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Marine Heatwaves

2023 JUL 13

Preliminary   > Disaster Management   >   Disasters   >   Disaster risk reduction

Why in news?

  • The northern Bay of Bengal has been experiencing an intense Marine Heatwave since 28th June 2023, leading to India’s usually arid northwest receiving extreme rainfall.

What are Marine Heatwaves?

  • Marine heatwaves are periods of extremely high temperatures in the ocean.
  • These events are linked to coral bleaching, seagrass destruction, and loss of kelp forests, affecting the fisheries sector adversely.
  • Study showed that 85% of the corals in the Gulf of Mannar near the Tamil Nadu coast got bleached after the marine heatwave in May 2020.
  • The most common drivers of marine heatwaves include ocean currents which can build up areas of warm water and air-sea heat flux, or warming through the ocean surface from the atmosphere.
  • Winds can enhance or suppress the warming in a marine heatwave, and climate modes like El Niño can change the likelihood of events occurring in certain regions.

What are the impacts of Marine Heatwaves?

  • Affect ecosystem structure:
    • Marine heat waves affect ecosystem structure, by supporting certain species and suppressing others.
    • It has been associated with the mass mortality of marine invertebrates, and may force species to change behaviour in a way that puts wildlife at increased risk of harm.
  • Change habitat ranges of certain species:
    • Marine heatwaves can change the habitat ranges of certain species
    • For example: Spiny sea urchin off southeastern Australia has been expanding southward into Tasmania at the expense of kelp forests which it feeds upon.
  • Economic Losses:
    • Marine heatwaves can cause economic losses through impacts on fisheries and aquaculture.
  • Affect Biodiversity:
    • Biodiversity can be drastically affected by marine heatwaves.
    • In 2016, marine heatwaves across northern Australia led to severe bleaching of the Great Barrier Reef.
  • Increase the risk of deoxygenation and acidification:
    • Often they occur alongside other stressors such as ocean acidification, deoxygenation, and overfishing.
    • In such cases, MHWs not only further damage habitats, but also increase the risk of deoxygenation and acidification.

Add ons:

  • The Western Indian Ocean region experienced the largest increase in marine heatwaves at a rate of about 1.5 events per decade, followed by the north Bay of Bengal at a rate of 0.5 events per decade.
  • From 1982 to 2018, the Western Indian Ocean had a total of 66 events, while the Bay of Bengal had 94 events.


With reference to ‘Marine Heatwaves’, consider the following statements:

1. They are periods of extremely high temperatures in the ocean.

2. Marine heatwaves can change the habitat ranges of certain species

Which of the statements given above is/are correct?

(a) 1 only

(b) 2 only

(c) Both 1 and 2

(d) Neither 1 nor 2