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Marine heatwaves (MHWs) have been examined at the ocean’s surface for over ten years, but fresh findings in Nature reveal that 80% of MHWs occurring below 100 meters operate independently of surface-level events. This emphasizes a previously ignored aspect of ocean warming.
This investigation was carried out by CSIRO, Australia’s national science agency, in collaboration with the Chinese Academy of Sciences.
MHWs are extended periods of elevated temperatures that can inflict substantial harm on marine ecosystems, affecting coral reefs and leading to species displacement. Global warming has made these events more frequent, with significant cases noted along Australia’s East Coast and Tasmania, as well as the northeastern Pacific and North Atlantic regions.
Historically, MHWs have been monitored using satellite data focused on surface temperatures. However, this recent study suggests that deep-water heatwaves might be greatly underreported, revealing a notable gap in our comprehension of their overall impact.
The groundbreaking global analysis utilized observational data from over two million ocean temperature readings gathered from oceans worldwide.
According to Dr. Ming Feng from CSIRO, information regarding subsurface events has been scarce—until now.
“Our findings show that MHWs frequently lurk beneath the surface, occurring independently from those at the top,” stated Dr. Feng.
“The deep ocean accommodates various marine life, including plankton and fish species.
“These results enhance our knowledge of how often and intensely extreme temperature events happen beneath the ocean’s surface and their potential consequences.”
The study also underscores how ocean currents, particularly eddies, affect MHWs, identifying them as vital contributors to subsurface phenomena.
“Eddies are swirling water movements that influence the absorption, redistribution, and storage of heat in the ocean. They are crucial to temperature variability,” Dr. Feng remarked.
“Our data indicates that deeper MHWs are frequently linked to ocean eddies.
“In recent decades, global warming has escalated temperature extremes in ocean eddies due to an increase in energy contained within them. This could lead to more frequent and intense MHWs beneath the surface.
In the region of the East Australian Current, data from Australia’s Integrated Marine Observing System indicates that over 70% of MHWs occurring below the surface take place in ocean eddies.
Ocean eddies can affect the levels of acidification, oxygen, and nutrients in the water.
By understanding the factors that drive subsurface MHWs, such as eddies, we can better evaluate these events in a warming world and make future predictions.
This research will also enhance our understanding of the effects of MHWs on the life cycle and distribution of marine species.
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