The real mystery behind Moana: After 1,700 years, why did Polynesians suddenly sail east?

《海洋奇缘》背后的真实谜团：为何波利尼西亚人在停滞1700年后突然向东航行？

The same question drives both the plot of Moana and decades of archaeological research: Why, after centuries of relative stability, did Polynesian voyagers suddenly begin settling islands thousands of kilometers away across the Pacific? The latest Moana movie is a live-action adaptation of a Disney animated movie of the same name. While the films are fictional, they draw inspiration from the rich seafaring heritage of Polynesian peoples, whose ancestors undertook one of the greatest episodes of maritime exploration in human history. New climate evidence may help us understand why they embarked on these voyages.

同一个问题既推动了电影《海洋奇缘》（Moana）的剧情，也驱动了数十年的考古研究：为什么在经历了几个世纪的相对稳定后，波利尼西亚航海家突然开始向太平洋深处数千公里外的岛屿定居？最新的《海洋奇缘》电影是迪士尼同名动画电影的真人版。虽然电影是虚构的，但它们从波利尼西亚民族丰富的航海遗产中汲取了灵感，这些民族的祖先完成了人类历史上最伟大的海上探险之一。新的气候证据或许能帮助我们理解他们为何踏上这些航程。

The backdrop to Moana is the mystery of the “long pause”. This was a period when Polynesian ancestors, the Lapita people, sailed east into the Pacific as far as the island archipelagos of Samoa and Tonga, arriving around 3,000 years ago. They brought with them distinct pottery styles and an island-based culture.

《海洋奇缘》的背景是“漫长停滞期”（long pause）之谜。在那段时期，波利尼西亚人的祖先——拉皮塔人（Lapita people）向东航行进入太平洋，最远到达了萨摩亚和汤加群岛，并于约3000年前抵达。他们带来了独特的陶器风格和以岛屿为基础的文化。

Yet, for the next 1,700 years, there was little voyaging further east. Archaeological evidence suggests that populations in Tonga and Samoa grew and developed their own distinct post-Lapita culture. Then, between 900 and 1100 AD, ancestral Polynesians suddenly undertook a massive phase of eastward migration. Over the next century, voyagers in huge double-hulled sailing canoes reached Hawaii, Aotearoa (New Zealand), and Rapa Nui (Easter Island). The spread of sweet potatoes around Pacific islands indicates they probably made contact with the continental Americas too. When European navigators finally arrived centuries later, they were astonished to find even the smallest atolls peopled by communities sharing deep cultural and linguistic commonalities.

然而，在接下来的1700年里，几乎没有向更东部航行的记录。考古证据表明，汤加和萨摩亚的人口不断增长，并发展出了自己独特的后拉皮塔文化。随后，在公元900年至1100年间，波利尼西亚人的祖先突然开启了大规模的东向迁徙。在接下来的一个世纪里，航海家们乘坐巨大的双体帆船抵达了夏威夷、奥特亚罗瓦（新西兰）和拉帕努伊（复活节岛）。红薯在太平洋岛屿间的传播表明，他们很可能也与美洲大陆取得了联系。当几个世纪后欧洲航海家最终抵达时，他们惊讶地发现，即使是最小的环礁上，也居住着拥有深厚文化和语言共性的族群。

For generations, anthropologists and historians have debated what ended the long pause. Was it new sailing technology able to combat the easterly trade winds? Was it driven by social pressures and growing populations? Or was there a physical, environmental catalyst behind their choice? To answer this, we have to look at the physical factors that make survival on a Pacific island possible: fresh water and food. As populations grow, resource demands intensify. While ancestral Polynesians were highly adaptable and accustomed to seasonal droughts, prolonged and severe droughts during times of high population density might mean an island could no longer support its human population. Ultimately, island survival hinges on a single critical resource: rainfall.

