Integrating mineral interactions with organic carbon in thawing permafrost to assess climate feedbacks

• Main Authors: Opfergelt, Sophie, Hirst, Catherine, Monhonval, Arthur, Mauclet, Elisabeth, Thomas, Maxime, EGU General Assembly 2020
• Other Authors: UCL - SST/ELI/ELIE - Environmental Sciences
• Format: Conference Object
• Language: English
• Published: 2020
• Subjects: Arctic; permafrost; Thermokarst
• Online Access: http://hdl.handle.net/2078.1/239919

Permafrost contains 1400-1660 Gt of organic carbon (OC), from which 5-15% will likely be emitted as greenhouse gases (GHG) by 2100. The soil organic carbon stock is distributed between a pool of particulate organic matter (POM), and a pool of mineral-associated OM (MOM). POM can be free, i.e., more readily available for microbial decomposition, or occluded within soil aggregates (involving clay minerals or Fe-Al (hydr)oxides), i.e., spatially inaccessible for microorganisms. MOM includes OC sorbed onto mineral surfaces (such as clay minerals or Fe-oxides) and OC complexed with metal cations (e.g., Al, Fe, Ca), i.e., stabilized OC. The interactions between OC and minerals influence the accessibility of OC for microbial decomposition and OC stability and are therefore a factor in controlling the C emissions rate upon thawing permafrost. In the warming Arctic, there is growing evidence for soil disturbance such as coastal erosion, thermokarst and soil drainage as a consequence of abrupt and gradual permafrost thaw. These disturbances induce changes in the physico-chemical conditions controlling mineral solubility in permafrost soils which directly affect the stability of the MOM and of the occluded POM. As a consequence, a portion of OC can be unlocked and transferred into the free POM. This additional pool of freely available OC may be degraded and amplify C emissions from permafrost to the atmosphere. Conversely, the concomitant release of metal cations upon permafrost thaw may partly mitigate permafrost C emissions by stabilization of OC via complexation or sorption onto mineral surfaces and return a portion of freely available OC to the MOM. The majority of C is emitted as CO2 but 1.5 and 3.5% of the total permafrost C emissions will be released as CH4, with implications for the atmospheric radiative forcing balance. Importantly, the proportion CH4 emitted relative to CO2 is likely to increase with increasing abrupt thaw and associated anoxic conditions, but a portion of CH4 emissions could be mitigated by the ...