Phytoplankton. Image:

Excess carbon dioxide added to the atmosphere through the combustion of fossil fuels interferes with the health of phytoplankton, which form the base of marine food webs, according to scientists from the Scripps Institution of Oceanography at UC San Diego and the J. Craig Venter Institute, whose findings were published Wednesday in the journal Nature.

Phytoplankton are microscopic plants whose growth in ocean surface waters supports ocean food webs and global marine fisheries. They are also key agents in the long-term removal of carbon dioxide.

The researchers found that a mechanism widely used by phytoplankton to acquire iron has a requirement for carbonate ions. Rising concentrations of atmospheric CO2 are acidifying the ocean and decreasing carbonate, according to the team, which said its study showed how the loss of carbonate affects the ability of phytoplankton to obtain enough of the nutrient iron for growth.

“Ultimately our study reveals the possibility of a ‘feedback mechanism’ operating in parts of the ocean where iron already constrains the growth of phytoplankton,” said Jeff McQuaid, lead author of the study, who made the discoveries as a doctoral student at Scripps. “In these regions, high concentrations of atmospheric CO2 could decrease phytoplankton growth, restricting the ability of the ocean to absorb CO2 and thus leading to ever higher concentrations of CO2 accumulating in the atmosphere.”

The negative effect acidification on corals and shellfish has been documented, but this study is the first to reveal how it affects life that forms the base of most marine food webs, according to the researchers, who say it revises a key oceanography concept that the growth of phytoplankton in vast areas of the ocean is regulated by the concentration of iron. In ocean regions that are high in dissolved nutrients such as nitrogen and phosphorous, iron limitation results in low numbers of phytoplankton relative to amounts of available nutrients.

“Studies investigating the effects of high CO2 on phytoplankton growth have shown mixed results to date. In some cases, certain phytoplankton seem to benefit from high CO2,” said Andrew E. Allen, a biologist with a joint appointment at Scripps and JCVI. “Most of these studies, however, have been conducted under high-iron conditions. Our study uncovers a widespread cellular mechanism that suggests high CO2 might be particularly problematic for phytoplankton growth in low-iron regions of the ocean.”

The study was funded by the National Science Foundation, the Gordon and Betty Moore Foundation and the U.S. Department of Energy.

–City News Service