Pacific Ocean

• 1. Introduction

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  The Pacific Ocean covers about 46 percent of Earth's water surface and roughly 32 percent of the entire planet's surface area. That single body of water is larger than all the land on Earth combined. Its mean depth runs to 4000 meters, and at one spot in the Mariana Trench, the seafloor falls away to 10928 meters below the surface. More than 25,000 islands rise above it, scattered from the Arctic in the north to the edges of Antarctica in the south. The name itself is a kind of joke played by history. A sailor crossed it in 1520 and found calm water, so he called it peaceful. How did a sea that hides the deepest place on Earth earn that gentle name? Who first dared to cross its open water, and what happens at the invisible line where its rock turns from one kind to another?

• 2. A Misnamed Sea

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  In 1513, the Spanish explorer Vasco Núñez de Balboa crossed the Isthmus of Panama and looked out at an unfamiliar ocean. He named it Mar del Sur, the Sea of the South, because it lay south of the coast where he first saw it. Ferdinand Magellan gave the ocean the name it still carries. In 1520, during the Spanish circumnavigation of the world, he reached its waters and met favorable winds after the storms off Cape Horn. He called it Mar Pacífico, meaning peaceful sea, a phrase that reads the same in Portuguese and Spanish. The name stuck, but the calm did not. Many tropical storms batter the islands of the Pacific. The lands around its rim are full of volcanoes and frequent earthquakes, and underwater quakes send tsunamis that have destroyed entire towns. For most of Magellan's crossing from the Strait of Magellan to the Philippines, the ocean did stay quiet. The cartographer Abraham Ortelius later labeled it Maris Pacifici, following Magellan's own description of a pacific sea.

• 3. First Crossings

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  More than 25,000 islands dot the Pacific, and people reached the western edge of this water tens of thousands of years before any European. Modern humans first arrived in the western Pacific during the Paleolithic, around 60,000 to 70,000 years ago. They came on a southern coastal migration out of Africa, reaching East Asia, the Philippines, New Guinea, and finally Australia. That last leg meant a sea crossing of at least 80 kilometers between Sundaland and Sahul. No one knows what boats they used. The presumption is large bamboo rafts, perhaps fitted with some kind of sail. Their descendants today are the Negritos, Melanesians, and Indigenous Australians. The seafaring skill of these early people shows in the dates. Buka was settled by 32,000 years before present, and Manus by 25,000, journeys of 180 and 230 kilometers across open water. A later wave, the Austronesian expansion, began from the island of Taiwan around 3000 to 1500 BCE. These sailors carried distinctive technologies, including outrigger boats, catamarans, and the crab claw sail. Around 2200 BCE they sailed south to settle the Philippines, reaching the Marianas by 1500 BCE and Palau and Yap by 1000 BCE. They were the first humans to cross vast distances of open water and reach Remote Oceania. One branch, the Lapita culture, reached the Bismarck Archipelago between 1300 and 1200 BCE and settled Tonga and Samoa by 900 to 800 BCE. A final surge of exploration around 700 CE carried them to Tahiti and the Marquesas, then Hawaii by 900 CE, Rapa Nui by 1000 CE, and New Zealand by 1200 CE.

• 4. Empires On The Water

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  In 1512, Portuguese expeditions under António de Abreu and Francisco Serrão reached the Maluku Islands, the first European contact with the western edge of the ocean. Magellan and his crew became the first to cross the whole Pacific in recorded history, stopping at one uninhabited island before reaching Guam in March 1521. Magellan died in the Philippines that same year. Juan Sebastián Elcano led the survivors home across the Indian Ocean and around the Cape of Good Hope, completing the first circumnavigation of the world in 1522. In 1564, five Spanish ships carrying 379 soldiers crossed from Mexico under Miguel López de Legazpi and colonized the Philippines and Mariana Islands. Spain then treated the ocean as a mare clausum, a sea closed to other naval powers, and at times patrolled the Strait of Magellan to keep foreign ships out. The Manila galleons ran for two and a half centuries, linking Manila and Acapulco in one of the longest trade routes in history. Other powers pushed in. The Dutch sailor Willem Janszoon made the first documented European landing in Australia in 1606, and Abel Janszoon Tasman reached Tasmania and New Zealand in 1642. In the 18th century, the Danish-born Russian officer Vitus Bering led expeditions into Alaska and the Aleutian Islands. The British made three voyages with James Cook across the South Pacific. In 1768, the young astronomer Pierre-Antoine Véron, sailing with Louis Antoine de Bougainville, measured the width of the Pacific with precision for the first time.

