Tiny Arctic Plankton Could Upset World's Oceans as Climate Changes

As the climate changes, the acidity increases in the world's oceans. Carbon dioxide mixes with seawater to create conditions that affect animals with calcium carbonate shells. This, in turn, can impact creatures further up the food chain. Now, scientists have discovered that tiny plankton are succeeding in these conditions of elevated CO2 levels. This could imbalance the food web and decrease ocean CO2 uptake, which could spell drastic consequences for our environment.

Large plankton play an important role when it comes to transporting carbon to the deep ocean. Yet with a system dominated by so-called pico- and nanoplankton, much less carbon is taken out of surface water. This, in turn, could mean that a lot less CO2 is absorbed in the future.

"If the tiny plankton blooms, it consumes the nutrients that are normally also available to larger plankton species," said Ulf Riebesell, one of the researchers, in a news release.

In order to study the effect of ocean acidification on the oceanic ecosystem, the researchers journeyed to the Kongsfjord off the Arctic archipelago of Svalbard. There, they deployed nine large "mesocosms," which are large flotation frames carrying plastic bags with a capacity of 5 cubic meters. These water enclosures allowed the scientists to study plankton communities in their natural environment under controlled conditions. By adding CO2 to the mesocom water to increase acidity, the researchers could see exactly how these communities changed.

In the end, the scientists discovered that when CO2 was elevated, pico- and, to a lesser extent, nanoplankton grew. This plankton drew down nutrients so that they were less available to larger plankton.

"The different responses we observed made it clear that the communities' sensitivity to acidification depends strongly on whether or not nutrients are available," said Riebsell. "Time and [time] again the tiniest plankton benefits from the surplus CO2, they produce more biomass and more organic carbon, and dimethyl sulphide production and carbon export are decreasing."

The findings are published in the journal Biogeosciences.