Comparing modeled and measured carbon dioxide data at five canadian peatlands revealed highly variable non-growing season fluxes

Peatlands hold up to one-third of the global organic carbon (C) stock and are considered a critical C sink. Climate models project that the rate of warming in northern peatlands will continue throughout the 21st century, with the greatest warming occurring during the non-growing season (NGS), which is poorly represented in current in-situ measurements. As a result, the contribution of NGS fluxes to annual peatland CO 2 budgets remains uncertain. Remotely sensed and modeled data products offer a potential means to estimate year-round fluxes, but their performance in peatland ecosystems has not been fully evaluated. In this study, we used the remotely sensed and modeled Soil Moisture Active Passive Level 4 Global Daily EASE-Grid C NEE (SMAP-NEE) data product to acquire 9 years (2015–2023) of SMAP-NEE data for five peatlands. We compared these values to a subset of year-round eddy covariance NEE (EC-NEE) measurements within this time frame at each of the five peatland sites. The analyses showed that the SMAP-NEE data product reports a stronger growing season (GS) sink and a weaker NGS source than the EC-NEE measurements. Using the relationship between SMAP-NEE and EC-NEE, we produced a Corrected-SMAP-NEE dataset, which provided an estimate of seasonal and annual carbon dioxide (CO 2 ) budgets. Our data analyses of the Corrected-SMAP-NEE dataset showed that NGS CO 2 emissions represented a highly variable proportion (33%–256%) of the GS CO 2 uptake, that reduced the annual CO 2 sink strength proportionally. This work demonstrates the necessity of monitoring during the NGS and highlights the importance of incorporating peatland data into model training to improve CO 2 flux estimates in these environments.