Just about everything at the top of the ocean will eventually find its way to the bottom. But just how long the trip will take varies from ocean to ocean, and even season to season.
Divers collecting marine snow. Credit: National Oceanic and Atmospheric AdministrationMost of the material that falls through the oceans is small -- grains of dust that have blown off the land, dead microscopic organisms, and the waste products of small animals. Some falls as single bits, but some of it clumps together, forming small flecks known as marine snow.
How fast this material falls toward the bottom depends on a lot of factors. Some are related to the particles themselves: how big and dense they are, for example, and how they’re shaped. Wide, lightweight particles fall more slowly than those that are compact and heavy.
Other factors are related to the water. Particles fall more slowly through water that’s colder and saltier, for example, because it’s denser than water that’s warmer and fresher. So particles tend to sink a little more slowly in the cold Southern Ocean than in the warm Sargasso Sea. Ocean currents also play a role -- they can push particles sideways, or even back toward the surface. And there can be seasonal differences, too.
When you put all these factors together, the rate at which particles sink varies from just a few feet to thousands of feet per day. In the deep ocean, that means it can take anywhere from a few days to a few years for a particle to reach the bottom. In the deep ocean, this “rain” of solid particles adds up -- to about half an inch every thousand years.
