The concept of ocean memory has nothing to do with homeopathy or other esoteric concepts but rather refers to the persistence of ocean conditions, which is measured by the year-to-year persistence of sea surface temperature anomalies. Now, a new study has found most of the ocean mass is steadily losing its important memory, and it’s all because of global warming.
It’s like the ocean is developing amnesia, says Hui Shi one of the researchers behind this new study.
Ocean memory is often used by researchers to predict ocean conditions. Compared to the fast changes that happen in the atmosphere, the ocean is much more persistent (it has a “memory”) and changes take a longer time to happen. But as we continue to spew our more and more gas emissions, this memory decline will become more evident — and more problematic.
The challenges of ocean memory
Ocean memory is related to the thickness of the uppermost layer of the ocean, known as the mixed layer, the researchers explained. Deeper mixed layers have more heat content, which gives more thermal inertia that translates into memory. However, the mixed layer is expected to become shallower because of global warming, leading to a reduced ocean memory.
“Other processes, such as changes in ocean currents, also contribute to changes in ocean memory, but the shoaling of the mixed layer depth and resulting memory decline happens in all regions of the globe, and this makes it an important factor to consider for future climate predictions,” Robert Jnglin Wills, co-author, said in a statement.
As well as declining the ocean’s memory, the fact that the mixed layer is becoming shallower also increases the random fluctuations of the sea surface temperature, the researchers found. This means that while the ocean won’t vary much from year to year in the future, the signals for predictions largely reduced, challenging the way marine ecosystems are managed.
Michael Jacox, a research scientist at NOAA Fisheries’ Southwest Fisheries Science Center in Monterey, California, and co-author of the research said there’s going to be less time to make a forecast because of the reduced ocean memory. This may challenge our ability to prepare for ocean change, such as marine heatwaves, which largely affect ecosystems, he added.
Reduced ocean memory can severely alter fisheries management, the researchers said. Stock assessments are done assuming a stable environment represented by the recent past. These could become inaccurate due to ocean memory loss and create the need for new ecosystem-based fisheries management schemes, such as real-time ocean monitoring.
But the list goes on. The researchers also said forecasting land-based impacts of temperature, precipitation, and extreme weather events can be affected by ocean memory loss because of their dependence on the persistence of sea surface temperature as a predictability source. Impacts on populations of biological resources are also expected.
“Reduced ocean memory together with increased random fluctuations suggest intrinsic changes in the system and new challenges in prediction under warming,” Fei-Fei Jin, an atmospheric sciences professor at the University of Hawai’i at Mānoa School of Ocean and Earth Science and Technology, and co-author of the research, said in a statement.
The study was published in the journal Science Advances.