sea stars
284
currents. Nevertheless, in the mediterranean, temperate, and boreal regions,
most biological and temperature-dependent physical and chemical processes follow the annual cycle of seasons. Examples may be growth rates of algae
and of the animals feeding on algae; the reproduction cycles related with
energy supply to the parent and survival conditions for the brood; migrations between feeding grounds, spawning grounds, and overwintering quarters, and many other biological events in the sea that are all governed by the
seasons. In tropical areas seasonal variation are related to the monsoon.
sea stars ~Asteroidea.
sea truth in order to interpret information obtained by means of remote sensing,
it is often necessary to apply a restricted number of observations made at
sea of the parameters actually studied, the so-called sea truth.
sea urchins ~E(hinoidea.
seawater covers 70 % of the earth's surface. It is saline because it contains different dissolved ions such as those of chlorine, bromine, sulfate, sodium,
potassium, magnesium, calcium. The content may vary according to the
addition (by rivers or precipitation) or extraction (by evaporation or freezing of seawater) of freshwater. The oceans have an almost constant composition of salts, which only differs proportionally with the addition of freshwater. For the conservative elements sea salt is composed of 30.7 % Na+, 1.2 %
Ca2+, and 1.1 % K+ as major cations, and 55.1 % CI- and 7.7 % 50 4 2- as
anions. The salt content is expressed in the so-called salinity, symbol 5, that is
defined on the basis of this constant composition. It is believed that the composition of seawater salt has remained constant over the last 400 million
years. On the basis of S and potential temperature, water masses can be characterized, and their density determined. Seawater composition has similarities
with that of the blood of living organisms. Hence there is little difference in
osmotic pressure between seawater and blood of marine organisms.
Physical properties of seawater such as density or compressibility depend on
salinity, temperature and pressure, and are calculated from these quantities
with standard tables (~thermodynamics). For accurate determination of the
salinity standard seawater is made available as a reference.
seawater sampler a device for taking water samples. The usual types are lowered
on a wire, and closed at a certain depth by means of an electrical or mechanical pulse. The seawater sampler that has been used most commonly in the
past is the mechanically triggered Nansen bottle. Since the introduction of electrical instruments like the CTD recorder electro-mechanically triggered Niskin
bottles have come into use. Often 12 or 24 of such bottles are mounted in a
rosette sampler which can be combined with a CTD recorder.
284
currents. Nevertheless, in the mediterranean, temperate, and boreal regions,
most biological and temperature-dependent physical and chemical processes follow the annual cycle of seasons. Examples may be growth rates of algae
and of the animals feeding on algae; the reproduction cycles related with
energy supply to the parent and survival conditions for the brood; migrations between feeding grounds, spawning grounds, and overwintering quarters, and many other biological events in the sea that are all governed by the
seasons. In tropical areas seasonal variation are related to the monsoon.
sea stars ~Asteroidea.
sea truth in order to interpret information obtained by means of remote sensing,
it is often necessary to apply a restricted number of observations made at
sea of the parameters actually studied, the so-called sea truth.
sea urchins ~E(hinoidea.
seawater covers 70 % of the earth's surface. It is saline because it contains different dissolved ions such as those of chlorine, bromine, sulfate, sodium,
potassium, magnesium, calcium. The content may vary according to the
addition (by rivers or precipitation) or extraction (by evaporation or freezing of seawater) of freshwater. The oceans have an almost constant composition of salts, which only differs proportionally with the addition of freshwater. For the conservative elements sea salt is composed of 30.7 % Na+, 1.2 %
Ca2+, and 1.1 % K+ as major cations, and 55.1 % CI- and 7.7 % 50 4 2- as
anions. The salt content is expressed in the so-called salinity, symbol 5, that is
defined on the basis of this constant composition. It is believed that the composition of seawater salt has remained constant over the last 400 million
years. On the basis of S and potential temperature, water masses can be characterized, and their density determined. Seawater composition has similarities
with that of the blood of living organisms. Hence there is little difference in
osmotic pressure between seawater and blood of marine organisms.
Physical properties of seawater such as density or compressibility depend on
salinity, temperature and pressure, and are calculated from these quantities
with standard tables (~thermodynamics). For accurate determination of the
salinity standard seawater is made available as a reference.
seawater sampler a device for taking water samples. The usual types are lowered
on a wire, and closed at a certain depth by means of an electrical or mechanical pulse. The seawater sampler that has been used most commonly in the
past is the mechanically triggered Nansen bottle. Since the introduction of electrical instruments like the CTD recorder electro-mechanically triggered Niskin
bottles have come into use. Often 12 or 24 of such bottles are mounted in a
rosette sampler which can be combined with a CTD recorder.