GLOSSARY - Introduction to the Physical and Biological Oceanography of Shelf Seas - page 375

acting on a water particle and the particle's
radial acceleration. The motion is in the
clockwise/anticlockwise sense in the
northern/southern hemisphere. Inertial
oscillations occur widely in the ocean,
especially near the surface in response to
changes in wind stress.
inertial period T I The period of an inertial
oscillation is the time required for a particle
to travel around a circle and is given by
T I ¼ 2p /f where f ¼ Coriolis parameter.
inertial subrange The middle section of the
turbulence spectrum, between the low-wave-
number (large eddy) part and the high-wave
number (small scale) part where energy is
dissipated to heat by viscous forces.
infinitesimal waves

scale depend only on the rate of energy
dissipation and the viscosity.
Lagrangian current Velocity measured over
time following a particle as opposed to the
Eulerian velocity which is measured at a
point.
Langmuir circulation Transverse circulation
in the surface layer set up by wind-driven
waves, often visible as parallel lines of
surface foam (called 'windrows') aligned
with the wind direction.
level of no motion Level in the water column
at which it is known, or can be assumed,
that there is no water movement.
limiting nutrient Phytoplankton require a

range of macronutrients and
micronutrients in order to grow. If a
nutrient reaches concentrations low
enough for it to be unavailable to the
phytoplankton, despite other nutrients
being in useable quantities, it is referred to
as the limiting nutrient. In temperate shelf
seas, nitrate tends to be the limiting
nutrient following the spring bloom.
local equilibrium (of turbulence) A simplified
version of the turbulent kinetic energy
equation in which it is assumed that only
the production and dissipation terms are
important. There is, therefore, a local
equilibrium in which production and
dissipation balance at each point in the
fluid.
macronutrients The nutrients required by
the phytoplankton in relatively large
quantities. The key macronutrients are
nitrate, phosphate and (for the diatoms)
silicate. Ammonium can also be included
as a source of nitrogen.
match-mismatch hypothesis

Waves of very small
(tending to zero) amplitude. The linear
theory of wave motions is based on the
assumption of infinitesimal waves but can
usually be applied to waves of finite height
without serious errors providing the waves
are not too steep.
internal Rossby radius Ro 0 A patch of
homogeneous fluid embedded in a
stratified water column will spread a
distance of order Ro 0 before coming into
geostrophic balance. This length scale is
important, for example, in controlling the
extent of a region of coastal upwelling.
internal tide Internal waves of tidal
frequency involving vertical oscillations of
the pycnocline. The internal tide is
generated principally by the barotropic tide
forcing stratified fluid to move over steep
topography.
Kelvin waves

Long waves which are
influenced by the Earth's rotation. They
travel along land boundaries and diminish
exponentially in amplitude away from the
coast.
Kolmogorov microscales

The hypothesis,
originally proposed by fisheries scientist
David Cushing, that higher trophic levels
in the marine food chain may need to time
their breeding with the flush of
phytoplankton at the spring bloom.
maximum quantum yield of
photosynthesis Parameter which describes
the maximum rate of carbon fixation via

In turbulent
motions, energy dissipation to heat
becomes increasingly important for eddies
whose scale is equal to or less than the
Kolmogorov microscale. This length
microscale and the corresponding velocity