▎ WuXi AppTec content team editor
Hotter summers, increasingly frequent extreme weather... We have a personal understanding of the consequences of global warming. At the same time, in the vast ocean that we can't see, some worrying changes are taking place.
What is already known is that global ocean currents are changing, the oceans are acidifying, and the living environment for marine life is becoming increasingly grim. Now, a study published in Science Advances has uncovered another unintended effect of global warming on the oceans: the oceans are losing their memory.
What is "ocean memory"? We know that the physical conditions of the atmosphere change very quickly, and the temperature may change significantly within a few hours. In contrast, conditions in the ocean are much more persistent and change is more slow. For example, today's sea temperature is likely to be very similar to yesterday's, with little change. Therefore, it can be said that the ocean is like "remembering" the past. Because of this nature, ocean memory can rule out the interference of short-term weather fluctuations and be used to predict the climate system.
But the latest research points out that, according to climate models, as the concentration of greenhouse gases in the atmosphere continues to rise, the decline in ocean memory becomes more pronounced.
According to simulations, by the end of the 21st century, the memory of most of the world's sea areas has declined significantly (Image source: Reference[1])
Ocean memory is related to the depth of the mixed layers close to the surface of the sea. The deeper the mixed layer, the more heat it holds, so there is a greater thermal "inertia" that can be converted into memory. But as the climate warms, the mixed layers of much of the world's oceans are shallower, leading to a decline in ocean memory.
Co-author Dr Robert Jnglin Wills, a scientist at the University of Washington, said: "Some other processes, such as altering ocean currents and the heat exchange between the ocean and the atmosphere, can also alter ocean memory. But in contrast, the decline in ocean memory due to the shallowing of the mixed layer occurs in various regions of the world, so it is also a factor to consider when predicting future climate. ”
▲Trends in ocean memory under different emission scenarios (Image source: Reference[1])
At the same time as ocean memory declines, shallower mixed layers also increase random fluctuations in surface seawater temperature. Otherwise stable sea temperatures can predict long-term changes in the climate system, but the increase in random fluctuations has undoubtedly affected this.
The loss of ocean memory affects not only the prediction of variables in the ocean, but also the way we manage marine ecosystems. As the length of time that can be predicted is shortened due to the loss of marine memory, the time left for people to respond to changes in marine ecology is also decreasing. In addition to predicting the ocean's information, the loss of ocean memory also affects predictions of land temperatures, precipitation, and extreme events — indicators that are also closely linked to seawater temperatures.
The decline in ocean memory and the increase in random fluctuations reveal the inherent variations of the system and the new challenges of making predictions in the context of warming. Co-corresponding author of the paper, Professor Fei-Fei Jin of the University of Hawaii, said.
Resources:
[1] Shi et al., Global decline in ocean memory over the 21st century. Science Advances(2022). DOI: 10.1126/sciadv.abm3468
[2] World’s ocean is losing its memory under global warming. Retrieved May 6th, 2022 from https://www.eurekalert.org/news-releases/951784
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