Carbon sink strength and allocation dynamics of a rich fen peatland in the warming Arctic

Arctic peatlands harbour enormous stocks of carbon (C) owing to the imbalance between photosynthesis and respiration rates. This carbon has been exposed to a changing climate, in particular warming, during the last century. The Arctic has warmed by on an average ~0.75°C (Post et al; 2019), which is almost double the rate of global average. There is a wide range of studies on Arctic peatland C cycle, but critical knowledge gaps remain. In particular, plant C traits such as allocation rates, residence time of C in foliage, structural, fine root and labile pools and their response to warming climate are rarely explored. In order to investigate these traits, we trained an intermediate complexity terrestrial ecosystem model (DALEC), which represents these key unknowns, with available in-situ data in order to generate a data constrained analysis of ecosystem function. DALEC is calibrated with a Bayesian model-data fusion framework (CARDAMOM) which retrieves a probabilistic estimate of DALEC’s parameters based on the combination of observations and their uncertainties. CARDAMOM’s analysis directly provides an estimate of our uncertainty. We used 7 years (2014–2020) of data from the Bonanza Creek rich fen peatland in Alaska using a weekly timestep. CARDAMOM used eddy covariance information, earth observation, and in-situ biophysical observations to calibrate DALEC. We found a switch from a C source to sink, which is forced by increase in photosynthesis and leaf area index . Gross and net primary production (GPP and NPP) almost doubled from 2014 to 2017, transforming the peatland from a C source to a sink. Our analysis also suggests that NPP allocation is directed primarily towards foliage over the fine root and structural C pools.