Factors affecting metal mobility in and near the low pressure supercritical region of seawater will be investigated in two specific areas of research: (1) The effect of temperature, pressure, pH, dissolved Cl and redox intensity on the thermodynamic stability of base metal (Fe, Pb, Zn and Cu) and Au-ion complexes. Results of recent experiments have unambiguously demonstrated the highly significant role of pressure on the relative stability of Fe- chloro complexes at elevated temperatures for fluids of seawater dissolved Cl. It is essential that these data be extended to higher temperatures and especially involve fluids of higher and lower dissolved Cl concentrations. (2) Phase equilibria constraints on dissolved concentrations of neutral species such as H2 and H2S. On-going research has clarified greatly the role of temperature and pressure on activity-concentration relations and "salting-out" behavior involving H2(aq) and H2S(aq) for fluids of seawater dissolved Cl concentration. These results need to be extended to higher temperatures, and especially higher and lower pressures and dissolved Cl concentrations. Dissolved H2 and H2S activities, and activity-concentration relations, constrain metal mobility, and can be used for some hot spring systems to reveal subseafloor temperatures and pressures.
