2:45 PM - 3:00 PM
[MIS14-11] Solubility of amorphous magnesium carbonate: rarity of Mg-carbonate on surface of closed-basin lakes that existed on early Mars
Keywords:solubility, amorphous magnesium carbonate
Recent advances in in-situ chemical and mineralogical analyses by exploration rovers and high-resolution remote-sensing data by orbiters have revealed the existence of aqueous environments and geochemical cycle on early Mars. Early Mars would have possessed liquid water on the surface in semiarid climates (Ehlmann et al., 2014), evidenced by the widespread presence of valley networks, lake deposits, and clay minerals. The presence of liquid water on early Mars is thought to have been maintained by warmer climates than today’s, possibly due to a denser CO2 atmosphere in addition to effective greenhouse effect gas, such as H2 and CH4 (David et al., 2017; Wordsworth et al., 2017).
On present-day Earth, authigenic carbonates are, in general, generated in closed-basin lakes developed in semiarid climates as monohydrocalcite and amorphous magnesium carbonate (AMC) (Fukushi and Matsumiya, 2018). Closed-basin lakes as saline, alkaline lakes have a role of fixing CO2 in the atmosphere through generating carbonates on Earth. On early Mars, saline, circumneutral-to-alkaline lakes, if present, should have also generated authigenic carbonates in a dense CO2 atmosphere, playing a role of a carbon sink in carbon cycles. Recent studies suggested that such saline, circumneutral-to-alkaline lakes developed within Gale Crater (Fukushi et al., 2019), where the Curiosity rover landed. Formation of authigenic Mg-carbonates is expected on early Mars given both the widespread occurrence of mafic/ultramafic basement rocks on Mars and the facts that Mg-/Fe-carbonates are found by remote-sensing data. However, in-situ mineralogical analyses performed by the Curiosity rover have found little carbonates, including Mg-carbonates, in lacustrine sediments of Gale Crater. from surface of Gale crater. Since AMC is the precursor of authigenic deposition of Mg-carbonates, such as hydromagnesite and magnesite, the lack of Mg-carbonates in early Gale lakes implies the possibility that no effective AMC deposition occurred despite of the presence of a dense CO2 atmosphere.
In this study, we perform field surveys for closed-basin lakes developed in cold and semiarid climates in Mongolia, which are promising terrestrial analogues of early Martian lakes. In addition to the field surveys, we conduct laboratory experiments on solubility of AMC at low temperatures to understand condition formation of AMC in saline lakes in cold environments.
On present-day Earth, authigenic carbonates are, in general, generated in closed-basin lakes developed in semiarid climates as monohydrocalcite and amorphous magnesium carbonate (AMC) (Fukushi and Matsumiya, 2018). Closed-basin lakes as saline, alkaline lakes have a role of fixing CO2 in the atmosphere through generating carbonates on Earth. On early Mars, saline, circumneutral-to-alkaline lakes, if present, should have also generated authigenic carbonates in a dense CO2 atmosphere, playing a role of a carbon sink in carbon cycles. Recent studies suggested that such saline, circumneutral-to-alkaline lakes developed within Gale Crater (Fukushi et al., 2019), where the Curiosity rover landed. Formation of authigenic Mg-carbonates is expected on early Mars given both the widespread occurrence of mafic/ultramafic basement rocks on Mars and the facts that Mg-/Fe-carbonates are found by remote-sensing data. However, in-situ mineralogical analyses performed by the Curiosity rover have found little carbonates, including Mg-carbonates, in lacustrine sediments of Gale Crater. from surface of Gale crater. Since AMC is the precursor of authigenic deposition of Mg-carbonates, such as hydromagnesite and magnesite, the lack of Mg-carbonates in early Gale lakes implies the possibility that no effective AMC deposition occurred despite of the presence of a dense CO2 atmosphere.
In this study, we perform field surveys for closed-basin lakes developed in cold and semiarid climates in Mongolia, which are promising terrestrial analogues of early Martian lakes. In addition to the field surveys, we conduct laboratory experiments on solubility of AMC at low temperatures to understand condition formation of AMC in saline lakes in cold environments.