A surprising shift is currently happening in the Arctic Ocean, a new study has found. Dark water is blooming with phytoplankton, the tiny algae at the base of the food web, as sunlight floods spaces that used to be obscured by ice that is no longer there.
Researchers from Stanford University found that there has been a 57% increase in phytoplankton in the Arctic ocean over the past two decades. This has exceeded the researcher’s expectations, as it’s changing the way the ocean stores carbon and sucking up resources needed for the rest of the ecosystem.
“The rates are really important in terms of how much food there is for the rest of the ecosystem,” Earth system scientist and co-author Kevin Arrigo told Science Alert. “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 Arctic is warming much faster than the rest of the planet, having experienced a temperature increase of 0.75 degrees Celsius (1.35 degrees Fahrenheit) in the last decade alone. Meanwhile, Earth as a whole has warmed by nearly the same amount, 0.8 degrees C, but over the past 137 years.
Arrigo and his colleagues looked at net primary production (NPP), which is a degree of how fast plants and algae convert sunlight and carbon dioxide into sugars that other creatures can eat. They found that NPP in the Arctic increased by 57% between 1998 and 2018. That's a record jump in productivity for an entire ocean basin.
Even more surprising, they discovered that while NPP increases were initially linked to retreating sea ice, productivity continued to climb even after melting slowed down around 2009. "The increase in NPP over the past decade is due almost exclusively to a recent increase in phytoplankton biomass," Arrigo said.
This means that phytoplankton was once metabolizing more carbon across the Arctic just because they were gaining more open water over longer growing seasons, thanks to changes in ice cover driven by climate change. Now, they are growing more concentrated, according to the study’s findings.
“In a given volume of water, more phytoplankton were able to grow each year,” said in a statement lead study author Kate Lewis, who worked on the research as a Ph.D. student in Stanford's Department of Earth System Science. “This is the first time this has been reported in the Arctic Ocean.”
Phytoplankton is absorbing more carbon year after year as new nutrients come into this ocean
Phytoplankton needs plenty of nutrients and light to grow. But their availability on the water column depends on complex factors. As a result, despite the fact that Arctic researchers have observed phytoplankton blooms going into overdrive in recent decades, they have debated how long the boom might last and how high it might climb.
The researchers assembled a massive collection of ocean floor measurements for the Arctic Ocean and built algorithms to estimate the concentration of phytoplankton. This allowed them to find new evidence that continued increases in production may no longer be as limited by scarce nutrients as once suspected.
"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."
The work will help to clarify how climate change will shape the Arctic Ocean's future productivity, food supply and capacity to absorb carbon. There's going to be winners and losers, according to Arrigo. “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,” he argued.
The study was published in the journal Science.