a planet of oceans 〰

Chagos Archipelago
6°0′S 71°30′E

For millennia, the coralline rock outcrops now known as the Chagos islands existed in almost total isolation – alone and geologically adrift on the empty Indian Ocean. Too far east of the Seychelles and too far south of the Maldives to be settled, they served as distant life-rafts for lost fisherman and travellers as the other territories slowly evolved into thriving cultures. Amid the archipelago’s crystal clear waters, a teeming abundance of marine life carried on as it had for eons, with coral reefs spawning annually with the full moon and slowly rising. Then, with the arrival of European explorers, things got complicated.

The Portuguese, French and British successively named and claimed the islands, and a native population of fishermen, farmers, slaves and plantation workers emerged, composed mainly of people of Malay, Mauritian, African and Indian ancestry. In the 1960s, at the height of the Cold War, the UK and US set up an Air Force base on the island of Diego Garcia and forcibly expelled the entire population, first to the island of Peros Banhos and then to Mauritius, where they continue to face difficulties thanks to differences in language and skills. Today, the entire archipelago is off-limits except for visiting researchers and military personnel, creating a surreal juxtaposition as jet black American stealth bombers glide in to land above untouched, sparkling coral ecosystems.

Below the surface, beyond the politics, life is thriving. The Chagos Archipelago is currently one of the healthiest and least polluted marine ecosystems on the planet. Half of the Indian Ocean’s healthy reefs are found there, including the world’s largest coral atoll – the Great Chagos Bank. Home to over 310 coral and a thousand fish species, it also serves as a refuge and breeding ground for endangered sharks, whales, turtles and birds. And that’s just what we know – perched atop a submarine mountain range than stretches north to form the Maldives, the archipelago is surrounded by deep trenches, seamounts and oceanic ridges that are likely home to hundreds or even thousands of undiscovered species.

Blue Hole, Belize
17°18′N 87°32′W

From the air, Belize’s Great Blue Hole appears as a perfectly circular void amid the speckled corals and shallow crystal waters of Lighthouse Reef. A mysterious blank in the seascape nearly a thousand feet across, it dwarfs the dive boats that meander in and out from the open sea. Gazing down, it’s impossible to see the bottom, over 400 feet below the waves. Instead, there is only deep, dark, perfect blue – like a hole in the very surface of the Earth.

Located some forty nautical miles offshore, this stunning geological formation lies beyond Belize’s vast barrier reef system; the world’s second-longest after Australia. A Caribbean atoll stretching 28 miles from north to south, Lighthouse is home to six islands dotted with palm trees, white sand beaches, iguanas and seabirds. Near its centre lies the Great Blue Hole. Even in satellite photos, the dark circle stands out from the shallows, an unreal geometric oddity in an otherwise turquoise dream. In its dark depths, divers have discovered corals, sharks and unmistakable clues to its ancient origins.

Mariana Islands
16°37′N 145°37′E

In a previous column, we looked at the deepest point in the world’s oceans: Challenger Deep. Now, we shift just a little to the West and trace a series of undersea volcanos as they rise to the surface and emerge to form the Mariana Islands. More than just a series of lush tropical paradises, these remote specks of land have revealed important clues about both humankind’s early migrations and the complex and volatile undersea geology of the western Pacific.

Let’s start by diving back down under the ocean for a minute and plunging into the Mariana Trench. Located off the eastern side of the Marianas, this vast underwater canyon curves around in an arc, stretching over 1500 miles from north to south. It’s formed by the subduction of the Pacific tectonic plate under the Mariana plate – like two carpet edges meeting and one being pushed under the other.

This tectonic action created the ultra-deep trench and is also driving the area’s ongoing volcanic activity, which forms a scythe-shaped string of volcanoes stretching up to meet Japan. Part of the larger Izu-Bonin-Mariana Arc, this geological system is home to the most volcanically active convergent plate boundary on Earth – with trapped water being pushed under the grinding plates to drive hydrothermal activity. One site produces liquid sulphur and another almost pure liquid carbon dioxide, one of only two places on the planet this is known to occur. In other areas, scalding acidic water spews forth, giving scientists a glimpse at what may happen when acidification threatens other areas.

Above the waves, the hellish scene is replaced by one of pure heaven. Covered in lush, untouched forests, blessed with abundant freshwater and surrounded by reefs and rich fishing grounds, the Marianas made ideal – if distant – outposts for early travellers. Archeological research on the island of Tinian reveals that people first arrived around 3500 years ago, making it the first place humans reached in Oceania. At the time, the more-than two thousand kilometre voyage from the nearest landmass meant these ancient explorers had to make the longest ocean crossing in human history. Their eventual ancestors carved immense megalithic ‘taga stones’ to support important buildings, some of which can still be seen standing.

