Global warming is causing glaciers around the world to retreat rapidly, exposing vast areas of land that were previously covered in ice. These newly exposed lands are undergoing significant changes that They influence the exchange of greenhouse gases between the land and the atmosphere, creating climate feedbacks. New research conducted in a partially glaciated basin in southwest Greenland provides key insights into this process.

Study focused on comparing carbon fluxes in different types of water within a single watershed: water from melting glaciers (melt water) and groundwater from drained areas. This allowed the researchers to avoid the problems of comparing different watersheds with different environmental characteristics, such as bedrock lithology, vegetation, or precipitation, which could bias the interpretation of the effect of soil exposure age.

Key findings show a significant difference in chemistry and biogeochemical processes between the two types of water. Water from a melting glacier contains low concentrations of reactive dissolved organic carbon (DOC). This water comes into contact with freshly crushed sediments that are chemically out of equilibrium with non-glacial conditions. Weathering of these minerals, particularly carbonic acid weathering of carbonate and silicate minerals, is more intense under these conditions and results in a net absorption of carbon dioxide (CO2) from the atmosphere. The study observed this situation during a period of higher glacial meltwater (Period 1), when the basin acted as a net sink of greenhouse gases.

On the contrary, soil water from drained areas that have been exposed for a longer period of time (up to 10.7 thousand years) has increased DOC concentrations. This organic carbon is mostly more resistant (recalcitrant) and originates from soil and terrestrial vegetation. The remineralization of this organic carbon by soil microorganisms, often under anaerobic conditions, significantly increases the production of CO2 and methane (CH4). Although both CO2 and CH4 contribute to warming, CH4 is a much more potent greenhouse gas with approximately 25 times the warming potential of CO2 over 100 years. During the period of higher soil water content (Period 2), the basin became a net source of CO2 equivalents, mainly due to the production of CH4.

These results indicate that The shift from sinks of greenhouse gases in melting glacier water to sources of greenhouse gases in soil water creates a transition from negative to positive feedback of warming during interglacial periods.As glaciers retreat and soils develop, shifts in biogeochemical reactions increase greenhouse gas emissions.

While the natural retreat of glaciers during interglacial periods causes this transition, current rapid anthropogenic warming could increase water production from melting glaciers in the short term, potentially leading to a return of the negative feedback on global warming.

The research highlights how small changes in water sources in a partially glaciated basin can alter the greenhouse gas balance. Observations from Greenland suggest that these findings about weathering and the greenhouse gas cycle are relevant to all areas that have experienced ice loss. Understanding these processes is key to more accurate predictions of the impact of glacier retreat on future climate. Spring

Article published in the journal nature.com