Study suggests phytoplankton populations are on the decline

GREENBELT, Md., Sept. 23 (UPI) -- According to NASA satellite data, phytoplankton populations are shrinking. Diatoms, the largest and most common form of the plant-like microorganisms, have declined 1 percent per year from 1998 to 2012.

In addition to anchoring most marine food chains, phytoplankton plan an important role in carbon storage, pulling CO2 out of the atmosphere and into the deep ocean via photosynthesis.

Diatoms are especially efficient and bringing carbon dioxide deep below the surface, as they are larger than most other types of phytoplankton and sink faster and deeper.

NASA satellites can track phytoplankton blooms by measuring chlorophyll levels. But satellites aren't able to distinguish between different types of plankton.

To get a better sense of the health of each type of the single-celled algae, scientists at NASA's Goddard Space Flight Center plugged satellite data into complex ocean models that simulate the development of different kinds of algae blooms. These models are fed with current data on ocean currents and nutrients levels -- data sourced from buoys and research ships.

"Inclusion of satellite data into this kind of biogeochemical modeling is really exciting," Jeremy Werdell, an oceanographer at Goddard, explained in a press release. "By combining satellite data, models, and additional environmental information, you can start telling a more holistic story."

The new analysis -- detailed in the journal Global Biochemical Cycles -- showed that diatoms are declines as a result of a shallower mixed layer, the upper layer of the ocean that features sunlight from above and nutrients churned from below. The shallower the mixed layer, the less nutrients available for phytoplankton blooms.

Researchers aren't yet sure why the mixed layers have shallowed over the last two decades, but say shifting wind and current patterns could be playing a role.

For now, the decline of diatoms is significant but not necessarily alarming. It is, however, something scientists say they will continue to monitor as they study how the ocean's biological systems are transformed by a changing climate.