Improved ELMv1-ECA Simulations of Zero-Curtain Periods and Cold-Season Methane and Carbon Dioxide Emissions at Alaskan Arctic Tundra Sites

The Science

Scientists have improved the Department of Energy’s (DOE) Energy Exascale Earth System Model (E3SM) land model (ELMv1) simulations of soil temperature, zero-curtain period durations (i.e., the fall period when soil temperatures linger around 0°C), and cold-season methane (CH₄) and carbon dioxide (CO₂) emissions at several Alaskan Arctic tundra sites. Results demonstrated that simulated CH₄ emissions during zero-curtain periods (Sep. and Oct.) accounted for more than 50% of total emissions throughout the entire cold season (Sep. to May). Results also showed that cold-season CO₂ emissions largely offset current warm-season net uptake and had increasing trends from 1950 to 2017.

The Impact

Field studies have shown that microbial respiration occurs under very cold conditions and may offset the growing-season net carbon uptake. However, cold-season carbon emissions from permafrost regions are not accurately represented in earth system land models, severely impeding predictability of permafrost carbon losses under warming. Results of this study (1) led to improved capability of ELMv1 to accurately simulate soil temperature and cold-season CH₄ and CO₂ emissions at tundra sites and (2) highlighted the importance of zero-curtain periods in facilitating cold-season carbon emissions from tundra ecosystems.

Summary

Field measurements have shown that cold-season methane (CH₄) and carbon dioxide (CO₂) emissions contribute a substantial portion to annual net carbon emissions in permafrost regions. Accurately representing cold-season carbon emissions is crucial for models to reasonably predict the permafrost carbon-climate feedback. However, prevailing Earth system land models cannot accurately simulate cold-season carbon emissions and their contributions to the annual totals. This study used DOE’s E3SM land model (ELMv1) to tackle this challenge. Through developing an optimization framework for multi-calibration, scientists improved the ELMv1 soil water phase-change scheme, environmental controls on microbial activity, and the methane module. Results demonstrate that the optimized ELMv1 greatly improved simulations of soil temperature and duration of zero-curtain periods. Furthermore, the improved model reduced the mean absolute errors of simulated cold-season carbon emissions by more than 70%. Overall, simulated CH₄ emissions during September and October, which often includes most of the zero-curtain period in the Arctic tundra, account for more than 50% of the cold-season total emissions, agreeing very well with observations. From 1950 to 2017, both CO₂ emissions during the zero-curtain period and during the entire cold season showed increasing trends. This study highlights the importance of zero-curtain periods in facilitating cold-season carbon emissions from tundra ecosystems.

Principal Investigator

Qing Zhu
University of Washington

Program Manager

Brian Benscoter
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
[email protected]

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
[email protected]

Funding

This research was supported by the Office of Biological and Environmental Research, within the U.S. Department of Energy’s (DOE) Office of Science (grant no. DE-SC0019063).

References