Drivers of Atmosphere-Ocean CO2 Flux in Northern Norwegian Fjords

Abstract

High-latitude fjords and continental shelves are shown to be sinks for atmospheric CO2, yet large spatial-temporal variability and poor regional coverage of sea-air CO2 flux data, especially from fjord systems, makes it difficult to scale our knowledge on how they contribute to atmospheric carbon regulation. The magnitude and seasonal variability of atmosphere-sea CO2 flux was investigated in high-latitude northern Norwegian coastal areas over 2018 and 2019, including four fjords and one coastal bay. The aim was to assess the physical and biogeochemical factors controlling CO2 flux and partial pressure of CO2 in surface water via correlation to physical oceanographic and biological measurements. The results show that the study region acts as an overall atmospheric CO2 sink throughout the year, largely due to the strong undersaturation of CO2 relative to atmospheric concentrations. Wind speed exerted the strongest influence on the instantaneous rate of sea-air CO2 exchange, while exhibiting high variability. We concluded that the northernmost fjords (Altafjord and Porsangerfjord) showed stronger potential for instantaneous CO2 uptake due to higher wind speeds. We also found that fixation of CO2 was likely a significant factor controlling ΔpCO2 from April to June, which followed phenology of spring phytoplankton blooms at each location. Decreased ΔpCO2 and the resulting sea-air CO2 flux was observed in autumn due to a combined reduction of the mixed layer with entrain of high CO2 subsurface water, damped biological activity and higher surface water temperatures. This study provides the first measurements of atmospheric CO2 flux in these fjord systems and therefore an important new baseline for gaining a better understanding on how the northern Norwegian coast and characteristic fjord systems participate in atmosphere carbon regulation.

Diversity and Selection of Surface Marine Microbiomes in the Atlantic-Influenced Arctic

“…The availability of nutrients and photosynthetically active radiation (PAR), which are both linked to the mixed layer depth (MLD), have been implicated to control regional differences in the phytoplankton community structure, more so than temperature (Barton et al, 2016 ; Oziel et al, 2017 ; Aalto et al, 2021 ). Phytoplankton blooms are also known to exert major influences on localized marine microbiomes (Cirri and Pohnert, 2019 ).…”

Microbial community dynamics during a harmful Chrysochromulina leadbeateri bloom in northern Norway

“…The second station, named as Finnfjord sampling station (FSS,69.19 N,18.03 E), is located 60 km south of GSSS, within the same interconnected fjord-sound system (Figure 1a). These time series stations were chosen because they present historical sample locations (Aalto et al, 2021) and provided long-term access to sampling facilities (vessel: ~5 m Polarcirkel and laboratories).…”

“…The spring-summer phytoplankton seasonal succession along the coast of northern Norway has been extensively studied in the past 40 years with specific focus on spring bloom dynamics. The majority of data collected to-date has used only morphology-based identification of microalgal taxa, which has limited the extent to which the full diversity of these communities has been described (Eilertsen et al, 1981;Reigstad and Wassmann, 1996;Degerlund and Eilertsen, 2010;Aalto et al, 2021). From previous studies, we know that the onset of the "spring bloom" occurs in late March/early April, and it is driven by increased irradiance as the region undergoes a shift from polar night to spring, which results in elevated winter nutrient concentrations and a well-mixed water column (Eilertsen and Taasen, 1984;Eilertsen and Frantzen, 2007;Aalto et al, 2021).…”

“…This leads to a rapid and intense increase of many chain forming centric diatoms that co-bloom with Phaeocystis pouchetii (haptophyte), who often outlasts the diatoms and persists throughout the summer (Degerlund and Eilertsen, 2010). The spatial and interannual variation of the late bloom (May-June) phytoplankton community can comprise a diverse mix of low-nutrient-tolerant, heterotrophic, and mixotrophic species belonging to dinoflagellates, cryptophytes, ciliates, and other small flagellates (Eilertsen et al, 1981; Aalto et al, 2021). HAB incidents in northern Norway tend to occur after the primary spring diatom bloom, although historical sampling of these events is sparse and the onset and development of HAB conditions is essentially unknown for the region.…”

“…The spring-summer phytoplankton seasonal succession along the coast of northern Norway has been extensively studied but the majority of data collected to-date has used only morphology-based identification of microalgal taxa, which limited the resolution of taxonomic diversity of these blooming patterns (e.g., Eilertsen et al, 1981;Reigstad and Wassmann, 1996;Degerlund and Eilertsen, 2010;Aalto et al, 2021). From previous studies, we know that the onset of the "spring bloom" occurs in late March/early April, and it is driven by increased irradiance as the region undergoes a shift from polar night to spring, within elevated winter nutrient concentrations and a well-mixed water column (Eilertsen and Taasen, 1984;Eilertsen and Frantzen, 2007;Aalto et al, 2021). These conditions lead to a rapid and intense increase of many chain forming centric diatoms that co-bloom with Phaeocystis pouchetii (haptophyte), which often outlasts the diatoms and persists throughout the summer (Eilertsen and Taasen, 1984;Degerlund and Eilertsen, 2010).…”