Towards large-scale application of 39Ar in ocean circulation studies

Wei Jiang1,2, A-Min Tong2, Ji-Qiang Gu2, Xi-Ze Dong2, Shui-Ming Hu1,2, Zheng-Tian Lu1,2, Florian Ritterbusch1,2 and Guo-Min Yang1,3, (1)Hefei National Laboratory for Physical Sciences at the Microscale, Hefei, China, (2)University of Science and Technology of China, Hefei National Laboratory for Physical Sciences at the Microscale, CAS Center for Excellence in Quantum Information and Quantum Physics, Hefei, China, (3)University of Science and Technology of China (USTC), Hefei, China
The noble-gas radioisotope 39Ar (half-life 269 y) is an ideal tracer for global ocean circulation studies. It covers the age range of 50 – 1,400 years, thus bridging the existing gap between the ranges of 14C and the young-age tracers (e.g. CFCs and SF­6). The emerging technology Atom Trap Trace Analysis (ATTA) has made possible to analyze 39Ar in a water sample of only a few liters, which can be collected in a single Niskin bottle. Here we report the latest progress on 39Ar dating in our laboratory, both on the analytical method and applications including a vertical 39Ar profile near the Yap-Mariana trench in the West Pacific.

ATTA is a laser based atom counting method capable of detecting noble gas isotopes with extremely low abundance (10-16 – 10-10). A laser trap is used to capture and detect atoms of the interested isotope. This method is highly selective and free of interference of any isobar or molecular species. Fig. 1 shows the performance of the 39Ar dating apparatus. New development is underway to increase the counting rate, a major limitation of the current instrument. This effort would improve the dating precision to 5% and the capacity to 300 samples per year.

Figure 1 39Ar dating uncertainty as a function of sample age. (Typical sample size is 1 mL STP of argon gas which can be extracted from 2-4 kg of seawater.).

Website: or Google “ATTA Primer”.