ALBERT

Description: Distinctive periglacial landscapes have formed in late-Pleistocene ice-rich permafrost deposits (Ice Complex) of northern Yakutia, Siberia. Thermokarst lakes and thermokarst basins alternate with ice-rich Yedoma uplands. We investigate different thermokarst stages in Ice Complex deposits of the Lena River Delta using remote sensing and geoinformation techniques. The morphometry and spatial distribution of thermokarst lakes on Yedoma uplands, thermokarst lakes in basins, and thermokarst basins are analyzed, and possible dependence upon relief position and cryolithological context is considered. Of these thermokarst stages, developing thermokarst lakes on Yedoma uplands alter ice-rich permafrost the most, but occupy only 2.2% of the study area compared to 20.0% occupied by thermokarst basins. The future potential for developing large areas of thermokarst on Yedoma uplands is limited due to shrinking distances to degradational features and delta channels that foster lake drainage. Further thermokarst development in existing basins is restricted to underlying deposits that have already undergone thaw, compaction, and old carbon mobilization, and to deposits formed after initial lake drainage. Future thermokarst lake expansion is similarly limited in most of Siberia's Yedoma regions covering about 106 km2, which has to be considered for water, energy, and carbon balances under warming climate scenarios.

Description: Distinctive periglacial landscapes have formed in late-Pleistocene ice-rich permafrost deposits (Ice Complex) of Northern Yakutia, Siberia. Thermokarst lakes and thermokarst basins alternate with ice-rich Yedoma uplands. We investigate different thermokarst stages in Ice Complex deposits of the Lena River Delta using remote sensing and geoinformation techniques. The morphometry and spatial distribution of thermokarst lakes on Yedoma uplands, thermokarst lakes in basins, and thermokarst basins are analyzed, and possible dependence upon relief position and cryolithological context is considered. Of these thermokarst stages, developing thermokarst lakes on Yedoma uplands alter ice-rich permafrost the most, but occupy only 2.2 % of the study area compared to 20.0 % occupied by thermokarst basins. The future potential for developing large areas of thermokarst on Yedoma uplands is limited due to shrinking distances to degradational features and delta channels that foster lake drainage. Further thermokarst development in existing basins is restricted to underlying deposits that have already undergone thaw, compaction, and old carbon mobilization, and to deposits formed after initial lake drainage. Therefore, a distinction between developmental stages of thermokarst and landscape units is necessary to assess the potential for future permafrost degradation and carbon release due to thermokarst in Siberian Yedoma landscapes.

Description: Samoylov Island is centrally located within the Lena River Delta at 72° N, 126° E and lies within the Siberian zone of continuous permafrost. The landscape on Samoylov Island consists mainly of late Holocene river terraces with polygonal tundra, ponds and lakes, and an active floodplain. The island has been the focus of numerous multidisciplinary studies since 1993, which have focused on climate, land cover, ecology, hydrology, permafrost, and limnology. This paper aims to provide a framework for future studies by describing the characteristics of the island's meteorological parameters (temperature, radiation, and snow cover), soil temperature, and soil moisture. The land surface characteristics have been described using high resolution aerial images in combination with data from ground-based observations. Of note is that deeper permafrost temperatures have increased between 0.5 to 1 °C over the last five years. However, no clear warming of air and active layer temperatures is detected since 1998, though winter air temperatures during recent years have not been as cold as in earlier years.

