Mercury Thermoforms and Their Distribution in the Sedimentary Sequence of the Juan De Fuca Ridge

Abstract

This paper addresses the vertical distribution of total mercury and its thermoforms in the Holocene–Upper Pleistocene sedimentary rocks from the Dead Dog active hydrothermal field in the Middle Valley, Juan de Fuca Ridge, Pacific Ocean. Sediment samples were taken from the core of Hole 858B drilled during ODP leg on the top of a sulfide hill, in a zone of ascending hydrothermal fluid, in the vicinity of high-temperature vent with temperature of 276°С. The contents of mercury and its thermoforms were measured by atomic absorption spectrometry (AAS) with thermal atomization. The highest mercury concentrations in the sediments reach 10.3 μg/g. Mercury is present in sediments in the following thermoforms: free mercury (FR), chloride (ChL), physically sorbed (PhS), chemically sorbed (ChS), sulfide (SF), and isomorphic (IS) forms. In the sedimentary section, contrasting concentrations of mercury alternate like a “layer cake” due to its accumulation at geochemical barriers.