Simulation And Analysis Of The Response Of Arctic Ocean Plankton To Environmental Change

Eco-dynamics of marine plankton are remarkably sensitive to changes in their environments.The Arctic Ocean is undergoing rapid environmental changes as the global climate change intensifies.Understanding the seasonal variation of primary production and seasonal succession of plankton communities,as well as the responses of these processes to the changing Arctic Ocean,is critical to explore Arctic ecosystem shift comprehensively.Thus,a coupled ocean/sea ice/biogeochemical cycling model(NAPA-BGC)is developed and applied to simulate the temporal and spatial characteristics of ocean/sea ice environmental factors,primary production and plankton community in the north Atlantic,Arctic and north Pacific Oceans.The hindcast results are evaluated with available observational data,suggesting that NAPA-BGC reproduces the seasonal and interannual variations of the Arctic sea ice,the effects of Pacific and Atlantic inflow on nutrients concentrations and structures in the Arctic Ocean,and the relatively high chlorophyll-a concentrations([Chl-a])in the Bering sea,Chukchi sea and waters between Greenland and Norway.Based on hindcast results,this study analyzes the seasonal variation of primary production and the seasonal succession process of plankton communities in the Arctic Ocean.A preliminary discussion on the differences in the low-trophic ecosystem between 1998 and 2012 is also presented.Conclusions are as follows:(1)The surface [Chl-a] mainly peaks in May,with the higher values on the Pacific sector than the Atlantic sector.Since stratification occurs,subsurface chlorophyll-a maximums(SCM)are found in areas having limited nutrients at surface.The depth of SCM gradually deepens from the shelf towards the basin.In September,the high [Chl-a] returns to the upper layer from the subsurface,presenting a sub-peak of surface [Chl-a] on the Pacific sector.Compared with 1998,the depth of SCM deepens in 2012,which was mainly caused by the decrease in nutrient concentration with a deepened nitracline.(2)Substantial regional differences in surface plankton communities exist in the Arctic Ocean due to the influences of the Pacific and Atlantic inflows with variations in nutrients concentrations and structures.Diatom and meso-zooplankton are dominant species on the Pacific sector where diatom biomass exhibits two peaks in spring and fall,meanwhile nanophytoplankton maintains relatively high biomass in spring and summer.Atlantic sector experiences a seasonal succession fromnanophytoplankton to diatom then to nanophytoplankton corresponding to early spring,late spring-early summer,and summer-autumn,respectively.Over the entire growth season,nanophytoplankton and microzooplankton dominate on the Atlantic sector.The peak biomass of zooplankton has a lag for half a month to the peak of phytoplankton biomass in the Arctic Ocean.In 2012,the phytoplankton,especially diatom,blooms earlier in the Chukchi Sea than in 1998.This difference was mainly associated with the difference in PAR.(3)Increased total primary production in the Arctic Ocean occurs in 2012 compared with 1998.This is related to the declined sea ice area in 2012,leading to more open water for phytoplankton growth.In addition,the overall higher water temperature in 2012 enhances the growth rate of phytoplankton,and thus contributes to the increase of total primary production.In the whole growth season,the contributions of microphytoplankton and diatom to the increased total primary production present obvious seasonal variation.In the early spring of 2012,favorable nutrient and light conditions induce the increment of diatoms.After the nutrients consumption,the increment of microphytoplankton presents a peak.From July to October of 2012,the increased primary production is mainly contributed by microphytoplankton.This contribution peaks in August.At the same time,the diatom plays a minor role,indicating that the proportion of microphytoplankton to the total primary production in 2012 is higher than that in 1998,which is consistent with phytoplankton miniaturization observed during late summer in the Arctic Ocean.