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Why observe the ocean’s interior ? How will GyroScope contribute ? Why are temperature and salinity important ? What happens to the floats at the end of their mission ?
Why observe the ocean’s interior ? ·
To better understand the Ocean’s role in the
Earth climate ·
To make possible and improve seasonal climate
forecasts ·
To monitor the state of the ocean and the impact
of human activities ·
To gain confidence in forecasts of future global
change ·
In support of commercial and military activities :
fisheries, deep sea oil exploration, shipping, near - shore protection, national
defence. How will GyroScope contribute ? ·
GyroScope is a contribution to the international
Argo
programme.
The goal of Argo
is to deploy worldwide some 3000 autonomous profiling floats ,
which measure every ten days temperature and salinity profiles from a maximum
depth of 2000 m to the surface. ·
Each time the float comes to the surface, the
data is immediately transmitted by satellite to the data centers.
After quality control, the data is transmitted to all the National
Weather Services, to scientists, and operational agencies in charge of ocean
monitoring. The data is used in
several complementary ways ·
Individual profiles are examined by
oceanographers to identify different water masses, which have originated
from such distant regions as the Labrador Sea, the Mediterranean, the Western
Atlantic, and to compare their characteristics (temperature, salinity, depth,
thickness) to older measurements. This
is one way to learn about ocean circulation and climate change; ·
The displacement of a float between the times it
comes back to the surface is a valuable indication of ocean currents at
depth; ·
The data can be combined to obtain maps of
ocean temperature and salinity at regular time intervals; ·
The data is combined with other observations (from
ships, buoys, satellites) and with numerical models to obtain analysis and
forecasts of oceanic conditions (circulation, temperature).
This is similar to the way weather forecasts are made by National Weather
Services Why are temperature and salinity
important ?
The ocean receives from the Sun, and exchanges with the atmosphere, huge amounts of heat. The ocean plays an important role in the Earth climate by storing, releasing or transporting to large distances that heat. Monitoring temperature variations at different depths gives a measure of those interactions. Salinity is the relative amount of salt in sea water; salinity changes whenever the ocean exchanges water with the atmosphere through rain (precipitation) or evaporation. Temperature and salinity combine to determine the density (or
specific mass) of the water: relatively warm or fresh water tends to be light
and to be found in the upper layers, relatively cold or salty water tends to be
heavier and to be found in the deeper parts of the ocean. Water
masses that originate in different ocean regions are characterized by specific
temperature – salinity relationships, and move along depth surfaces where they
mix very little. Observing
temperature and salinity allows to track the water masses and their circulation. The
pressure in the ocean is
found by the weight of the water above a given depth, that is by the
total density of the water column. Differences
in pressure between different locations give rise to ocean currents: that is
another way temperature and salinity give information on ocean currents. What happens to the floats at
the end of their mission ?
The European Community is dedicated to sound environmental practices and
the potential impact of the floats on the environment is a legitimate concern.
ARGO floats are meant to be expendable, so that at the end of their mission they
will usually sink to the ocean bottom. Floats have very little residual value
for re-use at the end of their mission. Nearly all floats will end their mission
at depth, gradually sinking to the sea bottom, where they will be crushed by the
ambient pressure. (If 600 floats are released in the Atlantic ocean, and ¼ sink
every year, this is equivalent to one float over an area the size of France or
Spain). Most (nearly 90%) of the float mass is aluminium, which
will eventually corrode to form harmless, soluble, aluminium oxide. The amount
of materials left in the sea will be minuscule compared to other, mostly
military and commercial operations, using similar materials. Indeed, each 35 kg float will replace more than 100 kg of (presently
deployed) Expendable Bathythermographs, hence resulting in a net savings of
unrecoverable material. A
very small percentage will find their way ashore.
Any reaching the coast may be picked up easily for proper storage
procedures until pick-up. A sticker will be affixed on the float to advise on
the procedure. As
the floats are rather small (typically 1.80 m, weighing about 35 kg), and as
they spend very little time on the surface, they do not present any danger to
navigation.. The small footprint of Argo floats in the environment is greatly outweighed by their critical and irreplaceable benefits in observing the evolving physical state of the ocean.
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