image: Conceptual diagram of the carbon cycle within a glacial basin in the Tibetan Plateau.
The cryosphere, a term used to describe the areas of the Earth's surface where water exists in solid form, plays an important role in regulating the Earth's climate. Due to cryospheric retreat; for example, the melting Greenland ice sheet in the Arctic, greenhouse gases that were formerly in "frozen storage" are now being released. High Mountain Asia, also known as the Tibetan Plateau, hosts the largest volume of glaciers outside the polar regions. However, Tibetan glaciers are currently excluded from global greenhouse gas budgets.
According to Shichang Kang, leader of a group of researchers who recently became the first team to measure the flux variations of greenhouse gases (CO2 and CH4) in typical glacial basins in High Mountain Asia, it's important that Tibetan glaciers are not only included in budget calculations, but are subject to more thorough investigation.
In a paper published in the KeAi journal Fundamental Research, he and his colleagues report that cryoconite holes on the glacier surface in southern and southeastern regions of the Tibetan Plateau are strong sources of carbon with positive CH4 and CO2 fluxes. However, this is mitigated to some extent by the fact that proglacial river runoff can be a significant sink of atmospheric CO2; a fact not identified in previous studies.
Kang, who is a Professor at the Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, explains: "Glaciers in High Mountain Asia contain large reservoirs of organic carbon that can influence glacial ecosystems under rapid melting. We have estimated the lateral export of carbon from glaciers to the downstream. However, no systematic data exist on the current footprint of greenhouse gases from glacial basins, which limits our understanding of the carbon cycle."
He adds: "Given the current climate change problems we are facing, the impact of glacier shrinking on CH4 and CO2 fluxes in this region needs to be further investigated and understood. Specifically, the CH4 and CO2 fluxes from the cryoconite holes, subglacial sediments and proglacial rivers."
According to Dr. Yulan Zhang, the investigator who led the study: "Until now, there were no estimates on the potential climate change caused by greenhouse gas emissions from cryosphere melting in High Mountain Asia. Determining how these data are coupled with biogeochemical models, including feedback between the glacial cryosphere and atmosphere, is required to test the sensitivity of carbon sinks or sources to changes in the terrestrial cryosphere." She adds: "Our results provide new insight about the projections in the cryospheric regions. It's clear that how the climate responds to carbon and nitrogen cycles in High Mountain Asia should be thoroughly studied in the future."