The ocean is starting to lose its memory, scientists warn

The oceans around us are changing. As our climate changes, so does the world’s waters, with anomalies evident not only in ocean temperature, but also in its structure, currents, and even color.

As these changes unfold, the generally stable environment of the ocean becomes increasingly unpredictable and erratic, and in some ways the phenomenon is akin to the memory loss of the ocean, suggest the scientists.

“Ocean memory, the persistence of ocean conditions, is a major source of predictability in the climate system beyond meteorological time scales,” the researchers explain in a new paper led by the first author and researcher on the climate Hui Shi from the Farallon Institute in Petaluma, California.

“We show that ocean memory, as measured by the year-to-year persistence of sea surface temperature anomalies, is projected to decline steadily over the next few decades over much of the globe.”

In the research, the team studied sea surface temperatures (SST) in the shallow upper layer of the ocean, called the Upper Mixed Layer (MLD).

Despite the relative shallow depth of the MLD – extending only to a depth of about 50 meters from the ocean surface – this upper water layer exhibits great persistence over time in terms of thermal inertia, especially in relation to the variations observed in the atmosphere above.

Looking ahead, however, modeling suggests that this “memory” effect of thermal inertia in the upper ocean is expected to decline globally over the remainder of the century, with considerably greater temperature variation. expected over the next few decades.

“We discovered this phenomenon by looking at the similarity of ocean surface temperature from year to year as a simple measure of ocean memory,” Hui says.

According to the researchers, shoaling effects in the MLD will introduce higher levels of water mixing into the upper ocean, effectively thinning the upper layer.

This should reduce the thermal massing capacity of the ocean, making the upper ocean more susceptible to random temperature anomalies.

What this means for marine fauna is unclear, but the researchers note that “consecutive impacts on populations are likely”, although some species are expected to fare better than others in terms of adaptation.

On another note, declining ocean memory is expected to make it much more difficult for scientists to predict future ocean dynamics, reducing reliable timelines for all sorts of SST-related predictions. This will hamper our ability to project monsoons, marine heatwaves (MHW) and periods of extreme weather, among others.

As extreme weather is expected to become more frequent in the future, our need to accurately forecast measurements for things like ocean temperature, precipitation levels, and atmospheric anomalies becomes even more important – but if the ocean loses its memory, we risk going the other way. , say the researchers.

“The projected decline in ocean memory is likely to hamper ocean forecasting efforts by reducing the lead times at which SST forecasts, including those for MHWs, are adept,” the authors write.

“Future warming-induced MLD shoals may also alter extreme temperature statistics…which, combined with a reduced lead time for predictions based on the persistence of ocean surface conditions, will pose challenges for the management of ecosystems and marine risk preparedness.”

The findings are reported in Scientists progress.

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