Article**: Oceans and Wetlands.
Marine heatwaves (MHWS), which last for days to months, have accelerated in frequency in recent years as the global oceans have warmed significantly. The MHWS event has had a knock-on effect on the economy and society as a result of changes in biological production, toxic algae blooms, changes in the structure of coral reef communities, large-scale bleaching of corals, and the death of large numbers of benthic marine communities. At the same time, extreme marine heatwave events have changed the distribution of fish communities, and ultimately changed the structure and function of regional marine ecosystems. All these impacts on marine ecosystems caused by marine heatwaves are likely to continue or even escalate in the future, depending on the extent of ocean warming.
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Based on satellite observations, researchers have conducted extensive studies of the surface signals and drivers of marine heatwaves, but their vertical structure in the global ocean remains unclear. A four-dimensional spatiotemporal framework based on three ocean reanalysis datasets was used to identify marine heatwave events in the upper ocean (0-200 m). The study found that only about half of the marine heatwave events had a continuous surface signal during their life cycle, and about one-third of the marine heatwave events were always present in the subsurface ocean without any effect on the ocean surface temperature and were undetectable at the ocean surface. The number of these potentially harmful events may be much higher than previously thought。The findings reveal the limitations of identifying marine heatwaves based on ocean surface temperature alone and highlight the need for subsurface observations to monitor marine heatwaves. The study was published in Nature Earth Sciences.
Marine heatwaves can have a range of adverse effects on marine ecosystems, as many life forms are unable to adapt quickly to changes in temperature. Given the interconnectedness of marine food webs, seabirds also suffer as a result.
Marine heatwaves are often identified by satellite observations that measure ocean surface temperatures. However, these data do not monitor the depth of the ocean. To gain a deeper understanding, the researchers simulated ocean temperature, salinity, and currents, among other parameters, in which the researchers pinpointed ocean heatwaves by looking for layers of water that remained unusually warm for at least five days, such events could be caused by changes in atmospheric circulation or changes in ocean currents.
Researchers find hundreds of marine heatwaves each year. But surprisingly, a third of these events are never visible at the top 10 meters of the water. "There are a lot of marine heatwaves hidden below the surface. The researchers said. As a result, marine life may face more marine heatwaves than previously thought, which means additional pressure on marine ecosystems.
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