'
\
Glossary
237
TERRIGENOUS DEPOSITS: composedpredominany of material from—the
land.
cover practically all of the.continental shelf
region
_
…
THERMOCLINE: region in the sea where the temperature differs markedly
…
from water either above or below it. The existence of a thermocline,
either seasonal or permanent, has important implications for biological
productivity as well as the use of sonar———see pages 29 and 205
ÀÏ É
TIDAL WAVE—see tsunami
'
TIDES: product of the astronomical forces of sun and moon acting on the
î
rotating Earth. When the two heavenly bodies pull together or are
‘
diametrically Opposed the dal currents show their greatest range—
the spring tides. When their forces act at right angles to one another
the tidal current has its shortest range—the neap tides. Thus, in
every lunar month there are two spring tides and two neap tides With
gradations between them according to the phase” of the moon—see
page 138
‘
-_
TRAWL: a shing net pulled along through the
One of the rst
î
trawls was the beam trawl, a cumbersome piece of gear which had a
'
heavy cross piece to keep the mouth open. The most important development came with the use of otter boards, ‘kite—like’ structures placed on
“ _
either side of the trawl, which shéared away from eaCh other to keep
‘
the mouth of the net wide open. Both beam and otter trawl were
;
designed for càtÇhing demersal sh: they are dragged Over the sea
oor. More reCently trawls have been designed for shing in the middle
waters of the
36
'
“
TSUNAMI: Ocean waves produced by a seismic distofbance in the ocean
00r. The wa'ves arè'not usually conspicüou's out Over the deep ocean
_
but they reveal their tremendous speed and energy by rising tens of
-
feet into the air when they reach the Shallows of
Because
tsunamis_ can Cause COnsiderzible’
an extensive advanced
been deVi‘s‘“ed in the Pacic
siiifer most
132
‘
.
CURRENT: ow pf suSpended‘ ._ material down a
’
Turbidity entr—cnrs are
thé“büild,çup iôf‘ëêdiment
on the edge of the continental slope f
"
‘
‘
ÜPWELLING: lwat‘e‘rf
parts of the
to the‘surface.
_
,
Although underwater banks and
déect deep water towards
“frthe sufface,the 'most:prQmihent
occur where‘fthe wind
blows parallel to…t‘he
The currents generated by the wind
…
cause the SurfaCe*wèrter:to
alldhdng£older water to rise
:frombelOw;Sinceîdeepl‘coldmater is”generayrich in mineral nutrients,
sheries—see page 29
\
Glossary
237
TERRIGENOUS DEPOSITS: composedpredominany of material from—the
land.
cover practically all of the.continental shelf
region
_
…
THERMOCLINE: region in the sea where the temperature differs markedly
…
from water either above or below it. The existence of a thermocline,
either seasonal or permanent, has important implications for biological
productivity as well as the use of sonar———see pages 29 and 205
ÀÏ É
TIDAL WAVE—see tsunami
'
TIDES: product of the astronomical forces of sun and moon acting on the
î
rotating Earth. When the two heavenly bodies pull together or are
‘
diametrically Opposed the dal currents show their greatest range—
the spring tides. When their forces act at right angles to one another
the tidal current has its shortest range—the neap tides. Thus, in
every lunar month there are two spring tides and two neap tides With
gradations between them according to the phase” of the moon—see
page 138
‘
-_
TRAWL: a shing net pulled along through the
One of the rst
î
trawls was the beam trawl, a cumbersome piece of gear which had a
'
heavy cross piece to keep the mouth open. The most important development came with the use of otter boards, ‘kite—like’ structures placed on
“ _
either side of the trawl, which shéared away from eaCh other to keep
‘
the mouth of the net wide open. Both beam and otter trawl were
;
designed for càtÇhing demersal sh: they are dragged Over the sea
oor. More reCently trawls have been designed for shing in the middle
waters of the
36
'
“
TSUNAMI: Ocean waves produced by a seismic distofbance in the ocean
00r. The wa'ves arè'not usually conspicüou's out Over the deep ocean
_
but they reveal their tremendous speed and energy by rising tens of
-
feet into the air when they reach the Shallows of
Because
tsunamis_ can Cause COnsiderzible’
an extensive advanced
been deVi‘s‘“ed in the Pacic
siiifer most
132
‘
.
CURRENT: ow pf suSpended‘ ._ material down a
’
Turbidity entr—cnrs are
thé“büild,çup iôf‘ëêdiment
on the edge of the continental slope f
"
‘
‘
ÜPWELLING: lwat‘e‘rf
parts of the
to the‘surface.
_
,
Although underwater banks and
déect deep water towards
“frthe sufface,the 'most:prQmihent
occur where‘fthe wind
blows parallel to…t‘he
The currents generated by the wind
…
cause the SurfaCe*wèrter:to
alldhdng£older water to rise
:frombelOw;Sinceîdeepl‘coldmater is”generayrich in mineral nutrients,
sheries—see page 29