"Thickening algae soup" is causing the Arctic Ocean to suck in more CO2
Climate change is causing profound changes in Arctic, with the region warming faster than the rest of the planet and experiencing a concerning loss of sea ice. Scientists at Stanford University have now observed a dramatic increase in the concentration of phytoplankton in the area, a phenomenon they liken to a “thickening algae soup” that will cause a big change in how effectively the Arctic Ocean absorbs carbon dioxide, though not nearly enough to apply the brakes to global warming.
The work was carried out by researchers at Stanford’s School of Earth, Energy & Environmental Sciences and focuses on tiny algae at the bottom of the food chain called phytoplankton. More specifically, it centers on how effectively phytoplankton biomass can convert sunlight and carbon dioxide into energy, measured by something scientists refer to as net primary production (NPP).
“The rates are really important in terms of how much food there is for the rest of the ecosystem,” says senior author Kevin Arrigo. “It’s also important because this is one of the main ways that CO2 is pulled out of the atmosphere and into the ocean.”
The team used a massive collection of ocean color measurements and newly developed algorithms to track the NPP of the phytoplankton in the Arctic over two decades, between 1998 and 2018. In that period, the team calculates that the NPP increased by 57 percent, which it describes as an unprecedented jump for an entire ocean basin.
This explosion of carbon-eating algae was a surprising revelation for the scientists, but equally interesting are the reasons behind it. For the first decade or so, the increase was tied to the loss of sea ice. This gave the algae more open water to work with and longer growing seasons, enabling them to metabolize more carbon than in the years past.
The team was surprised to find, however, that productivity continued to increase even when melting slowed down midway through, in around 2009. Their analysis revealed that this was because the algae was becoming far more concentrated, “like a thickening algae soup.”
“In a given volume of water, more phytoplankton were able to grow each year,” said lead study author Kate Lewis, who worked on the research as a PhD student in Stanford’s Department of Earth System Science. “This is the first time this has been reported in the Arctic Ocean.”
The team believes this uptick in algae concentration in the Arctic is being driven by a fresh supply of nutrients flowing into the area, providing them with plenty of fuel for growth. The researchers drew these conclusions via measurements of the green plant pigment chlorophyll, taken from satellite sensors and research cruises, and believe these nutrients are being pushed into the Arctic from other oceans.
“We knew the Arctic had increased production in the last few years, but it seemed possible the system was just recycling the same store of nutrients,” Lewis said. “Our study shows that’s not the case. Phytoplankton are absorbing more carbon year after year as new nutrients come into this ocean. That was unexpected, and it has big ecological impacts.”
Rather than exclusively a good thing or a bad thing, the scientists see this discovery as an important piece of the puzzle in understanding the fundamental changes taking place in the Arctic. The relationships between ice loss, warming waters, more productive algae and an increasing capacity for carbon absorption are complex, but observing the long-term trends can help form a clearer picture of the delicate ecosystem.
“There’s going to be winners and losers,” Arrigo said. “A more productive Arctic means more food for lots of animals. But many animals that have adapted to live in a polar environment are finding life more difficult as the ice retreats.”
Importantly, given the relatively small size of the Arctic and our current path in terms of greenhouse gas emissions, the scientists don’t expect this uptick in productivity to play a role in addressing global warming.
“It’s taking in a lot more carbon than it used to take in,” Arrigo said, “but it’s not something we’re going to be able to rely on to help us out of our climate problem.”
The research was published in the journal Science.
Source: Stanford University