A new study shows that North Atlantic phytoplankton populations have been stable since the industrial age, contradicting previous studies of decline. To paraphrase Mark Twain, reports of declining phytoplankton in the North Atlantic may be greatly exaggerated. A major study in 2019, using ice cores from Antarctica, suggested that marine productivity in the North Atlantic had declined by 10% during the industrial age, with worrying implications that this trend may continue.

But new research led by the University of Washington suggests that marine phytoplankton, on which larger organisms in the marine ecosystem depend, may be more stable in the North Atlantic than previously thought. The team’s analysis of an ice core from 800 years ago suggests that a more complex atmospheric process could explain recent trends. The study was recently published Proceedings of the National Academy of Sciences.

Understanding the role of phytoplankton

Small floating photosynthetic organisms known as phytoplankton form the basis of the marine ecosystem. These microscopic creatures are also important to the planet as a whole, as they produce approximately half of the oxygen in Earth’s atmosphere.

Phytoplankton is difficult to count, so scientists are trying to measure its abundance in other ways. Phytoplankton emits dimethyl sulfide, a foul-smelling gas that gives beaches their characteristic odor. When dimethyl sulfide mixes with air, it turns into methanesulfonic acid, or MSA, and sulfate. They eventually fall onto land or snow, making ice cores a way to measure population size in the past.

Information from Greenland ice

“Greenland ice cores show a decline in MSA concentrations during the industrial era, which is considered a sign of declining primary productivity in the North Atlantic,” said lead author Ursula Jongeblod, a doctoral student in atmospheric sciences at the UW. she said. “But our study of sulfate in the Greenland ice core shows that MSA alone cannot tell us the whole story when it comes to primary productivity.”

Since the mid-1800s, factories and their exhaust pipes have also been releasing sulfur-containing gases into the air. These gases have slightly different shapes of sulfur atoms, making it possible to distinguish between marine and terrestrial sources in the ice core.

A deeper historical perspective

The new study goes further than previous work by measuring several sulfur-containing molecules in an ice core in central Greenland, layers dating back to 1200-2006. The authors show that man-made pollutants change the chemical composition of the atmosphere. This changed the fate of the gases released by phytoplankton.

“When we looked at ice cores, we found that phytoplankton-derived sulfate increased during the industrial age,” Jongeblod said. said. “In other words, the decline in MSA is ‘balanced’ by a concomitant increase in phytoplankton-derived sulphate, indicating that phytoplankton-derived sulfur emissions remain generally stable.”

Implications and future research

If this balance is taken into account in calculations, phytoplankton populations appear to have been fairly stable since the mid-1800s. But researchers warn that marine ecosystems remain threatened in many ways.

“Measuring both MSA and phytoplankton-derived sulfate gives us a more complete picture of how emissions from marine primary producers are changing, or not changing, over time,” said senior author Becky Alexander, a professor of atmospheric sciences at the university.

“Ice core measurements, combined with other independent estimates of phytoplankton abundance (such as chlorophyll measurements) and modeling studies (which help us assess how atmospheric chemistry and climate change over time), can help us understand how marine productivity has changed in the past.” and how performance may change in the future.’