14C Profiles in the Norwegian and Greenland Seas by Conventional and AMS Measurements

Abstract

CO2 in the atmosphere is an important climate gas because of its absorption of infrared radiation. More knowledge about CO2 uptake in the ocean is of critical significance in predicting future climate development. For a period of approximately 30 years, radioactive carbon from nuclear tests has been a very useful tracer in CO2 exchange studies. Up to now, the measurements have been based mainly on the conventional counting technique with large CO2 samples (ca. 5 liters). Accelerator mass spectrometry (AMS) with small CO2 samples (1-2 ml) has made sampling much easier, and has especially stimulated the use of 14C as a tracer in the ocean. At higher latitudes, the ocean acts as a sink for CO2. In addition to Delta-14C measurements, we are concerned here with dissolved inorganic carbon (DIC) and delta-13C in the Norwegian and Greenland Seas. During cruises in 1989 and 1990, we obtained several Delta-14C profiles, and also repeated a few GEOSECS profiles taken in 1972. The shape of these profiles changes with time, and provides information about the mixing rate and the age of the deep water. From changes in the profiles, it appears that the deep water in the Greenland Sea has obtained about 25% of the 14C concentration in the ocean surface over a period of 25 years. The Norwegian Sea deepwater is estimated to be 50-100 years older than that of the Greenland Sea.