Glaciation weathers rocks and impacts climate
When atmospheric carbon dioxide (CO2) is dissolved in rainwater, it forms carbonic acid that can weather rocks. This CO2 may eventually be incorporated into aquatic organisms as organic carbon, removing it from the atmosphere and influencing the climate. Since weathering releases chemicals from rocks into the environment, the composition of surrounding sediments and stream water can reveal the extent of chemical weathering. To understand how glaciation is affecting weathering in the Arctic, the EU-funded LITING (Lithium isotopes as a tracer for changes in interglacial-glacial weathering processes) initiative studied the chemical composition of two streams from glaciated and unglaciated Arctic catchments. Researchers also identified the type of bacteria in the sediments of both streams, located in Svalbard (a group of Norwegian islands in the Arctic Ocean). Their analysis revealed that sulphuric acid, formed from the mineral pyrite (iron sulphide), weathered rocks in both unglaciated and glaciated catchments. However, while most weathering in the unglaciated catchment was due to sulphuric acid, in the glaciated catchment carbonic acid also contributed to weathering. Microbial chemical compositions also suggested that glaciation alters stream water chemistry through the interplay of biological, physical and chemical factors. Both streams contained a low amount of the type of carbon normally produced by photosynthesising organisms (for example, plants and algae). Instead, dissolved organic carbon appeared to originate from organisms that use methane, a greenhouse gas, as an energy source. Known as methanotrophs, these microbes may have influenced past climates by consuming methane from Arctic permafrost. The type of protozoa found in glaciated and unglaciated catchments also differed, predominantly obtaining their energy from chemicals (chemotrophs) or light (phototrophs), respectively. LITING's insight into weathering in high-latitude environments can be used to predict how these regions will respond to a warming climate. In particular, the study shows how nutrient supply to the Arctic Ocean may change with future weathering.
Keywords
Glaciation, climate, Arctic catchments, weathering, LITING
