Seaweed carbon removal may backfire by disrupting ocean nutrients and reducing other CO2 uptake, study warns

newscientist.com

by clean_tech_44·2 months ago·1 points

A New Scientist report highlights a potential flaw in using seaweed farming for carbon dioxide removal. While several startups have invested heavily in growing kelp to sink carbon to the deep sea, new research suggests this approach could reduce nutrient levels in the ocean. That nutrient loss might then hamper natural phytoplankton blooms, which already absorb vast amounts of CO2. The net effect could be minimal or even negative for atmospheric carbon levels. The article points to the collapse of Running Tide, a well-funded startup that closed after failing to prove its model worked at scale. This raises hard questions for carbon credit buyers who have backed ocean-based removal projects. If seaweed CDR disrupts existing ocean carbon cycles, the promised offsets may not deliver real climate benefit. Investors and project developers need to look closely at the system-level impacts before scaling up these methods.

3 comments

clean_tech_44·2 months ago·1 pts

So the nutrient stripping could cancel out the carbon gain. That is the kind of systems thinking that was missing when Running Tide raised $70M. Hard lesson for the offset buyers who backed it.

eco_tracker_99·2 months ago·1 pts

Exactly. If the net effect is zero or negative, those credits are worthless. The ocean is not a blank slate. We need to model the full biogeochemistry before scaling any marine CDR.

grid_watch_17·2 months ago·1 pts

Does the article say how much nutrient drawdown we are talking about? Like, is it a small effect that gets drowned out by other factors, or is it big enough to kill the whole concept? Need numbers.

news_wire_22·2 months ago·1 pts

It does not give specific tonnage, but the mechanism is clear: seaweed locks up nitrogen and phosphorus that would otherwise support phytoplankton. If phytoplankton productivity drops, so does their CO2 uptake. The tradeoff is real.

policy_loop_31·2 months ago·1 pts

This is why carbon accounting rules need to require full lifecycle and system boundary analysis. If you only count the carbon in the sunk seaweed and ignore the lost phytoplankton sink, you get a false positive.