Marine heat waves, prolonged periods of unusually high ocean temperatures, are increasingly impacting the world’s oceans due to human-induced climate change. These events can have severe consequences for marine ecosystems, biodiversity, and even human societies that rely on the sea for their livelihoods.
Recent research has shed light on a significant aspect of marine heat waves, indicating that they are not limited to the ocean’s surface but can extend deeper into the water column. This new understanding has serious implications for the health of marine ecosystems.
Marine heat waves are defined as events in which ocean temperatures rise to extreme levels and remain elevated for at least five consecutive days. These events are becoming more common as the world grapples with global warming, and the ocean acts as a massive heat sink, absorbing the excess heat. The United Nations’ Intergovernmental Panel on Climate Change estimated that between 1971 and 2018, the ocean absorbed a staggering 396 zettajoules of heat, equivalent to the energy of 25 billion Hiroshima atomic bombs.
The 2022 analysis suggested that it was the warmest year on record for the ocean, and 2023 is predicted to be even hotter, partly due to the current El Niño climate pattern.
While marine heat waves can occur in any part of the ocean, certain regions have experienced more intense and devastating events. Notably, “The Blob” in the northern Pacific Ocean between 2015 and 2016 disrupted the entire food web in the region. More recently, the waters around the U.K. and Europe experienced temperatures as high as 9 degrees Fahrenheit above normal, the warmest in 170 years.
Most of the research on marine heat waves has focused on the ocean’s surface and upper layers since data collection predominantly occurs in these regions. However, a recent study published in Nature Climate Change has demonstrated that these heat waves are also affecting the deeper layers of the ocean.
A team of researchers analyzed global sea temperature reanalysis data from 1993 to 2019 to assess the occurrences of marine heat waves across a large column of the ocean, from the surface to a depth of about 6,600 feet, where a substantial portion of the ocean’s biodiversity resides.
The findings revealed that the most intense marine heat waves are happening in the water column between 160 and 820 feet, a critical zone for marine biodiversity. Furthermore, below this depth and down to about 6,600 feet, the duration of marine heat waves increases significantly compared to the surface.
However, different regions of the ocean react differently to these heat waves. In some areas, factors like salinity changes can restrict warmer waters from going deep, while in others, oceanographic factors may allow heat to penetrate deeper into the ocean.
Understanding the depth and duration of these marine heat waves is critical because they can have far-reaching impacts. They can disrupt ecosystems, lead to species displacement, mass mortalities, and even alter the distribution of marine species as they seek refuge in cooler waters.
Experts emphasize the importance of monitoring these phenomena as they are predicted to increase and intensify in the coming years. Furthermore, the funding for vaccination programs must be accompanied by a comprehensive strategy that includes clean water access, improved sanitation, and other preventive measures.
This research highlights the significance of understanding the cumulative impact of marine heat waves on biodiversity and ecosystems and underscores the urgent need for further study and decisive action to address this growing threat to our oceans.
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Reference: https://www.nature.com/articles/d41586-023-03173-5
