Context: At present, Marine Heat Waves are occurring in several oceans, including the northern two-thirds of the Pacific Ocean, the southern Indian Ocean, and some parts of the Atlantic Ocean, as well as the Mediterranean Sea.

What Are Marine Heat Waves?

• A marine heat wave is an extreme weather event. It occurs when the surface temperature of a particular region of the sea rises to 3 or 4 degree Celsius above the average temperature for at least five days. MHWs can last for weeks, months or even years.
• Marine heatwaves can occur in summer or winter – they are defined based on differences with expected temperatures for the location and time of year.

What Causes Marine Heat Waves?

• The most common cause of marine heat waves are ocean currents which can build up areas of warm water and air-sea heat flux, or warming through the ocean surface from the atmosphere.
• Weak winds: Normally, sunlight passes through the atmosphere and heats the surface of the ocean. If there are weak winds this warm water doesn’t mix with the cooler waters below. It sits on top and continues to heat leading to marine heat waves.

How do we measure marine heatwaves?

• A marine heatwave occurs when seawater temperatures exceed a seasonally-varying threshold (usually the 90th percentile) for at least 5 consecutive days.
• Successive heatwaves with gaps of 2 days or less are considered part of the same event.

What are the Impacts of Marine Heatwaves?

• Affect Ecosystem Structure:
  • Marine heat waves affect ecosystem structure, by supporting certain species and suppressing others.
  • Scientists have associated marine heatwaves with the mass mortality of marine invertebrates and have observed that they may force species to change their behavior in a way that increases the risk of harm to wildlife.
• Change Habitat Ranges of Certain Species:
  • Marine heatwaves can change the habitat ranges of certain species, such as the spiny sea urchin off south eastern Australia which 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 affect 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.

Impact of marine heat waves on humans

• Stronger  storms like hurricanes and tropical cyclones:Higher ocean temperatures, leading to higher rates of evaporation.This results in more powerful winds, heavier rainfall and more flooding when storms reach the land — meaning heightened devastation for humans.
• Socio-Economic impact for coastal communities:Half a billion people depend on Coral reefs for food, income, and protection. So when MHWs destroy these reefs, humans relying on them also bear the brunt.

Way Forward

• The effects of MHWs often remain hidden from view under the waves until it is too late. By raising general awareness of these phenomena, and by improving our scientific understanding of their physical properties and ecological impacts, we can better predict future conditions and protect vulnerable marine habitats and resources.

FAQs Related with Marine Heat Waves

Ques 1: What are marine heat waves?

Answer : Prolonged periods of unusually warm ocean temperatures, known as marine heat waves, can have significant impacts on marine ecosystems.

Ques 2: What causes marine heat waves?

Answer :The warming of the ocean due to various factors, including climate change, El Niño events, and natural climate variability, primarily causes marine heat waves.

Ques 3: What are the impacts of marine heat waves?

Answer : Marine heat waves can lead to coral bleaching, disruptions in marine food chains, shifts in species distributions, and damage to marine habitats. They can also affect fisheries, aquaculture, and coastal communities that rely on healthy marine ecosystems.

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