On the 14 C to Tritium Relationship in the North Atlantic Ocean

• Published in: Radiocarbon
• Main Authors: Roether, Wolfgang, Münnich, Karl-Otto, Schoch, Hildegard
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 1980
• Subjects: North Atlantic
• Online Access: https://doi.org/10.1017/s0033822200010006; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0033822200010006

Nuclear-weapon produced 14 C (or bomb 14 C) in the ocean can be traced by simultaneous tritium observations. Data are presented on the general relationship of bomb 14 C and tritium in the North Atlantic. For the period 1965 to 1973, the excess 14 C to tritium ratios in the surface water vary, systematically, over a factor of 10: the ratios monotonically increase with time, and decrease with latitude, particularly so for the later observations. The sub-surface water ratios show that the mid- and low-latitude water below about the 15° C isothermal horizon (~500m depth) originates from higher northern latitudes, rather than being renewed by local vertical mixing. It is further shown that in the North Atlantic, bomb 14 C did not penetrate beyond the horizon where the presently observed 14 C concentration is Δ 14 C = —75‰. Observed concentrations up to about —40‰ can be corrected for a bomb contribution if the tritium concentration is known because the bomb 14 C to tritium concentration ratio is rather uniform in this range. A surface water 14 C concentration versus time curve is presented for the period since 1957. This curve is based on a North Atlantic mixing model and is fitted to the 14 C observations. Making use of a previously published tritium versus time curve obtained by the same model, a time curve for the average excess 14 C to tritium ratio in North Atlantic surface water is given. This curve reproduces the observations well. The presented data and theoretical curves show the usefulness of simultaneous 14 C and tritium observations for mixing studies and to provide corrections for bomb 14 C in sub-surface 14 C data in the North Atlantic.