MARINE HEATWAVES

MARINE HEATWAVES

Marine heatwaves (MHW) are prolonged extreme oceanic warm water events that can have devastating impacts on marine ecosystems. The number of annual MHW days has increased substantially since the early twentieth century. This number is projected to grow even more as the planet continues to warm.

Causes:

• Ocean Currents: Ocean currents can build up areas of warm water and air-sea heat flux, or warming through the ocean surface from the atmosphere.
• Poor Wind activity: The rays of the sun heat the surface of the water and without proper wind action, the heat is concentrated in a single region leading to rising temperatures and heatwaves.
• Global Warming: Melting of the polar ice caps also reduces the temperature of the water and contributes to the possibility of heat waves.
• Climatic Events: For example, with strong El Niño events and the suppression of upwelling, changes in surface heat fluxes and modified ocean advection.

Impact:

1. Marine Ecology:
   • Kelp Forests: Heat waves create temperatures that are unsustainable for the subsurface kelp forests and result in their destruction and death.
   • Habitat Destruction: Marine heatwaves can change the habitat ranges of certain species, such as the spiny sea urchin off southeastern Australia, which has been expanding southward into Tasmania at the expense of kelp forests, which it feeds upon.
   • Migration routes: Changes in the temperature of the sea surface and underlying currents can also impact the migration of fish and birds.
   • Coral Bleaching: Exposure to higher temperatures can result in coral bleaching and the destruction of reef ecosystems.
   • Unprecedented die-offs of sea birds: Due to a decline in fish stocks, the marine food cycle is disrupted.
   • Invasive Species: Changing conditions can also help invasive alien species to spread, which can be devastating for marine food webs.
2. Climatological:
   • Cyclones: Higher surface temperatures can lead to cyclones as water temperatures go higher than 26°C.
   • Ocean Currents: Disproportionate heating of various regions of the ocean can impact the flow and intensity of ocean currents, which perform various vital functions for world climate.
3. Humans:
   • Fishing Stocks: Heat waves will cause a decline in fishing stocks, thus impacting the fishing economy.
   • Disasters: Cyclones and storms formed due to marine heatwaves will destroy lives and property, especially for those who live on the coasts.
   • Tourism: Destruction of reef and marine ecosystems can also impact tourism economies, especially for small island states.

Way Forward

• Research Capacity: Funding agencies and governments must build research capacity to monitor MHWs, understand their impacts, and predict future heatwave events.
• Stakeholder Awareness: Local management agencies should therefore raise awareness across all stakeholders and implement forecast systems to help achieve a coordinated response.
• Social Protections: National and sub-national governments should design and implement measures to protect communities and build regional ocean resilience.