ANTAROTIO BENTHOS
33
tion and abundance for each species was recorded. Kennett found that
his faunas fell into two separate and completely contrasting groups.
1. A calcareous fauna, with abundant calcareous Foraminifera,
moderately abundant Ostracoda, Bryozoa, small Mollusca, etc. but
with relatively few arenaceous Foraminifera, generally a high number
of foraminiferal species present.
2. A dominantly non-calcareous fauna, with arenaceous Foraminifera, diatoms and siliceous sponge spicules. This group of faunas with
more than 85% of the benthic faunal constituents consisting of arenaceous Foraminifera was defined by Kennett as arenaceous faunas.
Arenaceous Foraminifera build their tests by cementing various
materials such as sand grains or sponge spicules with a predominantly
ferruginous secretion. Only a relatively small number of species is
usually present.
Most of the calcareous faunas occurred in depths shallower than
550 m, while all the arenaceous faunas were found deeper than 430 m.
Kennett stresses that approximately the same number of arenaceous
species occur in both calcareous and arenaceous faunas, and with some
exceptions they are essentially the same species. The arenaceous faunas
have much greater numbers of individuals. Arenaceous species characteristic of the calcareous fauna are Brachysiphon sp., and Ammodiscus
cf. anguillae Hoglund. The more characteristic species in the arenaceous
fauna include : Rhizammina indivisa Brady, Bathysiphon Jiliformis
Sars, Pelosina bicaudata (Parr), CJlomospira charoides (Jones & Parker),
Reophx distans Brady, R. spiculifer Brady, Adercotryma glomerata
(Brady), Verneuilina minuta Wiesner and Karreriella pusilla Parr.
There have been many attempts to determine the reasons for the
level a t which arenaceous species become dominant, at whatever depth
the phenomenon takes place. The general theory has been that there is
a solution boundary beyond which at least thin-shelled calcareous
foraminiferal tests are dissolved. General studies on this problem have
indicated that the solubility of calcium carbonate increases with
increasing salinity and with pressure. However it also appears that
different species differ in the ease with which the test dissolves. It has
been shown that in Antarctic waters generally quite abundant calcareous
foraminiferal faunas do exist down to at least 4 000 m. (Saidova, 1961 ;
Bandy and Echols, 1964).
Kennett (1968, p. 34) believes that solution of calcium carbonate
occurs at shallower depths in the Ross Sea because the water below
about 550 m is highly unsaturated for a number of reasons. The water
is at very low temperature even for Antarctic sea water ( O O C to -2°C)
at a very high salinity (34.75 to 35.00%). Such cold water would allow
33
tion and abundance for each species was recorded. Kennett found that
his faunas fell into two separate and completely contrasting groups.
1. A calcareous fauna, with abundant calcareous Foraminifera,
moderately abundant Ostracoda, Bryozoa, small Mollusca, etc. but
with relatively few arenaceous Foraminifera, generally a high number
of foraminiferal species present.
2. A dominantly non-calcareous fauna, with arenaceous Foraminifera, diatoms and siliceous sponge spicules. This group of faunas with
more than 85% of the benthic faunal constituents consisting of arenaceous Foraminifera was defined by Kennett as arenaceous faunas.
Arenaceous Foraminifera build their tests by cementing various
materials such as sand grains or sponge spicules with a predominantly
ferruginous secretion. Only a relatively small number of species is
usually present.
Most of the calcareous faunas occurred in depths shallower than
550 m, while all the arenaceous faunas were found deeper than 430 m.
Kennett stresses that approximately the same number of arenaceous
species occur in both calcareous and arenaceous faunas, and with some
exceptions they are essentially the same species. The arenaceous faunas
have much greater numbers of individuals. Arenaceous species characteristic of the calcareous fauna are Brachysiphon sp., and Ammodiscus
cf. anguillae Hoglund. The more characteristic species in the arenaceous
fauna include : Rhizammina indivisa Brady, Bathysiphon Jiliformis
Sars, Pelosina bicaudata (Parr), CJlomospira charoides (Jones & Parker),
Reophx distans Brady, R. spiculifer Brady, Adercotryma glomerata
(Brady), Verneuilina minuta Wiesner and Karreriella pusilla Parr.
There have been many attempts to determine the reasons for the
level a t which arenaceous species become dominant, at whatever depth
the phenomenon takes place. The general theory has been that there is
a solution boundary beyond which at least thin-shelled calcareous
foraminiferal tests are dissolved. General studies on this problem have
indicated that the solubility of calcium carbonate increases with
increasing salinity and with pressure. However it also appears that
different species differ in the ease with which the test dissolves. It has
been shown that in Antarctic waters generally quite abundant calcareous
foraminiferal faunas do exist down to at least 4 000 m. (Saidova, 1961 ;
Bandy and Echols, 1964).
Kennett (1968, p. 34) believes that solution of calcium carbonate
occurs at shallower depths in the Ross Sea because the water below
about 550 m is highly unsaturated for a number of reasons. The water
is at very low temperature even for Antarctic sea water ( O O C to -2°C)
at a very high salinity (34.75 to 35.00%). Such cold water would allow