ALBERT

Description: About 25 % of the land mass of northern hemisphere is underlain by permafrost, which is one of the largest carbon pools. Yedoma Ice Complex is a particularly ice-rich type of permafrost. As a consequence of rapid climate warming of the Arctic, permafrost is affected by degradation processes like thermokarst. Thereby organic carbon is partially dissolved (DOC) in thermokarst lakes, and transported via rivers into the Arctic Ocean. On this way, large parts of DOC are mineralized by microbial processes and emitted as CO2 and CH4 to the atmosphere. The influence of different landforms in thermokarst affected permafrost regions on DOC concentration has not been thoroughly investigated. Addressing this research gap, this thesis examined the relationship between landscape units, water chemistry and hydrology for a small study site in the Lena River Delta, Siberia. On the basis of GeoEye satellite imagery eight landscape units were determined. These include thermokarst lakes and streams on the first terrace and on Yedoma Ice Complex, Yedoma Ice Complex streams, which are fed by the Ice Complex, Yedoma Ice Complex uplands, first terrace relict lake, and the Olenyokskaya Channel. Concerning pH value, electrical conductivity, isotopic composition and DOC concentration summer surface water samples and soil water samples of 2013 and 2014 were analyzed. These analyzes revealed that the system of the thermokarst lake Lucky Lake, its drainage flow path and source waters on Yedoma Ice Complex, is divided by landscape units. Source waters show significantly higher DOC concentrations and lower electrical conductivity than Lucky Lake and the drainage flow path. This suggests that labile organic carbon of Yedoma Ice Complex reaches the lake by degradation. Yedoma Ice Complex lake processes, despite evaporation, further reduce DOC concentration rapidly, probably by mineralization of labile DOC. Along the drainage flow path no further decrease of DOC concentration was observed, despite of changing discharge. Using discharge data of 2013 a DOC flux of about 220 kg in 29 days for the study site was calculated. A temporal variability of DOC concentration during the sampling periods was not determined using the utilized data.

Description: Thermo-erosional landforms (valleys, gullies) and their associated streams are the main connecting pathways between inland permafrost areas and rivers and coasts. Surface and ground waters are routed along these streams, which transport particulate and dissolved matter from the catchments to the rivers and coastal waters. Regions of ice-rich permafrost, such as the Yedoma-type Ice Complex, are not only characterized by a high abundance of thermo-erosional landforms, which formed during the Holocene, but are subject to extensive degradation under current arctic warming by processes such as thermal erosion, thermokarst, and active layer deepening. In the Siberian Lena River Delta Yedoma-type Ice Complex deposits occur on insular remnants of a Late-Pleistocene accumulation plain that has been dissected by Lena River branches and degraded by thermal erosion and thermokarst during the Holocene. This region serves as suitable exemplary study area for estimating the contribution of 1) different permafrost degradation landforms to the export of water and dissolved matter from Yedoma-type Ice Complex to the river and 2) active degradation of old permafrost versus seasonal runoff from the surface and active layer. In the summers of 2013 and 2014 we sampled surface and soil waters from streams and their watersheds in Yedomatype Ice Complex landscapes of the Lena River Delta and analyzed them for a range of hydrogeochemical parameters including electrical conductivity (EC), dissolved organic carbon (DOC) and stable isotopic composition. The sampling sites were spread over an E-W-extent of about 150 km and are characterized by very diverse geomorphological and hydrological situations in terms of distance to the river branches, catchment size, discharge, degree of thermo-erosional activity, and connection to other permafrost degradation landforms (thermokarst lakes and basins). Three key sites were sampled three and four times from June to September 2013 and 2014, respectively, in order to analyze intra-seasonal changes. The results show large variances in EC (25 to 1205 μS/cm), DOC concentrations (2.9 to 119.0 mg/l), �18O (-29.8 to -14.6 ‰ vs. SMOW), and �D (-228.9 to -117.9‰ vs. SMOW) over the whole dataset, with distinct characteristics in the parameter combination for different degradation landform and water types. The temporal variability at the repeatedly sampled sites is low, which implies that there is not much change in the processes that determine the water composition throughout the summer season. By comparing differences in surface water chemistry between flow path systems that tap into varying amounts of source water (precipitation, surface and ground water, ground ice) and have differing residence times and extents, we explore the effect of future changes in thermokarst and thermo-erosional intensity and resulting changes in flow path hydrogeochemistry for thermoerosional features draining ice-rich permafrost.

