Frequent marine heatwaves in Indian Ocean disrupt India‘s monsoon patterns

Frequent marine heatwaves in Indian Ocean disrupt India‘s monsoon patterns

TOPIC: Environment

Context- Marine heat waves (MHW) in the Indian Ocean region have increased significantly in the past few decades, according to a new study published in the journal JGR Oceans showed.

Concept-

Marine heat waves (MHW)

• Marine heat waves (MHW) are periods of increased temperatures over seas and oceans.
• Such heat waves are caused by an increase in the heat content of oceans, especially in the upper
• Worldwide, they are one of the major results of human-induced global warming.
• During an MHW, the average temperatures of the ocean surface (up to a depth of 300 feet) goes 5-7 degrees Celsius above normal.

Marine Heat Waves in Indian Ocean:

• The number of MHWs in the West Indian ocean increased by around 1.5 events per decade between 1982 and 2018.
• The occurrences went up by around 0.5 events per decade in North Bay of Bengal in the same period.
• There were a total of 66 events in West Indian Ocean and 94 in North Bay of Bengal in the 36 years.

Link between marine heatwaves and atmospheric circulation and Monsoon rainfall

• Around 90 per cent of the warming caused by greenhouse gas emissions is absorbed by the oceans.
• The increase in marine heat waves was due to rapid warming in the Indian Ocean and strong El Nino events.
  • El Nino is one phase of the El Nino Southern Oscillation (ENSO) phenomenon which has a generally warming effect on the world’s ocean and land surfaces.
• The marine heat waves in the Indian Ocean are also majorly impacting the southwest monsoon — the main rain-bearing system over the Indian subcontinent.
• The MHWs in the two worst-hit regions reduce monsoon rainfall over central India, the study established.
• The occurrence of MHW in North Bay of Bengal increases rainfall over the southern peninsular area.

Impacts of Marine Heat waves

• Impacts on weather conditions around the world.
• Habitat destruction due to coral bleaching,
• Seagrass destruction and loss of kelp forests,
• Affecting the fisheries sector adversely.

Case Study-

• An underwater survey showed 85 per cent of corals in the Gulf of Mannar near the Tamil Nadu coast got bleached after the marine heatwave in May 2020.