Carbon emissions from emerging glacier-fed Himalayan lakes

Glacial lakes are rapidly emerging in the Himalayas as glacier mass wastage rates in the region nearly doubled in recent times. Yet, the weathering-carbon feedbacks in the glacial lakes are poorly constrained limiting our ability to predict how these newly forming and expanding lakes will modulate atmospheric carbon dioxide levels. In this study, we quantify the sources and process of carbon cycling in small-sized (<= 0.4 km2) glacier-fed Himalayan lakes during summer time and evaluated the role of glacial lakes and streams in the atmospheric carbon budget. We find that glacier-fed Himalayan lakes and streams are expected to emit CO2 up to 1746 +/- 139 mg C m- 2 d-1 and 1960 +/- 176 mg C m- 2 d-1, respectively, which is mostly controlled by dissolved inorganic carbon (DIC) fluxes. Using the glacial-lake inventory database, we estimate that the smaller glacial lakes in the Himalayas have the potential to emit-0.1 Tg C yr- 1 to the atmosphere. As recent findings suggest that the existing lakes in the Third Pole have undergone >45% expansion in an area with a rapid expansion rate of +14.44 km2 yr- 1 be-tween 1976 and 2018, we conclude that CO2 emission from these smaller and newly developed Himalayan glacier-fed lakes and streams would be an important emerging component of carbon budgets in the glacierized Himalayan catchments, and its contribution will increase in future.Plain language summary: Glacial lakes are emerging worldwide in response to melting glaciers. However, their role in carbon cycling is still underexplored. The lack of direct observational datasets on carbon fluxes, as well as their CO2 feedback mechanisms in glacial catchments has made it challenging to determine the impact of glacier -weathering-carbon feedbacks on the concentration of atmospheric CO2. Here, we quantify the CO2 emitting potential of glacier-fed lakes and streams. By studying the carbon biogeochemistry of small (<= 0.4 km2) glacier -fed Himalayan lakes and streams, we show that small lakes are a significant emitter of atmospheric CO2 controlled by dissolved inorganic carbon. We suggest that CO2 emission from small glacial lakes is an emer-ging-and not an inert-component of the regional carbon budget.One-sentence summary: Small glacial-fed Himalayan lakes emit -0.1 Tg C yr- 1 to the atmosphere contributing to the annual carbon budget estimates of glacierized Himalayan catchments.

Automated summary

Glacial lakes in the Himalayas are rapidly increasing and contribute significantly to the atmospheric carbon dioxide levels. However, our understanding of the carbon cycling in these lakes is limited, which hinders our ability to predict their impact on the carbon budget.