I don't want to pick over old scabs or to be a pedant but... could some one just check that my reading of Stumm and Morgan (3rd edition, 1996) is correct and that there is an error in the calculation of d13Csol. Page 201. CT is given as 3.7 x 10-3 M, but [H2CO3*] = 5.4 x 10-4, [HCO3-] = 3.2 x 10-3 M and [CO32-] = 2 x 10-6 M... total = 3.742 x 10-3 M. the weighted mean equation to calculate the d13Csol, eq (viii), has the term d13Csol in the demominator. Surely this factor should be just the total concentration of the DIC. These may not seem like much but for my peace of mind I would be grateful if someone would consider these points as some years ago I spent a considerable amount of time worrying about this calculation. Yours in hope. Andrew Dr A.M.Johnston SPDU Scottish Crop Research Institute Invergowrie Dundee DD2 5DA Scotland Tel No: (44) 1382 562731 ext 3732 Fax No: (44) 1382 562426