几代以来，人类学家和历史学家一直在争论是什么结束了这段“漫长停滞期”。是能够对抗东风信风的新航海技术吗？是社会压力和人口增长的驱动吗？还是他们的选择背后存在某种物理或环境催化剂？要回答这个问题，我们必须审视使太平洋岛屿生存成为可能的物理因素：淡水和食物。随着人口增长，资源需求加剧。虽然波利尼西亚人的祖先适应能力极强，且习惯了季节性干旱，但在人口密度高时，持续且严重的干旱可能意味着岛屿已无法再供养其人口。归根结底，岛屿的生存取决于一个关键资源：降雨。

Until recently, scientists lacked evidence from the Tonga and Samoa region of what the climate was like in this critical migration era. But we were able to reconstruct these past changes by analyzing hydrogen isotopes—slightly different forms of the same element—preserved in ancient mud from swamps and lakes. In the tropics, the isotopic composition of rainwater reflects the amount of rainfall. As algae and plants grow and absorb this water, they lock this chemical signature into molecules that can survive in sediment for thousands of years, providing a natural archive of past rainfall.

直到最近，科学家们还缺乏汤加和萨摩亚地区在这一关键迁徙时代气候状况的证据。但我们通过分析保存在沼泽和湖泊古老泥土中的氢同位素（同一元素略有不同的形式），成功重建了这些过去的气候变化。在热带地区，雨水的同位素组成反映了降雨量。当藻类和植物生长并吸收这些水分时，它们会将这种化学特征锁定在分子中，这些分子可以在沉积物中保存数千年，从而提供了一份关于过去降雨量的天然档案。

Using this technique, we found evidence of a sustained, severe dry period in the southwest tropical Pacific between 850 and 1200 AD. Our results, recently published in the Journal of Pacific Archaeology, indicate this was the driest period the region had experienced in the past 2,000 years. Crucially, this drought coincided with a time when island populations were larger.

利用这项技术，我们发现了公元850年至1200年间西南热带太平洋地区持续严重干旱的证据。我们的研究结果最近发表在《太平洋考古学杂志》（Journal of Pacific Archaeology）上，表明这是该地区过去2000年来经历的最干旱时期。至关重要的是，这次干旱恰逢岛屿人口规模较大的时期。

Why would some islands experience a decades or centuries-long drought? Rainfall in the tropical South Pacific depends on the position of the South Pacific Convergence Zone, or SPCZ, a major belt of clouds and rain that shifts east and west over time, driven by patterns of sea surface temperature. Short-term shifts are linked to El Niño and La Niña, but the SPCZ can also move over much longer timescales, bringing decades of unusually dry or wet conditions to different parts of the Pacific.

为什么一些岛屿会经历长达数十年甚至数百年的干旱？南太平洋热带地区的降雨取决于南太平洋辐合带（SPCZ）的位置，这是一个主要的云雨带，受海面温度模式驱动，会随时间向东或向西移动。短期移动与厄尔尼诺和拉尼娜现象有关，但SPCZ也可以在更长的时间尺度上移动，给太平洋的不同地区带来长达数十年的异常干旱或潮湿气候。

All this matches up with genetic data that indicates Samoa’s population rapidly increased around 1000 AD, perhaps thanks to the arrival of new people. This suggests several factors aligned—severe climate stress, expanding populations, better canoe technology—to prompt daring exploration eastward. The story of Polynesian expansion is remarkable in its own right. As Moana introduces new audiences to Pacific voyaging traditions, scientists are continuing to deepen our understanding of the environmental challenges these extraordinary navigators faced—and how they responded with ingenuity, resilience and exploration on an oceanic scale.

这一切与遗传学数据相吻合，数据表明萨摩亚人口在公元1000年左右迅速增加，这或许得益于新移民的到来。这表明多种因素——严重的气候压力、人口扩张、更先进的独木舟技术——共同促成了向东的大胆探索。波利尼西亚人的扩张史本身就非常了不起。随着《海洋奇缘》将太平洋航海传统介绍给新的观众，科学家们也在继续加深我们对这些非凡航海家所面临的环境挑战的理解，以及他们如何以独创性、韧性和海洋规模的探索来应对这些挑战。

David Sear, Professor in Physical Geography, University of Southampton; Manoj Joshi, Professor of Climate Dynamics, University of East Anglia, and Mark Peaple, Research Fellow, Palaeoclimate, University of Southampton. This article is republished from The Conversation under a Creative Commons license.

大卫·希尔（David Sear），南安普顿大学自然地理学教授；马诺吉·乔希（Manoj Joshi），东安格利亚大学气候动力学教授；马克·皮普尔（Mark Peaple），南安普顿大学古气候学研究员。本文根据知识共享许可协议从《对话》（The Conversation）重新发布。