the gulf, the Chao Phraya River, the main tributary of this gulf, flows into a wide canalized delta (khlongs) in the Bangkok metropolitan area.

The gulf has an area of 320,000 km² and is relatively shallow, averaging 45 to 80 meters deep. The latter causes slow water circulation and the Chao Phraya and Mekong rivers exert a strong influence on it, such as low salinity and great sediment richness. During the coldest times of the Ice Age, the Gulf of Thailand did not exist due to its shallowness and was just an extension of the Chao Phraya River valley.

Due to the tropical climate, the waters of the gulf are home to a good number of coral reefs and therefore there are many projects to exploit them. It also houses oil and gas wealth; and it is a means of tourist and commercial exchange between the countries that have a coast on it.

The main islands of the gulf are Koh Samui, Koh Pha Ngan, Koh Chang and Koh Kut belonging to Thailand, Koh Kong and Koh Rong to Cambodia and Phu Quoc to Vietnam.

Delimitation of the IHO

The highest international authority on the delimitation of seas, the International Hydrographic Organization (IHO), considers the Gulf of Thailand to be a sea. In his world-renowned publication, “Limits of oceans and seas”, 3rd edition of 1953, he assigns it the identification number 47 and defines it as follows:

South.
A line that goes from the western end of Cambia or Punta Camau (8°36'N) to the north end of the tip of the east side of the Kelantan river estuary (6°14'N, 102°15'S).

Limits of oceans and you are, p. 23.

Geography

The Gulf of Thailand borders Cambodia, Thailand, Malaysia and Vietnam. It occupies a seabed area of 304,000 km² from 6°N to 13°30'N latitude and from 99°E to 104°E longitude. The northern end of the gulf is Bangkok Bay at the mouth of the Chao Phraya River. The southern boundary of the gulf is defined by a line from Cape Bai Bung in southern Vietnam (just south of the mouth of the Mekong River) to the town of Tumpat and Pengkalan Chepa on the coast of Malaysia.

The gulf is relatively shallow: its average depth is 58 meters (190.3 ft) and the maximum depth is only 85 meters (278.9 ft). This makes water exchange slow and the strong inflow of water from the rivers reduces the salinity level in the gulf (3.05-3.25 percent) and enriches the sediments. Only at greater depths does water of higher salinity (3.4 percent) from the South China Sea flow into the gulf. It fills the central depression below a depth of 50 meters (164 ft). The main rivers that flow into the gulf are the Chao Phraya, including its distributor Tha Chin River, the Mae Klong, and Bang Pakong rivers in Bangkok Bay, and to a lesser extent the Tapi River which flows into Bandon Bay in the southwest gulf.

The International Hydrographic Organization defines the southern limit of the gulf as "[a] line running from the western end of Cambodia or Punta Camau (8°36'N) to the northern end of the point located at the eastern side of the Kelantan River estuary (6°14′N 102°15′E / 6.233, 102.250)".

Seafloor morphology

The morphology of the seafloor in the central depression of the gulf is characterized by the presence of elongated mounds and ridges arranged parallel to the axis of the basin. This morphology, widespread in the interior of the gulf in water depths greater than 50 m, covers an area of tens of thousands of square kilometers.

It reflects an interaction between sediment dehydration and the erosive activity of current bottom currents. Sediment dehydration and fluid filtration result in the formation of numerous small pits and pockmarks. Long-term erosion imposed by stable-oriented currents modifies the pockmarks into long runnels and depressions, and ultimately leads to the formation of the large fields of mounds and elongated ridges, as well as the residual outliers of the laminae. uneroded mud and clay.