• 5. Carving Up Oceania

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  Growing imperialism in the 19th century left much of Oceania occupied by European powers, then by Japan and the United States. France made Tahiti and New Caledonia protectorates in 1842 and 1853. After navy visits to Easter Island in 1875 and 1887, the Chilean navy officer Policarpo Toro negotiated the island's incorporation into Chile with the native Rapanui in 1888. By 1900, nearly all Pacific islands were controlled by Britain, France, the United States, Germany, Japan, and Chile. The science of the ocean grew alongside the empires. The voyages of HMS Beagle in the 1830s carried Charles Darwin, and HMS Challenger surveyed during the 1870s. The American USS Tuscarora worked the water from 1873 to 1876, and the German Gazelle did the same from 1874 to 1876. In 1898, during the Spanish-American War, the United States took control of Guam and the Philippines from Spain. The Washington Naval Treaty of 1921 ended the Anglo-Japanese Alliance, and the Royal Navy left the South Pacific that same year. Japan occupied many Pacific islands during the Pacific War from 1941 to 1945. By the war's end Japan was defeated, and the Japanese-ruled Northern Mariana Islands came under United States control.

• 6. Where The Rock Changes

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  The andesite line is the most significant regional distinction in the Pacific. It is a petrologic boundary that separates the deep, mafic igneous rock of the Central Pacific Basin from the partly submerged continental areas of felsic rock at its margins. The line runs past the Aleutian arc, along the Kamchatka Peninsula, the Kuril Islands, Japan, the Mariana Islands, the Solomon Islands, and New Zealand's North Island. Indonesia, the Philippines, Japan, New Guinea, and New Zealand lie outside it. Inside the loop, basaltic lavas flow gently from rifts and build dome-shaped volcanic mountains whose eroded summits form island arcs and chains. Outside the line, the volcanism turns explosive. The Pacific Ring of Fire is the world's foremost belt of explosive volcanism, named for the several hundred active volcanoes that sit above its subduction zones. The Pacific is the only ocean mostly bounded by such zones. Only the central part of the North American coast and the Antarctic and Australian coasts lack nearby subduction. This ocean is also old and restless. It was born 750 million years ago at the breakup of Rodinia, though it is generally called Panthalassa until the breakup of Pangea about 200 million years ago. The oldest Pacific seafloor is only about 180 million years old, the older crust already subducted away. Plate tectonics is shrinking the ocean by roughly 2.5 centimeters a year on three sides, even as the Atlantic grows.

• 7. Islands And Currents

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  The Pacific holds most of the islands in the world, sorted into three groups: Micronesia, Melanesia, and Polynesia. Melanesia contains New Guinea, the world's second largest island after Greenland and by far the largest in the Pacific. Polynesia stretches from Hawaii in the north to New Zealand in the south, reaching east to Easter Island. Islands here come in four basic types, including continental islands, high volcanic islands, coral reefs, and uplifted coral platforms. The Great Barrier Reef off northeastern Australia is one of the most dramatic, a chain of reef patches built up on basaltic lava under the surface. The water itself moves in great wheels. Motion is generally clockwise in the Northern Hemisphere and counter-clockwise in the Southern. The North Equatorial Current runs westward along latitude 15 degrees north, then turns north near the Philippines to become the warm Kuroshio Current. Surface temperatures range from -1.4 degrees Celsius, the freezing point of seawater, in the polar areas to about 30 degrees near the equator. Salinity peaks at 37 parts per thousand in the southeastern area and drops below 32 in the far north. In the tropical and subtropical Pacific, the El Niño Southern Oscillation shapes the weather. Its phase is judged by the recent three-month sea surface temperature average for an area about 3000 kilometers southeast of Hawaii, with a swing of more than half a degree marking an El Niño or La Niña.

• 8. The Ocean Under Pressure

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  The Northwestern Pacific is the most vulnerable to microplastic pollution, sitting close to heavily populated countries like Japan and China. The amount of small plastic floating in the north-east Pacific rose a hundredfold between 1972 and 2012. The Great Pacific Garbage Patch between California and Japan is now three times the size of France, holding an estimated 80,000 metric tons of plastic in roughly 1.8 trillion pieces. The ocean has absorbed deliberate damage as well. From 1946 to 1958, the Marshall Islands served as the Pacific Proving Grounds, host to 67 nuclear tests across various atolls. A one-megaton bomb was lost during the 1965 Philippine Sea A-4 incident. In 2021 the Japanese Cabinet approved discharging radioactive water from the Fukushima nuclear plant into the Pacific over a course of 30 years, concluding the water would be diluted to drinkable standard. A newer threat is deep-sea mining, aimed at manganese nodules that hold magnesium, nickel, copper, zinc, and cobalt. The largest deposits lie between Mexico and Hawaii in the Clarion Clipperton fracture zone, on a seafloor whose great depth has long kept its mineral wealth out of reach.