APPROACHES TO THE CONTINUOUS MONITORING OF SEAWATER PH AND ITS ROLE IN THE GLOBAL CARBON-CYCLE

Seawater pH reflects the status of the carbonate system in seawater. A ccurate, on-line, shipboard measurements are required to aid modelling of the global oceanic uptake, or release, of atmospheric carbon dioxi de. Potentiometric methods, although highly precise, exhibit inherent inaccuracies due to residual liquid junction and standing potentials. Discrete spectrophotometric determination displays very high precision , with implied high accuracy, limited only by the accuracy of indicato r pK values and system temperature control. Recent trials of the conti nuous spectrophotometric method, in the Southern Ocean, have shown exc ellent precision, and internal accuracy. It is predicted that diode ar ray spectrophotometry will become the method of choice for continuous shipboard and in situ pH monitoring.