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

Thermal processes of thermokarst lakes in the continuous permafrost zone of northern Siberia - observations and modeling (Lena River Delta, Siberia)

© Author(s) 2015. 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

Прорыв озера Прогресс (Восточная Антарктида): подходы к оценке характеристик прорывного паводка

On January 14, 2019, a breakthrough of water masses occurred on the Lake Progress (the oasis of the Larsemann hills, East Antarctica) with the formation of a flash flood. During the summer field seasons of the 63rd and 64th Russian Antarctic Expeditions (2017–2019), comprehensive hydrological, GPR and geodetic surveys were conducted in this area to ensure the safety of transport operations. The results of field measurements and calculations based on mathematical modeling of the breakthrough flood from the Lake are presented. The purpose of this study was to compare field observations and model calculations of the breakthrough flood and then to verify the existing model of Yu.B. Vinogradov on real data, since detailed observations of breakthrough floods of lakes of the Antarctic oases have not been previously carried out. The results of complex hydrological and geophysical investigations of LH73–Progress–Sibtorp lake system focused on areas where lake outburst are possible (snow-ice dams) made possible to formulate phenomenological model of the outburst process. It was emphasized that the lake water was discharged through a tunnel developed in the snow–ice dam, which subsequently evolved into a real riverbed. The maximum water discharge was formed approximately in 7.5 h after the start of the outflow, and it was estimated 5.4 m3s-1 according to the in-situ measurements, and 4.94 m3s-1 – by the model. The calculated volume of the flood is 76 320 m3. The differences between the model and in-situ measurements are about 9% that can be explained by the fact that the time of water retention by the snow-ice dam is not considered in the model.При исследованиях в 2018/19 г. в районе станции Прогресс (Восточная Антарктида) авторы наблюдали прорыв системы озёр Прогресс–Сибторп. Приводятся феноменологическое описание этого процесса, а также результаты наблюдений и математического моделирования

Гидрологические и гидрохимические исследования в дельте р. Лены весной 2015 и 2016 гг.

The results of hydrological and hydrochemical research of on bodies of water: ducts and lakes of the delta of the Lena River are reported here. Studies were performed during the 2015/16 summer (July-August) and winter (April) expeditionary seasons. The present work also introduces the results of field hydrochemical analyzes made immediately after sampling. The values of hydrochemical and hydrophysical indicators of ducts and lakes such as electrical conductivity, pH, permanganate oxidability, concentration of dissolved organic carbon, water color and absorption of colored organic matter were received. This obtained values supplemented significantly the available information on the delta water bodies in winter.Приведены результаты выполненных во время экспедиционных сезонов 2015–2016 гг. в летний (июль–август) и зимний (апрель) гидрологических и гидрохимических исследований на водных объектах — протоках и озерах дельты реки Лены. В работе представлены также результаты гидрохимических анализов, выполненных непосредственно в поле, сразу после отбора проб. Получены величины таких гидрохимических и гидрофизических показателей воды проток и озер, как электропроводность, водородный показатель рН, перманганатная окисляемость, концентрация растворенного органического углерода, цветность воды и абсорбция окрашенного растворенного органического вещества (CDOM), что существенно дополнило имеющиеся сведения о водоемах дельты в зимний период

Эоплейстоценовые отложения гыданского побережья Енисейского залива (север Западной Сибири)

In the north of Western Siberia, natural outcrops of marine Eopleistocene sediments are described. Eopleistocene age is confirmed by SIS-chemostratigraphic studies of samples. For this time, the gradual regression and desalination with the buffing was reconstructed. This is evidenced by the thin-stratification of deposits, the disappearance of foraminifera and marine mollusks and the appearance of brackish and freshwater algae and ostracods. According to the spore-pollen data, Eopleistocene time was warm, coniferous and coniferous-deciduous forests grew on the banks.Описаны естественные обнажения морских эоплейстоценовых отложений на севере Западной Сибири. Эоплейстоценовый возраст подтвержден путем SIS-хемостратиграфических исследований образцов. Для этого времени реконструировано постепенное обмеление и опреснение моря, с заболачиванием осушенного дна. Об этом свидетельствует ленточная слоистость отложений, исчезновение фораминифер и морских моллюсков и появление солоноватоводных и пресноводных водорослей и остракод. По спорово-пыльцевым данным эоплейстоценовое время было теплым, на берегах произрастали хвойные и хвойно-лиственные леса