The expedition LENA 2005

Introduction The purpose of the expedition LENA 2005 was to fill gaps of knowledge and to answer scientific questions that arose during former expeditions. Additionally, the monitoring program based at Samoylov Island was continued and expanded. Scientific investigations were focused on the following topics: A. Permafrost soils and ecosystems (• Chapter 3: Microbiological processes, trace gas fluxes and hydrobiology in permafrost ecosystems of the Lena Delta) B. Periglacial landscape dynamics (• Chapter 4: Studies of periglacial landscape dynamics and surface characteristics studies in the western Lena Delta) C. Ground ice as climate archive (• Chapter 5: Holocene ice wedges of the 1st Lena terrace) D. Modern delta hydrology (• Chapter 6: Report of the hydrological work in the Lena River Delta in August 2005

Lena Delta hydrology and geochemistry: long-term hydrological data and recent field observations

The Lena River forms one of the largest deltas in the Arctic. We compare two sets of data to reveal new insights into the hydrological, hydrochemical, and geochemical processes within the delta: (i) long-term hydrometric observations at the Khabarova station at the head of the delta from 1951 to 2005; (ii) field hydrological and geochemical observations carried out within the delta since 2002. Periods with differing relative discharge and intensity of fluvial processes were identified from the long-term record of water and sediment discharge. Ice events during spring melt (high water) reconfigured branch channels and probably influenced sediment transport within the delta. Based on summer field measurements during 2005–2012 of discharge and sediment fluxes along main delta channels, both are increased between the apex and the front of the delta. This increase is to a great extent connected with an additional influx of water from tributaries, as well as an increase of suspended and dissolved material released from the ice complex. Summer concentrations of major ion and biogenic substances along the delta branches are partly explained by water sources within the delta, such as thawing ice complex waters, small Lena River branches and estuarine areas

Samoylov Deep Drilling Spring Campaign 2018

Permafrost thaw is associated with impacts on climate, land surface and coastal and river bank structures. Pro-cesses such as thermokarst and thermo-erosion lead to ground subsidence, which can have drastic e˙ects on the topography. One of the main drivers of surface subsidence vulnerability is the sedimentological composition, including ground ice content, and the temperature state of permafrost. This drilling campaign aimed to retrieve a deep, frozen sediment core from Samoylov Island to cover several scientific disciplines including geocryology, sedimentology and geochemistry. This campaign provides sample material from much greater depths (65.7 m) than previous boreholes on the island (27 m in 2006) and the anal-ysis of the sediments will therefore lead to a better understanding of the deep permafrost deposits on Samoylov Island. Furthermore, a temperature chain was installed in the borehole for long-term temperature monitoring