Abstract
Glacial meltwater discharge in fjords on the west coast of Spitsbergen is increasing due to climate change. The influence of this discharge on phytoplankton nutrient limitation, composition, productivity and photophysiology was investigated in central (M) and inner (G) Kongsfjorden (79°N, 11°40’E). Freshwater influx intensified stratification during June 2015, coinciding with surface nutrient depletion. Surface nutrient concentrations were negatively correlated with stratification strength at station M. Here, nitrate addition assays revealed increasing N limitation of surface phytoplankton during the second half of June, which was followed by a pronounced compositional change within the flagellate-dominated phytoplankton community as dictyochophytes (85% of chl a) were replaced with smaller haptophytes (up to 60% of chlorophyll a) and prasinophytes (20% of chlorophyll a). These changes were less pronounced at station G, where surface phosphate, ammonium and nitrate concentrations were occasionally higher, and correlated with wind direction, suggesting wind-mediated transport of nutrient-enriched waters to this inner location. Therefore, glacial meltwater discharge mediated nutrient enrichment in the inner fjord, and enhanced stratification in inner and central Kongsfjorden. Surface chlorophyll a and water column productivity showed 3–4-fold variability, and did not correlate with nutrient limitation, euphotic zone depth, or changed taxonomic composition. However, the maximum carbon fixation rate and photosynthetic efficiency showed weak positive correlations to prasinophyte, cryptophyte, and haptophyte chlorophyll a. The present study documented relationships between stratification, N limitation, and changed phytoplankton composition, but surface chlorophyll a concentration, phytoplankton photosynthetic characteristics, and water column productivity in Kongsfjorden appeared to be driven by mechanisms other than N limitation.
Highlights
The Arctic is experiencing pronounced changes in climate, which impact the conditions of phytoplankton growth (Arrigo, 2013)
Atlantic advection in Kongsfjorden occurs in winter and summer, whereas its circulation in the fjord appears to be driven by along-fjord winds (Sundfjord et al, 2017)
The surface phytoplankton community experienced nutrient depletion in June 2015, with chl a concentrations that were typical for the post-bloom period in June (Hegseth and Tverberg, 2013; van de Poll et al, 2016)
Summary
The Arctic is experiencing pronounced changes in climate, which impact the conditions of phytoplankton growth (Arrigo, 2013). Increased Atlantic advection and associated relatively high heat content has resulted in decreased wintertime sea ice formation on the west coast of Spitsbergen (Kortsch et al, 2012). This process has intensified melting of marine-terminating glaciers on the west coast of Spitsbergen and on the east coast of Greenland (Straneo and Heimbach, 2013; Luckman et al, 2015). Atlantic advection can introduce Atlantic phytoplankton and zooplankton populations into fjords like Kongsfjorden (Willis et al, 2008)
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