About The Marine Heatwave

Context:

A recent study published in the journal Nature Communications reveals the occurrence of unprecedented Marine Heatwave (MHW) events in the Arctic Ocean since 2007. Titled ‘Arctic marine heatwaves forced by greenhouse gases and triggered by abrupt sea-ice melt,’ the research highlights 11 MHW events between 2007 and 2021, coinciding with significant declines in Arctic sea ice.

Relevance:

GS I: Geography

Dimensions of the Article:

1. Key Highlights of the Study on Arctic Marine Heatwaves (MHWs):
2. Marine Heatwave
3. Impact of Marine Heatwave on Rainfall in Northwest India
4. Impacts of Marine Heatwaves

Key Highlights of the Study on Arctic Marine Heatwaves (MHWs):

Arctic MHW Occurrences (2007-2021):

• 11 MHW events observed in the Arctic during this period.
• Characterized by prolonged high Sea Surface Temperatures (SST).
• Coincide with significant declines in Arctic Sea ice.

Arctic MHWs in 2022:

• Severe and extreme marine heatwaves occurred in the Laptev and Beaufort seas from spring to autumn.
• Reported in the State of the Global Climate 2022 report.

Changes in Arctic Sea Ice Cover:

• Perennial sea ice cover over the Arctic Ocean has significantly decreased since the mid-1990s.
• Shift from thicker and deformed ice cover to thinner and more uniform ice since 2007.
• Thinner ice is less durable, leading to faster melting and increased solar radiation absorption.

Arctic MHW Regions:

• Primarily observed in marginal seas, including Kara, Laptev, East Siberian, and Chukchi seas.
• Shallow mixed-layer depths and predominantly first-year ice cover contribute to MHW development.
• Abrupt sea ice retreat could trigger MHW events.

Role of Greenhouse Gas (GHG) Forcing:

• GHGs identified as a sufficient cause for moderate marine heatwaves.
• 66-99% probability that GHGs contribute to MHW occurrences exceeding 1.5°C.

Long-Term Warming Trend in Arctic:

• Pronounced warming trend observed in the Arctic.
• SST increasing at a rate of 1.2°C per decade (1996-2021).
• Increased frequency of extreme SST events in eastern Arctic marginal seas over the last two decades.

Consequences and Impacts:

• Warns of dramatic consequences, including impacts on food chains, fish stocks, and overall biodiversity.
• Emphasizes the need to address the consequences of Marine Heatwaves in the Arctic.

Methodology – Extreme Event Attribution (EEA):

• Study employs EEA technique to assess the role of GHG forcing in Arctic MHWs.
• EEA determines the influence of human-induced climate change on the likelihood and severity of specific extreme weather events.

Marine Heatwave:

• Marine heatwaves are prolonged periods of abnormally high Sea Surface Temperature (SST).
• These events can lead to coral bleaching, seagrass destruction, and loss of kelp forests, impacting the fisheries sector negatively.
• Common drivers of marine heatwaves include ocean currents that accumulate warm water and air-sea heat flux, which is warming from the atmosphere through the ocean surface.
• Winds can amplify or dampen the warming effects of a marine heatwave, and climate modes like El Niño can influence the occurrence of these events in specific regions.

Impact of Marine Heatwave on Rainfall in Northwest India:

• The marine heatwave in the Bay of Bengal elevated sea surface temperatures, resulting in increased evaporation rates and a higher supply of moisture in the atmosphere.
• This surplus moisture contributed to above-average rainfall in northwest India.
• The marine heatwave likely influenced the formation and behavior of low-pressure systems called depressions in the Bay of Bengal.
• These depressions play a significant role in monsoon and rainfall patterns.
• The marine heatwave, along with changing timescales of depressions, affected the path and trajectory of these weather systems.
• Depressions were more inclined to move towards northwest India rather than north-central India, leading to a concentration of rainfall in the northwest region and resulting in above-average rainfall in that area.

Impacts of Marine Heatwaves:

• Ecosystem Structure: Marine heatwaves can alter ecosystem structure by favoring certain species while suppressing others.
• Mass Mortality: Marine heatwaves have been associated with mass mortality events in marine invertebrates, leading to significant ecological disruptions.
• Behavioral Changes: Species may be forced to change their behavior in response to marine heatwaves, putting them at increased risk of harm.
• Habitat Range Shifts: Marine heatwaves can cause shifts in the habitat ranges of species, resulting in changes to ecosystem dynamics. For example, the expansion of spiny sea urchins into new areas can negatively impact kelp forests.
• Economic Losses: Marine heatwaves can have significant economic impacts, particularly on fisheries and aquaculture industries.
• Biodiversity Loss: Marine heatwaves can lead to drastic declines in biodiversity, affecting the overall health and functioning of marine ecosystems.
• Corals and Bleaching: Marine heatwaves can cause widespread coral bleaching, leading to coral mortality and ecosystem degradation.
• Interaction with Other Stressors: Marine heatwaves often occur alongside other stressors such as ocean acidification, deoxygenation, and overfishing. These combined stressors can further damage habitats and increase the risks of deoxygenation and acidification in affected areas.

-Source: Down To Earth