Early human activities impacted Earth's atmosphere more than previously
known
New study links an increase in black carbon in Antarctic ice cores to
Maori burning practices in New Zealand more than 700 years ago

Date:
October 6, 2021
Source:
Desert Research Institute
Summary:
An international team of scientists used data from Antarctic
ice cores to trace a 700-year old increase in black carbon to
an unlikely source: ancient Maori land-burning practices in New
Zealand, conducted at a scale that impacted the atmosphere across
much of the Southern Hemisphere and dwarfed other preindustrial
emissions in the region during the past 2,000 years. Their results
make it clear that human activities have impacted Earth's atmosphere
and climate earlier and at larger scales than previously known.



FULL STORY ========================================================================== Several years ago, while analyzing ice core samples from Antarctica's
James Ross Island, scientists Joe McConnell, Ph.D., and Nathan Chellman,
Ph.D., from DRI, and Robert Mulvaney, Ph.D., from the British Antarctic
Survey noticed something unusual: a substantial increase in levels
of black carbon that began around the year 1300 and continued to the
modern day.


========================================================================== Black carbon, commonly referred to as soot, is a light-absorbing
particle that comes from combustion sources such as biomass burning
(e.g. forest fires) and, more recently, fossil fuel combustion. Working
in collaboration with an international team of scientists from the United Kingdom, Austria, Norway, Germany, Australia, Argentina, and the U.S., McConnell, Chellman, and Mulvaney set out to uncover the origins of the unexpected increase in black carbon captured in the Antarctic ice.

The team's findings, which published this week in Nature, point to an
unlikely source: ancient Maori land-burning practices in New Zealand,
conducted at a scale that impacted the atmosphere across much of the
Southern Hemisphere and dwarfed other preindustrial emissions in the
region during the past 2,000 years.

"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 McConnell, research professor of hydrology at
DRI 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." Tracing the black carbon to its source
To identify the source of the black carbon, the study team analyzed an
array of six ice cores collected from James Ross Island and continental Antarctica using DRI's unique continuous ice-core analytical system. The
method used to analyze black carbon in ice was first developed in
McConnell's lab in 2007.



========================================================================== While the ice core from James Ross Island showed a notable increase in
black carbon beginning around the year 1300, with levels tripling over the
700 years that followed and peaking during the 16th and 17th centuries,
black carbon levels at sites in continental Antarctica during the same
period of time stayed relatively stable.

Andreas Stohl, Ph.D., of the University of Vienna led atmospheric model simulations of the transport and deposition of black carbon around the
Southern Hemisphere that supported the findings.

"From our models and the deposition pattern over Antarctica seen in the
ice, it is clear that Patagonia, Tasmania, and New Zealand were the most
likely points of origin of the increased black carbon emissions starting
about 1300," said Stohl.

After consulting paleofire records from each of the three regions, only
one viable possibility remained: New Zealand, where charcoal records
showed a major increase in fire activity beginning about the year
1300. This date also coincided with the estimated arrival, colonization,
and subsequent burning of much of New Zealand's forested areas by the
Maori people.

This was a surprising conclusion, given New Zealand's relatively small
land area and the distance (nearly 4,500 miles), that smoke would have travelled to reach the ice core site on James Ross Island.



========================================================================== "Compared to natural burning in places like the Amazon, or Southern
Africa, or Australia, you wouldn't expect Maori burning in New Zealand to
have a big impact, but it does over the Southern Ocean and the Antarctic Peninsula," said Chellman, postdoctoral fellow at DRI. "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 Maori arrival and settlement of New Zealand 700 years ago was really amazing." Research impacts The study findings are important for a number of reasons. First, the results have important implications for our understanding of Earth's atmosphere and climate. Modern climate models
rely on accurate information about past climate to make projections for
the future, especially on emissions and concentrations of light-absorbing
black carbon linked to Earth's radiative balance. Although it is often
assumed that human impacts during preindustrial times were negligible
compared to background or natural burning, this study provides new
evidence that emissions from human-related burning have impacted Earth's atmosphere and possibly its climate far earlier, and at scales far larger,
than previously imagined.

Second, fallout from biomass burning is rich in micronutrients such
as iron.

Phytoplankton growth in much of the Southern Ocean is nutrient-limited so
the increased fallout from Maori burning probably resulted in centuries of enhanced phytoplankton growth in large areas of the Southern Hemisphere.

Third, the results refine what is known about the timing of the arrival of
the Maori in New Zealand, one of the last habitable places on earth to be colonized by humans. Maori arrival dates based on radiocarbon dates vary
from the 13th to 14th century, but the more precise dating made possible
by the ice core records pinpoints the start of large scale burning by
early Maori in New Zealand to 1297, with an uncertainty of 30 years.

"From this study and other previous work our team has done such as on
2,000- year old lead pollution in the Arctic from ancient Rome, it is
clear that ice core records are very valuable for learning about past
human impacts on the environment," McConnell said. "Even the most remote
parts of Earth were not necessarily pristine in preindustrial times." ========================================================================== Story Source: Materials provided by Desert_Research_Institute. Original
written by Kelsey Fitzgerald. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. Joseph R. McConnell, Nathan J. Chellman, Robert Mulvaney, Sabine
Eckhardt, Andreas Stohl, Gill Plunkett, Sepp Kipfstuhl, Johannes
Freitag, Elisabeth Isaksson, Kelly E. Gleason, Sandra O. Brugger,
David B.

McWethy, Nerilie J. Abram, Pengfei Liu & Alberto J. Aristarain.

Hemispheric black carbon increase after the 13th-century Māori
arrival in New Zealand. Nature, 2021 DOI: 10.1038/s41586-021-03858-9 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/10/211006112621.htm

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