Global phytoplankton weighs as much as 250 million elephants

Using 903 robotic buoys, a team at Dalhousie University, Canada, estimated the global phytoplankton biomass at about 346 million tonnes, equivalent to 250 million elephants.

Half of the biomass lies at depths that satellites cannot detect, according to the research team, Interesting Engineering reported on October 28. Ecosystems and biogeochemical processes on Earth depend heavily on marine phytoplankton. Satellite ocean color data allow for estimates of chlorophyll-a (Chla), or chlorophyll a , which is often used to understand carbon biomass. However, satellites do not directly monitor phytoplankton biomass in the ocean because they only measure a small area on the surface. In addition, cell physiology fluctuates greatly, making Chla a poor proxy for carbon biomass.

Scientists deploy the BGC-Argo robotic buoy in the Labrador Sea. (Photo: Adam Stoer).

In a new study published in the journal Proceedings of the National Academy of Sciences , the Biogeochemical (BGC)-Argo network of robotic buoys helps fill in the gaps left by satellites. The buoys can peer deeper to measure what's going on below. The combined approach provides a more complete picture of ocean conditions and phytoplankton, the team says.

They used a network of 903 robotic buoys to collect nearly 99,350 bio-optical records over the past decade. By analyzing the data from them, the team gained new information about the global distribution and changes in phytoplankton over time and region. The new findings highlight the importance of using robotic buoys to complement satellite observations, providing a clearer view of what is happening below the ocean surface.

The new results have important implications for long-term monitoring of ocean health, especially in light of human-caused climate change, the researchers say. They also suggest that geoengineering projects should take changes in phytoplankton biomass into account when assessing potential environmental impacts.