Anomalous wet summers and rising atmospheric CO ₂ concentrations increase the CO ₂ sink in a poorly drained forest on permafrost

At the northern high latitudes, rapid warming, associated changes in the hydrological cycle, and rising atmospheric CO₂ concentrations, [CO₂], are observed at present. Under rapid environmental changes, it is important to understand the current and future trajectories of the CO₂ budget in high-latitude ecosystems. In this study, we present the importance of anomalous wet conditions and rising [CO₂] on the long-term CO₂ budget based on two decades (2003-2022) of quasicontinuous measurements of CO₂ flux at a poorly drained black spruce forest on permafrost peat in interior Alaska. The long-term CO₂ budget for the black spruce forest was a small sink of -53 ± 63 g C m^-2 y^-1. The CO₂ sink increased from 49 g C m^-2 y^-1 for the first decade to 58 g C m^-2 y^-1 for the second decade. The increased CO₂ sink was attributed to an 11.3% increase in gross primary productivity (GPP) among which 9% increase in GPP was explained by a recent increase in precipitation. Furthermore, a 3% increase in GPP in response to a 37-ppm increase in [CO₂] was estimated from the data-model fusion. Our study shows that understanding the coupling between hydrological and carbon cycles and the CO₂ fertilization effect is important for understanding the current and future carbon budgets of high-latitude ecosystems in permafrost regions.