Abstract
Permafrost is a large reservoir of soil organic carbon, accounting for about half of all the terrestrial storage, almost equivalent to twice the atmospheric carbon storage. Hence, permafrost degradation under global warming may induce a release of a substantial amount of additional greenhouse gases, leading to further warming. In addition to gradual degradation through heat conduction, the importance of abrupt thawing or erosion of ice-rich permafrost has recently been recognized. Such ice-rich permafrost has evolved over a long timescale (i.e., tens to hundreds of thousands of years). Although important, knowledge on the distribution of vulnerability to degradation, i.e., location and stored amount of ground ice and soil carbon in ice-rich permafrost, is still limited largely due to the scarcity of accessible in situ data. Improving the future projections for the Arctic using the Earth System Models will lead to a better understanding of the current vulnerability distribution, which is a prerequisite for conducting climatic and biogeochemical assessment that currently constitutes a large source of uncertainty. In this study, present-day circum-Arctic distributions (north of 50° N) in ground ice and organic soil carbon content are produced by a new approach to combine a newly developed conceptual carbon-ice balance model, and a downscaling technique with the topographical and hydrological information derived from a high-resolution digital elevation model (ETOPO1). The model simulated the evolution of ground ice and carbon for the recent 125 thousand years (from the Last Interglacial to the present) at 1° resolution. The 0.2° high-resolution circum-Arctic maps of the present-day ground ice and soil organic carbon, downscaled from the 1° simulations, were reasonable compared to the observation-based previous maps. These data, together with a map of vulnerability of ice-rich permafrost to degradation served as initial and boundary condition data for model improvement and the future projection of additional greenhouse gas release potentially caused by permafrost degradation.
Highlights
Permafrost is a large reservoir of soil organic carbon (SOC), accounting for about half of all the terrestrial storage, almost equivalent to two times of the atmospheric carbon storage (IPCC 2013; Hugelius et al 2013a, 2013b, 2014)
The decrease in litterfall is more rapid than the adapted subsurface carbon dynamics because litterfall responds simultaneously to the change in climate conditions (Eq 1)
Decomposition is slower compared to the increased carbon input, and the accumulation of carbon is more apparent for the case of the larger τ
Summary
Permafrost is a large reservoir of soil organic carbon (SOC), accounting for about half of all the terrestrial storage, almost equivalent to two times of the atmospheric carbon storage (IPCC 2013; Hugelius et al 2013a, 2013b, 2014). Knowledge on the location and stored amount of ground ice and soil carbon in ice-rich permafrost is still limited, largely due to the scarcity of accessible in situ data (Hugelius et al 2014; Olefeldt et al 2016; Morris et al 2018). Understanding of the current geographical distribution of SOC and ground ice as well as their vulnerability to degradation is necessary for the enhancement of Earth System Models as the permafrost-carbon process remains one of the large sources of uncertainty in climatic and biogeochemical assessment and projections of the Arctic (Schuur et al 2015; IPCC 2013; MacDougall and Knutti 2016; AMAP 2017; Dean et al 2018b)
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