significant wave height
294
significant wave height is used to characterize a wave field. The significant wave
height is defined as the average of the highest one-third of the waves in a
record. It appears that a trained observer visually estimating the average
wave height actually estimates the significant wave height by eliminating the
smaller perturbations of the sea level. The significant wave height is a measure of wave energy.
silicates are salts of silicic acid H 4 Si0 4 • This very weak acid (pK = 9.66) occurs in
all natural waters mainly as the undissociated molecule, which has a solubility of about 900 mmol m- 3 at 0 °C and of 1500 mmol m- 3 at 200 °C.Alternative
names for silicic acid are dissolved silica and reactive silicate. The anion has
a tetrahedral structure; it easily polymerizes in one, two or three directions.
The three-dimensional polymer is called silica; when amorphous it contains
water, the stable form of silica is quartz. Especially Al may substitute for Si in
silicates. This property and the ease of polymerization explain the many different types of silicates present in rocks and clay minerals.
siliceous ooze ~ooze.
silicoflagellates belong to the Dictyochophyceae, a class of the phylum Chrysophyta.
Silica-secreting marine microplanktonic flagellates (early Cretaceous to
present), cosmopolitan, autotrophic, with single flagellum, unicellular. Useful in
biostratigraphy and paleoclimatology (esp. late Cenozoic, ~geological time scale),
especially in high latitudes. ~microfossil.
silicon (Si) is, after oxygen, the most abundant element in the earth crust. It always
occurs in compounds, mainly with oxygen (~silicates). There are three stable
isotopes, 28Si (92.21 %), 29Si (4.7 %), and 30Si (3.09 %). The beta emitter 32Si is
formed by interaction of high-energy cosmic rays with argon in the atmosphere. This isotope has found some use in the dating of sediments and in
circulation studies of groundwater, lakes, and oceans. The activity is
extremely low and only sediments with high amounts of biogenic silica
(Si0 2 ) can be dated. Artificially prepared isotopes have a very short half-life
(31Si, 2.62 h), which limits their use to tracer studies of short duration. Also
mixtures of different isotopic composition (artificially prepared) are used in
tracer studies.
sill lowest point on a submarine ridge or saddle at a relatively shallow depth,
separating a basin from an adjacent sea or another basin. ~sea-f1oortopography.
silt ~grain size.
Silurian ~geological time scale.
294
significant wave height is used to characterize a wave field. The significant wave
height is defined as the average of the highest one-third of the waves in a
record. It appears that a trained observer visually estimating the average
wave height actually estimates the significant wave height by eliminating the
smaller perturbations of the sea level. The significant wave height is a measure of wave energy.
silicates are salts of silicic acid H 4 Si0 4 • This very weak acid (pK = 9.66) occurs in
all natural waters mainly as the undissociated molecule, which has a solubility of about 900 mmol m- 3 at 0 °C and of 1500 mmol m- 3 at 200 °C.Alternative
names for silicic acid are dissolved silica and reactive silicate. The anion has
a tetrahedral structure; it easily polymerizes in one, two or three directions.
The three-dimensional polymer is called silica; when amorphous it contains
water, the stable form of silica is quartz. Especially Al may substitute for Si in
silicates. This property and the ease of polymerization explain the many different types of silicates present in rocks and clay minerals.
siliceous ooze ~ooze.
silicoflagellates belong to the Dictyochophyceae, a class of the phylum Chrysophyta.
Silica-secreting marine microplanktonic flagellates (early Cretaceous to
present), cosmopolitan, autotrophic, with single flagellum, unicellular. Useful in
biostratigraphy and paleoclimatology (esp. late Cenozoic, ~geological time scale),
especially in high latitudes. ~microfossil.
silicon (Si) is, after oxygen, the most abundant element in the earth crust. It always
occurs in compounds, mainly with oxygen (~silicates). There are three stable
isotopes, 28Si (92.21 %), 29Si (4.7 %), and 30Si (3.09 %). The beta emitter 32Si is
formed by interaction of high-energy cosmic rays with argon in the atmosphere. This isotope has found some use in the dating of sediments and in
circulation studies of groundwater, lakes, and oceans. The activity is
extremely low and only sediments with high amounts of biogenic silica
(Si0 2 ) can be dated. Artificially prepared isotopes have a very short half-life
(31Si, 2.62 h), which limits their use to tracer studies of short duration. Also
mixtures of different isotopic composition (artificially prepared) are used in
tracer studies.
sill lowest point on a submarine ridge or saddle at a relatively shallow depth,
separating a basin from an adjacent sea or another basin. ~sea-f1oortopography.
silt ~grain size.
Silurian ~geological time scale.