Humans are causing the ocean to lose its memory, study shows

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Earth’s oceans are feeling the wrath of human-induced climate change. 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 losing its memory altogether. 

Unlike weather, which can change wildly and rapidly day-to-day, Earth’s oceans usually only have slight changes throughout the week. This persistence is called “memory” and is related to the thickness of the ocean’s top mixed layer. Similar to how a thicker mattress provides better cushioning, a thicker sea surface layer allows for a better memory because of the thermal inertia at play. 

But as global warming increases and the ocean temperature rises, that top layer thins out. And like a thinning mattress, the support, or in this case the year-to-year “memory,” weakens. 

“It’s almost as if the ocean is developing amnesia,” study lead author Hui Shi said. 

This memory is what helps scientists predict ocean conditions, and its decline will make it harder to keep up with changes. 

Study co-author Fei-Fei Jin, a professor at the University of Hawai’i Mānoa, said that this, along with random fluctuations that have been found in sea surface temperature, “suggest intrinsic changes in the system and new challenges in prediction under warming.” 

And the impact of these changes will be seen within our lifetime. 

Using a comprehensive array of Earth system models, researchers project that the ocean’s memory will decrease throughout 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 have ocean memory reductions of up to 100%. 

Shoaling induced by climate change is primarily responsible for the decline, researchers found, and human activities, primarily burning fossil fuels, are the main source of global warming.

Along with making it more difficult to predict changes at the ocean surface, a declining ocean memory could negatively impact how we’re able to manage sensitive ecosystems. 

Fisheries, for example, rely on a stable marine environment. But if the ocean’s memory has declined, then condition estimates could become more unreliable. The researchers of the study also say it could impact marine life populations that are adapted to more constant environmental conditions. 

Unstable ocean conditions can also influence temperature, precipitation and extreme weather events around the world. 

This was seen even in 2019 during the Northwest Pacific marine heatwave, when the mixed layer depth reached a record low because of higher winds and stronger surface heating. According to a post from the U.S. Climate Variability and Predictability Program last year, climate model projections show that global warming will only continue to drive such conditions. 

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