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The Seas of Asia

Asia is caught between two huge oceans, the Indian Ocean to the west and the Pacific to the east. In between is a complex geography of land & water that has given rise to some of the most fascinating & species rich seas on our planet.

Much of the geography of south-east Asia is dictated by the Pacific Ring of Fire, a geologically active zone around the edges of the Pacific, that encompasses the region and shapes the landscape, producing volcanoes, mountains, island chains & trenches.

This complex geography has also produced 15 unique seas and many straits, which between them comprise the most complex & diverse eco-system on the planet.
Seas of Asia
Asia's complex geography & history has created many different seas, which between them comprise the most complex & diverse eco-system on the planet.
From Ocean to Ocean
Whaleshark & Sea Starting the the west, the Andaman Sea sits between the Indian Ocean & the coasts of Burma, Thailand, Malaysia & Indonesia, drifting into the Bay of Bengal in the north. Its western perimeter is marked by the remote Andaman Island chain. The Similans, Mergui Archipelago & Pulah Weh are some of the great diving spots in the Andaman.

Thailand, Peninsular Malaysia & the giant Indonesian island of Sumatra separate the Andaman Sea from the South China Sea, the largest in Asia. This sea stretches across to the Philippines in the east and laps the shores of Borneo to the south, and Vietnam & China to the north.

The South China Sea comes to a head in the shallow Gulf of Thailand. This is one of the few parts of Asia’s where the flow of water is slow, meaning the water is not as rich in nutrients as other seas in the region.

To the east, the sea increases in depth as it reaches the Philippines, giving rise to some spectacular dive spots, such as Layang Layang & the sites of northern Palawan.

Separated from the South China Sea by the island of Palawan is the Sulu Sea. The Sulu Sea is one of the smallest, but most productive of Asia’s seas, marking the northern tip of the now famous Coral Triangle, the most biologically diverse marine region on earth. It reaches northern Borneo to the south and the islands of the Visayas & Mandanao in the Philippines to the east.

The Sulu Sea is deep, bringing nutrient rich upwellings from great depths, which support the spectacular congregations of marine life found at sites such as Sipadan & the remote Tubbataha Reefs. The popular dive sites of the Visayas region also fall within the Sulu Sea.

To the east, the Philippines Sea reaches out to the Pacific Ocean. Here, where the Pacific techtonic plate disappears below the Philippine plate, the sea plunges to the greatest depths on the planet. This trench is known as the Mariana trench, reaching a staggering depth of 10.9 km.
The Line & The Triangle
Lembeh Strait is considered to be an engine room of evolution.
To the south of the Philippines, separated from the Sulu Sea by an ocean ridge, is the Celebes Sea.

Part of the Coral Triangle, the Celebes Sea reaches the coast of northern Sulawesi, an incredibly rich & diverse part of Asia that is home to Bunaken National Park and the legendary Lembeh Strait- considered by many to be the earth’s engine room of marine evolution. The Celebes Sea is part of an ancient ocean basin and plummets to depths of over 6km.

To the east, the Celebes Sea opens out in the the Pacific Ocean, while to the south, it meets the Makassar Strait.
This region sprung to prominence among scientists in the 19th century, when the Wallacea Line theory was proposed. This line passes from the Celebes Sea, through the straits of Makassar & Lomok then out into the Indian Ocean. It marks the boundary between two distinct groups of wildlife. To the south & east, animals are of Australian origin, while to the west, wildlife is distinctly Asian. In days of lower sea levels, many of south east Asia’s islands were linked by land, but this deep stretch of water that marks the line of Wallacea prevented further expansion, explaining the distinct wildlife groups on adjacent islands.

Crossing to the southern hemisphere and heading east to Papua New Guinea, we find the Bismark & Soloman Seas. The marine life here bears greater similarities to that of the Great Barrier Reef and Coral Sea off Australia’s north-eastern coast. The area marks the south-eastern tip of the Coral Triangle and, until fairly recently, was thought to possess the greatest diversity of coral & fish species on earth.

That accolade is currently held by the tiny Halmahera Sea off the north eastern tip of Western Papua. Sitting almost exactly on the equator, this sea is home to 600 different species of coral and around 1300 fish species. It is possible to dive at Raja Ampat & Fak-Fak, in the Halmahera Sea, by Liveaboard from slightly less remote parts of Indonesia.

To the south of here, the shallow Arafura Sea stretches across to the northern coast of Australia and, in the west, meets the Timor Sea. The Timor Sea, like the Arafura, is primarily a shallow sea, with the exception of a deep trough to the north. It empties out into the southern Indian Ocean to the west.
To the north of this area, we re-enter the Coral Triangle through the strait of Alor and find the seas Banda & Molucca - home to the Moluccas, a group of islands famed in days gone by as the Spice Islands. The Banda Islands and Ambon are two of the excellent dive spots in the area, along with Alor to the south.

Wakatobi, off the south-eastern arm of Sulawesi, lies between the Banda Sea the Flores Sea. Wakatobi is one of the few areas that has all 3 types of reef system - fringing reef, barrier reef and atolls. The Flores Sea is another incredibly productive sea, with spectacular marine life off the southern arms of Sulwesi and all around Flores, Komodo & Sumbawa to the south.

The straits between the Nusa Tengarra island chain of Indonesia, including Flores, Sumbawa & Lombok, have some of the strongest currents on earth due to the Indonesia Throughflow. The Indonesian throughflow is a massive transference of water from the Pacific to the Indian Oceans, which has to squeeze through the small channels between the islands. These ripping currents make for tricky diving conditions, but incredibly healthy marine eco-systems as they flood the area with the nutrients required to support a huge array of life.

Bali, to the west, is where the Flores Sea meets the Java Sea and marks the south-western tip of the Coral Triangle. The relatively shallow Java Sea separates Java, Indonesia’s most populous island from Borneo, the world’s largest island to the north. To the west, it meets Sumatra, separating it from the Andaman Sea and the Indian Ocean, where our journey began.

  Batfish Clownfish Squirrelfish Snapper
The Triangle of Life         
The underwater world of South-East Asia has long been famed for its wealth & diversity of marine life. But it is only relatively recently that scientists have begun to get a hold on just how diverse and special the area is...



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