The Oceans Are Stratifying Into a Layer Cake


A wave cresting near shore.

Photo: Patrick Smith (Getty Images)

The oceans are facing a host of maladies, from acidification to sea level rise. Turning them into a ginormous liquid layer cake may sound comparatively benign (and delicious). But while Earther is decidedly pro-cake, this is in fact a bad situation.

New research published in Nature Climate Change on Monday shows that oceans are stratifying faster than previous research indicated. It’s due largely to rising temperatures, and the layer cake-ification of the oceans imperils carbon storage and could upend ecology around the world.

By now, it’s blindingly obvious that the planet is trapping more heat, thanks to a blanket of human-driven greenhouse gas emissions. But the ocean stratification impact is not one of the easily seen consequences, unlike *gestures wildly at the world right now.* To get a grasp on how climate change is splitting the ocean into layered slabs, scientists used a mix of modeling and data captured from networks of autonomous floats that rove the ocean loaded with sensors that record temperature, salinity, density, and other ocean variables.

The datasets allowed them to look at the period from 1960 to 2018. They found that parts of every ocean basin were seeing water become less dense up and down the water column, which is to be expected, since warmer water is less dense than colder water. But the changes weren’t uniform throughout the water column. Heat at the surface of the ocean takes longer to propagate to the depths, which means the upper layers of the ocean are getting hotter than the lower ones. That temperature-driven gradient is leading to greater stratification; according to the study, temperature changes made ocean stratification more extreme in more 90% of the areas they observed.