Geoscience Reference
In-Depth Information
Arctic, such as the Bering Sea, the waters are very fresh (20 g of
salt/kg).
One characteristic property of a fluid is its volumic mass. That of the
ocean depends on three quantities: temperature, salinity and pressure.
The volumic mass of seawater varies between 1,022 and 1,029 kg/m
3
with an average value of 1,025 kg/m
3
, which is around 1,000 times the
volumic mass of air. The anomaly of volumic mass is usually
introduced, which corresponds to the difference in volumic mass
between seawater and fresh water: σ = ρ - ρ
0
= ρ - 1,000 kg/m
3
. This
quantity is generally called “density”, surfaces with equal density in
the ocean are called isopycns.
The oceans' thermal capacity is much larger than that of air: the
top two meters of the ocean have a thermal capacity equivalent to that
of the entire column of air above them. Because of weight and thermal
inertia, oceans leave a very special mark on changes in the climate.
2.3.1.
Rotation, Coriolis, geostropy
Like all points on Earth, the oceans spin east because of their
rotation around the axis of the poles. Each point possesses an intrinsic
speed of rotation to the east, which depends on its distance from the
axis of the poles. This speed is maximal at the equator, then decreases
progressively to cancel out at the poles. The existence of this rotation
speed dependent on latitude affects the trajectory of fluid masses.
Thus, a mass of water that moves from the North Pole toward the
Equator will have a rotation speed to the east that is weaker than the
surrounding masses: it will veer toward the west on its right relative to
the surrounding milieu. Similarly, a mass of water moving from the
Equator toward the North Pole, will have a rotation speed greater than
the surrounding masses and will veer toward the east, to its right. The
Earth's rotation imposes a spin toward the right on all movement
occurring in the northern hemisphere and reciprocally, toward the left
in the southern hemisphere. This spin causes a complementary
acceleration, orthogonal to the trajectory, which is called Coriolis
acceleration. The force that this engenders does not work and manifests
itself only for a moving mass. We will designate the Coriolis
