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Dramatic changes in the Arabian Sea due to decreasing snow cover in the Himalayas

Last modified August 04, 2005 21:55

When the snow cover of southwest Asia and the Himalayas is low, the land mass heats up more in summer, creating a larger temperature difference between the land and the sea. This gives rise to stronger winds from the sea to the land. In the western Arabian Sea, these winds reach speeds of up to 36 knots (almost 67 km/hour), leading to upwelling of cooler nutrient-rich water.

When the snow cover of southwest Asia and the Himalayas is low, the land mass heats up more in summer, creating a larger temperature difference between  the land  and the sea. This gives rise to stronger winds from the sea to the land. In the western Arabian Sea, these winds reach speeds of up to 36 knots (almost 67 km/hour), leading to upwelling of cooler nutrient-rich water.

Reduced Himalayan snow cover affects marine life in the Arabian Sea
This decreasing snow cover is threatening marine life in central and western parts of the Arabian Sea, which lie thousands of kilometers (km) away. Reduced winter and spring snow cover in these mountains is creating ideal conditions for widespread blooms of phytoplankton – the microscopic marine plants in the Arabian Sea. Marine creatures feed on phytoplankton but its uncontrollable growth deprives the region of oxygen, putting other life forms under fatal stress. The Arabian Sea already hosts one of the world’s largest zones with minimum oxygen – spread over 1.4 million square km – located at a depth of 150-1,000 meters.
  The mentioned winds are strong enough to churn water from depths of about 150 meters or more. The phytoplankton that inhabits the surface layers of water, where there is enough light for  photosynthesis, quickly absorbs the nutrients and proliferates. The surface layers of water have high oxygen content but the deep layers have little. The upwelling of water  means that the deep layers  replace the oxygen-rich surface layer. While the phytoplankton blooms every summer and uses up the oxygen, the marine life  forms, especially fish, get less oxygen, eventually leading to their death.
 Since 1997, scientists have observed a close link between reduction in snow cover and increasing numbers of dead fish in the Arabian sea. During the period from 1997-2003, they noticed average summertime phytoplankton biomass along the coast going up to more than four times that in 1997. Fishermen off  the coasts of Somalia, Oman and Yemen have been witnessing increased  incidence of fish mortality.

Effect on climate change
But the problems do not stop there. Bringing deep water to the surface in this part of the globe could also dramatically increase global warming. Some bacteria have found a way of dealing with the low oxygen levels at the bottom of the Arabian Sea. They extract oxygen from nitrate found in the water. The process, known as ‘de-nitrification’, produces nitrous oxide, a powerful greenhouse gas. When de-nitrification occurs deep down, the nitrous oxide is trapped. But when the deep water rises to the surface as a consequence of the decreasing snow cover, the gas is released into the atmosphere. There it acts as a greenhouse gas that is about 300 times more active in the environment than carbon dioxide. If the Himalayas continue to receive less winter snow, the Arabian Sea will become a chimney for nitrous oxide. That positive feedback could induce climate change much worse than anticipated.

[Information in this contribution has been taken from “Reduced Himalayan snow cover affects marine life”, appearing in the “Science and Technology” section of the journal “Down to Earth” (May 31, 2005, page 32), published by the Centre for Science and Environment, India.]

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