Elena Zakharova

Western Siberia wetlands as indicator and regulator of climate change on the global scale

Western Siberia is a unique bog region. Siberian peatlands have been a major sink of atmospheric carbon since the last deglaciation and, on the other hand, in some epochs – like the present – they are the most powerful source of methane emission. About 104 Mha of Russian peatlands are located in Western Siberia, which consists almost completely of pristine peatland ecosystems. This paper considers the role of the Western Siberian peatlands in a global carbon balance and their possible influence on the formation of Earth’s climate.

One of the possible mechanisms of thermokarst lakes drainage in West‐Siberian North

During the 2008 expedition carried out within the framework of the Russian–French network project CAR‐WET‐SIB, one of the possible mechanisms of drainage of thermokarst lakes in the north of Western Siberia was revealed. The discovered natural process is significantly amplified by climate warming and gains special urgency in this regard.

Soil moisture sensor calibration for organic soil surface layers

This paper’s objective is to present generic calibration functions for organic surface layers derived for the soil moisture sensors Decagon ECH2O 5TE and Delta-T ThetaProbe ML2x, using material from northern regions, mainly from the Finnish Meteorological Institute’s Arctic Research Center in Sodankylä and the study area of the Danish Center for Hydrology (HOBE). For the Decagon 5TE sensor such a function is currently not reported in the literature. Data were compared with measurements from underlying mineral soils including laboratory and field measurements. Shrinkage and charring during drying were considered. For both sensors all field and lab data showed consistent trends. For mineral layers with low soil organic matter (SOM) content the validity of the manufacturer’s calibrations was demonstrated. Deviating sensor outputs in organic and mineral horizons were identified. For the Decagon 5TE, apparent relative permittivities at a given moisture content decreased for increased SOM content, which was attributed to an increase of bound water in organic materials with large specific surface areas compared to the studied mineral soils. ThetaProbe measurements from organic horizons showed stronger nonlinearity in the sensor response and signal saturation in the high-level data. The derived calibration fit functions between sensor response and volumetric water content hold for samples spanning a wide range of humus types with differing SOM characteristics. This strengthens confidence in their validity under various conditions, rendering them highly suitable for large-scale applications in remote sensing and land surface modeling studies. Agreement between independent Decagon 5TE and ThetaProbe time series from an organic surface layer at the Sodankylä site was significantly improved when the here-proposed fit functions were used. Decagon 5TE data also well-reflected precipitation events. Thus, Decagon 5TE network data from organic surface layers at the Sodankylä and HOBE sites are based on the hereproposed natural log fit. The newly derived ThetaProbe fit functions should be used for hand-held applications only, but prove to be of value for the acquisition of instantaneous large-scale soil moisture estimates.

L-Band Relative Permittivity of Organic Soil Surface Layers—A New Dataset of Resonant Cavity Measurements and Model Evaluation

Global surface soil moisture products are derived from passive L-band microwave satellite observations. The applied retrieval algorithms include dielectric models (relating soil water content to relative permittivity) developed for mineral soils. First efforts to generate equivalent models for areas where organic surface layers are present such as in the high-latitude regions have recently been undertaken. The objective of this study was to improve our still insufficient understanding of L-band emission of organic substrates in prospect of enhancing soil moisture estimations in the high latitudes undergoing most rapid climatic changes. To this end, L-band relative permittivity measurements using a resonant cavity were carried out on a wide range of organic surface layer types collected at different sites. This dataset was used to evaluate two already existing models for organic substrates. Some samples from underlying mineral layers were considered for comparison. In agreement with theory the bulk relative permittivity measured in organic substrate was decreased due to an increased bound water fraction (where water molecules are rotationally hindered) compared to the measured mineral material and corresponding output of the dielectric model for mineral soils used in satellite algorithms. No distinct differences in dielectric response were detected in the measurements from various organic layer types, suggesting a generally uniform L-band emission behavior. This made it possible to fit a simple empirical model to the data obtained from all collected organic samples. Outputs of the two existing models both based on only one organic surface layer type were found to lie within the spread of our measured data, and in close proximity to the derived simple model. This general consensus strengthened confidence in the validity of all these models. The simple model should be suitable for satellite soil moisture retrieval applications as it is calibrated on a wide range of organic substrate types and the entire wetness range, and does not require any auxiliary input that may be difficult to obtain globally. This renders it generically applicable wherever organic surface layers are present.

Ice Cover and Associated Water Structure in Lakes Baikal and Hovsgol from Satellite Observations and Field Studies

Lakes Baikal (Russia) and Hovsgol (Mongolia) are covered every year by ice for several months. The distribution and state of the ice cover and snow on the ice affect the hydrophysical structure, spring bloom of diatoms and primary productivity, as well as transport on ice. In this respect combination of satellite remote sensing data with dedicated field measurements provide a unique tool for investigating ice cover state and development. Comparison of ENVISAT and SARAL radar altimetry missions data for Lake Baikal shows that SARAL’s AltiKa instrument can be successfully used for ice discrimination. We observe large decrease of radar return echo in late spring for both ENVISAT and SARAL and discuss it in the context of ice metamorphism. We then address an interesting natural phenomenon—giant ice rings on lakes Baikal and Hovsgol. Using satellite imagery and photography for 1974–2015 we have identified 45 rings on Lake Baikal (compared to 13 previously known) and also for the first time 4 rings on Lake Hovsgol. The results of our hydrographic surveys beneath the ice rings show the presence of warm double-convex lens-like eddies before and during manifestation of ice rings. These eddies are the driving factor for the formation of ice rings in these lakes. We reassess the existing hypotheses of ice ring formation and discuss the potential mechanisms of eddy formation.