Continuous measurements of SO2-4 and electrical conductivity (ECM) along the GISP2 ice core record the Toba mega-eruption at a depth 2590.95 to 2091.25 m (71,000¿5000 years ago). Major chemical species were analyzed at a resolution of 1 cm per sample for this section. An ~6-year long period with extremely high volcanic SO2-4 coincident with a 94% depletion of nitrate and 63% depletion of chloride is observed at the depth of the Toba horizon. Such a reduction of chloride in a volcanic layer preserved in an ice core has not been observed in any previous studies. The nearly complete depletion of nitrate (to 5 ppb) encountered at the Toba level is the lowest value in the entire ~250,000 years of the GISP2 ice core record. We propose possible mechanisms to explain the depletion of nitrate and chloride resulting from this mega-eruption. ¿ American Geophysical Union 1996