Description: The Lena River forms one of the largest deltas in the Arctic; studying this delta has raised many questions regarding processes that occur there that remain open today. Comparing long-term hydrometric observational data of Russian Federal Service for Hydrometeorology and Environmental Monitoring (Roshydromet) from the Khabarova polar station, located at the head of the delta not far from where the Lena River divides into its main branches, with field observations, which have been carried out since 2002 revealed new insights into the hydrological, hydrochemical, and geochemical processes within the delta. Three periods with various water volumes and intensity of fluvial processes were chosen from the long-term record of water and sediment discharge. The role of ice event (ice blockage and ice floating) during high water in reconfiguring branch channels and influencing the volume of sediment runoff was identified. Results were obtained quantifying the increase of water and sediment discharges in the middle part of the delta main branches. This increase is to a great extent connected with an additional influx of water, as well as an increase of suspended and dissolved material released from the ice complex. A range of major ion and biogenic element contents in the delta branches in summer is introduced, and differences specified between the hydrochemical composition of thawing ice complex waters, of small Lena River branches, and of estuarine areas. The conservative character of some dissolved substances was analyzed along the length of the river branches. The contents of carbon and geochemical substances in suspended and bottom sediments are reported.

Description: The thermal regimes of five lakes located within the continuous permafrost zone of northern Siberia (Lena River Delta) have been investigated using hourly water temperature and water level records covering a three year period (2009–2012), together with bathymetric survey data. The lakes included thermokarst lakes located on Holocene river terraces that may be connected to Lena River water during spring flooding, and a thermokarst lake located on deposits of the Pleistocene Ice Complex. The data were used for numerical modeling with FLake software, and also to determine the physical indices of the lakes. The lakes vary in area, depths and volumes. The winter thermal regime is characterized by an ice cover up to 2 m thick that survives for more than 7 months of the year, from October until about mid-June. Lake-bottom temperatures increase at the start of the ice-covered period due to upward-directed heat flux from the underlying thawed sediment. The effects of solar radiation return prior to ice break-up, effectively warming the water beneath the ice cover and inducing convective mixing. Ice break-up starts the beginning of June and takes until the middle or end of June for completion. Mixing occurs within the entire water column from the start of ice break-up and continues during the ice-free periods, as confirmed by the Wedderburn numbers. Some of the lakes located closest to the Lena River are subjected to varying levels of spring flooding with river water, on an annual basis. Numerical modeling using FLake software indicates that the vertical heat flux across the bottom sediment tends towards an annual mean of zero, with maximum downward fluxes of about 5 W m−2 in summer and with heat released back into the water column at a~rate of less than 1 W m−2 during the ice-covered period. The lakes are shown to be efficient heat absorbers and effectively distribute the heat through mixing. Monthly bottom water temperatures during the ice-free period range up to 15 °C and are therefore higher than the associated monthly air or ground temperatures in the surrounding frozen permafrost landscape. The investigated lakes remain unfrozen at depth, with mean annual lake-bottom temperatures of between 2.7 and 4 °C. The data are available in the Supplement for this paper and through the PANGAEA website (http://www.pangaea.de/).

Description: 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.

Description: Thermokarst lakes are typical features of the northern permafrost ecosystems, and play an important role in the thermal exchange between atmosphere and subsurface. The objective of this study is to describe the main thermal processes of the lakes and to quantify the heat exchange with the underlying sediments. The thermal regimes of five lakes located within the continuous permafrost zone of northern Siberia (Lena River Delta) were investigated using hourly water temperature and water level records covering a 3-year period (2009–2012), together with bathymetric survey data. The lakes included thermokarst lakes located on Holocene river terraces that may be connected to Lena River water during spring flooding, and a thermokarst lake located on deposits of the Pleistocene Ice Complex. Lakes were covered by ice up to 2 m thick that persisted for more than 7 months of the year, from October until about mid-June. Lake-bottom temperatures increased at the start of the ice-covered period due to upward-directed heat flux from the underlying thawed sediment. Prior to ice break-up, solar radiation effectively warmed the water beneath the ice cover and induced convective mixing. Ice break-up started at the beginning of June and lasted until the middle or end of June. Mixing occurred within the entire water column from the start of ice break-up and continued during the ice-free periods, as confirmed by the Wedderburn numbers, a quantitative measure of the balance between wind mixing and stratification that is important for describing the biogeochemical cycles of lakes. The lake thermal regime was modeled numerically using the FLake model. The model demonstrated good agreement with observations with regard to the mean lake temperature, with a good reproduction of the summer stratification during the ice-free period, but poor agreement during the ice-covered period. Modeled sensitivity to lake depth demonstrated that lakes in this climatic zone with mean depths 〉 5 m develop continuous stratification in summer for at least 1 month. The modeled vertical heat flux across the bottom sediment tends towards an annual mean of zero, with maximum downward fluxes of about 5 W m−2 in summer and with heat released back into the water column at a rate of less than 1 W m−2 during the ice-covered period. The lakes are shown to be efficient heat absorbers and effectively distribute the heat through mixing. Monthly bottom water temperatures during the ice-free period range up to 15 °C and are therefore higher than the associated monthly air or ground temperatures in the surrounding frozen permafrost landscape. The investigated lakes remain unfrozen at depth, with mean annual lake-bottom temperatures of between 2.7 and 4 °C.

