ABSTRACT
Fjords in the Arctic regions are extremely sensitive to the increased climate warming (rise in global temperature), which triggers fresher, nutrient-rich, turbid glacial meltwater discharge influencing its hydrography and associated biological processes. Thus, it is imperative to monitor the impact of glacial melt on the ecological aspects of the fjord’s ecosystem. This chapter attempts to explain the influences of underwater light environment and nutrient limitation on the phytoplankton biomass, composition and light absorption in the sunlit zone of the Kongsfjorden (KG)-Krossfjorden (KR) twin-fjord ecosystem during summer (July–August) when maximum meltwater discharge occurs. Systematic observations conducted in two phases (in 1 week apart) in each fjord revealed pronounced spatial hydrographic variations between the phases and among the fjords. Intrusion of Atlantic water into both the fjords was evident with stronger thermohaline gradients in KG compared to KR. Difference in water mass characteristics resulted in manifestation of increased phytoplankton biomass (chlorophyll-a) in the second phase. Optically active constituents originating from meltwater discharge controlled the light penetration and restricted the euphotic zone in both fjords at places. Nutrient (nitrate and silicate) limitations were conducive for non-siliceous (flagellates) phytoplankton growth in both the fjords. Analyses of phytoplankton pigments revealed inter-fjord difference in surface phytoplankton composition (micro > nano > pico) and depicted higher diversity index for phytoplankton group (H’) in KR (0.71) than in KG (0.55). Higher phytoplankton light-absorption coefficient (a ph) and chlorophyll-a in KR implied its higher productivity potential; however, the light-absorption efficiency of microplankton at surface was affected by ‘pigment package’ effect indicating decreased productivity. The environmental settings in both fjords were quite dissimilar, where better underwater light conditions enabled Krossfjorden to be more productive and richer in phytoplankton diversity than the Kongsfjorden. This study reveals that increased warming can have different levels of impacts on fjord ecosystems despite their close geographical proximity.
