Dispatch 9: Radioactivity in the Arctic     Print

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Mengnan Zhao

September 26, 2015

Today was supposed to be our first ice station, but low visibility due to snow and fog did not allow for a helicopter recon to hunt for an ice floe as our base. Conditions didn’t improve by the early afternoon, and chief scientist Bill Williams and WHOI team leader Rick Krishfield decided to postpone our ice station until tomorrow. In the extra time we would head to the next rosette station.

The longer steaming time between stations allowed scientists who need to analyze their water samples as soon as they are collected enough time to wrap up their to-do lists. Christopher Charles (University of Ottawa) is one of them. His research concerns radioactive isotopes in seawater; primarily Iodine (I), Caesium (Cs), Plutonium (Pu) and Uranium (U). The abundance of these isotopes in seawater are below 1 part in 10 to the power 13, thus Christopher must collect jugs of 20 liter water samples at each depth level in order to obtain sufficient quantities of these elements. Final samples are reduced to 50-100 mL of precipitate containing Pu and U, and even less for Cs – only about 5 mL. The analysis was fascinating and educational since I hadn’t done any chemistry experiments since high school. Different chemical reagents are added to the water samples for the Cs, Pu and U precipitation before they are transferred to smaller containers for further analysis. To a layman’s eyes (me), the water samples were turned to a beautiful lemonade color (for Cs) and apple juice (for U and Pu).

Analyses of these radioisotopes has multiple applications. For example, results can shed light on ocean circulation patterns; as chemical tracers, radioisotopes can offer information both in time and space with understanding of the changing isotope ratio during its decay period (we have some knowledge about the source regions and lifetimes of these isotopes). Charles is currently working on the challenging project of improving the accuracy of these isotope measurements using a novel radiofrequency quadrupole (RFQ) gas-reaction device, designed for accelerator mass spectrometry. Let’s hope by improving the technique Charles and his colleagues can use radioisotopes to make a breakthrough in our understanding of Arctic Ocean circulation and change.