EFFECT OF SELECTED CALCULATION ROUTINES AND DISSOCIATION-CONSTANTS ONTHE DETERMINATION OF TOTAL CARBON-DIOXIDE IN SEAWATER

During the 1989 and 1990 JGOFS North Atlantic Pilot Study a comparison was made between the Coulometric and the acid titration method for de termination of total carbon dioxide (TCO2) in seawater. TCO2 and alkal inity have been calculated from acid titration using either the modifi ed Gran plot or the curve-fitting routine. Depth profiles showed fair agreement (on average 0.6% or about 12.5 mumol l-1) between the TCO2 c alculated from the acid titration method and the TCO2 measured indepen dently by Coulometry. It is shown that different data processing routi nes combined with the proper use of dissociation constants can influen ce the acid titration result considerably. There appears to be a sligh t offset between calculated and Coulometric data which is smallest whe n using the combined dissociation constants of HANSSON (Deep-Sea Resea rch, 20, 461-478, 1973) with GOYET and PoissoN (Deep-Sea Research, 36, 1635-1654, 1989). No statistically significant difference could be fo und between the two used calculation methods (Gran plot and curve-fitt ing). The agreement between the independent methods of Coulometry and acid titration is encouraging and furthermore independent of depth, fo r this dataset there is no reason for invoking the existence of interf ering (organic) protolytes.