On the Composition of Putative Oceans on Early Venus

Introduction: Venus once had substantially more water and possibly even oceans early in its history. Given the close proximity of Venus and Earth, the planets could have accreted comparable amounts of volatiles. The high D/H ratio in the atmosphere of Ve-nus implies an elevated water abundance earlier in the history of Venus [1,2]. This water was lost by mechanisms that may have involved evaporation under runaway greenhouse conditions, photo-dissociation of H 2 O, and water-rock reactions [1]. Preferential hydro-dynamic escape of hydrogen released through H 2 O dissociation [3] could have caused net oxidation of rocks and atmospheric gases, and accumulation of deu-terium in the atmosphere [1-3]. The existence of early oceans should have affected the subsequent evolution of the atmosphere and litho-sphere. The involvement of aqueously altered and oxidized rocks, and oceanic sediments (e.g., salts) in lithospheric processes could have influenced rock deformations , melting and degassing patterns, the composition of igneous rocks, and distribution of volatiles in the lithosphere-atmosphere system. In addition to the D/H ratio, signatures of ancient aqueous processes could be manifested in the chemical and isotopic composition of the current atmosphere and lithosphere, in geological features, and in lithospheric geophysical data. These signatures could vary depending on formation scenarios, composition, and loss mechanisms of the early hydrosphere. Here we discuss and roughly evaluate chemical scenarios of early aqueous evolution .