Etudes et évaluation de processus océaniques par des hiérarchies ...

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8 CHAPTER 2. OBSERVING THE OCEAN
tel-00545911, version 1 - 13 Dec 2010
their position with respect to the gulf stream. During the cold war, Russian submarines used
the same trick to approach the east coast of the US along the northern border of the Gulf
Stream, where they could hide due strong density gradients and turbulent ocean dynamics
deflecting the sonar signal.
Scientists were then interested in measuring other properties of sea water to determine the
path ways of water masses in the ocean. Salinity measurements are easy to perform due to the
strong relation to the electric conductivity of the sea water. Today a variety of constituents of
the oceanic water masses are measured including: oxygen, carbon-dioxide, freon, radioactive
tracers and the concentration of biological constituents. Freon gases, were released to the
atmosphere starting from the first part of the 20th century and was stopped when it was found
that they are responsible for the destruction of the atmospheric ozone layer, are dissolved in the
ocean. By measuring their concentration in oceanic waters the age of the water masses, that
is the time since their last contact with the atmosphere, can be obtained. The same applies to
some radioactive traces which were released to the atmosphere during atomic bomb explosions
in the atmosphere during the mid twentieth century.
Tracers as temperature and salinity which change the density of the water masses are called
active tracers as they act on the dynamics through their buoyancy, tracers that have no substantial
impact on density of the water mass and thus on the dynamics are named passive tracers
. The measurement of passive tracers is nevertheless important as they provide information
about the movement of water masses.
Exercise 2: Search the Internet for maps of sea surface temperature (SST) and sea surface
salinity (SSS).