Trace element speciation in Ryugu samples: implications for water solubility of elements in a sulfide-dominated paleoocean.

Abstract

The current ocean is an "oxide world" in which adsorption of oxides dominates the dissolved concentration of trace elements. On the other hand, the paleo ocean is estimated to be a "sulfide world" in which the reaction with sulfides dominates the water solubility of the element. In this study, I examine the factors that govern the solubility of elements in water in the early materials of the solar system. By clarifying which elements are affected by sulfides in the sulfide world, I aim to contribute to the evolution of life, the behavior of elements, and the elucidation process of metal concentration. I focused on trace elements such as manganese, nickel, zinc, and iron, and identified the host phase of these elements by X-ray absorption fine structure (XAFS) using the resin-embedded samples of Ryugu as C-type asteroid and the Orgueil meteorite. I attempted to identify the factors that govern the water solubility of each element. Based on the results, adsorption experiments on sulfides (mainly pyrrhotite) under various conditions are conducted, the partition coefficient is determined. The host phase is determined by XAFS, and the systematics of the water solubility of elements in a system where sulfides dominate solid-liquid partitioning are examined.