Springtime phytoplankton dynamics in Arctic Krossfjorden and Kongsfjorden (Spitsbergen) as a function of glacier proximity

[摘要] The hydrographic properties of the Kongsfjorden–Krossfjorden system(79° N, Spitsbergen) are affected by Atlantic water incursions aswell as glacier meltwater runoff. This results in strong physical gradients(temperature, salinity and irradiance) within the fjords. Here, we testedthe hypothesis that glaciers affect phytoplankton dynamics as early as theproductive spring bloom period. During two campaigns in 2007 (late spring)and 2008 (early spring) we studied hydrographic characteristics andphytoplankton variability along two transects in both fjords, usinghigh-performance liquid chromatography (HPLC)-CHEMTAX pigment fingerprinting, molecular fingerprinting(denaturing gradient gel electrophoresis, or DGGE) andsequencing of 18S rRNA genes. The sheltered inner fjord locations remainedcolder during spring as opposed to the outer locations. Vertical lightattenuation coefficients increased from early spring onwards, at alllocations, but in particular at the inner locations. In late springmeltwater input caused stratification of surface waters in both fjords. Theinner fjord locations were characterized by overall lower phytoplanktonbiomass. Furthermore HPLC-CHEMTAX data revealed that diatoms andPhaeocystis sp. were replaced by small nano- and picophytoplankton during late spring,coinciding with low nutrient availability. The innermost stations showedhigher relative abundances of nano- and picophytoplankton throughout,notably of cyanophytes and cryptophytes. Molecular fingerprinting revealed ahigh similarity between inner fjord samples from early spring and latespring samples from all locations, while outer samples from early springclustered separately. We conclude that glacier influence, mediated by earlymeltwater input, modifies phytoplankton biomass and composition alreadyduring the spring bloom period, in favor of low biomass and small cell sizecommunities. This may affect higher trophic levels especially when regionalwarming further increases the period and volume of meltwater.

[学科分类] 地球化学与岩石