SCIENCE sciencemag.orgPHOTO: MARTIN FORTIER/UNIVERSITÉ LAVAL
ECOLOGYClimate change tweaks Arctic marine ecosystems
Nutrient input might enhance productivity in the Arctic Ocean of the future
By Marcel BabinI
cepack reduction enhances exposure
of the fairly dark Arctic Ocean (AO) to
sunlight, thus promoting microalgae
biomass buildup and productivity of
the marine ecosystem. This seemingly
reasonable assertion is a matter of lively
debate centered on the function and fate
of the Arctic marine ecosystem under cli-
mate change pressure. A second paradigm
postulates that additional inputs of nitro-gen, which is chronically low over large
stretches of the AO, would be required to
enable the algae to take full advantage of
greater availability of light. On page 198 of
this issue, Lewis et al. ( 1 ) confirm the lat-
ter notion with observations of recent bio-
mass buildup at the AO surface that is likely
driven by hydrodynamical processes that
replenish essential nitrogen fuel.
The AO hosts a rich community of living
organisms. From microbes to mammals,
nearly all depend directly or indirectly on
primary production (PP) of plant biomass by
microscopic marine algae (phytoplankton).
In this most polar of oceans, phytoplank-
ton must cope with two extraordinary con-straints: a roller coaster–like seasonal light
cycle and a water column vertically orga-
nized into a “mille-feuille” structure. The un-
derwater light regimen is controlled by the
polar night and midnight Sun alternation
as well as by sea ice, which acts as a blind
on top of the AO before abruptly vanishing
over most of the AO each summer. The AO
vertical structure is characterized by a den-
sity gradient formed from massive inputs of
lightweight fresh water from rivers and ice
melts at the surface. The resulting stratifi-
cation limits vertical exchanges of solutes
and thus the replenishment, in the surface
layer, of inorganic nutrients necessary to the
growth of microalgae. This phenomenonTakuvik International Research Laboratory, Université Laval
and CNRS, Université Laval, Quebec City, QC G1V 0A6,
Canada. Email: [email protected]PERSPECTIVES
10 JULY 2020 • VOL 369 ISSUE 6500 137An aerial view of summer ice in the Canadian Beaufort Sea, adjacent to the Arctic Ocean. Here, climate change has greatly altered the icepack, making it less extensive,
thinner, more dynamic, and covered with more melt ponds.