Fig. 4.

Measurements of Hg speciation within LY2 sediment. (A) Plot of relative percentage cinnabar and matrix-bound phases of Hg. (B) Concentration of Hg as cinnabar down-core. Before anthropogenic enrichment a combination of cinnabar dust and matrix-bound Hg make up the sediment Hg record. During the height of Chavín mining (ca. 400–800 BC), cinnabar dust was the vast majority of sediment Hg. After Inca control of the mine (ca. 1450 AD), matrix-bound phases of Hg predominate, despite a synchronous rise in the concentration of Hg as cinnabar. This relationship suggests a shift in the phase of Hg emitted, from cinnabar dust to Hg⁰ (or possibly Hg²⁺). Both would subsequently be available for oxidation/reduction cycling within the atmosphere, sorption by organic matter, methylation, and subsequent bioaccumulation within aquatic food-webs.