Hydrogeochemical Study on Closed-Basin Lakes in Cold and Semi-Arid Climates of the Valley of the Gobi Lakes, Mongolia: Implications for Hydrology and Water Chemistry of Paleolakes on Mars

Abstract

Previous studies suggested that, generally, the climate of early Mars would have been semi-arid when the surface temperatures were above freezing. On early Mars, closed-basin lakes would have been created; however, the hydrogeochemical cycles of the lake systems are poorly constrained. Here we report results of our field surveys to terrestrial analogs of closed-basin lake systems that developed in cold and semi-arid climates: The Valley of the Gobi Lakes of Mongolia. Our results show that groundwater plays a central role not only in hydrology, but also in geochemical cycles in the lake systems. We find that groundwater predominantly flows into the lakes through local seepage and regional flows in semi-arid climates. Through the interactions with calcite-containing soils, local groundwater seepage provides Ca2+ and HCO3− to the lakes. In the wetland located in between the lakes, high-salinity shallow pools would provide Cl− and Na+ to the groundwater through infiltration. If similar processes occurred on early Mars, local seepage of groundwater would have provided magnesium and alkalinity to the early Jezero lakes, possibly leading to authigenic precipitation of lacustrine carbonates. On early Mars, infiltration of surface brine may have transported salts and oxidants on the surface to lakes via regional groundwater flows. We suggest that inflows of multiple types of groundwater in semi-arid climates could have caused redox disequilibria in closed-basin lakes on early Mars.

Field Investigations of Chemical Partitioning and Aqueous Chemistry of Freezing Closed‐Basin Lakes in Mongolia as Analogs of Subsurface Brines on Icy Bodies

“…Our previous study investigated the hydrology around Orog and Olgoy lakes through field surveys in warm seasons (Sekine et al., 2020). Based on this previous study, the major water source of Orog Lake during summer is the Tuin River, along with underground water flow along the river and local springs (Sekine et al., 2020). In the surveys of the present study, the surface of the Tuin River was completely frozen.…”

“…However, we found that a small input of underground water occurs along the river into the central Orog Lake, even in February. The major water source of Olgoy Lake during summer is local springs, which originates melting of permafrost (Sekine et al., 2020). In the surveys of February 2019 and January 2020, we recorded no significant inputs of spring water into Olgoy Lake due to the low temperatures (−20°C).…”

“…Both lake waters have a salinity of 1–2 g/kg and a pH of 9–10 (Fukushi et al., 2020). The lake waters are sodium bicarbonate type, which means that Na + and HCO 3 − are the major cation and anion, respectively (Sekine et al., 2020). In addition, the concentrations of Cl − and Mg 2+ are substantial in Orog and Olgoy lakes, respectively.…”

“…In Orog and Olgoy lakes, the hyposaline and alkaline lake waters are the results of evaporative concentration of the lake water and accumulation of conservative Na + (and Cl − ) in the lakes in the semiarid climate and in the absence of any outlet rivers (Sekine et al., 2020). Under these alkaline conditions, authigenic precipitation of carbonate minerals, such as monohydrocalcite (MHC; CaCO 3 ·H 2 O), occurs in the water column of the lakes (Fukushi et al., 2020; Fukushi & Matsumiya, 2018).…”

Thermodynamic Impact of Mineral Surfaces on Amino Acid Polymerization: Aspartate Dimerization on Two-Line Ferrihydrite, Anatase, and γ-Alumina

“…The formation constants from Asp 2− of all the dissolved and adsorbed AspAsp species were calculated by setting the logK value for the zwitterionic Asp dimerization in water (i.e., Asp ± + Asp ± → AspAsp ± + H 2 O) to -3.0 [16] and by combining this value with the respective AspAsp protonation and adsorption constants (Table A4). The examined pH and NaCl concentrations were 3-10 (5-10 for γ-alumina) and 1-100 mM, respectively, corresponding to a range of natural waters in rivers, soil, terrestrial springs, saline lakes, and rainfall [63][64][65][66][67]. There is no definitive constraint on the α-amino acid abundance in primitive environments.…”