-248
THE SEAS
_
_
.
As a result of the formation of this discontinuity layer
we nd the clue to the poor plant—life during the summer
.
giving rise to a fresh outburst in the autumn.
For while all
the nutrient salts have become used up in the surface
layers a fresh supply is being formed in the deeper layers
'
from the,sinking down of dead and dying animals and from
other organic remains.
But owing to the inability of the
,
upper and lower layers to mix', this supply of food substance
is completely cut off from those plants living in the surface
waters
above
the discontinuity layer where the light
conditions are best for growth.
In the autumn, when the
surface layers begin to cool down, the waters become once
mOre of the same temperature from top to bottom.
All the
'
water _masses can now be mixed and this is soon brought
,
»
about by the autumnal gales.
As a result fresh supplies
are brought-up into the surface layers where there is still
sufcient light for the plants to grow actively and a renewed
owering of the diatoms takes place. » Soon, however,
.
with the onset of winter, the sun’s light becomes too weak
and the plants die down until they are wakened once more
into life in the following spring.
*
'
From the changes in the amount of phosphates in the
waters of the English Channel, off Plymouth, a minimum
'
estimate has…been made of the actual extent of this diatom
.
crop during the year., Assuming a depth of thirty—eight
fathoms the minimum annual yield of diatoms would be as
.
much as ve and a half tons (wet weight) in the water
layers 1ying beneath one acre of the surface.
It is interest_
ing to compare this with the'quantity of crops obtained on
land.
For instance, between the years 1895 to 3904 the '
average annual yield of potatoes Was 484 tdm. per acre,
_
the highest value for any one year being 581 tons.
Over
,
the Same‘period that for tumipsand swedes was I 3‘21 tons
'
per acre.
'
THE SEAS
_
_
.
As a result of the formation of this discontinuity layer
we nd the clue to the poor plant—life during the summer
.
giving rise to a fresh outburst in the autumn.
For while all
the nutrient salts have become used up in the surface
layers a fresh supply is being formed in the deeper layers
'
from the,sinking down of dead and dying animals and from
other organic remains.
But owing to the inability of the
,
upper and lower layers to mix', this supply of food substance
is completely cut off from those plants living in the surface
waters
above
the discontinuity layer where the light
conditions are best for growth.
In the autumn, when the
surface layers begin to cool down, the waters become once
mOre of the same temperature from top to bottom.
All the
'
water _masses can now be mixed and this is soon brought
,
»
about by the autumnal gales.
As a result fresh supplies
are brought-up into the surface layers where there is still
sufcient light for the plants to grow actively and a renewed
owering of the diatoms takes place. » Soon, however,
.
with the onset of winter, the sun’s light becomes too weak
and the plants die down until they are wakened once more
into life in the following spring.
*
'
From the changes in the amount of phosphates in the
waters of the English Channel, off Plymouth, a minimum
'
estimate has…been made of the actual extent of this diatom
.
crop during the year., Assuming a depth of thirty—eight
fathoms the minimum annual yield of diatoms would be as
.
much as ve and a half tons (wet weight) in the water
layers 1ying beneath one acre of the surface.
It is interest_
ing to compare this with the'quantity of crops obtained on
land.
For instance, between the years 1895 to 3904 the '
average annual yield of potatoes Was 484 tdm. per acre,
_
the highest value for any one year being 581 tons.
Over
,
the Same‘period that for tumipsand swedes was I 3‘21 tons
'
per acre.
'