of alkenones in the spring transitional season, concurrent with the period of lake ice melt and isothermal mixing. Together, these data provide a framework for evaluating lacustrine alkenone distributions and utilizing alkenone unsaturation as a spring lake temperature proxy in freshwater lakes. 70

The aim of this study is to evaluate the definition of water chemical type, with particular attention to soda brine characteristics by assessing ionic composition and pH values on a large geographic scale and broad salinity (TDS) range of Eurasian inland saline surface waters, in order to rectify the considerable confusion about the exact chemical classification of soda lakes and pans. Data on pH and on the concentration of eight major ions were compiled into a database drawn from Austria, China, Hungary, Kazakhstan, Mongolia, Russia, Serbia, and Turkey. The classification was primarily based on dominant ions exceeding an equivalent percentage of 25 (> 25e%) of the total cations or anions, and the e% rank of dominant ions was also identified. We identified four major types: waters dominated by (1) Na-HCO3 (10.0%), (2) Na-HCO3 + CO3 (31.4%), (3) Na-Cl (45.9%), and (4) Na-SO4 (12.7%), considering only the first ion by e% rank. These major types can be divided into 30 subtypes in the dataset, taking into account the e% rank of all dominant ions. The major and subtypes of soda brine can be divided into “Soda” and “Soda-Saline” types. “Soda type” when Na+ and HCO3– + CO32– are the first in the rank of dominant ions (> 25e%), and “Soda-Saline type” when Na+ is the first in the rank of dominant cations and the sum of HCO3– + CO32– concentration exceeds 25e%, but it is not the first in the rank of dominant anions. Soda-saline type can be considered as a separate evolutionary stage between Soda and Saline types respect to the geochemical interpretation by saturation indexes of brines. The obtained overlapping ranges in distribution demonstrate that a pH measurement alone is not a reliable indicator to classify the permanent alkaline “soda type” and various other types of temporary alkaline waters.

No abstract

Lake‐level reconstructions, related to terrestrial hydrological changes, are important for our understanding of past and future climates. Currently, however, reliable lake‐level proxies are still limited. Here we report distributions of archaeal tetraether lipids in 70 surface sediment samples collected from 55 lakes in midlatitude Asia. We have found that among various lake physico‐chemical characteristics, the relative abundances of crenarchaeol and Hydroxylated isoprenoid glycerol dialkyl glycerol tetraethers (%cren and %OH‐GDGTs) are best correlated with lake water depth, due to a preference of Thaumarchaeota, the producer of these biomarkers, for a niche in subsurface lake water. This supports the recent hypothesis based on single‐lake investigations that %cren and %OH‐GDGTs are potentially novel lake‐level proxies. Our results also suggest that %OH‐GDGTs is less affected by soil input than %cren. Nevertheless, other confounding factors should be well constrained and local/site‐specific calibrations are needed before the two molecular proxies are used quantitatively in down‐core applications.