A climate archive in ice
Gongga Mountain, also known as Minya Konka, is the highest peak in Sichuan province at 7,556 meters. It is the world's easternmost 7,000-meter peak and is located on the southeastern edge of the Tibetan Plateau, a region highly sensitive to shifts in the Asian summer monsoon. The mountain and its surrounding range, the Daxue Shan, host at least 159 glaciers. These glaciers, formed by annually accumulating layers of snowfall, record past atmospheric conditions.
Scientists drill into these glaciers to extract ice cores, long cylinders of ice recording the climate. Each layer captures atmospheric dust, chemicals, and precipitation from the time it was formed. By analyzing the physical and chemical properties of these layers, researchers can reconstruct past temperature, precipitation, and atmospheric circulation patterns. The ice core from Gongga Mountain provides a high-resolution record of the Indian and East Asian monsoon systems, which provide water for billions of people.
Researchers analyze ice cores using on climate proxies. For example, the thickness of annual ice layers indicates the amount of precipitation in a given year—thicker layers mean more snow, suggesting a stronger monsoon. The concentration of dust particles can also signal changes in atmospheric circulation and aridity in the dust's source regions.
Decoding the monsoon's past
The Gongga Mountain ice core record reveals significant fluctuations in the strength of the Asian monsoon over recent centuries, correlating with broad climate phases like the Little Ice Age. The Little Ice Age was a period of regional cooling, conventionally dated from the 16th to the 19th centuries. Tree-ring data from the southeastern Tibetan Plateau shows several distinct cold periods that align with this era, such as 1567–1573 and 1604–1608. Moraines—accumulations of glacial debris—in front of Gongga's glaciers suggest three distinct glacial advances during the Little Ice Age, between the 15th and 19th centuries.
Data from the ice core shows that during cooler periods, corresponding to a weaker summer monsoon, the annual ice layers are thinner. A weaker monsoon carries less moisture, resulting in less snowfall on the glacier. These periods of weakened monsoons recorded in the ice align with historical records of drought in China. The transition from the Medieval Warm Period to the Little Ice Age, for instance, marks a dramatic weakening of the East Asian summer monsoon.
Increased dust concentrations within the ice layers also point to a weaker monsoon. A less powerful monsoon wind system allows for greater transport of dust from arid inland areas. The interaction between temperature, monsoon strength, and dust deposition creates a record of past climate dynamics, allowing scientists to understand the natural variability of this important climate system.