Genesis of the Dawadi potassium nitrate deposit in Lop Nor, China

Nitrate deposits are rare worldwide, especially potassium nitrate deposits; furthermore, their genesis remains disputed. There is a rare salt-lake type potassium nitrate deposit in the Dawadi area of Lop Nor at the eastern margin of the Tarim Basin, and the ore bodies show coexisting solid and liquid phases. Additionally, there are large sulphate-type potash deposits in the adjoining Luobei Depression, south of the Dawadi area. To determine why there are two different types of potash deposits in adjacent depressions with similar climates, field geological surveys were conducted and samples collected. It was found that the Tertiary clastic layer at the periphery of the Dawadi deposit was rich in high-salinity brine, with nitrate contents of up to 495–16,719 mg/L, much higher than those in the Luobei Depression, 1–35 mg/L. Additionally, a type of deep hydrothermal (Ca–Cl) brine was found in the fault zones, with nitrate contents of up to 8044 mg/L, dozens of times greater than that of ordinary groundwater. Using comprehensive analysis and research, we concluded that the Dawadi and Luobei depressions belong to different hydrological systems with no connection between them; thus, the two deposits belong to different metallogenic systems. Furthermore, groundwater played an important role in the mineralization of the potassium nitrate deposit, and a deep source may have been an important source of the ore-forming materials. The fault system widely developed in Lop Nor provides favorable channels for deep hydrothermal recharge, and the groundwater and deep hydrothermal brine could provide the source for the nitrate mineralization in the Dawadi Depression through water–rock reactions.

Influence of Zooplankton and Environmental Factors on Clear-Water Phase in Lake Paldang, South Korea

Lake Paldang is a complex water system with both fluvial and lacustrine characteristics and the largest artificial dam lake in South Korea. In this study, the different occurrence patterns and causes of the clear-water phase (CWP) were investigated using water quality and hydrological factors at four sites in Lake Paldang. Among the environmental and other factors associated with CWP occurrence, secchi depth and turbidity exhibited significant correlations with precipitation, hydraulic retention time (HRT), and individual and relative abundance (RA) of zooplankton (Cladocera) (p < 0.01). Hence, a change in the HRT because of precipitation could alter the CWP. The Cladocera individuals and RA showed significant correlations with the water temperature, indicating that the emergence of Cladocera in spring as the water temperature rises could cause the CWP. Sensitivity assessments conducted using Bayesian models demonstrated different CWP occurrence sensitivity relationships for the river-type, lake-type, and shallow and deep sites. Turbidity, secchi depth, and zooplankton factors also showed sensitive relationships with CWP occurrence for all sites. The sensitivity to precipitation and HRT was higher in the river-type sites. The lake-type sites, with common Cladocera emergence and long HRT, favored CWP occurrence. Thus, CWP occurrence was dependent on the site characteristics and climate conditions.

A New Thermal Categorization of Ice-covered Lakes

&lt;p&gt;Lakes are traditionally classified based on their thermal regime and trophic status. While this classification adequately captures many lakes, it is not sufficient to understand seasonally ice-covered lakes, the most common lake type on Earth. We describe the inverse thermal stratification in 19 highly varying lakes and derive a model that predicts the temperature profile as a function of wind stress, area, and depth. The results suggest an additional subdivision of seasonally ice-covered lakes to differentiate under-ice stratification. When ice forms in smaller and deeper lakes, inverse stratification will form with a thin buoyant layer of cold water (near 0&lt;sup&gt;o&lt;/sup&gt;C) below the ice, which remains above a deeper 4&lt;sup&gt;o&lt;/sup&gt;C layer. In contrast, the entire water column can cool to ~0&lt;sup&gt;o&lt;/sup&gt;C in larger and shallower lakes. We suggest these alternative conditions for dimictic lakes be termed &amp;#8220;cryostratified&amp;#8221; and &amp;#8220;cryomictic.&amp;#8221;&lt;/p&gt;

