The Real Mystery Behind Moana: After 1,700 Years, Why Did Polynesians Suddenly Sail East?

David
Sear, University
of Southampton; Manoj
Joshi, University
of East Anglia, and Mark
Peaple, University
of Southampton

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 kilometres 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.

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.

Human migrations into
the Pacific:

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
Hawai’i, Aotearoa (New Zealand) and Rapa Nui (Easter
Island). The spread of sweet potatoes around Pacific islands
indicate 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.

The mystery
of the ‘long pause’

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.

Unlocking the climate
record

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 analysing hydrogen
isotopes – slightly different forms of the same element
– preserved in ancient mud from swamps and lakes.

In the tropics, the isotopic composition of rain
water 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.

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.

The great
migration into the eastern Pacific coincided with a dry
climate in the western Pacific:

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.

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 eastwards.

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.

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. Read the
original
article.