Scientists report long-term dip in world’s phytoplankton
LOS ANGELES — The world’s phytoplankton appears to have been disappearing at a rate of about 1 percent a year for the past century, researchers said Wednesday, a disturbing long-term trend for the microscopic algae that form the basis of the marine food chain and produce much of the world’s oxygen.
In reporting their findings in the journal Nature, the Canadian team said that, since 1950, phytoplankton biomass has shrunk by about 40 percent. Scientists had known the population was shrinking, but the long-term nature of that reduction came as a surprise.
“A global decline of this magnitude? It’s quite shocking,” said Dalhousie University marine scientist Daniel Boyce, the study’s lead author.
The new study combines historical records of ocean clarity with modern satellite data, the latter of which has only been available since the 1970s. Together, the modern and historical information provide an accurate long-term view of the state of phytoplankton, something scientists haven’t had before now.
The historical data were based on measurements of ocean clarity, which involved lowering what looked like a white dinner plate into the ocean until observers lost sight of it. Water murkiness increases or decreases depending on the amount of phytoplankton or, more specifically, The decline in phytoplankton could have long-term effects on the marine food chain and the world’s oxygen supply, researchers say. Marine diatom cells are an important group of phytoplankton. the plant’s green chlorophyll. The fewer phytoplankton, the clearer the ocean.
Thus, the scientists were able to convert historical data into specific measures of phytoplankton populations, using it with the modern information to create a timeline of the algae over the past century.
“They’re creating a climate record out of something that really wasn’t designed to do this, using sophisticated techniques,” said David Siegel, a University of California, Santa Barbara, marine scientist who co-wrote a commentary on the paper.
The scientists noted that the global decline, which was observed in eight out of 10 ocean basins, also corresponded with a rise in ocean temperatures during the past century.
The scientists suspect that warming near the surface of the ocean makes each ocean layer more distinct — preventing the bottom layer, which is rich in nutrients, from mixing effectively with the upper layers and thus fertilizing the phytoplankton.
Boyce said he hopes the research will encourage more study of the decline. Looking into the past could help scientists determine how to reverse the declines, he said.
“This is the tip of the iceberg, in some respects,” Boyce said. “Phytoplankton are key to the whole ecosystem. In terms of climate changes, the effect on fisheries, we don’t know exactly what these effects will be.”