34
R. K. DELL
an increase in the amount of dissolved carbon dioxide, which is readily
available in the Ross Sea since sunlight is lacking for about half the
year, and since many animals live permanently away from light under
the Ross Sea shelf.
These are of course factors which can be checked, and the work
planned for examining the water beneath the Ross Ice Shelf will add
some firm knowledge in this respect. On the face of it, however, it
seems difficult to see that such a great difference in depth should exist
between the “ calcium solution ” layer at about 530 m in the Ross Sea,
and at 4 000 m in the Antarctic waters just outside the Ross Sea area.
If this factor is to work on the tests of Foraminifera, it should also
work to obliterate the shells of Mollusca. It may very well do this in
the course of time but dead shells occur below 500 m in the Ross Sea in
numbers. The shells of live Mollusca from deeper water contain little
calcium carbonate, but that is rather a different matter.
The cores studied by McKnight (1962) from the Ross Sea showed an
increase in the percentage of calcareous benthic specimens present from
top to bottom in his cores. He postulated two possible reasons for this.
The first supposed that arenaceous forms had not yet entered the Ross
Sea in strength and had gradually done so over the time the sediments
in the cores were being deposited. The second required a change in
water masses because of climatic change. Kennett (1968) believed that
the second explanation fitted the facts of the situation better. An
increase in the percentage of calcareous forms would represent a warmer
period with the calcium-solution boundary lowered correspondingly.
As Kennett (1968, p. 35) suggested, “A study of the distribution of
calcareous and arenaceous foraminifera1 assemblages in long cores
from the Ross Sea may provide evidence of the climatic history of the
area ”.
From his analysis of bathymetric ranges for Foraminifera from his
own samples, and from those recorded by McKnight (1962) and Pflum
(1963) in the Ross Sea, ranging in depth from 90 to 3 570 m Kennett
(1968) noted several abrupt changes with increasing depth. These
main changes occurred a t about 270, 450 to 550 m, and at 1 300 and
2 200 m. The boundary a t 270 m was the upper depth limit for some
19 species. The relatively broad boundary between 450 and 550m
seems to represent the calcium solution boundary and was the lower
limit for practically every calcareous species. Ten arenaceous species
reach their shallow depth boundary in this zone. Two species Hyperammina novaexealandiae Heron-Allen and Earland, and a species of
Rhabdammina do extend into shallower depths but only occur in quantity from this zone down to about 2 200 m. At 1 300 m, the upper
R. K. DELL
an increase in the amount of dissolved carbon dioxide, which is readily
available in the Ross Sea since sunlight is lacking for about half the
year, and since many animals live permanently away from light under
the Ross Sea shelf.
These are of course factors which can be checked, and the work
planned for examining the water beneath the Ross Ice Shelf will add
some firm knowledge in this respect. On the face of it, however, it
seems difficult to see that such a great difference in depth should exist
between the “ calcium solution ” layer at about 530 m in the Ross Sea,
and at 4 000 m in the Antarctic waters just outside the Ross Sea area.
If this factor is to work on the tests of Foraminifera, it should also
work to obliterate the shells of Mollusca. It may very well do this in
the course of time but dead shells occur below 500 m in the Ross Sea in
numbers. The shells of live Mollusca from deeper water contain little
calcium carbonate, but that is rather a different matter.
The cores studied by McKnight (1962) from the Ross Sea showed an
increase in the percentage of calcareous benthic specimens present from
top to bottom in his cores. He postulated two possible reasons for this.
The first supposed that arenaceous forms had not yet entered the Ross
Sea in strength and had gradually done so over the time the sediments
in the cores were being deposited. The second required a change in
water masses because of climatic change. Kennett (1968) believed that
the second explanation fitted the facts of the situation better. An
increase in the percentage of calcareous forms would represent a warmer
period with the calcium-solution boundary lowered correspondingly.
As Kennett (1968, p. 35) suggested, “A study of the distribution of
calcareous and arenaceous foraminifera1 assemblages in long cores
from the Ross Sea may provide evidence of the climatic history of the
area ”.
From his analysis of bathymetric ranges for Foraminifera from his
own samples, and from those recorded by McKnight (1962) and Pflum
(1963) in the Ross Sea, ranging in depth from 90 to 3 570 m Kennett
(1968) noted several abrupt changes with increasing depth. These
main changes occurred a t about 270, 450 to 550 m, and at 1 300 and
2 200 m. The boundary a t 270 m was the upper depth limit for some
19 species. The relatively broad boundary between 450 and 550m
seems to represent the calcium solution boundary and was the lower
limit for practically every calcareous species. Ten arenaceous species
reach their shallow depth boundary in this zone. Two species Hyperammina novaexealandiae Heron-Allen and Earland, and a species of
Rhabdammina do extend into shallower depths but only occur in quantity from this zone down to about 2 200 m. At 1 300 m, the upper