Deep-Sea Nutrients Could Temper Global Change

The world’s biggest fisheries have something in common: their productivity comes from the bottom of the sea. In areas where deep, nutrient-rich water flows up to the ocean’s surface, the benefits are felt all the way up the food chain: phytoplankton bloom, zooplankton flourish, and fish populations thrive.

Senior Research Scientist Steve Archer wants to harness that productivity and mitigate global climate change in the process. Last summer, he worked alongside Research Associate Kevin Posman, collaborators from the GEOMAR Helmholtz Centre for Ocean Research, and collaborators from Universidad de Las Palmas de Gran Canaria to run an experiment in the Canary Islands studying the effectiveness of generating upwelling in the oceans.

The experiment took place in pelagic mesocosms, 60-foot containers that isolate a column of seawater for experimentation. The team added large volumes of nutrients to the containers, mimicking the upwelling of deep, nutrient-rich water that occurs in the region. Over the next twenty-five days, they measured the gases that the phytoplankton produced.

“The phytoplankton responded very quickly and more strongly than we expected,” Archer said. “The added nutrients from the deep water definitely increased their productivity.”

On day six, Archer and Posman noticed a large spike in dimethyl sulfide, a gas produced by certain types of phytoplankton. This is where the potential for geoengineering comes in: dimethyl sulfide helps form clouds, which reflect the sun’s rays and help keep the planet cool.

“That's what’s amazing about conducting research on the gas exchange between the air and the ocean,” Archer said. “It takes you from working with little cells in a test tube all the way up to the scale of global climate.”

Ultimately, Archer envisions that it may be possible to install wave-powered pumps in areas of circular flow called eddies. This would artificially enhance upwelling at target locations and create self-powered, productive patches in the ocean.

“There’s a potential double benefit here, of enhancing food production and tempering climate change,” Archer said.

However, as global warming progress, it will become increasingly difficult to temper. Archer and collaborators ran another version of the mesocosm experiment in 2014, in which they first increased the water’s acidity before adding deep water to simulate upwelling. This simulated the future ocean conditions that scientists project will result from global climate change.

The scientists found that, the more acidic the water, the less dimethyl sulfide was produced—a result that, in the real world, would translate to fewer clouds and a warmer planet, effectively compounding the temperature rise predicted to accompany climate change.

“We must understand these systems as well as we can in order to look for solutions for both food safety and the environment,” Archer said.