South China Sea

The South China Sea is a large marginal sea of the western Pacific Ocean, bordered by diverse landmasses and archipelagos and recognised as one of the most strategically and economically significant maritime regions in the world. It is bounded to the north by South China, to the west by the Indochinese Peninsula, to the east by Taiwan and the north-western islands of the Philippines—particularly Luzon, Mindoro and Palawan—and to the south by Borneo, eastern Sumatra and the Bangka Belitung Islands. The sea connects several major water bodies, including the East China Sea through the Taiwan Strait, the Philippine Sea through the Luzon Strait, the Sulu Sea around Palawan, the Java Sea via the Karimata and Bangka Straits, and the Gulf of Thailand. The Gulf of Tonkin forms part of its north-western extent.
The South China Sea has immense economic relevance: by 2016 approximately USD 3.4 trillion of global maritime trade passed through it. Significant oil and natural-gas reserves have been identified in the area, and its waters form part of the Western Central Pacific region, responsible for around 14 per cent of global commercial fish production in 2010. The sea includes hundreds of small islands, islets, cays, reefs and shoals arranged in several archipelagic clusters, many of which are subjects of complex territorial disputes.

Etymology and Historical Naming

The English term South China Sea became standard largely due to early European engagement with Asian maritime trade routes. Portuguese navigators of the sixteenth century referred to it simply as the “China Sea”, with the qualifier “South” later adopted to distinguish it from adjacent waters. The International Hydrographic Organization continues to use “South China Sea” as the official name in English.
Chinese historical texts provide some of the earliest recorded names. The Yizhoushu of the Western Zhou dynasty used the term Nanfang Hai, while the Classic of Poetry, Zuo Zhuan and Guoyu of the Spring and Autumn period referred to the water body as Nan Hai. In Chinese literary tradition, the South Sea represented one of the “Four Seas” surrounding the civilised world. During the Han period, the name Zhang Hai was used, and Fei Hai became common in the Northern and Southern dynasties. The modern Chinese name Nan Hai grew widespread in the Qing era.
Across Southeast Asia, the sea was historically known as the Champa Sea or Sea of Cham, named after the maritime kingdom of Champa in present-day central Vietnam. During the Second World War the region came under Japanese naval control and was referred to as “Nan-kai”, a term modified in spelling after 2004 to align with contemporary Japanese use. Vietnam refers to the sea as the East Sea, while Malaysia, Indonesia and the Philippines long retained the English form “South China Sea”.
In 2011 the Philippines adopted the name West Philippine Sea for the portion of the sea lying within its Exclusive Economic Zone. An administrative order in 2012 formalised this naming across all Philippine government agencies. In 2017 Indonesia designated the northern part of its Exclusive Economic Zone in these waters as the North Natuna Sea, complementing the already-named Natuna Sea to its south. These national-level renamings reflect ongoing jurisdictional disputes and differing interpretations of maritime boundaries.

Hydrography and Boundaries

Neighbouring states with coastlines along the sea include China, Taiwan, the Philippines, Malaysia, Brunei, Indonesia and Vietnam. Numerous large rivers discharge into the South China Sea, contributing to its sedimentary and ecological dynamics. Major examples include:

• Pearl River, Min River and Jiulong River in China
• Red River and Mekong River in Vietnam
• Chao Phraya in Thailand
• Rajang, Baram, Kapuas, Batang Hari, Musi, Kampar and Indragiri in Indonesia
• Pahang, Agno, Pampanga and Pasig in Malaysia and the Philippines

The International Hydrographic Organization, in its 1953 third edition of Limits of Oceans and Seas, defined the southern boundary of the South China Sea through the eastern and southern limits of the Singapore and Malacca Straits, then tracing the eastern coast of Sumatra and the northern limits of Bangka and Belitung. The eastern boundary extends along the west coast of Borneo, across the Palawan region and northward around Luzon and Taiwan. The northern limit runs from Taiwan to the Fujian coast, while the western limit follows the Malay Peninsula and the boundary of the Gulf of Thailand. A provisional revised edition in 1986 introduced recognition of the Natuna Sea, shifting the southern boundary further north, but this edition has not been formally ratified.

Geological Evolution

Geologically, the sea lies upon a drowned continental shelf that was exposed during Quaternary glaciations when global sea levels were significantly lower, linking Borneo to mainland Southeast Asia. The South China Sea basin is understood to have opened during the Eocene as the region known as the “Dangerous Ground” rifted from southern China. Seafloor spreading began around 30 million years ago, progressing southwestward and producing a distinctive V-shaped basin, before ceasing roughly 17 million years ago.
Debate continues over the role of tectonic extrusion in the basin’s formation. One school of thought suggests that the collision of the Indian subcontinent with Asia pushed Indochina southeastward, generating shear relative to China and facilitating the opening of the basin. Critics argue that Indochina has not moved sufficiently to support this model. Marine geophysical studies in the Gulf of Tonkin indicate that the Red River Fault was active at least 37 million years ago, contributing to early basin development and supporting some elements of the extrusion hypothesis.
Since its formation, the basin has accumulated vast sediment loads delivered by major rivers such as the Mekong, Red and Pearl Rivers. Several sedimentary basins within the region host significant hydrocarbon reserves, contributing to its economic and strategic value.

Islands and Archipelagos

The islands scattered across the South China Sea comprise multiple archipelagic groups containing reefs, atolls, shoals, cays and seamounts. Most of these landforms are uninhabited and small in extent, yet they hold disproportionate geopolitical significance because of their associated maritime zones and resource potential. Competing territorial claims by China, Taiwan, Vietnam, the Philippines, Malaysia and Brunei have resulted in long-standing disputes, with differing names for islands and waters further reflecting contested sovereignty.