New Insights into Climate Variability from Ice Cores in Tropical Mountain

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Ice cores extracted from the highest tropical mountain in the world, Nevado Huascarán in the central Peruvian Andes, have provided researchers with unique insights into climate variability in the Amazon Basin over the last six decades. These ice cores preserve the climate records of the entire region and offer valuable information on phenomena such as El Niño and seasonal monsoons. This study, conducted by researchers from The Ohio State University and published in JGR Atmospheres, involved the analysis of four ice core samples, two from the mountain col (the lowest point between two ridges) and two from the summit, almost 7,000 meters above sea level.

The researchers compared the oxygen-stable isotope records preserved in the glacial ice at different elevations on the mountain. Oxygen-stable isotopes are used as proxies for temperature change over time, but interpreting the isotope records in tropical regions is more complex. The findings revealed a significant relationship between the isotope records and sea surface temperatures in the Pacific, as well as rainfall over tropical South America. The isotope records from the summit were also found to be more sensitive to large-scale changes in tropical Pacific sea surface temperature compared to those from lower levels of the mountain.

This discovery is significant because it suggests that past climate histories recorded by the isotope records may reveal different mechanisms or stories about the region depending on the elevation. The results also indicate that the influence of tropical Pacific climate on the summit isotope records is increasing, likely due to rapid climate change observed in recent decades.

The study highlights the potential of these ice cores for examining the history of El Niño in the tropics, which is not well-documented due to limited observational and historical records. During El Niño years, warm sea surface temperatures in the equatorial Pacific weaken trade winds and cause reduced rainfall in the Amazon Basin. As a result, the isotopes in the ice cores fractionate differently than normal.

The researchers also emphasize the importance of tropical ice core samples for understanding Earth’s ocean-atmosphere system. These samples provide insight into natural variability before human-induced climate change. Over the past 60 years, rising temperatures have significantly contributed to the retreat of the ice on Nevado Huascarán, which is concerning considering their crucial role as proxies for climate research.

Reaching the summit of Nevado Huascarán had long been challenging due to the risk of avalanches and hidden snow-lined crevasses. However, in July 2019, a research team led by Lonnie Thompson successfully reached the peak and collected two ice cores from the summit and two from the col drill site, recovering a total of 471 meters of glacial ice cores. Despite the difficulties and dangers faced during the expedition, this research marks the first publication in a series that will shed light on these unique ice core samples.

The study was supported by the National Science Foundation and involved collaboration with researchers from Ohio State’s Byrd Polar & Climate Research Center, including Mary Davis, Ellen Mosley-Thompson, Emilie Beaudon, Don Kenny, Ping-Nan Lin, and Roxana Sierra-Hernández.

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