Description: The effect of climate warming on the degradation of permafrost in Arctic coastal lowlands and associated hydrological and biogeochemical processes varies between different types of permafrost deposits. The Lena River Delta consists of three geomorphological main terraces that differ in their genesis and stratigraphic, cryological, geomorphological and hydrological characteristics. The third terrace was formed during the late Pleistocene and consists mainly of Yedoma-type Ice Complex deposits, whereas the first terrace has formed during the Holocene by deltaic processes. Permafrost degradation on both terraces releases dissolved organic carbon (DOC) to thermokarst lakes and via streams DOC gets transported to the Lena River channels and the Arctic Ocean. This presentation shows 1. differences in the surface water chemistry between the first terrace and the Yedoma Ice Complex and their landforms, 2. analyses of the temporal variability of DOC during the summer, and 3. an estimation of summer DOC flux for the considered catchment of about 6.45 km2. Between June and September 2013 and 2014, respectively summer surface water and soil water samples were collected in a small catchment in the south of Kurungnakh Island in the central Lena River Delta. This catchment covers the first terrace as well as the Yedoma Ice Complex and is characterized by thermokarst lakes and streams on both terraces. Two weirs were installed in the main stream along the drainage flow path to continuously measure discharge during summer 2013. We divided the study area into landscape units and compared pH, electrical conductivity, stable isotopic composition and DOC concentrations between units and between terraces. The considered landscape units are streams and thermokarst lakes on Yedoma Ice Complex and on the first terrace, Yedoma uplands, streams, which are fed by the Ice Complex, a relict lake on the first terrace and the Olenyokskaya Channel, a main branch of the Lena River. DOC concentrations in the landscape units on Yedoma Ice Complex ranged between 3.5 mg L-1 (streams) and 52.5 mg L−1 (soilwater of Yedoma uplands) and on the first terrace between 2.8 mg L−1 (streams) and 15.6 mg L−1 (relict lake). The electrical conductivity on Yedoma Ice Complex ranged between 35 μS cm-1 (soilwater of Yedoma uplands) and 151 μS cm−1 (streams) and on the first terrace between 54 μS cm−1 (streams and relict lake) and 140 μS cm−1 (streams). δ18O values on Yedoma Ice Complex and first terrace ranged between -22.4 ‰ (soilwater of Yedoma uplands) and -16.4 ‰ (streams) and between -20.4 ‰and -14.7 ‰ (streams), respectively. δD ranged between -165.6 ‰ (soilwater of Yedoma uplands) and 125.5 ‰ (streams, which are fed by the Ice Complex) and between -160.8 ‰ and -119.4 ‰ (streams). Source waters on the Yedoma Ice Complex had higher DOC concentrations and lower electrical conductivity than Yedoma Ice Complex thermokarst lakes and the drainage flow path. This suggests that more labile organic carbon, perhaps derived from permafrost degradation on the Yedoma Ice Complex, enriches the lake but is removed from the lake, for example, by mineralization in the water column. Along the drainage flow path no further decrease of DOC concentration was observed, despite increasing discharge from weir 1 at the beginning of the flow path to almost two and a half times at weir 2 at the end of the flow path, and despite decreasing discharge during the measuring period from 1814 m3 d−1 in the end of July to 199 m3 d−1 in the end of August for weir 1 and from 2819 m3 d−1 in the end of July to 567 m3 d−1 in the end of August for weir 2. The temporal variability of DOC concentration during the sampling periods was low. In 2013 one sample site of soil water collection fluctuated slightly in August between 10.5 mg L−1 and 13.3 mg L−1, whereas the remaining landscape units showed no temporal variability. In 2014 the DOC concentration of the relict lake on the first terrace decreased from July (13.5 mg L−1) to September (11.1 mg L−1). Otherwise there were no changes in DOC concentration in the remaining landscape units. DOC measurements of the Olenyokskaya Channel show a decrease in DOC concentration from 12.4 mg L−1 in June to 7.6 mg L−1 in September. Using discharge data of 2013 a summer DOC flux of about 220 kg in 29 days for the study site above weir 2 with an area of 6.45 km2 was calculated.