Earth’s oceans feel man-made anger. Glaciers are melting, sea levels are rising and reefs are dying – and now, according to a new study published in Science Advances, the sea is completely losing its memory.
Unlike the weather, which can change wildly and rapidly from day to day, Earth’s oceans generally have only slight changes throughout the week. This persistence is called “memory” and is related to the thickness of the ocean’s upper mixed layer. Similar to how a thicker mattress provides better cushioning, a thicker sea surface layer allows for better memory due to the thermal inertia involved.
But as global warming increases and the temperature of the ocean rises, this upper layer is thinning. And like a thinning mattress, the support, or in this case the “memory” from year to year, weakens.
“It’s almost like the ocean is developing amnesia,” said the study’s lead author, Hui Shi.
This memory is what helps scientists predict ocean conditions, and its decline will make it harder to track changes.
Study co-author Fei-Fei Jin, a professor at the University of Hawai’i Mānoa, said that this, along with the random fluctuations that were found in sea surface temperature, “suggests intrinsic changes in the system and new challenges in prediction under heating.”
And the impact of these changes will be felt in our lifetime.
Using a full range of Earth system models, the researchers predict that the memory of the ocean will decline across most of the world by the end of the 21st century – just 79 years from now. At the time, models suggest that some regions will experience reductions in ocean memory of up to 100%.
Climate-change-induced shoals are primarily responsible for the decline, the researchers found, and human activities, primarily the burning of fossil fuels, are the primary source of global warming.
In addition to making it more difficult to predict ocean surface changes, a declining ocean memory could negatively impact how well we are able to manage sensitive ecosystems.
Fishing, for example, depends on a stable marine environment. But if the memory of the ocean has diminished, state estimates could become less reliable. The study researchers also say it could impact populations of sea life that are adapted to more constant environmental conditions.
Unstable ocean conditions can also affect temperature, precipitation, and extreme weather events around the world.
This was seen even in 2019 during the Pacific Northwest Marine Heat Wave, when mixed layer depth reached an all-time high due to stronger winds and stronger surface warming. According to a paper by the US Climate Variability and Predictability Program last year, climate model projections show that global warming will only continue to cause such conditions.