Hydrological intensification causes multiple ecosystem effects in the Arctic

• Main Authors: Christensen, Torben Røjle, Lund, Magnus, Skov, Kirstine, Abermann, Jakob, López-Blanco, Efrén, Scheller, Johan, Scheel, Maria, Jackowicz-Korczynski, Marcin Antoni, Langley, Kirsty, Murphy, M.J., Mastepanov, Mikhail
• Format: Conference Object
• Language: English
• Published: 2019
• Subjects: Arctic; Greenland; permafrost; Thermokarst; Tundra; Zackenberg
• Online Access: https://pure.au.dk/portal/en/publications/71a24ac2-faa5-43e8-9c50-2199efa08a0b

Predictions of the future Arctic climate point towards overarching warming, but also towards more precipitation and an intensified hydrological cycle. Here we document how synoptic conditions causing special extreme weather patterns translate into hydrological intensification with severe implications within a high arctic ecosystem. The connection documented between the large-scale weather pattern and local consequences of the intense precipitation events is rarely seen with solid observational data. Here we focus in detail on two recent events: an episode with extreme summer rain (in 2015) and on one with extreme snow conditions (in 2018). These observations are from long time-series of data from Zackenberg, NE Greenland, providing a basis for comprehensive analyses of changes in weather patterns and their subsequent consequences for biogeochemical dynamics and ecosystem functioning. In the first event, during August 2015, one-quarter of the average annual precipitation fell during a nine-day intensive rain event. This extreme event ranked number one for daily sums during the 1996-2018 period and it had large impacts on the radiation, surface energy balance and fluvial sediment transport. The strong and prolonged reduction in solar radiation decreased CO2 uptake in the order of 18-23 g C m-2 in a wetland ecosystem, a reduction comparable to typical annual C budgets in Arctic tundra. The second event in 2018 represents a consequence of an extreme melt season that triggered a rapid thermokarst development (permafrost vulnerable due to warming trend). This caused a dramatic transformation in the ecosystem trace gas exchange within a few weeks. A grassy heathland ecosystem in homogenous flat terrain with a known small, but consistent annual CO2 uptake and very low methane exchange became collapsed scars with highly elevated methane concentrations in the cracks and a substantial wash-away of soil organic material towards downstream riverine and coastal carbon input. Predicted more frequent occurrence of such extreme ...