Chukchi Borderland Project

Daily Updates from

our Teacher at Sea


September  18

Tracking Water Motion with Tracers

Measuring for Cesium (137) and Iodine (129)

  The radioactive isotopes Cesium-137 (Cs) and Iodine-129 (I) are waste products from the reprocessing of used nuclear fuel.  Oceanographers use them as ocean tracers.

  Over the last thirty years these tracers have been released from the nuclear fuel reprocessing plants in Sellafield (United Kingdom) and LaHague (France), which discharge some of their waste into the Irish Sea and the English Channel. 

  Within a few years, the water currents carry these isotopes into the Arctic Ocean via the Fram Strait and Barents Sea.

Kellie sampling for Cesium.


Kellie sampling for Iodine.
  Knowing from where and when the isotopes were originally discharged, we can use Cs and I measurements to track the movement of Atlantic water through the Arctic Ocean. 

  Since the journeys of the isotopes began in Europe, the Atlantic waters have much higher levels of Cs and I than the waters of the Pacific, and we can use Cs and I levels to distinguish between the Atlantic and Pacific waters.


Measuring for Helium (3He) and Tritium (3H)

  Helium-3 and Tritium are also radioactive isotopes.  Tritium occurs in small quantities naturally, but in far larger quantities from nuclear bomb testing of the 1950's and 1960's. 

  Tritium in the atmosphere is washed into the oceans by water vapor exchange, precipitation, and river runoff.  It has a half-life of 12.4 years, which means that in 12.4 years, half of it is broken down to Helium-3.

  Tritium and Helium-3 enter the ocean only at the surface, so we can use them as tracers of surface waters.

Trapping water in Helium tube.


Wendy sampling for Helium.
  The ratio of the quantity of Tritium to Helium-3 will tell you about the "age" of the water, or when it was last at the surface of the ocean. 

  For example, if the concentration of Tritium is higher than Helium-3, then not much decay has occurred and you know that the water is not that old. 

  If the concentration of Helium-3 is greater than that of Tritium, (Tritium has had time to break down into Helium-3), the water sample is older.