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- Title
Field Investigations of Chemical Partitioning and Aqueous Chemistry of Freezing Closed‐Basin Lakes in Mongolia as Analogs of Subsurface Brines on Icy Bodies.
- Authors
Yoda, Masahiro; Sekine, Yasuhito; Fukushi, Keisuke; Kitajima, Takuma; Gankhurel, Baasansuren; Davaasuren, Davaadorj; Gerelmaa, Tuvshin; Ganbat, Shuukhaaz; Shoji, Daigo; Zolotov, Mikhail Y.; Takahashi, Yoshio
- Abstract
Several icy bodies (e.g., Europa and Ceres) likely possess near‐surface brine reservoirs, which are considered to be sources of salts on their surfaces. Previous studies have proposed processes whereby an overlying ice layer captures salinity from a freezing, subsurface reservoir. However, few field investigations have been conducted to investigate chemical partitioning and aqueous chemistry in freezing brine reservoirs in terrestrial analogs. Here we report results of winter field surveys to ice‐covered, closed‐basin saline lakes in the Valley of the Gobi Lakes, Mongolia. We found that the surface ice exhibited complex features, including both pressure ridges formed by compressive forces and wet cracks formed by tensile forces. The latter provides salinity to the ice layer and surface. In addition to wet cracks, saline lake bottom‐water, along with suspended matter, was continuously captured within the pores of the ice layer during downward freezing. Using a combined mass balance and low‐temperature aqueous chemistry model, we reproduced the ice salinity due to entrapment of Na+, Cl−, and SO42−, suggesting that chemical partitioning of these species in freezing brine reservoirs on icy bodies can be understood based on our current knowledge. In the lake bottom‐water, the metastable phase of carbonates (i.e., amorphous Mg‐carbonate and monohydrocalcite) play key roles in controlling the concentrations of precipitable Mg2+ and Ca2+ and alkalinity, highlighting the importance of metastable phase of carbonate in the aqueous chemistry of subsurface brine reservoirs on icy bodies. Metastable phases might be indicators of freshly erupted materials from brine reservoirs. Plain Language Summary: Icy bodies that have subsurface brines in the Solar System attract attention because of their potential habitability. Recent observations by spacecraft and ground‐based telescopes have identified the existence of salt materials on such icy bodies, such as Europa and Ceres. The salt compositions may reveal the aqueous chemistry of the subsurface liquid reservoirs. However, transport of salt materials to the icy surface is poorly understood and has been subject to limited field investigations of terrestrial analogs. Here we report results from field surveys of ice‐covered saline lakes in Mongolia. We found that cracks and pores in the surface ice capture lake bottom‐water and suspended matter. Similar processes may operate on icy bodies and transport salt materials to the surface. Key Points: Freezing closed‐basin saline lakes could be terrestrial analogs of chemical partitioning of salinity in subsurface brines on icy bodiesSalinity in ice and aqueous chemistry in bottom lake water were investigated through field surveys and geochemical modelingMetastable carbonate minerals could control dissolved CO2 and alkalinity of freezing lake water, implying their importance in ocean worlds
- Subjects
PERMEABLE reactive barriers; EARTH analogs; METASTABLE ions; GEOCHEMICAL modeling; CARBONATES
- Publication
Journal of Geophysical Research. Planets, 2021, Vol 126, Issue 11, p1
- ISSN
2169-9097
- Publication type
Article
- DOI
10.1029/2021JE006972