GLOSSARY - Introduction to the Physical and Biological Oceanography of Shelf Seas - page 374

Fick's law The diffusive flux of a scalar is
proportional to the gradient of the scalar
and in the down-gradient direction.
flagellate A single-celled eukaryotic
phytoplankton, typically a few to O(10) m m
diameter. The term generally refers to any
organism that uses one or more whip-like
flagella for locomotion (e.g. as in
dinoflagellate). In marine studies there is a
tendency to use 'flagellate' to refer to cells
with one whip-like flagella, usually smaller
than dinoflagellates. Flagellates can be
autotrophic, heterotrophic or mixotrophic.
flux Richardson number R f The ratio of the
buoyancy flux to the rate of turbulent
kinetic energy production in stratified
shear flow. R f can be thought of as an
'efficiency of mixing'.
frontal jet

phytoplankton within an autotrophic
community.
gross primary production The rate at which
the autotrophs fix inorganic carbon. It
includes the carbon fixation that is later
used in cellular respiration. (See also net
primary production.)
group velocity Waves tend to travel in
groups which advance at the group
velocity. It is important because it is also
the speed at which waves transport their
energy.
harmonic method Analysis of tidal data in
terms of a sum of sine waves (tidal
constituents) at different frequencies set by
the regular motions of the Sun and Moon.
The amplitude and phase of the
constituents, determined from the data
analysis, are used to construct the sum of
constituents for future times and thus
predict the tides.
heterotrophs (heterotrophic) Organisms that
cannot fix inorganic carbon, but instead
need to consume other organisms
(autotrophs or heterotrophs) in order to
acquire the organic compounds needed
for growth.
hydrostatic approximation A balance in the
vertical direction between pressure forces
and gravity which requires that vertical
accelerations can be neglected. The
hydrostatic approximation is generally
applicable to slowly varying processes in
the ocean but is not valid at high
frequencies, for example in surface waves
and short period internal waves, both of
which may involve large vertical
accelerations.
hypoxia (hypoxic)

A core of high-velocity flow
located in the baroclinic region of an
oceanographic front.
gelbstoff Literally 'yellow stuff', also known
as Coloured Dissolved Organic Matter
(CDOM) and 'gilvin'. Gelbstoff refers to a
collection of dissolved organic compounds,
mainly tannins arising from the decay of
organic material.
geostrophic flow or current In geostrophic
flow, there is a balance between Coriolis
and pressure forces which requires that the
flow direction is at right angles to the
pressure gradient. This simple balance is
applicable to much of the flow in the deep
ocean and the atmosphere and can be
applied in many situations in shelf seas.
global overturning circulation Large-scale
circulation of the global ocean involving
sinking near the poles and slow upwelling
in lower latitudes. Also referred to as the
'meridional overturning circulation'.
gradient Richardson number Ri

Water is hypoxic if the
dissolved oxygen concentration drops
below 30% of its saturated value, or
typically less than 2 mg l 1 . Water with a
dissolved oxygen concentration of 0% is
referred to as anoxic. (See also
eutrophication.)
inertial oscillation Circular motion in which
there is a balance between Coriolis force

A measure
of the ratio of water column stability to the
kinetic energy available to drive mixing. Ri
is important in deciding whether
turbulence and mixing will occur.
gross community production The gross
primary production achieved by all