While analysing ice core samples taken from James Ross Island in Antarctica, scientists from the British Antarctic Survey noticed something unexpected – the levels of black carbon, or soot, began to increase dramatically about 700 years ago.
Black carbon is a part of the fine particulate air pollution that contributes to climate change. It is one of many particles that are emitted by the burning of diesel, coal, or by biomass burning such as forest fires.
The team analysed the ice core taken from James Ross Island and compared it to several others taken from across continental Antarctica. While the ice core from James Ross Island showed a notable increase in black carbon starting in the year 1300 and tripling over the next 700 years, black carbon levels across continental Antarctica stayed relatively stable.
To pinpoint the source of the black carbon, the team used atmospheric model simulations of the movements of its around the Southern Hemisphere. They found that the most likely candidates for the point of origin were Patagonia, Tasmania, and New Zealand.
To narrow this down further, they then checked the charcoal records of each of the three regions and found that there was a major increase in fire activity in New Zealand around the year 1300 – the estimated arrival date of the Māori people.
“The idea that humans at this time in history caused such a significant change in atmospheric black carbon through their land clearing activities is quite surprising,” said Joe McConnell, research professor of hydrology at Desert Research Institute who designed and led the study.
“We used to think that if you went back a few hundred years you’d be looking at a pristine, pre-industrial world, but it’s clear from this study that humans have been impacting the environment over the Southern Ocean and the Antarctica Peninsula for at least the last 700 years.”
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The finding was unexpected due to New Zealand’s relatively small land area and the 7,000km distance that the smoke would have had to travel to reach James Ross Island.
“Compared to natural burning in places like the Amazon, or Southern Africa, or Australia, you wouldn’t expect Māori burning in New Zealand to have a big impact, but it does over the Southern Ocean and the Antarctic Peninsula,” said Nathan Chellman, postdoctoral fellow at Desert Research Institute.
“Being able to use ice core records to show impacts on atmospheric chemistry that reached across the entire Southern Ocean, and being able to attribute that to the Māori arrival and settlement of New Zealand 700 years ago was really amazing.”