ABSTRACT

Siliceous ooze was reacted with NaCl solution at temperatures of 100-250°C to evaluate the effect of the mineralogical and chemical properties of host sediments on the thermal stability of amino acids (AAs). Results were compared with those previously reported from calcareous ooze. The siliceous ooze preserved more AAs than did the calcareous ooze, and the solution with the siliceous ooze preserved the AAs for a longer time than did the solution with the calcareous ooze. When siliceous ooze was reacted under hydrothermal conditions, the AAs were released easily and were more stable in alkaline solution than in the NaCl solution. Solubility of silica was greater in alkaline solution than in NaCl solution, and an excess of hydroxyl ion and/or carbonate species in the alkaline solution underwent exchange more frequently with AAs in the siliceous ooze than in the NaCl solution. The thermal stability of neutral AAs was enhanced significantly in alkaline solution at temperatures higher than 200°C. When montmorillonite and saponite were heated in NaCl solution with a known amount of AAs at 250°C, some AA concentrations increased, probably due to negatively charged AAs binding to cations in the clay minerals. The results suggest that the AAs are dissolved into the solution from the sediments primary via ion exchange, and that polymerization of silica that included AAs in its framework stabilized AAs in siliceous ooze.