As the Arctic Ocean warms and sea ice shrinks, will the newly exposed sea surface see a plankton population boom and a burgeoning ecosystem in the open Arctic Ocean? Not likely, say a team of scientists who have examined the history and supply rate of nitrogen, a key nutrient. 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.
Not so fast, says a team of scientists led by Princeton University and the Max Planck Institute for Chemistry.
They point to nitrogen, a vital nutrient. The researchers used fossilized plankton to study the history of sources and supply rates of nitrogen to the western and central open Arctic Ocean. Their work, detailed in a paper in the current issue of the journal Nature Geoscience, suggests that under a global warming regime, these open Arctic waters will experience more intense nitrogen limitation, likely preventing a rise in productivity.
«Looking at the Arctic Ocean from space, it’s difficult to see water at all, as much of the Arctic Ocean is covered by a layer of sea ice,» said lead author Jesse Farmer, a postdoctoral research associate in the Department of Geosciences at Princeton University who is also a visiting postdoctoral fellow at the Max Planck Institute for Chemistry in Mainz, Germany. This sea ice naturally expands during winters and contracts during summers. In recent decades, however, global warming has caused a rapid decline in summer sea ice coverage, with summer ice cover now roughly half that of 1979.
As sea ice melts, photosynthesizing plankton that form the base of Arctic food webs should benefit from the greater light availability. «But there’s a catch,» said contributing author Julie Granger, an associate professor of marine sciences at the University of Connecticut. «These plankton also need nutrients to grow, and nutrients are only abundant deeper in the Arctic Ocean, just beyond the reach of the plankton.» Whether plankton can acquire these nutrients depends on how strictly the upper ocean is «stratified,» or separated into layers. The upper 200 meters (660 feet) of the ocean consists of distinct layers of water with different densities, determined by their temperature and saltiness.
«When the upper ocean is strongly stratified, with very light water floating on top of dense deep water, the supply of nutrients to the sunlit surface is slow,» said Farmer.
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Materials provided by Princeton University. Original written by Liz Fuller-Wright. Note: Content may be edited for style and length.