Earth's oceans show decline in microscopic plant life

http://www.eurekalert.org/pub_releases/2015-09/nsfc-eos092315.php

Public Release: 23-Sep-2015
Earth's oceans show decline in microscopic plant life
NASA/Goddard Space Flight Center

The world's oceans have seen significant declines in certain types of microscopic plant-life at the base of the marine food chain, according to a new NASA study. The research, published Sept. 23 in Global Biogeochemical Cycles, a journal of the American Geophysical Union, is the first to look at global, long-term phytoplankton community trends based on a model driven by NASA satellite data.

Diatoms, the largest type of phytoplankton algae, have declined more than 1 percent per year from 1998 to 2012 globally, with significant losses occurring in the North Pacific, North Indian and Equatorial Indian oceans. The reduction in population may reduce the amount of carbon dioxide drawn out of the atmosphere and transferred to the deep ocean for long-term storage.

"Phytoplankton need carbon dioxide for photosynthesis, just like trees," said oceanographer and lead author Cecile Rousseaux, of Universities Space Research Association and NASA's Goddard Space Flight Center in Greenbelt, Maryland. Carbon dioxide (CO2) from the atmosphere dissolves in cold ocean water. During a phytoplankton bloom, which can span hundreds of miles and be seen from space, the tiny organisms take up the dissolved CO2 and convert it to organic carbon - a form that animals can use as food to grow, the essential base of the marine food web. Then when the phytoplankton cell dies, it sinks to the ocean floor, taking with it the carbon in its body.

Because they are larger than other types of phytoplankton, diatoms can sink more quickly than smaller types when they die. A portion will circulate back to the surface because of ocean currents, and, like fertilizer, fuel another phytoplankton bloom. But the rest will settle on the sea floor miles below, where they will accumulate in sediment and be stored for thousands or millions of years. The process is one of the long-term storage options for carbon removed from the atmosphere.

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