Iron-rich dust from South America played a role in the last two ice ages, study suggests
Seafloor sediment from the South Pacific, seen from the deck of a research vessel north starOpens a window into how iron-rich dust blown in from South America played a role in past glacial cycles. (Catherina Pank)
Dust from the high Andes in southern Bolivia and northern Argentina was an important source of nutrient-deficient South Pacific iron during the last two glacial cycles, especially at the beginning of these cycles.This is the key finding a new study in the magazine Proceedings of the National Academy of Sciences of the United States of America.
Using sediment cores collected from the southern seafloor in 2009, the researchers were able to reconstruct the contributions of various dust sources on the surrounding continents. According to the authors, the jet stream, a powerful set of air currents that flow for several kilometers from west to east, collects fine mineral grains on the eastern flank of the Andes and transports them almost all the way around Antarctica to the southeastern Pacific Ocean.
Atmospheric dust is considered a key component of the climate system. Dust particles affect Earth’s energy budget because they reflect incoming sunlight at high altitudes, creating a cooling effect. Mineral particles can also carry nutrients such as iron and manganese to remote ocean areas, where they stimulate algae growth. When the algae die and sink into the deep ocean, they remove carbon dioxide from the atmosphere, which also has a cooling effect. These mechanisms are particularly effective in the remote and iron-deficient southern regions of the Pacific, Indian and Atlantic Oceans, so changes in southern hemisphere dust cycles may have played an important role in past natural fluctuations between cold glacial periods and warm interglacial periods. Therefore, in recent years, the source and transmission route of dust has been the subject of in-depth research.
For the study, a team led by Torben Struve of the University of Oldenburg in Germany analyzed sediment cores from the subpolar seafloor of the South Pacific Ocean. The core contains sediments dating back 260,000 years, covering two glacial cycles. Using the geochemical fingerprints of the core dust, the researchers were able to determine the proportion of particles from South America, South Africa, Australia and New Zealand at different stages of the two glacial cycles.
Researchers aboard the Polarstern retrieved cores taken from the South Pacific seafloor. (Catherina Pank)
“We were surprised to find that dust from South America dominated throughout the study period, even though it had to travel a long distance,” Struve said. According to the analysis, as many as two-thirds of the particles originated there, a finding The ratio is especially high at the beginning of the glacial cycle when temperatures start to drop. Land masses closer to the sampling sites, including Australia and New Zealand, contributed smaller amounts, mainly at the end of the ice age when temperatures began to increase again.
South American dust is injected into jet streams from high altitudes in the eastern Andes and travels around Antarctica in the upper atmosphere, the researchers said. By contrast, dust particles from the lower altitudes of Australia and New Zealand are washed out of the atmosphere by rain more quickly, so they rarely reach the heights needed for long-distance transport.
Studies have shown that most of the South American dust comes from regions as high as 5,000 meters above sea level. These include parts of the Puna Plateau and the dry high valleys of the central Andes. So far, this region has received little attention from researchers.
co-author Gisela Winklera geochemist at the Columbia Climate Institute Lamont-Doherty Earth Observatory, pointing out that the study has modern significance. Some scientists have proposed artificially seeding the oceans with iron to encourage the growth of algae that can absorb atmospheric carbon. “The topic is enjoying a renaissance as nature-based ‘solutions’ to the climate crisis, including ocean iron fertilization, gain traction,” she said.
The study concluded that dust production from all sources increased between three and six times during glacial periods compared with warmer interglacial periods. The finding confirms earlier research showing that it is drier in colder climates than in warmer ones, and may also be windier. The team also found evidence that the prevailing westerly winds around Antarctica moved or weakened southward during the end of the ice age and subsequent interglacial periods.
Struve noted that the findings may contribute to a better understanding of natural climate fluctuations in the Southern Hemisphere. “Exactly how natural iron fertilization in the Southern Ocean amplifies these climate changes is not fully understood,” he said. He added that the study does not answer the question of whether it would make sense to artificially fertilize nutrient-deficient ocean areas with iron to slow human-induced climate change, he said.
