Some Patterns of the Distribution of Bottom Fauna in the Indian Ocean
469
much poorer than that of the Arabian Sea, its biomass varying between some fractions
of a gram to 10 g m- 2 , although in the immediate proximity of the mouth of the Ganges
a value of 42.8 g m- 2 was recorded (SOKOLOVA and PASTERNAK, 1962). A similar increase
in the development of bottom life was observed at the mouth of the Irrawaddy River.
In all other coastal regions of the tropical zone of the Indian Ocean the biomass of bottom
invertebrates is generally fairly low, seldom attaining 10 g m- 2 . Local bursts of bottom
fauna development are observed around certain parts of the Andaman Sea and the
Malay Archipelago, along the western coasts of Java and Sumatra, in the region of
intensive upwelling. A low benthos biomass is characteristic of the NW part of the
Australian shelf (2.6-8 g m- 2 ). To the south, according to the general scheme of the
development of life in the ocean, the productivity of bottom fauna increases again. On
the shelf of western Australia its biomass averages 15 g m- 2 and on the shelf of the Great
Australian Bight 16 g m- 2 . The insignificant increase in biomass observed along the
western coast of Australia may be explained by the fact that here the shore is washed by
subtropical waters of low productivity (NEYMAN, 1965).
In the western part of the Great Australian Bight a cyclonic winter circulation results in
a local increase of productivity: here the benthos biomass reaches an average of 22 g m -2.
In the tropical, as in the southern temperate part of the ocean, the biomass of benthos
decreases with increasing depth. However, in the tropical zone the process is not as
sharply expressed as in the boreal zone because the abundant inflow of organic matter
from the neritic region overrides the effect of increasing depth beyond the upper 1000 m.
Therefore at all depths greater than 1000 m the biomass of benthos is expressed by values
of the same order, ranging between 2.75 and 1.76 g m- 2 (BELYAEV and VINOGRADOVA,
1961).
In the northern part of the ocean a high biomass of benthos is characteristic not only of
the coastal regions but also of the whole Arabian Sea. Here at a considerable distance
from the shore and at a depth of more than 3000 m the biomass reaches 1.92 g m- z and
more, a value quite unusual for the open waters of the tropical zone. The analysis of
dynamic charts shows that the circulation of the Arabian Sea is represented by nonstationary eddies, producing intensive turbulent exchange and replenishment of the
surface water with biogenic substances. The extreme richness of plankton in the Arabian
Sea is favored by an intensive ascent of subsurface water along its western coasts during
the period of winter monsoons. Another characteristic feature of the Arabian Sea is the
presence of a thick O2 minimum layer extending from the layer of density discontinuity
to a depth of 1000-1250 m. In the upper part of this layer (down to 600 m) free HzS
was discovered. A quantitative minimum of plankton was recorded in the whole thickness
of the layer of the Oz minimum, but at a depth of 1500 m the biomass of zooplankton
abruptly increases again. The deep-sea plankton of the Arabian Sea is even richer relative
to the surface plankton than is usually observed in the ocean (VINOGRADOV, 1962). The
explanation of this phenomenon suggested by VINOGRADOV is fully applicable to the
extreme abundance of the benthos: the intermediate waters are poor in plankton and
oxygen, and active consumption and oxidation of the precipitated organic matter proceed
slowly, so that large amounts of nutrients are conveyed to the deep-water layers and the
ocean floor. The presence of an 02-minimum layer and of HzS also has a direct effect on
the distribution of bottom organisms. Thus a minimum biomass is characteristic of some
areas of the Murray Ridge. In separate regions, directly washed by water containing up
to 0.1 mg HzS 1-\ the bottom fauna is extremely impoverished e.g. 0.01 g m- z , or may be
469
much poorer than that of the Arabian Sea, its biomass varying between some fractions
of a gram to 10 g m- 2 , although in the immediate proximity of the mouth of the Ganges
a value of 42.8 g m- 2 was recorded (SOKOLOVA and PASTERNAK, 1962). A similar increase
in the development of bottom life was observed at the mouth of the Irrawaddy River.
In all other coastal regions of the tropical zone of the Indian Ocean the biomass of bottom
invertebrates is generally fairly low, seldom attaining 10 g m- 2 . Local bursts of bottom
fauna development are observed around certain parts of the Andaman Sea and the
Malay Archipelago, along the western coasts of Java and Sumatra, in the region of
intensive upwelling. A low benthos biomass is characteristic of the NW part of the
Australian shelf (2.6-8 g m- 2 ). To the south, according to the general scheme of the
development of life in the ocean, the productivity of bottom fauna increases again. On
the shelf of western Australia its biomass averages 15 g m- 2 and on the shelf of the Great
Australian Bight 16 g m- 2 . The insignificant increase in biomass observed along the
western coast of Australia may be explained by the fact that here the shore is washed by
subtropical waters of low productivity (NEYMAN, 1965).
In the western part of the Great Australian Bight a cyclonic winter circulation results in
a local increase of productivity: here the benthos biomass reaches an average of 22 g m -2.
In the tropical, as in the southern temperate part of the ocean, the biomass of benthos
decreases with increasing depth. However, in the tropical zone the process is not as
sharply expressed as in the boreal zone because the abundant inflow of organic matter
from the neritic region overrides the effect of increasing depth beyond the upper 1000 m.
Therefore at all depths greater than 1000 m the biomass of benthos is expressed by values
of the same order, ranging between 2.75 and 1.76 g m- 2 (BELYAEV and VINOGRADOVA,
1961).
In the northern part of the ocean a high biomass of benthos is characteristic not only of
the coastal regions but also of the whole Arabian Sea. Here at a considerable distance
from the shore and at a depth of more than 3000 m the biomass reaches 1.92 g m- z and
more, a value quite unusual for the open waters of the tropical zone. The analysis of
dynamic charts shows that the circulation of the Arabian Sea is represented by nonstationary eddies, producing intensive turbulent exchange and replenishment of the
surface water with biogenic substances. The extreme richness of plankton in the Arabian
Sea is favored by an intensive ascent of subsurface water along its western coasts during
the period of winter monsoons. Another characteristic feature of the Arabian Sea is the
presence of a thick O2 minimum layer extending from the layer of density discontinuity
to a depth of 1000-1250 m. In the upper part of this layer (down to 600 m) free HzS
was discovered. A quantitative minimum of plankton was recorded in the whole thickness
of the layer of the Oz minimum, but at a depth of 1500 m the biomass of zooplankton
abruptly increases again. The deep-sea plankton of the Arabian Sea is even richer relative
to the surface plankton than is usually observed in the ocean (VINOGRADOV, 1962). The
explanation of this phenomenon suggested by VINOGRADOV is fully applicable to the
extreme abundance of the benthos: the intermediate waters are poor in plankton and
oxygen, and active consumption and oxidation of the precipitated organic matter proceed
slowly, so that large amounts of nutrients are conveyed to the deep-water layers and the
ocean floor. The presence of an 02-minimum layer and of HzS also has a direct effect on
the distribution of bottom organisms. Thus a minimum biomass is characteristic of some
areas of the Murray Ridge. In separate regions, directly washed by water containing up
to 0.1 mg HzS 1-\ the bottom fauna is extremely impoverished e.g. 0.01 g m- z , or may be