Amundsen Sea Specific Ecosystem Model: Results of the Lower-trophic Level

Abstract

Amundsen Sea ecosystem is expected to undergo dramatic changes by fast glacier melting (by stronger intrusion of the circumpolar deep water), water temperature increase, strong stratification, and ocean acidification. Therefore, it is required to assess further insights into how the ecosystem respond to rapid environmental change. In order to comprehend and diagnose this area, the community structure of producers and primary production (PP) depending on the environmental changes, detailed simulations were conducted combining the pelagic ecosystem model (ERSEM-European Regional Seas Ecosystem Model) with one-dimensional water column model. We enhanced the model by incorporating the sea ice effects and the dynamics of Phaeocystis and diatom, two dominant species in this area. The sea ice effects contain modulating the ocean surface irradiance by calculating sea ice albedo proportionate to the ice concentration obtained from ECMWF reanalysis data. For dynamics of the two species, the physiological parameters related to the biomass-specific growth rate were determined as the optimal values for simulating surface PP within the limit of observations. The model shows good performance in simulation of the seasonal variation of surface PP (RMSE of Chl-a 0.1) although the inter-annual variations are required to be improved. Model results exhibit that the PP and community structure are fluctuated by iron concentration, while much less sensitive to light or inhibited under the intense light. These imply that the efficiency of carbon uptake in this area might be primarily limited by iron. The simulation of inter-annual variability of PP can be further improved by constraining the strength of each source for dissolved iron as well as light availability, adaptation to the temperature and salinity, grazing pressure, and the interaction with the sea ice ecosystem.