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Browsing by Subject "nutrient upwelling"

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  • Ihalainen, Vilma (2020)
    Ongoing climate warming has unprecedented impacts on glacial melt and associated fjord systems in Greenland. As the glaciers are shrinking, freshwater inflow to the sea is increasing resulting in increased nutrient supply by upwelling. In this study I examined environmental factors impacting marine primary productivity, biomass (chlorophyll a), phytoplankton abundance and species composition along a transect from the glacier front to the outer fjord in Godthåbsfjord, SW-Greenland, in August 2019. Gradients in nitrogen and phosphate concentrations were explained by glacial runoff and coastal water inflow while silicate concentration did not follow these patterns. The main variables explaining phytoplankton biomass distribution were nitrogen together with phosphate concentrations, salinity, and depth. Silicate limited waters were strongly dominated (≥ 90%) by the diatom Chaetoceros socialis, which had a strong influence on phytoplankton community response to environmental conditions. High dominance of C. socialis was also related to high species richness. Nitrogen depleted waters were usually related to relatively high abundances (9–46%) of mixotrophic Dinobryon balticum. Higher number of species and higher dominance of C. socialis was detected closer to the glacier. Phytoplankton abundance and biomass (chlorophyll a) were higher in the inner fjord region, whereas primary productivity had the opposite pattern (higher productivity in the outer fjord). This suggested that an autumn bloom was peaking in the inner fjord, whereas in the outer fjord the autumn bloom was still developing. Thus, glacial surface runoff and subglacial discharge contributed to higher phytoplankton abundance and chlorophyll a concentrations, whereas primary production was also dependent on other factors such as light availability and vertical mixing. Melting of Greenland Ice sheet is predicted to accelerate in the future. Thus, the upwelling effect might increase, leading to transitory increase in marine primary production. Increased surface runoff might increase silicate concentrations benefiting diatom species, although turbid runoff water will also decrease the primary productivity due to light limitation. Nevertheless, if marine-terminating glaciers retreat further and become land-terminating glaciers, lack of nutrient upwelling will lead to faster exhaustion of nitrogen in the upper water column and primary productivity will eventually decrease. Thus, global warming and retrieving of glaciers will change the productivity of the fjord and inevitably shape the rich and unique fjord ecosystems of the Arctic.