Estimated rates of carbon tetrachloride removal in the thermocline and deep waters of the East Sea (Sea of Japan)

Dissolved carbon tetrachloride (CCl4) was measured for the first time in the East Sea (Sea of Japan) during the summer of 1999. Fairly high concentrations (> 0.5 pmol kg−1 at the minimum) of CCl4 were observed throughout the water column to the bottom (> 3500 m), with evidence of significant depletion of this compound in the well-oxygenated thermocline waters. CCl4 loss rates below 200 m depth were estimated to range from near zero to 0.05 yr−1 using a tracer-calibrated mixing model, and from 0.04 to 0.07 yr−1 using the CFC-12 partial pressure (pCFC-12) age technique. The results from the mixing model and pCFC-12 age technique are in fairly good agreement in the upper 1500 m of water column, but show systematic differences in the deep waters below 1500 m that are likely due to biases in the pCFC-12 age technique. Despite relatively rapid removal in the upper 500 m water column, the low removal rates for CCl4 in the cold, deep waters of the East Sea estimated using the mixing model (< 0.02 yr−1 for depths > 2000 m) indicate that this compound can be a potentially useful quantitative ocean tracer in certain regions.