Carlsberg Ridge
Ponathil Sivadas
Abstract—The Carlsberg Ridge, an important physiographic feature situated on the floor of the Arabian Sea, has significant regional
effects on biodiversity, atmospheric circulation, and climate variability. The Ridge and adjoining areas thus warrant protection and
further investigation and should be included in the category of
protected areas in the high seas.
Carlsberg Ridge was discovered during the John Murray
expedition (1933-1934). This expedition was sponsored by
the Carlsberg Foundation, and the discoverer appropriately
named it Carlsberg Ridge. The Ridge is situated almost in
the middle of the Arabian Sea and can be traced from there
through the Gulf of Aden to the Ethiopian Ridge system. The
Ridge runs in a northwest -southeast direction, at an average depth of 3 km.
The Owen Fracture Zone (OFZ) is one of the largest fracture
zones of the ocean floor and lies between the Equator and the
middle of the Arabian Sea. Carlsberg Ridge intersects the
OFZ at its northwest edge and then continues as the Sheeba
Ridge into the Gulf of Aden. The Carlsberg Ridge and the
Sheeba Ridge lie laterally about 300 km along the OFZ.
The Ridge came into existence approximately 63 million
years ago when the spreading system in the Mascarene
Basin creased and jumped to the north, separating India
from Seychelles. This has created two oceanic conjugate
basins: the Eastern Somali Basin and the Western Arabian
Basin. It is an active plate boundary between the Somali and
Indian Plates. Presently, the Ridge is generating new sea
floors at the rate of 24 to 30 km per million years. The right
valley is contributing a significant amount of driving force
for the Indian Plate, which is currently moving in a northeast/southwest direction.
Ridge System Dynamics and
Effects ________________________
Carlsberg Ridge acts as a barrier both for sediments coming
from the Indus River and for deep water circulation to the
southwest. However, some of the fracture zones like the OFZ
and others act as conduits to the bottom water entering the
Eastern Arabian Sea, thus flowing to the west of the Carlsberg
Ridge. Such circulation patterns lead to an upwelling and
high productivity off the west coast of India. The upwelling
and the disposition of the magma chambers along the central
In: Watson, Alan E.; Aplet, Greg H.; Hendee, John C., comps. 2000.
Personal, societal, and ecological values of wilderness: Sixth World Wilderness Congress proceedings on research, management, and allocation, volume II;
1998 October 24–29; Bangalore, India. Proc. RMRS-P-14. Ogden, UT: U.S.
Department of Agriculture, Forest Service, Rocky Mountain Research Station.
Ponathil Sivadas is Senior Deputy Director of the National Institute of
Oceanography, P.B. No. 1913, Cochin-682018, Kerala, India.
USDA Forest Service Proceedings RMRS-P-14. 2000
part of the ridge transfer large amounts of heat to the sea
bottom, perhaps resulting in the formation of black smokers.
The National Institute of Oceanography (Kerala, India)
has undertaken one cruise to the Carlsberg Ridge between
3∞30'N–4∞30'N and 62∞30'E–63∞30'E, covering an area of
about 15,000 km2. In addition, thermal anomalies in sediments have been studied. The composition shows basaltic
ultra basic salts. The bathymetry studies in this area have
been done through sonars. The temperature of the bottom
water has been measured at various places, and preliminary
studies indicate the presence of hydrothermal vents and
black smokers. Although we have no photographic evidence
of such black smokers in that area, possibilities are very high
for them to occur. If such is the case, the areas are locales of
sulphur-reducing bacteria forming large mats. The biodiversity in that area much depends on availability of the homogenous environment.
There are no ridge systems present in the central Indian
Ocean. However, the rich diversity of animal life shows the
possibility of a community surviving on trophic systems
different from the primary, secondary, and tertiary systems
prevailing in the photic zone. The presence of animal communities at such depths in other areas with similar environmental conditions would suggest the existence of sulphidefriendly biodiversity in the Carlsberg Ridge area, also.
Another significant role of this volcanically active ridge
system is its control of the Indian monsoon pattern. The
horizontal forces generated during the outpouring of the
magma from the volcanically active ridge has been driving
the Indian plate northeastward, resulting in an Indian and
Eurasian plate collision and thus the formation of the
Himalayas. The high Himalayan mountain range effectively
controls atmospheric circulation and the present day Indian
monsoon pattern.
Cold Antarctic water from the southwest finds it way into
the Somali Basin, warming as it passes through fracture zone
magma chambers and thermal vents. As a result of this
warming of the dense nutrient-rich water surface along the
Somali coast, a highly productive zone rich in phyto-zooplankton and fish is created. The warm deep-sea water along
the ridge also becomes habitat for a diverse animal community.
Conclusion _____________________
The high seas lying over the Arabian and Somali Basins on
the east and west side of Carlsberg Ridge and the adjoining
areas in close proximity warrant protection and further
investigation of the biodiversity of the pelagic, mid-sea, and
abyssal realm. The abyssal animal community is not being
investigated currently, owing to the fact that it is not easily
reachable. Ridge system dynamics have varied and significantly affect biodiversity, atmospheric circulation, and climate variability. Therefore, the Ridge should be included in
the category of protected areas in the high seas.
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