A Method for Continuous 239PU Determinations in Arctic and Antarctic Ice Cores

Atmospheric nuclear weapons testing (NWT) resulted in the injection of plutonium (Pu) into the atmosphere and subsequent global deposition. We present a new method for continuous semiquantitative measurement of Pu-239 in ice cores, which was used to develop annual records of fallout from NWT in ten ice cores from Greenland and Antarctica. The Pu-239 was measured directly using an inductively coupled plasma sector field mass spectrometer, thereby reducing analysis time and increasing depth-resolution with respect to previous methods. To validate this method, we compared our one year averaged results to published Pu-239 records and other records of NWT. The Pu-239 profiles from the Arctic ice cores reflected global trends in NWT and were in agreement with discrete Pu profiles from lower latitude ice cores. The Pu-239 measurements in the Antarctic ice cores tracked low latitude NWT, consistent with previously published discrete records from Antarctica. Advantages of the continuous Pu-239 measurement method are (1) reduced sample preparation and analysis time; (2) no requirement for additional ice samples for NWT fallout determinations; (3) measurements are exactly coregistered with all other chemical, elemental, isotopic, and gas measurements from the continuous analytical system; and (4) the long half-life means the Pu-239 record is stable through time.