Chapter 7
THE DEEP INDIAN OCEAN FLOOR
Amanda W.J. DEMOPOULOS, Craig R. SMITH and Paul A. TYLER
INTRODUCTION
The Indian Ocean is the world’s third largest, stretching
9600 km from Antarctica to the Bay of Bengal and
7600 km from Africa to Australia. Compared to the
Atlantic and Pacific, the Indian Ocean remained
poorly explored scientifically until the International
Indian Ocean Expedition (IIOE) in 1962–1965, the
results of which were published in the Atlas of the
Indian Ocean (Wyrtki, 1971). Prior to the IIOE, the
voyages of the ‘heroic age’ of deep-sea exploration
had sampled relatively little in the Indian Ocean.
During the circumnavigation of the world’s oceans by
HMS Challenger (1872–1876), study of the Indian
Ocean was confined to circumpolar waters south of
the Polar Front. The Valdivia expedition (Chun, 1900)
sampled the free-swimming larvae of the deep-water
brachiopod Pelagodiscus in surface waters of the Indian
Ocean, benthic adults being collected from depths
as great as 2490 m (Helmcke, 1940). In the 1930s,
the John Murray Expedition to the Indian Ocean
worked mainly in shallow water, but some deepwater sampling provided material for monographs (e.g.,
Knudsen, 1967). The Swedish Deep Sea Expedition
of 1947–1948 on the Albatross sampled extensively
in all the oceans (Pettersson, 1957), taking bottomliving specimens and cores from the deep sea (for a list
of publications see Menzies et al., 1973). The last of
the ‘heroic age’ cruises, on the Galathea (1950–1952),
sampled deep-water fauna between Sri Lanka (formerly
Ceylon) and the Kenyan coast, as well as along the
Mozambique Channel to South Africa (for a list of
publications see Menzies et al., 1973). The taxonomic
studies of these major expeditions were supplemented
by Soviet cruises to the Indian Ocean, particularly on
the Vityaz, again resulting in monographic treatments
(e.g., Pasternak, 1964, 1976). The IIOE also gave the
opportunity for quantification of the bottom fauna of
the Indian Ocean (Neyman et al., 1973). A historical
perspective of the major early cruises, including those
to the Indian Ocean, has been given by Mills (1983).
Since the IIOE, deep-sea research in the Indian
Ocean has focused on the Arabian Sea. Because few
systematic surveys or conceptually integrated studies
exist, deep-sea ecosystems in the Indian Ocean remain
poorly known (Banse, 1994).
The Indian Ocean is characterized by a number of
unusual oceanographic features. Patterns of circulation
are unlike those in any other oceans, owing to largescale monsoonal shifts in wind stress and current
directions north of 5ºS. In addition, the Indian Ocean is
landlocked to the north and lacks temperate and polar
regions north of the equator, further modifying oceanic
circulation and hydrology. The basin also harbors one
of the largest and most intense intermediate-depth oxygen minimum zones in the world ocean (Kamykowski
and Zentara, 1990; Rogers, 2000). These unusual
features of the Indian Ocean substantially affect the
spatial and temporal variability of primary production,
the deep flux of particulate organic carbon (POC) and
the oxygen concentration, profoundly influencing the
nature of the deep seafloor habitats.
Deep-sea habitats studied with modern techniques in
the deep Indian Ocean include the Kenya slope, the
oxygen minimum zone of the Oman Margin, and the
abyssal Owen Basin in the Arabian Sea. In addition,
limited deep-sea data exist for continental-rise and
abyssal habitats in the central Indian Ocean and in
the Bay of Bengal. In this chapter, we first describe
physical characteristics and key habitat variables of the
deep Indian Ocean; we then summarize the limited
deep-sea benthic data available from this ocean, and
highlight topics of interest for future research.
219
THE DEEP INDIAN OCEAN FLOOR
Amanda W.J. DEMOPOULOS, Craig R. SMITH and Paul A. TYLER
INTRODUCTION
The Indian Ocean is the world’s third largest, stretching
9600 km from Antarctica to the Bay of Bengal and
7600 km from Africa to Australia. Compared to the
Atlantic and Pacific, the Indian Ocean remained
poorly explored scientifically until the International
Indian Ocean Expedition (IIOE) in 1962–1965, the
results of which were published in the Atlas of the
Indian Ocean (Wyrtki, 1971). Prior to the IIOE, the
voyages of the ‘heroic age’ of deep-sea exploration
had sampled relatively little in the Indian Ocean.
During the circumnavigation of the world’s oceans by
HMS Challenger (1872–1876), study of the Indian
Ocean was confined to circumpolar waters south of
the Polar Front. The Valdivia expedition (Chun, 1900)
sampled the free-swimming larvae of the deep-water
brachiopod Pelagodiscus in surface waters of the Indian
Ocean, benthic adults being collected from depths
as great as 2490 m (Helmcke, 1940). In the 1930s,
the John Murray Expedition to the Indian Ocean
worked mainly in shallow water, but some deepwater sampling provided material for monographs (e.g.,
Knudsen, 1967). The Swedish Deep Sea Expedition
of 1947–1948 on the Albatross sampled extensively
in all the oceans (Pettersson, 1957), taking bottomliving specimens and cores from the deep sea (for a list
of publications see Menzies et al., 1973). The last of
the ‘heroic age’ cruises, on the Galathea (1950–1952),
sampled deep-water fauna between Sri Lanka (formerly
Ceylon) and the Kenyan coast, as well as along the
Mozambique Channel to South Africa (for a list of
publications see Menzies et al., 1973). The taxonomic
studies of these major expeditions were supplemented
by Soviet cruises to the Indian Ocean, particularly on
the Vityaz, again resulting in monographic treatments
(e.g., Pasternak, 1964, 1976). The IIOE also gave the
opportunity for quantification of the bottom fauna of
the Indian Ocean (Neyman et al., 1973). A historical
perspective of the major early cruises, including those
to the Indian Ocean, has been given by Mills (1983).
Since the IIOE, deep-sea research in the Indian
Ocean has focused on the Arabian Sea. Because few
systematic surveys or conceptually integrated studies
exist, deep-sea ecosystems in the Indian Ocean remain
poorly known (Banse, 1994).
The Indian Ocean is characterized by a number of
unusual oceanographic features. Patterns of circulation
are unlike those in any other oceans, owing to largescale monsoonal shifts in wind stress and current
directions north of 5ºS. In addition, the Indian Ocean is
landlocked to the north and lacks temperate and polar
regions north of the equator, further modifying oceanic
circulation and hydrology. The basin also harbors one
of the largest and most intense intermediate-depth oxygen minimum zones in the world ocean (Kamykowski
and Zentara, 1990; Rogers, 2000). These unusual
features of the Indian Ocean substantially affect the
spatial and temporal variability of primary production,
the deep flux of particulate organic carbon (POC) and
the oxygen concentration, profoundly influencing the
nature of the deep seafloor habitats.
Deep-sea habitats studied with modern techniques in
the deep Indian Ocean include the Kenya slope, the
oxygen minimum zone of the Oman Margin, and the
abyssal Owen Basin in the Arabian Sea. In addition,
limited deep-sea data exist for continental-rise and
abyssal habitats in the central Indian Ocean and in
the Bay of Bengal. In this chapter, we first describe
physical characteristics and key habitat variables of the
deep Indian Ocean; we then summarize the limited
deep-sea benthic data available from this ocean, and
highlight topics of interest for future research.
219