Tracer studies of ¹⁴C in the Nordic Seas by AMS measurements

At a time of important interest in climate, the Nordic Seas are especially in focus as a sink for CO₂ and the further transfer to the deep water in the Atlantic Ocean. The relatively short time constant in this process provides possibilities to study the circulation by application of tracers. ¹⁴C is one of the most representative isotopes in this study, and several deep sea profiles have been obtained in seven summer cruises during the last years. For modelling studies it has been especially important to repeat some GEOSECS profiles obtained 20 years earlier in this area. Some of the first ¹⁴C profiles were obtained with conventional CO₂ counting technique based on 100-200 l seawater. Most of the later profiles have, however, been measured with the AMS technique at the Arizona AMS facility, based on 0.5 l seawater. The small samples make this technique especially preferable for sample collection on board ship and in further laboratory treatment. The precision in the isotope ratio measurements is generally 6%. for a counting time of 20 min per sample. Higher precision (3-5%.) has, however been achieved with several accelerator targets.