Marine Heatwave
- Marine Heatwaves are prolonged periods of anomalously high Sea Surface Temperature (SST). These events are linked to coral bleaching, seagrass destruction, and loss of kelp forests, affecting the fisheries sector adversely. 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.
Impacts on Rainfall
- The marine heatwave in the Bay of Bengal increased sea surface temperatures, causing higher evaporation rates
and a greater moisture supply in the atmosphere. This surplus of
moisture contributed to above-average rainfall in northwest India. The marine heatwave likely influenced the formation and behavior of depressions in the Bay of Bengal, which may have contributed to an increase in the frequency and intensity of depressions, particularly on faster timescales (3-10 days). The marine heatwave, along with changing timescales of depressions, affected the path and trajectory of these weather systems. Depressions tended to move more towards northwest India rather than north-central India, causing a higher concentration of rainfall in the northwest region, leading to above-average rainfall in that area. 
Other impacts
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,
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.
Economic Losses: Marine heatwaves can cause economic losses through impacts on fisheries and aquaculture.
Affect Biodiversity: A study from 2020 (Genesis and Trends in Marine Heatwaves
Over the Tropical Indian Ocean and Their Interaction With the Indian
Summer Monsoon) reveals that a previous marine heatwave led to bleaching of 85% of corals in the Gulf of Mannar near the Tamil Nadu coast.
Coral Bleaching: When corals face stress by changes in conditions
such as temperature, light, or nutrients, they expel the symbiotic algae
zooxanthellae living in their tissues, causing them to turn completely
white. This phenomenon is called coral bleaching.
Increase the Risk of Deoxygenation and Acidification: Often, they occur alongside other stressors such as ocean acidification, de-oxygenation, and over-fishing. In such cases, MHWs not only further damage habitats, but also increase the risk of de-oxygenation and acidification.
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