Soil organic carbon stocks in permafrost-affected soils in West Greenland

Abstract

Little is known about soil organic carbon (SOC) stocks in permafrost-affected soils in Greenland. Generally, occurrence and stocks of SOC in permafrost-affected soils of the Arctic were underestimated for many years. Compared to the assumed dimension of the influence of carbon dynamics on climate change this knowledge should be substantially widened. A total of 155 soil samples were used to get a better understanding about SOC stocks, depth function and spatial distribution of SOC in permafrost-affected soils in a characteristic deglaciated valley in West Greenland southeast of Kangerlussuaq. The valley is characterized by a high variability of active layer thickness and pedo-variance mainly caused by topography.The average SOC stock of the Umimmalissuaq valley is 9.9kgm−2 in the upper 30cm and around 30kgm−2 in the first meter, which is remarkably higher than regional predictions with 6–15.9kgm−2 in the first 100cm. To account for spatial heterogeneity landscape units are developed which are most useful for grouping and predicting SOC stocks. The SOC store measured 14.2kgm−2 in the upper 30cm, 11.5kgm−2 on north-facing slopes, and 8.4kgm−2 on south-facing slopes. Little SOC stocks with around 6kgm−2 were found under abrasion fields particularly on hilltops and moraine ridges. Soils on south-facing slopes usually have very low SOC stocks in deeper soil horizons except of organic rich horizons in rarely occurring paleosols. North-facing soils and valley bottom slopes generally have high SOC stocks of around 19kg SOC m−2 in soil horizons with a depth of 30–100cm.In general, the main influencing parameter on SOC stocks is the soil organic matter input from the vegetative cover. The vegetative cover is mainly a result of topographic position and aspect related to the ice margin and katabatic winds. Soil moisture and high active layer may influence SOC stocks positively.