Scientists have been puzzled by high concentrations of “black carbon” (soot) in ice cores taken from the Antarctic Peninsula. New research indicates a 300-400-year surge in the black carbon concentrations found there was a result of a change in burning regimes in Aotearoa New Zealand after Māori settlement. The results surprised scientists who hadn't expected a relatively small landmass could have such large consequences 7,000 kilometers (4,200 miles) away.
Ice cores preserve a record of changes in global climate conditions. In the Anthropocene, they sometimes keep track of human influences, such as the rise and fall of the Roman lead smelting industry being traceable in Greenland ice.
Professor Joe McConnell of the Desert Research Institute (DRI) led a team that more precisely dated the burst of black carbon previously detected in the Antarctic Peninsula, but not elsewhere on the frozen continent. In Nature, McConnell and co-authors show the only plausible explanation is the upsurge of burning that followed Māori arrival in Aotearoa, despite the islands’ size.
Southern hemisphere fires have long left a residue in the Peninsula’s ice, but “Rapid deposition increases started in 1297 (±30 s.d.),” the paper reports. Black carbon tripled between the late 13th century and a peak around 1700. By modeling airflow over the southern ocean the authors concluded the fires must have been located at least 40º S, excluding Africa and the Australian mainland. A few small islands, and icebound Antarctica itself aside, this makes Tasmania, Patagonia, and New Zealand the only potential sources.
Evidence from Aotearoa itself shows fires increased after Māori arrival, while Tasmania and Patagonia, both of which had been occupied by humans for thousands of years, experienced no change.
“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,” McConnell said in a statement.
“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 the DRI's Dr Nathan Chellman. In fact, the area responsible is probably even smaller than is immediately obvious. Most of Aotearoa’s North Island is north of the 40 parallel.
“The 40-degree line is approximate, but the modeling does indicate that the Antarctic Peninsula is more sensitive to burning on the South Island of New Zealand than on the North Island,” co-author Professor Nerilie Abram of the Australian National University told IFLScience.
There was no equivalent change in soot deposited in other parts of Antarctica at the time. Abram told IFLScience this “is because of the way air travels around the southern ocean,” and helped the team identify New Zealand as the most likely source of the Antarctic black carbon.
Today black carbon is an important contributor to global heating, and analysis of its historic sources can improve our understanding of its movements and effects today.
Smoke from the fires could also have had positive effects by fertilizing the Southern Ocean and stimulating phytoplankton growth.
The work has attracted some criticism, however. Dr Priscilla Wehi of New Zealand’s Te Pūnaha Matatini Centre of Research Excellence in Complex Systems described the paper as “fascinating”, but criticized the lack of New Zealander scholars among the authors. “‘Helicopter science’, where research is led and conducted by those who live and work far from the subject of their work, is currently under scrutiny in the research community,” she said.