Antarctic ice cores help pinpoint timing of human arrival in New Zealand

Smoke from human-made fires traveled thousands of miles to end up in Antarctic ice

Scientific detective work has helped researchers determine when humans first arrived in New Zealand, one of the last places on Earth to be settled.

When early humans settled forested areas, they often set fires to clear the land for agriculture and housing. Smoke and soot particles from those fires can travel through the atmosphere and wind up thousands of miles away.

New research finds soot from widespread fires in New Zealand started showing up in Antarctic ice cores around 1297, suggesting humans likely arrived on the island nation around that time. Polynesian peoples were the first to settle New Zealand and eventually developed their own distinct culture, the Māori.

Archaeologists and the Māori themselves knew Polynesian peoples arrived in New Zealand sometime between the 13th and 15th centuries but had been unsure of the exact timing. The new results narrow the window for that arrival and show that ice cores from Antarctica can give scientists insights into past human activity that happened thousands of miles away.

The results provide the first evidence of human settlement of New Zealand to come from outside of New Zealand itself. Additionally, according to the researchers, the results show that this relatively small population had a large effect on the environment of the Southern Hemisphere.

“The change we see in the ice is almost like turning on a light switch and the timing corresponds to when humans arrived,” said Joseph McConnell, an ice core scientist at Desert Research Institute in Reno, Nevada and lead author of a new study detailing the findings.

An accidental discovery

Photo Credit: Stein Tronstad

This photo shows the Norwegian-American scientific traverse crossing East Antarctica in November 2007. The traverse carried the team who collected two ice cores used in the new study.

Researchers study ice cores to learn what Earth’s climate and atmosphere were like in ages past. As snowfall accumulates on an ice sheet, impurities in the air called aerosols are deposited along with the snow, and scientists analyze these impurities in ice cores to reconstruct Earth’s past climate. One type of aerosol scientists can analyze in ice cores is soot, which comes from fires and other types of combustion.

McConnell and his colleagues were analyzing how soot concentrations in six Antarctic ice cores varied over the past 2,000 years when they noticed something odd. They saw that around the year 1297, there was a sharp increase in soot concentrations in ice cores drilled from the northern Antarctic Peninsula but not in four ice cores drilled from the main part of the continent.

The team decided to look more closely at the puzzling results and figure out why soot concentrations would increase in northern Peninsula ice cores but not all of them. They used computer models to simulate how winds travel around the Southern Hemisphere and found it would be easy for soot from large fires to settle on the Antarctic Peninsula without making it to the main part of the continent. But for this to happen, the fires would have to have burned on land further than 40 degrees South latitude.

The only forested land masses south of 40 degrees are New Zealand’s South Island, the Australian island of Tasmania, and southern Patagonia in South America. To figure out which of these three locations the soot came from, the researchers looked at charcoal deposits in lake sediments from these areas, which provide a local record of past natural and human-caused fire activity. They analyzed the charcoal deposits to see if any change around the end of the 13th century could explain the findings.

A record of human activity

Indigenous hunter-gatherers had already been living in Tasmania and Patagonia for thousands of years by the end of the 13th century. In addition, Tasmania and Patagonia had relatively wet climates during this time and there was no evidence of increased fire activity in their lake charcoal records. So the researchers concluded it is unlikely the soot came from these regions.

New Zealand doesn’t have a natural wildfire cycle, but lake charcoal records from New Zealand confirmed what the researchers saw in the ice cores: there was an increase in fire activity around the year 1300. The researchers concluded that the increase in soot particles in the ice had to be a result of human settlement of New Zealand because it’s the only environmental change that matches the time frame, according to the authors.

“It was pretty clear that the only local fire records that matched the pattern was New Zealand,” McConnell said. “That's how we linked the changes in the Antarctic ice to early human settlement in New Zealand.”

It's not the first time ice cores have captured a record of human activity. Ice cores taken from the Arctic show pollution from mining and smelting during the Roman era, and ice cores from around the world show the unprecedented warming humans are experiencing now. But it’s surprising that a small group of settlers had an impact that can be measured from so far away, McConnell said.

The study has garnered criticism from New Zealanders who feel the researchers should have included a Māori perspective on the results or consulted the Māori about the study’s implications. Recent research suggests Māori seafarers explored Antarctic waters as early as the 7th century (long before Europeans arrived on the southernmost continent) and the Māori have been involved in Antarctic exploration ever since. Therefore, indigenous researchers argue that a Māori lens should be included in Antarctic science and policy.

However, the study authors maintain that the research focuses solely on past atmospheric chemistry and that the results aren’t a judgment of the Māori or their lifestyle.

“This is based on observation and evidence in Antarctica, not any sort of criticism of land stewardship, or anything else by the Māori,” McConnell told Radio New Zealand.

This research is supported by the National Science Foundation, which manages the U.S. Antarctic Program. NSF-funded research in this story: Joseph McConnell, Desert Research Institute, Award No. 0538416, Award No. 1702830, and Award No. 1925417; Edward Brook, Oregon State Universyity, Award No. 0968391; Loretta Mickley, Harvard University, Award No. 1702814; and David McWethy, Montana State University, Award No. 1832486.