89
density
with the gravitational restoring forces. It equals the (long-) wave velocity
divided by the Coriolis parameter. It is of the order of 100 to 1000 km for surface
waves (depending on the sea depth), but it can become smaller (order 10
km) for baroclinic internal waves, where the internal phase speed is the pertinent velocity scale.
delta accumulation of river-supplied sediment deposited at the coast where a
stream decelerates by entering a large body of water. The stream may be of
any size, and the outflow may be into an ocean gulf, a lagoon, an estuary or
a lake. The term "delta" originated with Herodotus (5th century B.C.), who
described the triangular plain of river alluvium at the Nile river mouth,
broadly resembling the Greek capital letter delta (d). Other types of deltas
that have no triangular form are also called deltas, the best-known being the
Mississippi river delta, which has a "bird-foot" configuration with extended
lobes and digitate tributaries. Deltas show a large variety of morphological
and depositional features, reflecting variations in river discharge regime,
coastal (marine) energy conditions, and geological structure: deltas are
complexes of river mouths, distributary channels, flats, bays, swamps,
beaches, beach ridges, and dunes. The delta plain is the subaereal part of the
delta. Usually a lower delta plain can be distinguished, extending inland to
the limit of tidal influence; further landward is the upper delta plain. The
subaqueous part can be divided into a basal prodelta, consisting of more or
less horizontal layers of primarily fine silts and clays deposited from suspension, and a delta front of coarser sediment including river mouth bar
sands, tidal ridges, and beach deposits.
demersal organisms bottom-dwelling aquatic organisms, e.g., demersal fish, in
contrast to pelagic organisms, which live in the water column.
Demospongiae class of the phylum Porifera (sponges) with a skeleton of spongin
(horny) fibers and/or siliceous spicules which are never six-rayed. Flagellate
collar cells (choanocytes) are situated in small and rounded chambers. Most
sponges belong to this dominant and widely distributed class; they occur
both in freshwater and in the sea. Well known is the bath-sponge, Spongia.
denitrification the conversion of nitrate by bacteria into nitrogen gas, resulting
in the loss of nitrogen from ecosystems. This process occurs mainly in anaerobic systems but is also possible in aerobic systems.
density (1) (phys.) the mass per unit of volume (symbol p). In olderliterature
this physical property is also called specific weight. The density of seawater
has been determined empirically as a function of temperature, salinity and
pressure, the equation of state. This empirical relation is given as a polynomial
expression. Since the density of seawater is only slightly larger than 1000 kg
density
with the gravitational restoring forces. It equals the (long-) wave velocity
divided by the Coriolis parameter. It is of the order of 100 to 1000 km for surface
waves (depending on the sea depth), but it can become smaller (order 10
km) for baroclinic internal waves, where the internal phase speed is the pertinent velocity scale.
delta accumulation of river-supplied sediment deposited at the coast where a
stream decelerates by entering a large body of water. The stream may be of
any size, and the outflow may be into an ocean gulf, a lagoon, an estuary or
a lake. The term "delta" originated with Herodotus (5th century B.C.), who
described the triangular plain of river alluvium at the Nile river mouth,
broadly resembling the Greek capital letter delta (d). Other types of deltas
that have no triangular form are also called deltas, the best-known being the
Mississippi river delta, which has a "bird-foot" configuration with extended
lobes and digitate tributaries. Deltas show a large variety of morphological
and depositional features, reflecting variations in river discharge regime,
coastal (marine) energy conditions, and geological structure: deltas are
complexes of river mouths, distributary channels, flats, bays, swamps,
beaches, beach ridges, and dunes. The delta plain is the subaereal part of the
delta. Usually a lower delta plain can be distinguished, extending inland to
the limit of tidal influence; further landward is the upper delta plain. The
subaqueous part can be divided into a basal prodelta, consisting of more or
less horizontal layers of primarily fine silts and clays deposited from suspension, and a delta front of coarser sediment including river mouth bar
sands, tidal ridges, and beach deposits.
demersal organisms bottom-dwelling aquatic organisms, e.g., demersal fish, in
contrast to pelagic organisms, which live in the water column.
Demospongiae class of the phylum Porifera (sponges) with a skeleton of spongin
(horny) fibers and/or siliceous spicules which are never six-rayed. Flagellate
collar cells (choanocytes) are situated in small and rounded chambers. Most
sponges belong to this dominant and widely distributed class; they occur
both in freshwater and in the sea. Well known is the bath-sponge, Spongia.
denitrification the conversion of nitrate by bacteria into nitrogen gas, resulting
in the loss of nitrogen from ecosystems. This process occurs mainly in anaerobic systems but is also possible in aerobic systems.
density (1) (phys.) the mass per unit of volume (symbol p). In olderliterature
this physical property is also called specific weight. The density of seawater
has been determined empirically as a function of temperature, salinity and
pressure, the equation of state. This empirical relation is given as a polynomial
expression. Since the density of seawater is only slightly larger than 1000 kg