Ice at sea

Arctic phytoplankton face competition in warming seas


As Arctic seas warm, important phytoplankton communities could find themselves competing for nutrients with encroaching Atlantic species, suggests new research from Plymouth Marine Laboratory.

The Barents Sea, an area of ocean between Norway and Russia, is a warming hotspot within the Arctic, with higher sea surface temperatures accompanied by increasing amounts of warmer Atlantic water flowing in. These changes, along with decreasing sea ice coverage, have led to a longer growing season for phytoplankton, with knock on impacts for nutrient availability and primary production.

In 2018, the researchers behind the paper focused their attention particularly on the role played by phosphorus, a key nutrient for phytoplankton and other organisms, in the Barents Sea.

The first key finding was that the most southern area assessed (and the one most influenced by the Atlantic) had the highest rates of primary production and the shortest turnover of dissolved inorganic phosphate (DIP), the form most easily used by phytoplankton.

To investigate this further, the team looked at two phytoplankton species: Phaeocystis pouchetti, the dominant phytoplankton in Arctic water communities; and Emiliana huxleyi, which is prevalent in Atlantic phytoplankton communities. E. huxleyi is now commonly found in the southern Barents Sea during summer months, as the water warms to the phytoplankton’s required temperature.

The results showed the Atlantic, E. huxleyi-majority communities taking up DIP more rapidly and retaining a higher portion of the phosphorus than the P. pouchetti-dominated Arctic communities.

These findings suggest that as Atlantic waters and their associated phytoplankton species, with greater phosphorus requirements, continue intruding into the Arctic, the amount of available phosphorus could be a key factor in limiting primary production.

Phosphorus Barents Sea

Lead author Patrick Downes, a PhD student with PML and the University of Bristol, said: "If the 'Atlantification' of these waters continues intensifying, then we're likely to see faster and tighter cycling of phosphorus in phytoplankton communities. This ultimately means their population size could be much more controlled by the availability of phosphorus than they are now.

"Our findings mean that we now have some baseline information in order to continue observing this highly productive region. As Arctic shelf seas continue to warm, it’s essential that we're able to monitor and understand these amazing but at-risk ecosystems."

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