Geomorphology, cryostratigraphy and Holocene landscape dynamics in the Zackenberg valley, NE-Greenland
Stefanie Cable, PhD Student, CENPERM
Our knowledge about the history, state and sensitivity of permafrost in North-Eastern coastal Greenland is very limited. Small-scale variation in topography, sediments and hydrology leads to complex geomorphological processes and creates contrasting permafrost conditions. This study investigates the landscape and permafrost history of the 130 km2 high-arctic Zackenberg valley in NE-Greenland (74º28’N, 20º34’W). We combined geomorphological mapping with the analysis of 13 permafrost cores from 5 different landforms. The analyses included the grain size distribution, ice and carbon contents, electrical conductivity and radiocarbon dating. A geocryological map of the ice content in the top permafrost was then created based on the mapping and ground ice results.
The geomorphology in Zackenberg differs between the two valley sides. Sedimentary rock in the eastern and gneisses in the western valley side create contrasts of gentle vs. steep terrain, fine grained vs. coarse grained sediment, vegetated vs. barren surfaces, high vs. low water retention, and high vs. limited periglacial reworking and transport. The eastern hillslopes are affected by solifluction (14% coverage in the total mapping area), nivation (4%) and fluvial processes (6%), and are underlain by ice-rich permafrost. They feed fine-grained sediment to alluvial fans (11%) aggrading at the foot of the hillslope since the Early Holocene. Shifts between stable and sedimentary phases under consistent water supply favored the formation of ice and carbon-rich, syngenetic permafrost. In contrast, the ice and carbon contents in coastal deltaic deposits (3%) are low and permafrost developed epigenetically. We lack ground ice data from weathered bedrock (37%) and glacial deposits (18%) covering the rest of the study area. However, the limited availability of water, nutrients and fine-grained sediment at these landforms suggests the permafrost ice contents are low to variable and the carbon contents very low.
We conclude that the sensitivity of the permafrost in Zackenberg valley to degradation (thermally and subsidence) and to changes in the geomorphological processes are highly spatially variable. The uneven distribution of carbon in the landscape, however, increases the relevance of the alluvial fans for evaluating the impact of change on greenhouse gas dynamics in this region. Whether they remain a carbon sink or become a source will be controlled by slope processes, which determine the amount of sediment and water supplied to the alluvial fans, and by vegetation succession and distribution of the thermo-erosional degradation.
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