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our Teacher at Sea
Sampling for Barium and O18
|| O18 and Barium
are tracer elements. That means you can figure out where water containing
these substances is coming from by the amount of these two tracers in the
They are both found in the waters of the Arctic
Ocean. When studying the ocean, one of the things we are looking
at is a surface layer that contains fresher water, which could have its
origin in continental river water runoff, or melting sea ice. Both
river water and sea ice have low salinity, so oceanographers use a trick
to distinguish between them.
There are two common forms (isotopes) of the atom
oxygen. O16 is a more common isotope
than O18. O18
weighs more than O16 and has two more neutrons.
The chemical formula for water is H2O.
The oxygen in water can be either O16 or
O18. When evaporation from the sea
surface occurs, it is easier to lift the lighter O16
than the heavier O18. Thus precipitation
contains more O16 than O18.
When the precipitation containing O16 is
returned to the ground, it flows as river runoff. By determining
whether your seawater sample contains more O16
or O18, you can determine whether it is
from land or ocean.
In simple terms, when we find an input of fresh water, "O18" tells us if we are looking at sea ice melting or river water.
Scientists have been studying Barium since the early 90's. It is known that sediments contain Barium.
The North American continent contains higher levels of Barium than the lands of Russia. By looking at the levels of Barium in the seawater along with the salinity and the O18, you can figure out which continent the river water came from.
Barium is not a simple tracer element, because it can be dissolved, consumed by critters, or changed into something else which then sinks to the bottom of the ocean. Barium travels to the ocean from rivers by attaching itself to clay matter. Once this clay enters the ocean, the Barium is released. Barium can then be traced back to a particular river. If you know which river it came from, the Barium tells you something about the circulation of the Arctic Waters.
In the pictures you can see two sample bottles. The glass container is for O18 and the plastic is for Barium. You can see the cast number identifier, station number identifier, and which niskin bottle it was taken from. This is how the data are logged for reference and storage.