Bays

Thailand

• Bangkok Bay
• Bay of Prachuap
• Ao Manao
• Sattahip Bay
• Bandon Bay

Cambodia

• Kompong Som Bay (Chhak Kompong Som)
• Bay of Veal Rinh
• Kep Bay
• Chhak Koh Kong

Vietnam

• Vinh Thuan Yen
• Vinh Ba Hon
• Vinh Hon Chong

Islands

The largest islands in the Gulf are:

• Ko Chang
• Ko Mak
• Ko Kut
• Ko Samui
• Ko Pha Ngan
• Ko Tao
• Ko Phaluai
• Ko Sichang
• Ko Lan
• Ko Phai
• Ko Khram
• Ko Samae San
• Ko Samet
• Ko Rang
• Ko Khangkhao
• Ko Man Nok
• Ko Wai
• Ko Phi
• Ko Kham
• Ko Sai
• Ko Kra
• Ko Losin
• Phú Qugilc
• Th Islas Chu Islands
• Islands Hà Tiên
• Bà Laa Islands
• Nam Du
• Koh Kong
• Koh Rong
• Koh Sdach
• Koh Rong Sanloem
• Koh Puos
• Koh Dek Koul
• Koh Russei
• Koh Ta Kiev
• Koh Preab
• Koh Thmei
• Koh Seh
• Koh Ach Seh
• Koh Tonsay
• Koh Tang
• Koh Pring
• Koh Poulo Wai

Environment

Coral reefs

There are 75,590 rai of coral reefs in the Gulf, of which five percent are considered to be in fertile condition. In 2010, severe coral bleaching occurred in most of the country's reefs. Reef bleaching in the Andaman Sea was more severe and extensive than that in the Gulf of Thailand. In 2016, coral bleaching was detected in Ko Thalu and Ko Lueam in Prachuap Khiri Khan province for the first time. Scientists have determined that bleaching begins when sea water temperatures rise above 30°C for more than three weeks. Given the prolonged period of temperatures of up to 32°C on Ko Thalu in Prachuap Khiri Khan, between five and ten percent of the corals in the area have already bleached.

Water quality

The results of coastal water monitoring in 2015 from 202 sampling sites, collected twice a year, indicate that none of the Thai coastal waters were found in excellent condition. 16% of coastal waters were of good quality, 72% were of fair quality, 9% were of poor quality and 3% were of very poor quality. The quality of all coastal waters had similar percentages - most were of fair quality - except in the Inner Gulf of Thailand, where the coastal water was poor to very poor. Compared with the coastal water quality measured in 2014, the water quality has deteriorated. Some gulf waters off Chachoengsao Province, Samut Sakhon Province, Samut Prakan Province, Bangkok, Rayong Province, Chonburi Province, Phetchaburi Province, Prachuap Khiri Khan Province and Surat Thani Province were considered as coastal waters in "poor" or "very poor". Songkhla was the only Gulf province with coastal waters rated "good" quality.

Fishing

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.

Coastal erosion

Thailand has 1,660 kilometers of coastline bordering the gulf. 'Severe erosion', more than five meters of coastline loss per year, affects 670 kilometers of that total. At least part of the erosion is attributable to the clearing of mangroves to make way for shrimp farms.

Plastic pollution

In February 2017, a 10-kilometre-long patch of plastic waste was found floating off Chumphon province. Thailand is among the world's worst plastic polluters. More than half of the "leaks of plastic waste on land" towards the sea originate in only five countries: China, Indonesia, the Philippines, Thailand and Vietnam.

The Thai Department of Marine and Coastal Resources has noted that at least 300 marine animals on average - 60% of which are whales and dolphins - die from eating plastic fishing gear and trash each year. The invertebrates that Filter-feeding waters analyzed off the coast of Chonburi province showed high levels of microplastics, leading the authors to warn that "there may be health risks when people consume these contaminated marine organisms, particularly seafood. "

Thailand's Pollution Control Department (PCD) estimates that plastic waste in the country is increasing at an annual rate of 12 percent, or about two million tons a year.

Oil spills

In 2013, a leak in an oil pipeline caused an oil spill that covered a beach on the nearby island of Ka Samet.

At the end of January 2022, a leak in the pipeline operated by Star Petroleum Refining Public Company Ltd caused a spill of between 20 and 50 tons across 47 square kilometers of water, with some of the oil reaching the coast of Rayong province 20 kilometers away.