Solar radiation and solar radiation driven cycles in warming and freshwater discharge control seasonal and inter‐annual phytoplankton chlorophyll a and taxonomic composition in a high Arctic fjord (Kongsfjorden, Spitsbergen)

Abstract

Fjords on the west coast of Spitsbergen experience variable Arctic and Atlantic climate signals that drive seasonal and inter‐annual variability of phytoplankton productivity and composition, by mechanisms that are not fully resolved. To this end, a time series (2013–2018) of Kongsfjorden (N 78°54.2, E 11°54.0) phytoplankton pigments, ocean physics, nutrient concentrations, and microbial abundances was investigated. Kongsfjorden phytoplankton dynamics were predominantly governed by solar radiation and cycles of warming and freshwater discharge that caused pronounced changes in light and nutrient availability. Phytoplankton growth after the polar night commenced in March in a mixed, nutrient loaded water column, and accelerated in April after weak thermal stratification. Spring (weeks 10–22) showed high diatom relative abundance that ceased when silicic acid and nitrate reached limiting concentrations. Summer (weeks 23–35) was characterized by sixfold stronger stratification due to increased freshwater discharge and continued ocean heating. This caused a warm, low salinity surface layer with low nutrient concentrations. Small and diverse flagellates, together with high bacterial and viral abundances, thrived in this regenerative, N or P‐limited system. Elevated late summer chlorophyll a (Chl a), and ammonium suggested increased regeneration and nutrient pulses by glacial upwelling. Fall (weeks 36–48) caused rapidly declining Chl a and increasing diatom relative abundance, which persisted throughout the polar night, causing high diatom relative abundance during spring. Despite inter‐annual variability in ocean temperature and salinity we observed relatively stable seasonal phytoplankton taxonomic composition and Chl a.

The interacting effect of prolonged darkness and temperature on photophysiological characteristics of three Antarctic phytoplankton species

“…Furthermore, cultures of P. antarctica (4 and 7°C), G. cryophila (7°C), and C. simplex at (7°C) showed further losses of chl a concentration after the recovery experiments. This indicates that other, less reversible processes have a role in the reduced chl a F0 , and F v /F m of these cultures (van de Poll et al, 2011). Here, the decrease of chl a F0 and F v /F m may imply a progressive decline of functional PSII reaction centers during long darkness, with antennae chl a possibly degrading upon reillumination due to reactive oxygen species formation during the recovery experiment.…”

“…The decline in photosynthetic fitness during darkness and the subsequent ability to recover after long darkness differs among species and possibly among taxonomic groups (van de Poll et al, 2019). By influencing fitness and survival of the phytoplankton species, long darkness can change the over wintering phytoplankton community composition and that of the following spring (van de Poll et al, 2020). Southern Ocean sea water temperature varies between −1.9 and 6.9°C within the Polar Front (Freeman & Lovenduski, 2016).…”

Transcriptomics reveal a unique phago-mixotrophic response to low nutrient concentrations in the prasinophyte Pterosperma cristatum

“…However, the latter is a primarily phagotrophic algae and only relies on photosynthesis for carbon assimilation when prey are limiting growth [ 16 ]. Ochromonas BG-1 grows in the dark [ 21 ], which P. cristatum and other prasinophytes are not capable of [ 12 , 27 , 28 , 66 ].…”

Nutrient Analysis in Arctic Waters Using a Portable Sensing Platform

“…− and PO 4 3− do not follow the same trend and show a uniform distribution in the fjord except for station 001 where both concentrations were significantly elevated (22.63 μM PO 4 3− compared to the average of all the other stations of 2.68 μM; and 4.14 μM NO 2 − compared to the average of 0.36 μM). This increase of phosphate and nitrites at 001 may arise from the anticlockwise summer circulation described by (Svendsen et al, 2002;Aliani et al, 2016;Poll et al, 2021).…”