Dr. Amber Annett from Southampton University and Sean Selzer from Oxford university are both measuring Radium and Thorium Isotopes during the FRidge JC156 cruise.
These differents isotopes (four naturally occuring Ra isotopes, Th isotopes, Ac isotopes) have different half lives that allow us to follow processes from weeks to months to years. Moreover they have different chemistry that allow us to study different processes, Th is particulate reactive while Ra is very soluble.
To sample these isotopes present in extremely low concentration, Dr. Annett and Sean Selzer are using two different techniques to collect large sample volumes.
The first one is the « Fish» to collect liters of shallow water every day (8 meters depth) through a pump. 300 to 400 liters of this water are needed to measure one sample of Radium isotopes. 40 to 50 samples will be collected during this cruise with this method.
Fish going in water © Lise Artigue
The second method used is the SAPS (Stand Alone Pumps), these pumps collect deep samples. In one hour 500 to 900 Liters of deep water (until 5000m depth). Once the water is pumped, the Radium and thorium are adsorbed onto manganese dioxide fibers (for the SAPS a cartridge containing the fiber is directly connected to the pump filter).
Ingeneer Pete (left) and Dr. Amber Annett (right) behind SAPS © Lise Artigue
Then detectors called RaDECCS (Radium Delayed Coincidence Counters) are used to measure the isotope ratio thanks to the isotope decay of these elements. The isotopes circulate in this dectectors through a gas and radon is then generated from decay of radium and quantified.
Dr Amber Annett behind the RaDECCS © Lise Artigue
During this cruise Dr. Annett and Sean Selzer are particularly interested in :
- In shallow water : detect dust/aerosol inputs in the differents sites (Ra and Th input).
- In deep water : looking at understanding the timescale of chemical changes and physical advection of the term plums.
As in the cruise, samples are often collected for several uses, filters are also present on the top of cartridges in the SAPS to collect the particulate fraction. These filters will then be analysed for trace metals. Sean Selzer is also in charge of collecting aerosols for Dr. Alex Baker who is looking at trace metals in the aerosols.
Sean Selzer collecting aerosol filter during FRidge JC156 cruise @Sean_Selzer_© Lise Artigue