Description: Samoylov Island is centrally located within the Lena River Delta at 72° N, 126° E and lies within the Siberian zone of continuous permafrost. The landscape on Samoylov Island consists mainly of late Holocene river terraces with polygonal tundra, ponds and lakes, and an active floodplain. The island has been the focus of numerous multidisciplinary studies since 1993, which have focused on climate, land cover, ecology, hydrology, permafrost and limnology. This paper aims to provide a framework for future studies by describing the characteristics of the island's meteorological parameters (temperature, radiation and snow cover), soil temperature, and soil moisture. The land surface characteristics have been described using high resolution aerial images in combination with data from ground-based observations. Of note is that deeper permafrost temperatures have increased between 0.3 to 1.3 °C over the last five years. However, no clear warming of air and active layer temperatures is detected since 1998, though winter air temperatures during recent years have not been as cold as in earlier years. Data related to this article are archived under: http://doi. pangaea.de/10.1594/PANGAEA.806233 .

Description: Thermokarst lakes are typical features of the northern permafrost ecosystems, and play an important role in the thermal exchange between atmosphere and subsurface. The objective of this study is to describe the main thermal processes of the lakes and to quantify the heat exchange with the underlying sediments. The thermal regimes of five lakes located within the continuous permafrost zone of northern Siberia (Lena River Delta) were investigated using hourly water temperature and water level records covering a 3-year period (2009–2012), together with bathymetric survey data. The lakes included thermokarst lakes located on Holocene river terraces that may be connected to Lena River water during spring flooding, and a thermokarst lake located on deposits of the Pleistocene Ice Complex. Lakes were covered by ice up to 2 m thick that persisted for more than 7 months of the year, from October until about mid-June. Lake-bottom temperatures increased at the start of the ice-covered period due to upward-directed heat flux from the underlying thawed sediment. Prior to ice break-up, solar radiation effectively warmed the water beneath the ice cover and induced convective mixing. Ice break-up started at the beginning of June and lasted until the middle or end of June. Mixing occurred within the entire water column from the start of ice break-up and continued during the ice-free periods, as confirmed by the Wedderburn numbers, a quantitative measure of the balance between wind mixing and stratification that is important for describing the biogeochemical cycles of lakes. The lake thermal regime was modeled numerically using the FLake model. The model demonstrated good agreement with observations with regard to the mean lake temperature, with a good reproduction of the summer stratification during the ice-free period, but poor agreement during the ice-covered period. Modeled sensitivity to lake depth demonstrated that lakes in this climatic zone with mean depths 〉 5 m develop continuous stratification in summer for at least 1 month. The modeled vertical heat flux across the bottom sediment tends towards an annual mean of zero, with maximum downward fluxes of about 5 W m−2 in summer and with heat released back into the water column at a rate of less than 1 W m−2 during the ice-covered period. The lakes are shown to be efficient heat absorbers and effectively distribute the heat through mixing. Monthly bottom water temperatures during the ice-free period range up to 15 °C and are therefore higher than the associated monthly air or ground temperatures in the surrounding frozen permafrost landscape. The investigated lakes remain unfrozen at depth, with mean annual lake-bottom temperatures of between 2.7 and 4 °C.