Tun Mustapha Marine Park
7°2'N 116°56'E

After over a decade of planning, Malaysia recently unveiled a massive new Marine Protected Area at the northern tip of Borneo. Located in the vast Coral Triangle (a vast region stretching across the Philippines, Indonesia, Malaysia, Papua New Guinea, the Solomon Islands and Timor-Leste) the new park will serve as a safe haven for a staggering array of marine life – and the local people who depend on it.

The protected area runs along the jagged north coast of Malaysia’s Sabah province, where mangroves and seagrass beds provide vital habitats for birds, dugongs and fish. Offshore, in the waters where the Sulu and South China seas meet, the vast new park covers nearly a million hectares of open ocean, coral reefs and 50 islands.

The safeguarding of the Tun Mustapha MPA (named after the first governor of Sabah) couldn’t have come at a better time, with the ongoing dispute over the nearby Spratly Islands in the South China Sea worrying marine biologists. The offshore reefs and undersea habitats of the Spratlys have been found to play an important role in ‘reseeding’ marine life and maintaining fish stocks in the region. With the ongoing dredging, reclamation and outright destruction of these formerly-pristine habitats, protecting large areas in nearby waters could help balance the losses.

Enewetak Atoll, South Pacific
11°30′N 162°20′E

A tiny, perfect, dazzling ring of coral surrounded by thousands of miles of open ocean, it’s hard to imagine a more beautiful place on Earth than Enewetak Atoll. For millions of years, waves crashed endlessly over its pristine white sand as winged dinosaurs and then shorebirds alighted on this remote speck of land. Its waters teemed with fish and the island was colonised by drifting seeds, creating a sparkling green gem. Yet over the course of the World War that raged across this part of the planet from 1942 to 1945 and the potentially much more destructive Cold War that followed, Enewetak and other little worlds like it were nearly wiped off the face of the planet.

Part of the Marshall Islands, Enewetak is located over 2000 miles from the northernmost tip of Australia, beyond Papua New Guinea and the Solomon Sea. During the Second World War, Japanese and American forces fought their way across the Pacific, devastating many of its smaller islands in an intense battle for survival. On Enewetak, coral was bulldozed and filled in to create an airstrip, and later fighting saw further devastation on Engebi Islet and Parry Island, two islands that make up the atoll. But worse was yet to come.

One of thousands of such South Pacific paradises, Enewetak and the other atolls that dot this otherwise empty part of the planet are similar in geological make up and biodiversity. The region is home to over 1,000 species of fish and more than 250 species of soft and hard corals. Enewetak itself formed atop a seamount in the late Cretaceous. Seamounts are underwater mountains which rise almost to the surface, providing an ideal base for coral. Over eons, the reefs rose up above the waves and were colonised by life, even as the mountain sunk deeper into ocean. Delicate, pristine and perfect, such atolls unfortunately made ideal, very remote testing grounds for the devastating nuclear weapons that emerged as the Cold War dawned.

At 7:15am local time on November 1st 1952, the calm of yet another peaceful tropical morning on Enewetak was shattered when the United States detonated the world’s first hydrogen bomb. Codenamed ‘Ivy Mike’, the device was actually a massive 82-ton experiment housed in a purpose-built shed on the tiny islet of Elugelab. The resulting explosion vaporised the islet’s landmass completely, leaving a crater nearly 2km wide and 15 stories deep. Blast waves and surging water stripped the islands clean of vegetation and radioactive coral rained down on ships nearly 50km away. Within minutes, a 30km high mushroom towered over Enewetak. The 'Mike' test was the fourth largest nuclear test ever conducted by the US and left the area heavily contaminated, but 42 others detonations followed on Enewatak alone.

In the late 1970s, the US began a long, expensive and messy clean-up of this contaminated former paradise. Radioactive soil was treated with potassium or mixed with cement and buried a giant crater created by one of the tests, then covered with a massive concrete dome. Today, the southern and western parts of Enewatak Atoll have been declared safe and some of its exiled residents have returned – but much remains off-limits. As at sites within the Chernobyl exclusion zone, Enewetak’s isolation and reputation may in the end prove a plus for nature. Without human interference, wildlife may once again thrive undisturbed, as it did for millions of years before we arrived.

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all articles taken from our Where On Earth column, which explores amazing places around the world and the science behind them, for AnOther