Researchers have recently revealed the devastating impact of deep-sea marine heatwaves on ocean ecosystems. While satellites have allowed for daily measurements of surface ocean temperatures since the 1980s, they cannot provide insight into what is happening below. However, new research has shown that marine heatwaves can penetrate all the way down to the seabed, affecting life even in the deepest parts of the ocean.
These marine heatwaves are particularly damaging to the seas covering the continental shelf, where a variety of sea creatures reside. These creatures are sensitive to extreme temperatures, and even a slight increase from their usual cold water temperatures can be devastating. The severity of the heatwaves is exemplified by the death of over a billion sea creatures during a single heatwave off the coast of the western United States and Canada in 2021.
Marine heatwaves force fish and other mobile creatures to migrate towards the poles or to deeper waters in search of cooler temperatures. This migration can also lead to the arrival of new species, causing changes in the ecosystem. However, the true impact of these heatwaves on the seafloor is often overlooked, as it is difficult to gather data on temperatures below the surface.
Australia stands out as one of the few places that has been collecting valuable long-term data on ocean temperatures. One significant source of data comes from oceanographic moorings off the coast of southeast Australia. These moorings, equipped with sensors, have been measuring daily temperatures from the surface to the seafloor since 1993.
The analysis of this temperature data has revealed the different types and causes of marine heatwaves, as well as their seasonal variations. Winter marine heatwaves, for example, occur when the warm East Australian Current moves westward towards the coast, dragging warm water over the continental shelf. In contrast, summer heatwaves can result from clear skies allowing more heat from the sun to reach the ocean surface, or from weaker winds reducing the cooling effect of evaporation.
One particularly strange type of heatwave occurs close to the seafloor, where strong winds create currents that drive warm, shallow water down. These currents mainly originate from cold winds in the south, causing the seafloor to experience a heatwave while people on the coast shiver in cold winds from the Southern Ocean. These undersea heatwaves may be the most destructive to ecosystems, yet they often go unnoticed.
Understanding the different characteristics of marine heatwaves is crucial for predicting their occurrence and impact on our oceans. By obtaining more accurate predictions, we can take necessary measures to reduce the damage to ecosystems, tourism, and fishing industries. Ultimately, reducing carbon emissions is the key to slowing ocean warming and preventing these devastating events from occurring.
The research conducted by Australian scientists sheds light on the complex nature of marine heatwaves and emphasizes the importance of monitoring and protecting our oceans. With continued efforts to gather data and improve our understanding, we can work towards mitigating the threats posed by these heatwaves and safeguarding the diverse marine life that call our oceans home.