Ancient Polynesians Took a 1,700-Year Break From Voyaging. This Is Why They Returned to the Sea.

The Polynesians were perhaps the ancient world’s greatest sea voyagers. They crossed vast stretches of open ocean without maps, compasses, or other navigational instruments. Instead, they steered their double-hulled canoes, outfitted with sails woven from tree leaves, by observing the position of stars rising in the night sky, the flight paths of sea birds, and shifts in wind and wave directions.

These skilled mariners traversed huge distances of the Pacific Ocean to discover and settle previously unoccupied islands separated by thousands of miles—including Easter Island and the archipelagos of Hawaii and New Zealand. Along the way, they spread their culture, oral histories, and mythology, as well as staple crops such as bananas and coconuts.

“They were making these absolutely amazing, breathtaking journeys,” says David Sear, a National Geographic Explorer and geographer at the University of Southampton in England.

(This legendary Polynesian canoe will sail 43,000 miles, from Alaska to Tahiti)

But the epic explorations were not continuous. Clues in the archaeological record indicate that there was a period lasting roughly 1,700 years during which the Polynesians stopped making long-distance ocean voyages. Then, around A.D. 900, they returned to the waters and began a new era of exploration and discovery. Scholars call this gap “the Long Pause,” but the reason behind the hiatus remains a mystery.  

“Why did people who were able to expand so rapidly across islands suddenly come to a halt?” says Patrick Kirch, an archaeologist who studies Polynesian history at the University of Hawai'i at Mānoa. “And then, after more than a thousand years, why did they expand again across the rest of the Pacific?”

Sear and his colleagues think they have found one answer to why the Polynesians re-entered the seas. The team analyzed ancient lake sediment from several Pacific islands to glean clues about past climate conditions. They found that rainfall patterns across the Pacific Ocean changed dramatically around a thousand years ago.

The western Pacific Islands the Polynesians embarked from—such as Samoa and Tonga—experienced at least two centuries of what Sear calls “drying shocks,” during which overall rainfall was drastically reduced and punctuated by drought-like conditions that lasted for decades. Meanwhile, the eastern Pacific Islands which the Polynesians sailed toward—such as the Southern Cook Islands, the Society Islands, and the Marquesas Islands—saw lusher, more favorable growing conditions.

That created the ideal circumstances for the Polynesians to venture out again, voyaging eastward into new and unknown horizons and ultimately finding more hospitable soils. The canoe fleets may have been “chasing the rains,” says Sear, who published his team’s findings in the Journal of Pacific Archaeology in spring.

Kirch, who was not involved in the study, praises the work and says it shows “essential new evidence of a period of dryness” around the end of the Long Pause. He adds that the climatic shift was likely a significant prompt for the Polynesians to set sail again.

Launching Epic Ocean Voyages

The renewed age of Polynesian exploration and discovery began around a thousand years ago and lasted for about three hundred years, between about A.D. 900 and A.D. 1250. It was roughly the same era when Vikings were expanding across northern Europe, though the historic Polynesians traveled much further and created cultures that last to this day.

Many factors may have contributed to the end of the Long Pause, says Lisa Matisoo-Smith, a biological anthropologist at the University of Otago in New Zealand, who was not involved in the study. A prior analysis of genetic data from Samoa has revealed rapid population growth around a thousand years ago, which may have strained available food supplies, she says. Other experts have suggested that advances in canoe technology enabled safer and longer voyages, including difficult travel against the wind.

(This woman navigated a 3,000-mile Pacific voyage without maps or technology)

One idea that scientists have long speculated—though never properly tested or examined—is the impact of climate shifts across the Pacific Ocean. Researchers already knew that around a thousand years ago sea-surface temperature changes—with one side of the ocean warming up slightly more than the other—had shifted heavy bands of precipitation eastward. But how exactly the differences in rainfall showed up on the islands themselves has remained unclear until now.

Secrets in the Mud

There are no written records of rainfall from the Pacific Islands that date back a thousand years, so scientists had to look for other indicators—called “proxies”—that preserve clues.

In the new research, the authors studied waxy plant remains and algae buried in mud. When it rains, water is sucked up by plant roots and pushed out into growing leaves. Some leaf wax and algal lipids can preserve details about ancient water droplets for hundreds of years, which scientists can use to infer how much rain originally fell. 

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Imagine a rain cloud. Its water molecules are composed of hydrogen and oxygen atoms. Nearly all hydrogen atoms lack neutrons, though there is a minuscule percentage that have a single neutron—making them just a tiny bit heavier.

“When it rains, water molecules containing the heavier hydrogen atoms tend to condense and fall first,” says Mark Peaple, an organic geochemist also at the University of Southampton and a coauthor of the new study. “As rain continues, more of the lighter ones will fall.”

The ratio of these different water droplets “gets encoded in leaf wax,” he says.

By analyzing that ratio, scientists can estimate roughly how much rain fell over a specific period. And they can see changes in rainfall by carbon-dating other organic matter in the mud's sedimentary layers. For analysis, the ideal mud “looks like chocolate cake: dark, rich, and full of organic matter,” says Peaple.

Wearing full mesh suits to shield themselves from mosquitoes, Sear, Peaple, and their team traveled to several islands in both the western and eastern parts of the Pacific to collect undisturbed mud samples from the bottom of crater lakes.

To preserve the long chronological record, these mud “cores” were stored in 13-foot-long plastic drainpipes and shipped back to their lab in England.

“The fun bit was going to get the mud,” says Sear.

Chasing the Rains

Their analysis showed a clear pattern: In the period just before and after the new age of exploration began, the western islands the Polynesians sailed from experienced what Sear calls “high amplitude climate shocks.” These shocks, he adds, “were the largest drying shocks in the past 1,500 years.”

While ancient Polynesians had adapted to survive short-term weather fluctuations, such as those produced during El Niño years, this new era brought “intense drought phases” lasting decades, says Sear. On Samoa, one of the western Pacific islands considered a heartland of Polynesian culture, the reconstructed mean annual precipitation was around 64 percent lower a thousand years ago compared to recent years, according to the team’s algae-derived analysis, says Sears.

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“That was probably a large contributing factor in the timing of the migrations east,” says Sear. “There’s a tipping point where people decide to take a risk and start voyaging east again.”

Emily Milton, an environmental archaeologist at the Smithsonian Institution who was not involved in the study, praised the researchers for getting knee-deep in the mud.

“It’s really important that someone took the time to actually gather data and test” the climate hypothesis, she says. The leaf wax and algae data show “a pretty notable shift that supports their interpretation of the western region being drier,” she says.

Matisoo-Smith at the University of Otago in New Zealand agrees. “It’s a very interesting and exciting addition to the debates about what happened,” she says. “This clear shift in rainfall looks like a significant part of the story.”