Ice cores from the world's second-longest glacier outside polar regions record 500 years of Asian monsoon variability. Dust layers mark volcanic eruptions that disrupted agriculture thousands of kilometers away.
A climate archive on the third pole
The Siachen Glacier, 76 kilometers long, is the second-longest non-polar glacier in the world. It sits in the eastern Karakoram range of the Himalayas, a region sometimes called the "Third Pole" because of its vast ice reserves. The glacier flows from an altitude of 5,753 meters at Indira Col down to 3,620 meters at its terminus. This high-altitude, frozen landscape records a history of Earth's climate.
Scientists from the National Centre for Polar and Ocean Research (NCPOR) have drilled into this ice to extract cylindrical sections called ice cores. These cores are layered archives of past atmospheric conditions. Each layer of ice represents a season's snowfall, trapping atmospheric gases, dust, and chemical traces from the time it fell. By analyzing these layers, researchers can reconstruct past climate with remarkable detail. For this work, scientists often use specialized electro-mechanical or thermal drills, sometimes powered by solar panels in remote, high-altitude locations.
The analysis of oxygen isotopes within the ice is a technique. The ratio between heavy oxygen-18 and light oxygen-16 isotopes in the frozen water molecules acts as a thermometer. A decrease of one part per million in oxygen-18 can indicate a 1.5°C drop in air temperature at the time the water first evaporated. These measurements from Siachen provide a direct record of temperature and the intensity of the South Asian Monsoon over centuries.
Volcanic signatures and monsoon history
The Siachen ice cores contain distinct layers of dust and sulfate aerosols. These layers often correspond to major volcanic eruptions, even those that occurred thousands of kilometers away. When a large volcano erupts, it injects sulfur dioxide into the stratosphere, which then converts to sulfate aerosols that reflect sunlight and can cause short-term global cooling. These aerosols eventually fall back to Earth and are preserved in the glacier's annual ice layers.
Himalayan ice cores have successfully identified the chemical signatures of major historical eruptions, including the massive 1815 eruption of Mount Tambora in Indonesia. That event caused the "Year Without a Summer" in 1816, leading to crop failures in Europe and North America. The presence of these well-dated volcanic horizons in the ice provides scientists with precise timelines to calibrate the climate record.
Besides volcanic events, the cores from the Himalayas tell a longer story of monsoon variability. Other regional ice cores have identified catastrophic droughts linked to monsoon failures, such as a seven-year dry spell that began in 1790. The chemical data from the Siachen ice cores allows scientists to study the frequency and severity of these events, providing a baseline to understand modern climate dynamics in a densely populated part of the world.
💡Fun Facts
Siachen is located in the world's highest militarized zone, where Indian and Pakistani forces have been deployed since 1984.
The name "Siachen" means "the place of wild roses" in the local Balti language.
The average winter snowfall on the glacier is over 10 meters (35 feet), and temperatures can drop to -50°C (-58°F).
In addition to the glacier, India's National Centre for Polar and Ocean Research (NCPOR) manages the country's research stations in Antarctica and the Arctic.
The Siachen Base Camp area is now open to domestic tourists without special permits, but the glacier itself remains a restricted military zone and is not accessible for general tourism.
Admission
An environmental fee is collected by the district administration for visits to the base camp area.
Accessibility
Access is limited to the Siachen Base Camp, which sits at an altitude between 12,000 and 15,000 feet. Reaching the base camp requires a 9-10 hour drive from Leh, often via the high-altitude Khardung La pass. The terrain is extreme and only suitable for those acclimatized to high altitudes.