EES Departmental Seminar: Are We Digging Deep Enough to Get Permafrost Carbon?
Dr. Melissa Schwab
Earth and Environmental Sciences, Dalhousie University
Title: Are We Digging Deep Enough to Get Permafrost Carbon?
Abstract: Permafrost soils contain vast carbon reservoirs that emit greenhouse gases upon thaw. Yet current climate projections rely on simplified two-layer models distinguishing only the seasonally thawing “active layer” from underlying permanently frozen ground (“permafrost”). This framework obscures the complex thermal history and vertical structure of Arctic soils, particularly a temperature-sensitive “transition zone” that experiences episodic freezing and thawing over decadal to centennial timescales as active layer thickness adjusts to shifts inclimate, vegetation, and surface soil layers. Identifiable by its high suspended (“ataxitic”) ice content, this zone likely concentrates organic matter, mineral nutrients, and microbial assemblages percolated through soil water. As a result, the transition zone represents a disproportionately reactive substrate and a potentially important, underrepresented source of greenhouse gas emissions. We propose that applying change point detection to high-resolution radiocarbon measurements of bulk soil resolves five distinct layers—accumulation, mixing, transient, intermediate, and isothermal permafrost—that record thaw history and carbon dynamics within the upper two meters of the landscape. The active layer comprises an accumulation horizon, marked by nuclear bomb-spike carbon, and a homogenized mixing layer shaped by cryoturbation and inputs of modern dissolved organic matter and root exudates. Within the transition zone, the transient layer marks the maximum depth reached by the modern active layer each summer, whereas the intermediate layer stores millennial-aged carbon deposited during Holocene warm intervals. Isothermal permafrost, isolated from the contemporary carbon cycle for millennia, exhibits substantially older radiocarbon ages and a more gradual radiocarbon depth profile. Today, gradual thaw as well as disturbances such as wildfires are causing ground-ice melt and transition zone collapse, exposing much older permafrost carbon to the atmosphere. Therefore, expanding depth-resolved datasets is essential to capture the full vertical structure of the soil-permafrost complex and improve projections of Arctic landscape stability and carbon release.
Time
Location
Milligan Room – 8007 LSC
Additional Information
Meet the lecturer: FREE COFFEE and COOKIES in B-3078 at 10:45 am before the lecture