Scientists Test How Ocean 'Antacid' Affects Plankton in Giant Seawater Enclosures

The ocean absorbs about a quarter of the carbon dioxide humans emit each year, but it has natural limits on how much it can take up, and the CO2 it does absorb makes seawater more acidic. The surface ocean has grown about 30% more acidic on average since the Industrial Revolution, making life harder for corals and other shell-building organisms. Ocean alkalinity enhancement (OAE), a proposed method of adding minerals to seawater to help it absorb more CO2 and counter acidification, is one response being studied, but researchers say it has barely been tested at scale.

Steve Archer, a senior research scientist at Bigelow Laboratory for Ocean Sciences, has spent five years running large mesocosm experiments, using 8,000-litre seawater enclosures that replicate ocean conditions without affecting the sea directly. "There are already companies proposing to do this, but they're going into it without sufficient information on what's going to happen," Archer said.

OAE works by accelerating the natural weathering of rock, which Archer calls "an antacid for the ocean," restoring alkalinity that atmospheric CO2 emissions are currently outpacing. Since 2021, Archer's team, working with researchers in Germany and Spain, has run five mesocosm experiments in Gran Canaria, Bergen and two sites in Germany. They have tested different minerals including quicklime and brucite across ocean conditions ranging from the subtropics to the cold North Atlantic.

The experiments are the first major attempt to test OAE's effects on plankton communities under natural conditions, looking at how changing alkalinity affects plankton physiology and whether the effects cascade up the marine food web. Archer also measures how quickly and effectively plankton capture sunlight for photosynthesis, a process linked to how much CO2 they absorb.