THE STRUCTURE OF THE VARIABILITY OF THE HYDROCHEMICAL COMPOSITION OF WATER IN LAKE-TYPE RESERVOIR

A qualitative and quantitative analysis of hydrochemical parameters of water is given in order to identify the factors that determine their spatial and temporal changes in a lake-type reservoir. Water samples were taken in 2019 and 2020 from the average level in spring (April), summer (July) and autumn (September) in the first week of the month in accordance with the requirements of GOST R 51592-2000 in three sections. The first target (1) is the shallow upper part (depth from 2 to 4 m); the second target (2) is the central part (depth from 5 to 7 m) and the third target (3) is the near – dam part (depth up to 12.2 m). Statistical analysis of the obtained data was performed using the unlimited Principal component analysis (PCA) technique and the limited redundancy analysis (RDA) technique. The effects were considered statistically significant at P<0.05, and useful for discussion-at P<0.10. It was found that, despite the flood increase in the level of chemical components in the water of the reservoir, most of them meet the requirements for fishing waters, with the exception of iron, copper, manganese, zinc, nickel and lead, which exceed the MPCVR from 1.1 to 45.0 times. The total variability of the hydrochemical composition of water in the reservoir, estimated by the PCA method, depends on the season of the year by 71.4 %. A similar result was obtained by the RDA method in a model with a single regressor. When all factors are taken into account in the RDA model, the variability of the water chemical composition is affected by the season of the year by 74.3 %, the year of research by 11.1 %, and the location of the target by 1.9 %. The primary indicators of water for the proportion of unexplained variability in both the PCA and RDA methods are manganese, bicarbonates, lead and aluminum, and pH.

About the mechanism of the granite-free zones formation in the Black Sea

One of the important unsolved problems related to the evolution of living conditions on Earth is the mechanism of the rapid transformation of the Black Sea from a shallow lake-type sea into a deep-water basin, the earth's crust in the central part of which does not have a granite layer. There is no explanation as to how “granite-free depressions” were formed at the bottom of the sea, which are currently covered by sediment. Investigations of these processes were started in the middle of the last century by scientists-geologists of the Institute of Oceanology of the Russian Academy of Sciences and its South. In this article, the authors propose a mechanism for the destruction of the earth's crust and the formation of depressions in the inner seas during the Messinian crisis.

Water storage and drainage of short-lived lakes in the Teskey Range, Central Asia

In the Teskey Range of the Tien Shan (Kyrgyz Republic), four outburst flood disasters from short-lived glacial lakes caused severe damages in the downstream part in 2006, 2008, 2013, and 2014. The short-lived lake grows rapidly and drain within a few months, due to closure and opening of an outlet ice-tunnel in moraine complex at glacier front. The outburst flood of this lake type is a major hazard in this region, it differs from many cases of moraine-dam failure in the eastern Himalaya. To clarify how short-lived lakes store and drain water for short period, we examined its recent changes in water level, area, volume, and discharge with a field survey and satellite data analysis. Korumdu lake appeared and drained within about one month during all summers during 2014–2019 except that in 2016. Water-level data recorded by a data logger and time-lapse camera images show that the lake appeared and expanded suddenly from July to August in 2017–2019. The timing indicates that the lake formed when an outlet ice-tunnel (subsurface channel) drain was blocked by deposition of debris and ice due to ice melting, not by freezing of stored water. Based on calculation of UAV DSMs and water level in 2017, the lake's water volume reached 234,000 m3 within 29 days, and then the water discharged for 17 days at a maximum rate of 0.66 m3/s. The small discharge indicates that the diameter of the outlet ice-tunnel was much smaller than those of four short-lived lakes in the same range that caused large drainages (12–27 m3/s) in 2006, 2008, 2013, and 2014. As the results, the dimensions of the outlet ice-tunnel of short-lived glacial lakes presently are related to the flooding scale. Recent warming temperatures may increase both the size of the tunnels and the basin volumes leading to greater hazard from such lakes in the future. In addition, we investigated the timing of appearance of 160 short-lived glacial lakes in this region using Landsat-7/8, Sentinel-2, and PlanetScope satellite images (2013–2018). We conclude that tunnel closure of 117 lakes was due to deposition of debris and ice during summer. The appearance of a short-lived glacial lake is inevitable in summer when the melting rate is high. The characteristics of this lake type might be shown in another Asian mountain permafrost regions.