Increasing Arctic River Discharge and Its Role for the Phytoplankton
Responses in the Present and Future Climate Simulations
Abstract
Arctic amplification is known to accelerate the hydrological cycle in
high-latitude landmass, which eventually leads to increased river
discharge into the Arctic Ocean. However, the majority of climate models
in Coupled Model Intercomparison Project 5 (CMIP5) tend to underestimate
Arctic river discharge. This study elucidates the role of additional
Arctic river discharge for the phytoplankton responses in the present
and future climate simulations. In the present climate simulation, the
additional freshwater input showed a decrease in the phytoplankton in
spring due to the increasing sea ice, and in summer, it showed an
increase in phytoplankton due to the surplus nitrate leftover from
spring and induced vertical mixing. Similar processes occurred in future
climate simulations. However, in those simulations, the major response
region of phytoplankton to additional freshwater input was altered from
the Eurasian Basin to the Canadian Basin and the East-Siberian Sea. This
is because the current marginal ice zone in the Barents-Kara Sea, where
phytoplankton mainly responds, moves toward the East-Siberian-Chukchi
Sea. We suggest that Arctic river discharge is potentially an important
contributing factor for Arctic ecosystems in both present and future
climate that controls sea ice and nutrient distribution.