U.S. Department of Energy Office of Biological and Environmental Research

PI-Submitted Research Highlights for
Terrestrial Ecosystem Science Program

Large CO2 and CH4 Emissions from Polygonal Tundra During Spring Thaw in Northern Alaska

Naama Raz-Yaseef
Lawrence Berkeley National Laboratory

Highlight

Eddy-covariance fluxes measured near Barrow, AK. (A) CO2 fluxes (measured half hourly - black diamonds, gapfilled half hourly - gray diamonds, daily totals - blue line); (B) CH4 fluxes (measured half hourly - black diamonds, gapfilled half hourly - gray diamonds, daily totals – green line); (C) Half-hourly fluxes of CO2 during the main spring pulse event at the two eddy-covariance sites (ARM - green diamonds, BEO - blue diamonds, dashed line – Gaussian fit); (D) Half-hourly fluxes of CH4 during the main spring pulse event at the two eddy-covariance sites (ARM - green diamonds, BEO - blue diamonds, dashed line – Gaussian fit).

12/26/2016

Findings mean the Arctic may be even less of a carbon sink than previously thought

The Science  
Berkeley Lab scientists measured a large pulse of greenhouse gases (carbon dioxide and methane) released from the frozen Arctic tundra when soils started to thaw, during a two-week period in late May to early June 2014. Little has been known about such releases; the researchers investigated the circumstances, mechanism, likelihood and outcomes of these events. The researchers show that the pulse was the result of a delayed mechanism, in which gases produced in fall were trapped in the frozen soils and released in spring. A multi-institution team linked hydrology, biogeochemistry, and geophysics to uncover the pivotal roles of warmer fall weather and of spring rain-on-snow events, implying these pulses may be more frequent in the future.

The Impact
Our research identified a large, underrepresented source of carbon in the Arctic. The findings suggest that the Arctic may be even less of a carbon sink than previously thought. Our eddy covariance measurements imply that in order to calculate Arctic carbon budgets more accurately, early spring fluxes should be measured and taken under account. The dynamics of this offset in the context of climate change are not yet known, but it appears that the conditions that lead to the accumulation and the abrupt emission of the stored gases may become more frequent with warming.¬†

Summary
We measured a large pulse of carbon gases that were emitted from the tundra ecosystem near Barrow, Alaska, in May 2014. The pulse was large enough to offset nearly half of the following summer's net plant CO2 uptake, and added 6% to the CH4 summer fluxes. A similar pulse was measured 5 km away, indicating that this was a widespread phenomenon. To investigate, we preformed an array of field surveys and laboratory experiments, indicating that the spring carbon pulse was a result of a delayed mechanism, in which gases that are produced in the fall are trapped in the frozen soils and released in early spring. How do gases accumulate in the soil? As temperatures drop in late fall, the mid-soil layer remains above freezing for approximately a month after the surface layer has frozen. Microbial activity in the mid-layer produced gases that are trapped beneath the surface ice. How are gases rapidly released from the soils in spring?May 2014 was unique in that several rain on snow events took place, with the potential to enhance soil cracking. These cracks can serve as pathways for rapid gas release as soon as the surface ice thaws. How will things change in the future?Warmer fall seasons may lead a longer period of gas accumulation in the soils; more rain on snow events in spring may increase the likelihood of spring carbon pulse events.

Contacts (BER PM)
Naama Raz-Yaseef (first author)
Lawrence Berkeley National Laboratory
nryassef@lbl.gov

PI Contact
Margaret S. Torn
Lawrence Berkeley National Laboratory
mstorn@lbl.gov

Funding
The Next-Generation Ecosystem Experiments (NGEE Arctic) project and the Atmospheric Radiation Program of the Atmospheric System Research Program are supported by the Office of Biological and Environmental Research in the DOE Office of Science. Snow depth and density were measured with the support of Arctic Landscape Conservation Cooperative, U.S. Fish and Wildlife Service, project number ALCC2012-07.

Publications
Hubbard, S. S. et al, “Quantifying and relating land-surface and subsurface variability in permafrost environments using LiDAR and surface geophysical datasets,” Hydrogeol. J., 21(1), 149-169 (2012), doi:10.1007/s10040-012-0939-y.
Song, C. et al, “Large methane emission upon spring thaw from natural wetlands in the northern permafrost region”, Environ. Res. Lett., 7(3), 34009 (2012), doi:10.1088/1748-9326/7/3/034009.

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