sea foam
282
The large-scale sea-floor topography reflects the structure of the earth's
crust. The continental slope marks, in a general way, the boundary between
the lighter continental crust and the heavier oceanic crust. The trenches
mark subduction zones where a plate edge is moving downward below an
adjacent plate. The absence of trenches, (e.g., in the Atlantic Ocean) marks the
presence of passive ocean margins. Mid-ocean ridges are spreading areas where
new crust is formed at a rate of 1 to 6 cm y-I. The sea floor is younger than
ca. 150 million years, while on the continents rocks from 3.5 billion years ago
have been preserved.
sea foam along coasts, especially on beaches, sea foam is a regularly occurring
appearance in spring and summer. Such foam is formed during the degradation of algal blooms, particular of the mucus of colony-forming algae like
Phaeocystis (~Prymnesiophyta), and is blown onto the beaches at the end of the
bloom period. Some foam formation occurs throughout the year, also during winter, in the absence of algal blooms.
sea grass (syn. eel grass) the only organisms belonging to the kingdom Plantae
(angiosperms) that are adapted to living submerged in the sea (this separates them from plants on salt marshes and in mangrove swamps). They are not
true grasses, but belong to the order Helobiae, and are related to pondweeds
(Potamogeton). They grow in the euphotic zone, usually in shallow subtidal
waters, but in clear Mediterranean water Posidonia occurs down to 40 m
depth and Halophila in the Caribbean even down to 80 m. Sea grass communities occur all over the world and have a characteristic associated fauna,
many algae occurring as epiphytes on the sea-grass leaves. Sea grasses act as
sediment collectors and binders and help prevent coastal erosion. The name
sea grass refers to the grass-like leaves in one of the best-known genera,
Zostera.
sea ice any ice originating from the freezing of seawater (thus excluding icebergs). ~ice.
sea level as the sea level varies because of waves, tides, wind effects, seasonal
variation and long-time processes, the sea level has to be defined as a mean
over a certain time (often 19 years). The sea level is observed with tide
gauges that already filter out higher frequencies, and the results are usually
averaged over months or years (mean sea level). This determination gives a
relative position of the sea level with respect to the measuring site, and both
real sea-level changes and sinking or upheaval of the site (e.g., by compaction of sediments, by tectonic or isostatic movements of the bedrock)
may have their influence. Because of density differences and currents the sea
level normally does not coincide with a horizontal plane (~geoid). Sea-level
slopes may be related to geostrophic motions. In the long term, the absolute
282
The large-scale sea-floor topography reflects the structure of the earth's
crust. The continental slope marks, in a general way, the boundary between
the lighter continental crust and the heavier oceanic crust. The trenches
mark subduction zones where a plate edge is moving downward below an
adjacent plate. The absence of trenches, (e.g., in the Atlantic Ocean) marks the
presence of passive ocean margins. Mid-ocean ridges are spreading areas where
new crust is formed at a rate of 1 to 6 cm y-I. The sea floor is younger than
ca. 150 million years, while on the continents rocks from 3.5 billion years ago
have been preserved.
sea foam along coasts, especially on beaches, sea foam is a regularly occurring
appearance in spring and summer. Such foam is formed during the degradation of algal blooms, particular of the mucus of colony-forming algae like
Phaeocystis (~Prymnesiophyta), and is blown onto the beaches at the end of the
bloom period. Some foam formation occurs throughout the year, also during winter, in the absence of algal blooms.
sea grass (syn. eel grass) the only organisms belonging to the kingdom Plantae
(angiosperms) that are adapted to living submerged in the sea (this separates them from plants on salt marshes and in mangrove swamps). They are not
true grasses, but belong to the order Helobiae, and are related to pondweeds
(Potamogeton). They grow in the euphotic zone, usually in shallow subtidal
waters, but in clear Mediterranean water Posidonia occurs down to 40 m
depth and Halophila in the Caribbean even down to 80 m. Sea grass communities occur all over the world and have a characteristic associated fauna,
many algae occurring as epiphytes on the sea-grass leaves. Sea grasses act as
sediment collectors and binders and help prevent coastal erosion. The name
sea grass refers to the grass-like leaves in one of the best-known genera,
Zostera.
sea ice any ice originating from the freezing of seawater (thus excluding icebergs). ~ice.
sea level as the sea level varies because of waves, tides, wind effects, seasonal
variation and long-time processes, the sea level has to be defined as a mean
over a certain time (often 19 years). The sea level is observed with tide
gauges that already filter out higher frequencies, and the results are usually
averaged over months or years (mean sea level). This determination gives a
relative position of the sea level with respect to the measuring site, and both
real sea-level changes and sinking or upheaval of the site (e.g., by compaction of sediments, by tectonic or isostatic movements of the bedrock)
may have their influence. Because of density differences and currents the sea
level normally does not coincide with a horizontal plane (~geoid). Sea-level
slopes may be related to geostrophic motions. In the long term, the absolute