Long-term changes in the daytime growing season carbon dioxide exchange following increased temperature and snow cover in arctic tundra.

Increasing temperatures and winter precipitation can influence the carbon (C) exchange rates in arctic ecosystems. Feedbacks can be both positive and negative, but the net effects are unclear and expected to vary strongly across the Arctic. There is a lack of understanding of the combined effects of increased summer warming and winter precipitation on the C balance in these ecosystems. Here we assess the short-term (1-3 years) and long-term (5-8 years) effects of increased snow depth (snow fences) (on average + 70 cm) and warming (open top chambers; 1-3°C increase) and the combination in a factorial design on all key components of the daytime carbon dioxide (CO2 ) fluxes in a wide-spread heath tundra ecosystem in West Greenland. The warming treatment increased ecosystem respiration (ER) on a short- and long-term basis, while gross ecosystem photosynthesis (GEP) was only increased in the long term. Despite the difference in the timing of responses of ER and GEP to the warming treatment, the net ecosystem exchange (NEE) of CO2 was unaffected in the short term and in the long term. Although the structural equation model (SEM) indicates a direct relationship between seasonal accumulated snow depth and ER and GEP, there were no significant effects of the snow addition treatment on ER or GEP measured over the summer period. The combination of warming and snow addition turned the plots into net daytime CO2 sources during the growing season. Interestingly, despite no significant changes in air temperature during the snow-free time during the experiment, control plots as well as warming plots revealed significantly higher ER and GEP in the long term compared to the short term. This was in line with the satellite-derived time-integrated normalized difference vegetation index of the study area, suggesting that more factors than air temperature are drivers for changes in arctic tundra ecosystems.

Assessing the consequences of recent climate change on World Heritage sites in South Greenland.

In the Arctic region, microbial degradation poses a significant threat to the preservation of archaeological deposits, actively consuming irreplaceable cultural and environmental records. In this study we assess the potential effects of the last 40 years of climate change on organic archaeological deposits within the UNESCO World Heritage area Kujataa in South Greenland. We use the dynamic process-oriented model, CoupModel to simulate soil temperatures and soil moisture contents at four archaeological sites in the area. The results show that the organic deposits have experienced a substantial warming the last 40 years, which combined with decreasing soil moisture contents creates a dangerous combination that can accelerate the degradation of organic materials. Currently, there are 583 archaeological sites registered within the area. Our findings highlight that the current climatic conditions are not conducive to organic preservation. The greatest risk of degradation lies within the relatively dry continental inland areas of the study region, where all Norse Viking Age settlements are situated. However, even at the "cold" and "wet" outer coast, the combined effects of rising summer temperatures and declining soil moisture levels may already be exerting a noticeable impact.