Recent Advances and Challenges in Monitoring and Modeling Non-Growing Season Carbon Dioxide Fluxes from the Arctic Boreal Zone

Abstract

Purpose of Review While previously thought to be negligible, carbon emissions during the non-growing season (NGS) can be a substantial part of the annual carbon budget in the Arctic boreal zone (ABZ), which can shift the carbon balance of these ecosystems from a long-held annual carbon sink towards a net annual carbon source. The purpose of this review is to summarize NGS carbon dioxide (CO2) flux research in the ABZ that has been published within the past 5 years. Recent Findings We explore the processes and magnitudes of CO2 fluxes, and the status of modeling efforts, and evaluate future directions. With technological advances, direct measurements of NGS fluxes are increasing at sites across the ABZ over the past decade, showing ecosystems in the ABZ are a large source of CO2 in the shoulder seasons, with low, consistent, winter emissions. Summary Ecosystem carbon cycling models are being improved with some challenges, such as modeling below ground and snow processes, which are critical to understanding NGS CO2 fluxes. A lack of representative in situ carbon flux data and gridded environmental data are leading limiting factors preventing more accurate predictions of NGS carbon fluxes.

Solar-Induced Chlorophyll Fluorescence (SIF): Towards a Better Understanding of Vegetation Dynamics and Carbon Uptake in Arctic-Boreal Ecosystems

“…This artificial cutoff of growing season varies by instruments with different sampling frequencies leading to misshaped growth seasonality, particularly for instruments with low sampling frequency [120,121]. Missing the onset and cessation of GPP can cause large uncertainties in the net carbon flux during the shoulder seasons, when the majority of net carbon emission happens in the Arctic-Boreal region [122]. Such artificial cutoffs of growing season also fail to precisely track the temporal shifts of growth onset and cessation with climate change [33,123,124].…”

An increasing Arctic-boreal CO2sink offset by wildfires and source regions

“…Furthermore, it is not known how the widespread but spatially heterogeneous increase in vegetation productivity and greening 14,15 impacts the annual CO2 balance although links to enhanced CO2 sinks during the spring-summer period have been found 16,17 . Some of the enhanced uptake might be offset by CO2 losses associated with vegetation dieback ('browning'), and the escalating frequency and intensity of disturbances such as abrupt permafrost thaw (e.g., thermokarst), drought and fires, further complicating the understanding of ABZ carbon dynamics and climate feedbacks [18][19][20] . Current evidence on recent ABZ CO2 budget trends and their main drivers is limited to few insitu data-driven synthesis and modeling studies without a regional perspective on where and why CO2 budgets are changing 1,5,9,10 .…”