gases, dissolved
136
gases, dissolved a useful assumption in chemical oceanography is that at some
time any parcel of water in the world's ocean has been at the sea surface, and
become equilibrated with atmospheric gases. Therefore equilibrium concentrations are defined at atmospheric pressure and not at in situ pressure.
According to Henry's Law, which holds for nonreactive gases, the equilibrium concentration (c) at a certain temperature in a liquid is proportional to
its partial pressure (p) in the gas phase: c=exp. The solubility coefficient ex is
characteristic of the gas; it decreases with increasing temperature and with
increasing salinity. The distribution of the concentration of gases in the
oceans are governed by the global (meridional) water circulation, by the
meridional temperature differences at the surface and, for gases like oxygen,
by in situ processes which consume or produce the gas involved.
gases, in air the total pressure of the atmospheric gases at sea level approaches
105 N m- 2 (l atm). The components (except for water vapor) in volume
percentages are for N 2 : 78.084 ± 0.004; 02: 20.946 ± 0.002; Ar: 0.934 ± 0.001;
CO 2 : 0.033 ± 0.001 and expressed in ppm volume for: neon 18.18 ± 0.04;
helium: 5.24 ± 0.004; krypton: 1.14 ± 0.01; xenon: 0.087 ± 0.001; H 2 : 0.5;
CH 4 : 2; N 2 0: 0.5 ± 0.1.
gastric digestion the process of food digestion in stomach and intestines (gastric
system) of animals.
Gastropoda (gastropods, snails) class of the phylum Mollusca. The shell, unlike that
of the Bivalvia, is an asymmetrical spiral, the axis of which is the columella;
the shell may be lost secondarily. When crawling on the extended foot and
feeding, the gastropod carries the shell; when disturbed, the body may be
completely withdrawn into the shell. For a majority of marine species the
shell can be closed with a corneous or calcareous lid (operculum), which sits
on the hind part of the foot. The head has in principle two tentacles and two
primitive eyes, and the mouth has a radula. Gastropods live on land, in freshwater, and in the sea, benthic as well as pelagiC, and are the most successfully
developed group of mollusks. They are divided according to the type and
position of gills into five subclasses: Prosobranchia (gills at the front),
Opisthobranchia (gill lateral or caudal), Heterobranchia, Gymnomorpha, and
Pulmonata (gills absent, lung developed from mantle), with marine snails
among all types. The abundance of gastropods as fossils is enormous; but
there are even more recent species known (ca. 40 000).
Gastrotricha phylum of microscopic aquatic Aschelminthes. The body is worm-like to
tenpin-shaped, but unsegmented, and often scales, spines or hooks are present. The gut is simple. Locomotion by cilia. They live mostly interstitially in bottom sediments in marine, brackish and moist areas. Hermaphrodite or parthenogenetic. May be confused with Ciliophora, and superficially also resemble Rotifera.
136
gases, dissolved a useful assumption in chemical oceanography is that at some
time any parcel of water in the world's ocean has been at the sea surface, and
become equilibrated with atmospheric gases. Therefore equilibrium concentrations are defined at atmospheric pressure and not at in situ pressure.
According to Henry's Law, which holds for nonreactive gases, the equilibrium concentration (c) at a certain temperature in a liquid is proportional to
its partial pressure (p) in the gas phase: c=exp. The solubility coefficient ex is
characteristic of the gas; it decreases with increasing temperature and with
increasing salinity. The distribution of the concentration of gases in the
oceans are governed by the global (meridional) water circulation, by the
meridional temperature differences at the surface and, for gases like oxygen,
by in situ processes which consume or produce the gas involved.
gases, in air the total pressure of the atmospheric gases at sea level approaches
105 N m- 2 (l atm). The components (except for water vapor) in volume
percentages are for N 2 : 78.084 ± 0.004; 02: 20.946 ± 0.002; Ar: 0.934 ± 0.001;
CO 2 : 0.033 ± 0.001 and expressed in ppm volume for: neon 18.18 ± 0.04;
helium: 5.24 ± 0.004; krypton: 1.14 ± 0.01; xenon: 0.087 ± 0.001; H 2 : 0.5;
CH 4 : 2; N 2 0: 0.5 ± 0.1.
gastric digestion the process of food digestion in stomach and intestines (gastric
system) of animals.
Gastropoda (gastropods, snails) class of the phylum Mollusca. The shell, unlike that
of the Bivalvia, is an asymmetrical spiral, the axis of which is the columella;
the shell may be lost secondarily. When crawling on the extended foot and
feeding, the gastropod carries the shell; when disturbed, the body may be
completely withdrawn into the shell. For a majority of marine species the
shell can be closed with a corneous or calcareous lid (operculum), which sits
on the hind part of the foot. The head has in principle two tentacles and two
primitive eyes, and the mouth has a radula. Gastropods live on land, in freshwater, and in the sea, benthic as well as pelagiC, and are the most successfully
developed group of mollusks. They are divided according to the type and
position of gills into five subclasses: Prosobranchia (gills at the front),
Opisthobranchia (gill lateral or caudal), Heterobranchia, Gymnomorpha, and
Pulmonata (gills absent, lung developed from mantle), with marine snails
among all types. The abundance of gastropods as fossils is enormous; but
there are even more recent species known (ca. 40 000).
Gastrotricha phylum of microscopic aquatic Aschelminthes. The body is worm-like to
tenpin-shaped, but unsegmented, and often scales, spines or hooks are present. The gut is simple. Locomotion by cilia. They live mostly interstitially in bottom sediments in marine, brackish and moist areas. Hermaphrodite or parthenogenetic. May be confused with Ciliophora, and superficially also resemble Rotifera.