The radioactive isotope ³⁹Ar is an ideal tracer for ocean ventilation, groundwater flow, and for dating mountain glaciers. With a half-life of 269 years, it covers the age range from a few tens to about 1800 years. We evaluate the input history of the atmospheric ³⁹Ar in the past 2500 years. By measuring the ³⁹Ar/Ar ratios of a modern argon sample and two old argon samples collected in 1959 and 1961, respectively, the anthropogenic contribution to the atmospheric ³⁹Ar in the past 60 years is determined to be less than 15%. The temporal variation of the atmospheric ³⁹Ar in the past 2500 years is calculated based on a cosmic-ray record derived from ice cores and tree rings. It is found that the atmospheric ³⁹Ar/Ar ratio has changed by as much as 17% in that period of time. This input variation has to be taken into account and corrected for in future ³⁹Ar dating applications.

放射性同位素³⁹ Ar 是海洋通风、地下水流和山地冰川测年的理想示踪剂。它的半衰期为 269 年，涵盖的年龄范围从几十年到约 1800 年不等。我们评估了过去 2500 年大气³⁹ Ar的输入历史。通过测量分别于 1959 年和 1961 年采集的现代氩气样本和两个古老的氩气样本的³⁹ Ar/Ar 比值，确定过去 60 年中人为对大气³⁹ Ar 的贡献小于 15%。过去 2500 年大气³⁹ Ar的时间变化是根据来自冰芯和树木年轮的宇宙射线记录计算的。发现大气³⁹ Ar/Ar 比在这段时间内变化了 17%。在未来的³⁹ Ar 测年应用中，必须考虑并纠正这种输入变化。