Radiocarbon analyses were performed on sediment cores from the sea lochs of the Clyde sea area and the data interpreted with regard to carbonaceous pollution of the area. In the Clyde sea area a large excess of fossil carbon from fuels and industrial wastes has been deposited thus diluting natural ¹⁴C concentrations and producing abnormally old ages near surface sediments. Radiocarbon data enables fossil carbon pollution indices to be estimated for the Clyde sea area. In addition points of radiocarbon inversion in sediment profiles are consistent with the commencement of large scale industrial pollution of the area around 200 years ago. A source of natural fossil carbon in the area is also evident.