Global climate change is warming the Arctic Ocean and shrinking sea ice. Here, the blue-white ice cap shows the coverage of sea ice at its smallest extent in summer 2020, and the yellow line shows the typical Arctic sea ice minimum extent between 1981 and 2010. Some have proposed that the newly exposed sea surface will lead to a plankton population boom and a burgeoning ecosystem in the open Arctic Ocean, but a team of Princeton scientists say that’s not likely. They have examined the history and supply rate of nitrogen, a key nutrient. Their recent work finds that stratification of the open Arctic waters, especially in the areas fed by the Pacific Ocean via the Bering Strait, will prevent surface plankton from receiving enough nitrogen to grow abundantly. Credit: Illustration by Jesse Farmer, Princeton University; modified from Rebecca Lindsey and Michon Scott, “Climate change: Arctic sea ice,” NOAA Climate.gov
As global warming leads to a hotter planet, the Arctic region is experiencing uncharacteristically warmer temperatures. This has raised hopes that the warmer temperatures might hasten a phytoplankton bloom leading to more productive waters that support fish and other animals.
But a team of scientists led by Princeton University and the Max Planck Institute for Chemistry disagrees. In the current issue of the journal Nature Geoscience, they suggest that under a global warming regime, open Arctic waters will experience more intense nitrogen limitation, likely preventing a rise in productivity.
Plankton need more than just sunlight to grow and thrive. They need abundant nutrients, such as nitrogen, which are typically supplied by deeper, denser waters. But the Arctic Ocean receives an influx of salty Pacific waters, which flows through the Bering Strait. These waters flow over the denser water layers, keeping nutrients at greater depths and limiting them from reaching upper levels.
By examining fossilized plankton from the past, the researchers found that during warmer periods, such as after the last Ice Age, nitrogen was subsumed under less dense water layers. With the Earth warming, a similar scenario will likely play out — limiting the amount of vital nutrients like nitrogen from reaching surface waters.
