GLOSSARY - Introduction to the Physical and Biological Oceanography of Shelf Seas - page 373

Ekman depth Depth of the water column
influenced by a stress imposed at surface or
bottom boundaries. The Ekman depth can
be related to the magnitude of the imposed
stress and the Coriolis parameter.
Ekman drain Downslope transport in the
bottomboundary layer inducedby friction in
an along-slope current moving with the shelf
to the right/left of the direction of motion
in the northern/southern hemisphere.
Ekman layer Section of the water column
influenced by a boundary stress. A stress,
imposed, for example, at the surface by
the wind, diminishes rapidly with depth so
that its influence is confined to a near-
surface layer whose thickness is the
Ekman depth.
Ekman number

equations of motion The rules of fluid
motion based on Newton's laws and the
principle of continuity.
Equilibrium theory of the tides The simplest
theory of the tides which involves a balance
between the tide generating force and the
surface slope of a uniform ocean covering
the whole Earth. This basic model of the
tides was used by Isaac Newton to explain
many of the qualitative features of the
observed tides.
eukaryotes (eukaryotic) Cells, or organisms
made up of cells, that contain a cell nucleus
enclosed in a membrane.
Eulerian current Velocity measured over

time at a fixed point as distinct from the
Lagrangian current which is measured
following a particle of water.
euphotic zone (see photic zone)
eutrophication (eutrophic)

Ratio of frictional forces to
Coriolis forces in fluid flow.
Ekman spiral Idealised form of velocity
profile induced by a steady wind blowing
over a homogeneous unbounded ocean.
The current, which at the surface is
deflected 45 to the right/left of the wind
direction, rotates clockwise/anticlockwise
in the northern/ southern hemisphere and
diminishes exponentially with increasing
depth.
Ekman transport The depth integrated
transport induced by a steady wind
blowing over a homogeneous unbounded
ocean. The Ekman transport is at 90 to
right/left of the wind direction in the
northern/southern hemisphere.
Ekman veering Deflection of a geostrophic
current near the seabed as the current
begins to slow due to the frictional drag at
the seabed boundary.
energy cascade

The addition of
nutrients, generally nitrates and
phosphates, to water leading to excessive
growth of phytoplankton. In coastal seas
these extra nutrients are largely derived
from the runoff of agricultural fertilizers
and sewage disposal. Subsequent decay of
the large amounts of phytoplankton can
reduce dissolved oxygen concentrations in
the water. (See also hypoxia.)
export production The amount of carbon
fixed by the autotrophs in the photic zone,
which sinks, or is otherwise transported,
below the thermocline to deeper water or
the sediments. If a steady state is assumed,
export production is the same as new
production.
export ratio

The fraction of carbon fixed by
the autotrophs that is exported to waters
below the winter thermocline, and thus
removed from the surface ocean and
atmosphere for a long time.
f-ratio

Process of kinetic energy
transfer from larger to progressively
smaller scales. The motion at the largest
scales in a fluid flow generates eddies which
lose energy to smaller eddies which, in turn,
power even-smaller eddies and so on,
through many steps, until the scale is so
small that viscosity becomes important and
the turbulent energy is dissipated to heat.

The fraction of total autotroph
primary production, which is supported
by a supply of new nutrients, rather
than utilising recycled nutrients. It is the
ratio of new production to total
production.