Stalagmites Tell the Story of Sky Change--Acid Rain and Asian Environmental Impacts as Read from Iriomote Island - June 2007

Stalagmites Tell the Story of Sky Change--Acid Rain and Asian Environmental Impacts as Read from Iriomote Island - June 2007

Stalactite caves spread over Iriomote Island, Okinawa Prefecture. In 2007, a research team from Kyushu University and the Institute for Global Environmental Studies conducted a long-term analysis of acid rain using stalactites on Iriomote Island and provided the clearest evidence yet of environmental change.

By precisely measuring the isotopic ratios of sulfur and carbon in stalactites on Iriomote Island, the study revealed the intensity of acid rain and its factors over the past 40 years. In particular, they found that the concentration of sulfate ions in rainwater has increased sharply by two to three times since the 1990s. This period coincided with a sharp increase in SO2 (sulfur dioxide) emissions due to increased coal use in China and other East Asian countries.

Iriomote Island is located in the path of prevailing westerly winds, a geographical feature that facilitates the arrival of transboundary air pollutants from the Asian continent. Although stalagmites grow at a rate of less than 1 mm per year, they function as natural "environmental recorders" because the components in the growing layer reflect chemical changes in the atmosphere.

The results of this analysis highlight the fact that, along with global warming and PM2.5, atmospheric environmental changes that are difficult to see have a significant impact on the nature of distant islands. Increased acid rain may also lead to soil acidification and ecosystem collapse in tropical forests, and is increasingly recognized as an environmental risk that is not limited to local areas.

The study also suggests that the effects of acid rain are geographically unevenly distributed within Japan, with nature-rich islands such as Iriomote Island, Okinawa, being particularly vulnerable. The research team intends to further analyze the data in conjunction with meteorological and atmospheric data for Asia as a whole, with the aim of reflecting the results in environmental policies.

This achievement reaffirms the role of stalagmites as "silent recorders" of environmental destruction and demonstrates once again to society the power of scientific observation of nature.