A study shows that the history of air pollution goes back surprisingly far back in the south of the world as well: Scientists were able to trace traces of soot in Antarctic ice cores to slash and burn in New Zealand, which the Maori apparently started about 700 years ago. The results are important for atmospheric research and also shed light on the settlement history of New Zealand, say the researchers.
Today traces of human activity can be found in every corner of the earth. We have put our stamp on the planet so intensely that scientists even speak of a new era in the history of the earth: the Anthropocene – the age of man. The beginning is difficult to define, because our ancestors influenced the original ecosystems and the atmosphere early on through clearing and incineration activities, among other things. One way of demonstrating far-reaching human effects in history is to examine ice cores. For example, researchers have been able to trace back substances in ice cores from the Arctic that are already 2000 years old to environmental pollution in the Roman Empire.
In the current case, however, ice cores from the Antarctic were now in the sights of the researchers led by Joe McConnel from the Desert Research Institute in Reno. The study began with the detection of unusual amounts of soot in ice core samples from James Ross Island, which is located on the northeastern tip of the Antarctic Peninsula. The black carbon particles are typically formed when biomass is burned, for example through forest fires, or through the use of fossil energy sources. Due to their light-absorbing effect, they can also influence the climate, the researchers explain. According to the dating of the traces, the significant increase in soot precipitation began around the year 1300. In order to investigate the findings more closely, the scientists analyzed further ice cores that came from James Ross Island and the Antarctic mainland.
On the trail of mysterious soot
It was thus confirmed that the ice on James Ross Island was exposed to increasing soot particle precipitation from around 700 years ago, which was particularly intense in the 16th and 17th centuries. In contrast, the researchers found stable soot concentrations in the ice samples from continental Antarctica during the same period. In order to determine the origin of the deposits from James Ross Island, the researchers then finally developed atmospheric model simulations for the southern hemisphere.
“Backward calculations with our transport model of all of these ice cores showed that the soot deposits on the Antarctic Peninsula in the absence of such deposits in East Antarctica can only be explained by emissions in Patagonia, Tasmania and New Zealand,” says co-author Andreas Stohl from the university Vienna. “We were able to exclude regions further north in Africa, Australia or the Amazon region as source regions, as these would have caused a similar increase in soot deposition in East Antarctica as on the Antarctic peninsula,” explains Stohl.
According to the researchers’ research, only New Zealand came into question as the origin of the particles. Because from there there is evidence of extensive combustion processes at the time in question: It is assumed that the Maori people reached this remote island world in the 13th to 14th centuries and then probably burned down large parts of the forested areas in a targeted manner. Apparently, emissions were created that had a significant impact on the atmosphere in large parts of the southern hemisphere, say the researchers.
A far-reaching factor early on
“The idea that humans, at this point in history, caused such a significant change in atmospheric black carbon through their logging activities is quite surprising,” says McConnell. “We used to think that if we go back a few hundred years, we would see a pristine, pre-industrial world – but from this study it is clear that humans have been influencing the environment over the Southern Ocean and the Antarctic Peninsula for at least 700 years “Said McConnell.
In addition to the possible influence on the climate through the light-absorbing effect of the soot particles, according to the scientists, there could also have been an indirect effect of the combustion residues. Because fallout from biomass incineration is rich in micronutrients like iron. Phytoplankton growth in much of the Southern Ocean is nutrient limited, so rainfall from the Maori burn likely spurred centuries of increased phytoplankton growth in large areas of the southern hemisphere, the scientists say.
The study results also have an anthropological significance, the team emphasizes in conclusion: They are now refining knowledge of the time of the Maori arrival in New Zealand – one of the last habitable places on earth to be inhabited by humans. So far, dating based on radiocarbon dates has roughly assigned the settlement to the period between the 13th and 14th centuries. The more precise dating made possible by the ice core records now points to the beginning of the large-scale slash and burn operations by the Maori in 1297, with an uncertainty factor of only 30 years.
Source: Desert Research Institute, article: Nature, doi: 10.1038 / s41586-021-03858-9