Diatoms, a plant-based plankton with a siliceous shell, are widely used as important indicators to understand past environmental and climate changes, as they are very sensitive to changes in the environment. South Korean researchers have found evidence of unusual climatic conditions that led to the decline of historical Mesopotamian and Indus civilizations, as well as droughts in northern China and floods in the south, on Jeju Island.
A research team from the Korea Institute of Geoscience and Mineral Resources (KIGAM) successfully confirmed climate changes during the 'Holocene' epoch, which is the time since the last ice age when modern humans have lived, by analyzing diatoms from sediment samples collected from the Sara Oreum on Hallasan. The research results were published in the March issue of the international scientific journal Palaeogeography, Palaeoclimatology, Palaeoecology.
The research team extracted samples of unconsolidated sediment layers, which have not yet completely hardened, and volcanic ash from a depth of 0 to 10 meters in the Sara Oreum wetland, measured the radiocarbon age, and analyzed diatom communities. Radiocarbon dating is a method for estimating past ages by measuring the composition ratio of radiocarbon isotopes in carbon compounds made by plants or animals. As a result, it was confirmed that there was a rapid increase in sandy sediment particles and planktonic diatoms on Jeju Island 4,200 years ago.
This suggests that heavy rain fell on Jeju Island during an unusual climate event about 4,200 years ago, which caused large-scale changes worldwide. This overturns the existing hypothesis that Jeju Island was in a very dry state. Through this, it has been confirmed that the Jeju wetland can serve as an important indicator of climate change.
Additionally, the research team confirmed that the southward movement of the 'westerly jet,' a wind that blows strongly from west to east in the upper troposphere of mid-latitude regions, is related to the increase in precipitation on Jeju Island. Due to changes in the Earth's orbit and axial tilt, solar radiation decreased, causing the westerly jet to shift from high latitudes to low latitudes, leading to the precipitation zone remaining over Jeju Island and southern China. As a result, it was observed that record heavy rainfall occurred in specific areas, including Jeju Island, while others experienced severe drought.
The research team noted, "The current climate change is also closely related to the movement of the westerly jet," adding that "this research provides very important clues for understanding today's unusual climate issues and preparing for the future." The team plans to study long-term climate pattern changes in Jeju Island and East Asia based on the results of this research.
Jo Ah-ra, a researcher, expressed hope that "this research will play an important role in finding solutions to the climate crisis," stating, "We will significantly contribute to dramatically improving the accuracy of future climate predictions by enhancing climate change prediction models and strengthening global research collaboration."
References
Palaeogeography, Palaeoclimatology, Palaeoecology (2025), DOI: https://doi.org/10.1016/j.palaeo.2025.112730