Ocean heatwaves are extreme marine weather and climate events that have important impacts on the marine environment, ecosystems and economic life. Hu Shijian, academician of the Chinese Academy of Sciences and researcher of the Institute of Oceanography of the Chinese Academy of Sciences, and other researchers of the Research Group of Hu Dunxin, based on long-term observation and research, have made important progress in the field of marine heat wave research. For the first time, the study has found super-strong subsurface marine heat waves in the tropical western Pacific Ocean, revealing the important impact of subsurface ocean heat waves on marine fishery resources. The results were recently published in The Journal Research Letters.
Marine heat waves are discrete and short-cycle extreme heat events that occur in the ocean, which occur widely in the global ocean and offshore waters, and have become the forefront of research in the field of marine climate and environment in recent years because of their strong destructive impact on the marine environment and ecosystems. Traditional research based on ocean surface temperature has been held to be one of the least intense marine heat waves in the world. However, Hu Shijian et al. used the TAO/TRITON buoy array to obtain long-term, high-temporal resolution observation data and found that there were strong ocean heat wave events in the subsurface of the tropical western Pacific Ocean, which were independent of surface heat waves, and called them "subsurface ocean heat waves" events. Studies have shown that the average intensity of subsurface ocean heatwaves in the tropical western Pacific Ocean peaks near a depth of 150 meters, with an average regional intensity of 5.2 °C, with some of the seas reaching an average maximum intensity of 8.9 °C, which is 3 to 6 times the intensity of surface ocean heat waves. Subsurface ocean heatwaves occur almost annually, with an average duration of about 17 days each, and their occurrence has no significant correlation with the ENSO index, but has seasonal variations, with stronger and more frequent April to June, and relatively weak and less frequent from September to October.
Further research found that the Ekman downflow caused by the aggregation of ocean surface wind fields is the main mechanism for the formation of subsurface ocean heat waves in the tropical western Pacific Ocean. Observations have shown that the convergence of the sea surface wind field in the tropical western Pacific Ocean causes the warm water of the sea surface to converge and cause the warm water to sink in the form of the Ekman downflow, which in turn leads to extreme abnormal warming of the subsurface ocean. The upper 300-meter layer is the living depth of deep-sea fish such as tuna, while the western Pacific Ocean is the largest tuna fishery in the world. The researchers compared and analyzed the relationship between tuna production and subsurface marine heat waves in Micronesia and other seas, and found that the occurrence of extreme subsurface ocean heat waves may significantly reduce tuna production.
The discovery of subsurface marine heat waves in the western Pacific Ocean has changed the traditional understanding of ocean heat waves, contributed to deepening the understanding of extreme weather and climate events and their marine ecological environment impacts, and has important scientific and applied value. The research work has been funded by the Chinese Academy of Sciences, the National Natural Science Foundation of China and the Natural Science Foundation of Shandong Province.
Schematic diagram of subsurface ocean heat wave events in the tropical western Pacific Ocean
The figure above shows the average intensity (a), annual occurrence (b) and duration (c) of subsurface marine heat waves in the tropical western Pacific Ocean. The middle figure shows the time series (d) of the surface ocean heat wave intensity of each station, and the following figure shows the seasonal change of the subsurface ocean heat wave intensity (c) and the percentage number (f).
Source: Institute of Oceanology, Chinese Academy of Sciences