The ocean floor is a sort of ultimate collection pan for the entire globe. The sediments that accumulate there come from a variety of sources. Bits of rocks and organic matter can be carried into the ocean by rivers, melting glaciers, or the wind; ocean animals—plankton in particular—die, decay, and settle downward; and minerals in the ocean can naturally precipitate and contribute to the mixture.
Scientists are extremely interested in determining how much sediment exists along the ocean floor—and how it’s distributed spatially—because sediments have a direct impact on plate tectonics. The amount and composition of sediment can even influence the dynamics of earthquakes originating from ocean floor subduction zones.
In a new study, Straume et al. report the results of the most complete survey of ocean floor sediment to date, drawing on data from past compilations that used, primarily, seismic reflection and refraction data. Both of these methods involve creating a loud sound at the water’s surface and then measuring how it bounces off the seafloor. The researchers combined these data into an overlapping grid system with the highest-ever resolution: 5 arc minutes. In total, the team reports that the planet’s oceans contain ~3.37 × 108 cubic kilometers of sediment. That’s roughly enough sediment to cover Earth’s continents in a 2-kilometer-thick layer.
In addition to a revised total, the researchers were also able to model how the sediment was distributed with respect to latitude, concluding that sediment thickness is lowest in the midlatitudes and increases both toward the equator and toward high latitudes in both hemispheres. Finally, the team was able to confirm the long-held belief that sediment thickness also directly correlates with the age of the lithosphere below, with older pieces of crust covered by deeper layers of sediment. This, combined with the observed trends from latitude, allowed the scientists to relate sediment thickness to lithosphere age and latitude in a simple mathematical formula.
This knowledge should help researchers better understand many of the dynamics that contribute to the observed relationships. Sediment thickness is often, for instance, related to chlorophyll patterns in the larger ocean because phytoplankton contributes a significant amount of sediment. Studying the sediment depth across time may allow researchers to infer more about these types of relationships both in the planet’s past and in the future. (Geochemistry, Geophysics, Geosystems, https://doi.org/10.1029/2018GC008115, 2019)
—David Shultz, Freelance Writer