Abstract
Abstract. This study investigates how warming and changes in precipitation may affect the cycling of carbon (C) in tundra soils, and between high Arctic tundra and the atmosphere. We quantified ecosystem respiration (Reco) and soil pore space CO2 in a polar semi-desert in northwestern Greenland under current and future climate conditions simulated by long-term experimental warming (+2 °C, +4 °C), water addition (+50% summer precipitation), and a combination of both (+4 °C × +50% summer precipitation). We also measured the 14C content of Reco and soil CO2 to distinguish young C cycling rapidly between the atmosphere and the ecosystem from older C stored in the soil for centuries to millennia. We identified changes in the amount and timing of precipitation as a key control of the magnitude, seasonality and sources of Reco in a polar semi-desert. Throughout each summer, small (<4 mm) precipitation events during drier periods triggered the release of very old C pulses from the deep soil, while larger precipitation events (>4 mm), more winter snow and experimental irrigation were associated with higher Reco fluxes and the release of recently fixed (young) C. Warmer summers and experimental warming also resulted in higher Reco fluxes (+2 °C > +4 °C), but coincided with losses of older C. We conclude that in high Arctic, dry tundra systems, future magnitudes and patterns of old C emissions will be controlled as much by the summer precipitation regime and winter snowpack as by warming. The release of older soil C is of concern, as it may lead to net C losses from the ecosystem. Therefore, reliable predictions of precipitation amounts, frequency, and timing are required to predict the changing C cycle in the high Arctic.
Highlights
Climatic changes and their effects on terrestrial ecosystems are amplified in the Arctic (Serreze and Barry, 2011)
Lupascu et al.: Controls on ecosystem respiration in a polar semi-desert in the high Arctic (> 70◦ N), where most non-Alpine tundra ecosystems currently exist within 100 km of the coastline (Bhatt et al, 2010; Post et al, 2013)
We found that interannual differences (F = 147; P < 0.0001) in snowfall and summer precipitation patterns have a strong influence on the seasonal soil water content (SWC) pattern (Fig. 1b, d, f)
Summary
Climatic changes and their effects on terrestrial ecosystems are amplified in the Arctic (Serreze and Barry, 2011). Other abiotic changes accompanying warming include increasing cold season precipitation, declining duration of snow cover and regionally distinct changes in snow depth (Callaghan et al, 2011), and wetting due to atmospheric transport of moisture into the Arctic (Zhang et al, 2013) and to enhanced sea evaporation resulting from retreating of winter sea ice (Bintanja and Selten, 2014). The implications of these changes for regional biogeochemistry are largely unknown, especially. Its coastal proximity makes this ecosystem vulnerable to changes in summer sea ice extent and the associated warming and changes in precipitation
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