Plot-level Microtopographical Controls on Arctic Growing Season and Fall Shoulder Season Soil CO2 Flux

Abstract:

Permafrost soils are among the most obvious environments in which current constraints on decomposition are likely to change as a result of climatic alterations, potentially exposing large amounts of previously stored carbon (C) to microbial degradation and emission during the next few decades (Davidson & Janssens, 2006). As a best estimate, the soils of the circumpolar Arctic store over 1,035 ± 150 Pg C in the near surface (0–3 m), approximately twice the amount of C that is currently in the atmosphere (Tarnocai et al., 2009; Hugelius et al., 2014). Currently, however, much of this previously stored carbon is at risk of loss to the atmosphere due to accelerated soil organic matter decomposition in warmer future climates (Dorrepaal et al., 2009; Schuur et al., 2015). Polygonization, a predominant cryogenic process, produces micro-topographical and hydrological heterogeneity, as polygon rims produce lower water tables and drier conditions and low polygon centers produce higher water tables and wetter conditions (Brown et al., 1980). As climate models increasingly suggest that current warming trends in the Arctic (4–8 °C higher annual surface air temperatures) will continue by century’s end, C cycling in these northern climes may be further amplified (IPCC, 2013). Much uncertainty remains in regard to the spatial and temporal extent of CO₂ emissions from these systems, especially in view of the potential for modifications to C cycling in response to increased warming and deeper summer thawing of the active soil layer (Mastepanov et al., 2013). Therefore, an LI-8100 Automated Soil Flux System (LI-COR Biosciences) was deployed in Barrow, AK, to gather high temporal frequency soil CO₂ fluxes from a wet sedge tundra ecosystem. Dark chamber fluxes were gathered from 5 microtopographical habitats (designated flat, high, low, polygon rim, and polygon troughs) to calculate daily average, diurnal, and monthly respiratory fluxes. With the addition of concurrently gathered environmental parameters (thaw depth, water table, soil temperature, and eddy covariance meteorological tower data), the relatively high temporal and microspatial extent of this dataset will allow us to better understand the controls of microtopography and water table height on C cycling in this ecosystem.