Arabian sea ‘Dead zone’: Humera Rind
Dead zones are oxygen depleted zone in the marine environment where none to very little organisms can survive or breath. Dead zones are major environmental problems and have dire consequences for coastal fishing communities in the context of local fisheries, marine food chain and the food supplies as well as the local economy. Dead zones appear in water depths ranging from 200 metres to 800 metres. As recent as 20 years ago appearance of dead zone in the Arabian sea was unheard of. This phenomenon
is attributed to a subsurface layer of water. This water originates during summer monsoon in the tropical north i.e. India, Pakistan and Bay of Bengal and in the west in the Somali coast. This tropical water is poor in oxygen but rich in nutrients (phosphate and nitrogen).
Arabian sea climate and marine life
The Arabian sea climate is a monsoon-dominated system, with the minimum sea surface temperature ranging between 24 to 250C in winter (December, January, and February) and about 28OC during summer (June-November). The monsoon system is a product of the Himalayan-Tibetan plateau and plays a key role in transforming regional atmospheric and oceanic circulations.
During the monsoon season, the southwest monsoon winds blows from the complex Somali current (April to November) and continues to the northeast along the coast of Arabia and in the south along the coast of India/Pakistan bringing much needed rains in the region. During winter, the Somali Current weakens and reverses direction to the northeast during winter, hence winter monsoon. This reversing monsoon currents have shaped Arabian sea’s waters, coasts lines, islands, and thousands of kilometres of shorelines over the millions of years. The reversing monsoon currents and winds have enriched the Arabian sea with the most spectacular marine habitats and coastal marine life. The reversing oceanic circulation creates the passage for coastal upwelling that is important to marine ecosystem and country’s economies. Coastal upwelling lifts the cold nutrient-rich water from deeper ocean layers to the surface.
The coastal upwelling transports nutrient-rich deep-water mass to the surface of water that supports marine biological productivity.
Balochistan’s coastline is located along the Arabian sea. Most marine life exists along the continental shorelines and along its islands where upwellings occur. Islands and continental shorelines provide favourable habitats for breeding grounds for fish, marine birds as well as migratory birds and provide food for marine and terrestrial animals. These costal and islandic shorelines are often teeming with life, includes coral reef, varieties of fish, sardines, tuna, megafauna such as whales, sharks, dolphins, dugongs, sea reptiles (turtles), stingrays. The sea floor contains filter feeders such as shrimps, mussels, sea urchins and the list go on. This abundance of marine life also attracts fishing as well as marine birds
including migratory birds for stop-overs and feed along the coast of Balochistan (Makran) and the nearby islands.
Causes of Dead Zones in the sea:
The appearance of ocean dead zones is directly linked to nutrient run-off from human activities on the land. In general, on land human use chemical fertilisers for cropping and farming animals. Fertilisers and manure provide crops with much needed nitrogen and phosphorus for growth and yield. However, mismanagement of waste containing fertiliser/manure have dire consequences on our water systems and aquatic and marine life. Coupled with this, inadequate liquid waste management from domestic use of water in the urban environments resulting in nutrient-runoff from homes into the sea and waterways. This excess nitrogen and phosphorus often washed from farmlands and urban environments are entering into our waterways from sources includes rainfall events, poorly managed irrigation systems and melting of snow in the mountains. This excess nutrient run-off is giving rise to a uniquely resilient organism called
Noctiluca scintillans, commonly known as the sea sparkle or green algae in the oceans and seas. It is reasonably argued that the Noctiluca blooms in the Arabian sea are resulting from untreated wastewater and mismanaged farmlands. The excess nutrients are directly being discharged into the Himalayan Rivers on the Indian sub-continent and in the Middle East.
Impacts of Noctiluca blooms (health & economy)
Noctiluca blooms first appeared in the late 1990s and now seems to be occurring annually and more regularly. Due to urban spawls, discharge of human effluent and costal developments are threatening our marine ecosystem and our food supplies. The green algae are threatening our marine ecosystem and costing millions in economy. These blooms are threatening the Arabian Sea’s vulnerable and fragile food chain. Noctiluca blooms are competing with phytoplankton (an essential food source for marine life) and feed on the phytoplankton themselves. Phytoplankton are essential for annual replenishment of coastal upwelling in the Arabian sea for fisheries. It is estimated that just over 20% of the total marine seafood catches originate from regions where coastal upwelling occurs. Sadly, this nutrient rich coastal upwellings by air-sea interaction (by convection) only amounts to 2% of the entire ocean surface area.
Noctiluca blooms also having large scale impacts on the Middle East economy when companies slow down their production due to choking of oil refineries from the bloom. In the urban areas the nutrients such as nitrogen and phosphorus rich water gets into our groundwater reducing water quality. Nitrogen is toxic to human health where groundwater is used for human consumption.
Climate change effects on coastal environment:
Climate change and its impact is already being felt around the globe. There is no argument to contrary that climate change is changing and shaping our global climatic system. It is silently creeping into our lives and causing millions of dollars in lost revenues. Changes in rainfall patterns will lead to alternative periods of drought and storm intensities and bushfires on the mainland. This also results in heatwaves giving rise to countries energy demand to keep homes and businesses cool by running air-conditions, further fuelling carbon dioxide (CO2 – a greenhouse gas) levels in the atmosphere. Algae need carbon dioxide to survive therefore high level of carbon dioxide in the air and water could nourish the algae for rapid growth.
Melting of ice caps, snow caps, ice bergs and glaciers in the alpine areas and arctics can lead to sea level rise. The rising sea levels could jeopardise our costal environment and communities from coastal erosion and flooding as well as loss of land from rising water. In addition to this the rising sea level will create shallow coastal water bodies that are perfect conditions for algal blooms further creating ideal conditions for toxic algae. Climate change is expected to alter the timing and the intensity of coastal upwelling and excess nutrient from upwelling could possibly lead to additional algal bloom.
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