Decadal Firn Dynamics and Environmental Change on Grigoriev Ice Cap, Tien Shan
The High Mountain Asia range is often described as the water towers of Central Asia due to its crucial role in providing water resources. Its glaciers, vital for sustaining human populations and ecosystems in this predominantly dry region, have earned the nickname the Third Pole. During the dry summer months, glacial meltwater accounts for over 75% of the region's water supply. Consequently, the livelihoods of local communities and sectors like agriculture (particularly irrigation), industry, and hydroelectric power generation depend heavily on this glacial meltwater.
Contributing to the pioneering scientific inquiry, Byrd Center Senior Research Scientist Lonnie Thompson, Distinguished University Professor at The Ohio State University's School of Earth Sciences (SES), conducted groundbreaking glacial ice core studies in this region of Asia since the 1980s, drilling the Grigoriev ice cap summit located in the inner Tien Shan Mountains of Kyrgyzstan in 1990.
Most recently, an international team of researchers, including SES and Byrd Center's Stanislav Kutuzov, conducted a comprehensive analysis of the firn changes on the Grigoriev ice cap. Their study, which spans the past fifty years, was published earlier this month in the European Geosciences Union's, The Cryosphere. The ice cap's comprehensive history of ice and firn core drilling and climate studies began in 1962 by Soviet glaciologists. The latest contribution to this data set is an 18-meter firn core extracted in 2018 at the summit, which provided a window into the firn's physical and chemical evolution since the early 1970s.
The findings from this core revealed that an increase in the melt index and depletion of major ions and black carbon since the early 2000s attributed to accelerated meltwater runoff. Surprisingly, despite a significant rise in air temperatures over the decades, the water stable isotope ratios (δ18O) in the firn no longer correlated with these changes, indicating their unreliability as temperature proxies at this location. The findings also corresponded with a general decline in mineral-dust-related ions, aligning with decreased dust storm activity in Central Asia.
However, anthropogenic ions from the 1970s to the 1990s remained consistent with other regional studies, reflecting historical emission trends even during periods of lesser melt influence.
Furthermore, the study noted that the thermal regime of the firn has remained relatively stable, with temperatures in 2018 reaching the highest recorded. Yet, recent measurements indicate a return to early 2000s levels.
Interestingly, the upper layers of the 2018 firn were denser and icier than earlier cores, with deeper stratigraphy essentially unchanged. Researchers hypothesized that near-surface infiltration ice could facilitate lateral runoff, potentially stabilizing firn temperatures by removing latent heat and flushing out major ions.
Despite the increased runoff, net accumulation rates have not decreased significantly since the 1990s, likely offset by higher snowfall or reduced wind scouring as supported by local weather data.
The research underscores the importance of integrating glacier surface mass balance and firn models to investigate further the impacts of environmental changes on the firn dynamics of the Grigoriev ice cap.
Learn more about this research by visiting "Fifty years of firn evolution on Grigoriev ice cap, Tien Shan, Kyrgyzstan." or download the PDF.
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