Environment

Diatom Numbers Dwindling in Some of World's Oceans

Populations of the largest phytoplankton in the ocean declined by more than 1 percent per year between 1998 and 2012, possibly reducing the amount of greenhouse gas being removed from the atmosphere, a new NASA study says.

Diatoms are at the base of most marine food chains. They also play a major role in pulling CO2 out of the atmosphere and depositing its carbon on the deep ocean floor.

Using a complex computer model to examine satellite observations, NASA was able to single out the chlorophyll of diatoms from other phytoplankton blooms.

Writing in the journal Global Biogeochemical Cycles, Goddard Space Flight Center researchers say they don’t know exactly why the diatom populations have declined, mostly in the northern Atlantic, Indian and Pacific oceans.

But they have linked the decline to a more shallow mixing layer of the upper ocean, where sunlight from above and nutrients churned up from below provide the best environment for phytoplankton growth.

They believe changing ocean and wind currents could be involved.

When diatoms die, they carry carbon from the atmospheric carbon dioxide they have absorbed to the deep ocean floor, where it remains in a reservoir called a "carbon sink."