Description: We conducted incubation experiments with the diatom Thalassiosira hyalina under present-day and future temperature and pCO2 treatments. Six fresh isolates from the same Svalbard population were incubated as mono- and multi-strain cultures. We were able to closely follow intraspecific selection within an artificial population in a 2-week experiment using microsatellites and allele-specific quantitative PCR. Our results show that there is substantial variation in how strains of the same species cope physiologically with the tested environments. Although highly reproducible within treatments, changes in genotype composition, production rates and cellular quotas in the multi-strain cultures differed from monoculture performance. Interestingly, we only detected significant strain sorting in those populations exposed to the future treatment. We show that individuals adjust their phenotype not only in response to their physico-chemical, but also to their biological surroundings.

Description: The project AWI-funded AMUST project aims at understanding at current and future controls of Arctic spring blooms and concurrrent effetcs on biogeochemistry,by combining experimental work with long-term monitoring in April and May each year to study the Kongsfjorden spring bloom. This dataset was also used in the FAABulous project to compare spring bloom phenology in open-water and ice-covered fjords. Environmental as well as biological (stoichiometry and photosynthesis) data from the years 2014, and 2016-2018 for the mid-fjord station KB3 were samples. Furthermore, daily average temperature and salinity from a nearby mooring (see Hop et al. 2019 for details) are provided for the study period.

Description: Arctic phytoplankton and their response to future conditions shape one of the most rapidly changing ecosystems on the planet. We tested how much the phenotypic responses of strains from the same Arctic diatom population diverge and whether the physiology and intraspecific composition of multistrain populations differs from expectations based on single strain traits. To this end, we conducted incubation experiments with the diatom Thalassiosira hyalina under present‐day and future temperature and pCO2 treatments. Six fresh isolates from the same Svalbard population were incubated as mono‐ and multistrain cultures. For the first time, we were able to closely follow intraspecific selection within an artificial population using microsatellites and allele‐specific quantitative PCR. Our results showed not only that there is substantial variation in how strains of the same species cope with the tested environments but also that changes in genotype composition, production rates, and cellular quotas in the multistrain cultures are not predictable from monoculture performance. Nevertheless, the physiological responses as well as strain composition of the artificial populations were highly reproducible within each environment. Interestingly, we only detected significant strain sorting in those populations exposed to the future treatment. This study illustrates that the genetic composition of populations can change on very short timescales through selection from the intraspecific standing stock, indicating the potential for rapid population level adaptation to climate change. We further show that individuals adjust their phenotype not only in response to their physicochemical but also to their biological surroundings. Such intraspecific interactions need to be understood in order to realistically predict ecosystem responses to global change.

Description: The project AWI-funded AMUST project aims at understanding at current and future controls of Arctic spring blooms and concurrrent effetcs on biogeochemistry,by combining experimental work with long-term monitoring in April and May each year to study the Kongsfjorden spring bloom. This dataset was also used in the FAABulous project to compare spring bloom phenology in open-water and ice-covered fjords. Environmental as well as biological (stoichiometry and photosynthesis) data from the years 2014, and 2016-2018 for the mid-fjord station KB3 were samples. Furthermore, daily average temperature and salinity from a nearby mooring (see Hop et al. 2019 for details) are provided for the study period.

Description: The potential for adaptation of phytoplankton to future climate is often extrapolated based on single strain responses of a representative species, ignoring variability within and between species. The aim of this study was to approximate the range of strain-specific reaction patterns within an Arctic diatom population, which selection can act upon. In a laboratory experiment, we first incubated natural communities from an Arctic fjord under present and future conditions. In a second step, single strains of the diatom Thalassiosira hyalina were isolated from these selection environments and exposed to a matrix of temperature (3°C and 6°C) and pCO2 levels (180 μatm, 370 μatm, 1000 μatm, 1400 μatm) to establish reaction norms for growth, production rates, and elemental quotas. The results revealed interactive effects of temperature and pCO2 as well as wide tolerance ranges. Between strains, however, sensitivities and optima differed greatly. These strain-specific responses corresponded well with their respective selection environments of the previous community incubation. We therefore hypothesize that intraspecific variability and the selection between coexisting strains may pose an underestimated source of species' plasticity. Thus, adaptation of phytoplankton assemblages may also occur by selection within rather than only between species, and species-wide inferences from single strain experiments should be treated with caution.

Description: Laboratory experiment on acclimated physiological responses of the Arctic diatoms Thalassiosira hyalina and Melosira arctica towards elevated irradiance (50 vs 300 µmol photons m-2 s-1) and CO2 partial pressures (380 vs. 1000 μatm). Next to growth, elemental composition and biomass production, we assessed detailed photophysiological responses through fluorometry and gas-flux measurements, including respiration and carbon acquisition. Both algal cultures were isolated from the field within 2 years before the experiment, T.hyalina in Kongsjorden, Svalbard, and M.arctica in the Fram Strait close to Svalbard.

Description: The project AWI-funded AMUST project aims at understanding at current and future controls of Arctic spring blooms and concurrrent effetcs on biogeochemistry,by combining experimental work with long-term monitoring in April and May each year to study the Kongsfjorden spring bloom. This dataset was also used in the FAABulous project to compare spring bloom phenology in open-water and ice-covered fjords. Environmental as well as biological (stoichiometry and photosynthesis) data from the years 2014, and 2016-2018 for the mid-fjord station KB3 were samples. Furthermore, daily average temperature and salinity from a nearby mooring (see Hop et al. 2019 for details) are provided for the study period.

Description: Sea ice retreat, changing stratification, and ocean acidification are fundamentally changing the light availability and physico-chemical conditions for primary producers in the Arctic Ocean. However, detailed studies on ecophysiological strategies and performance of key species in the pelagic and ice-associated habitat remain scarce. Therefore, we investigated the acclimated responses of the diatoms Thalassiosira hyalina and Melosira arctica toward elevated irradiance and CO2 partial pressures (pCO2). Next to growth, elemental composition, and biomass production, we assessed detailed photophysiological responses through fluorometry and gas-flux measurements, including respiration and carbon acquisition. In the pelagic T. hyalina, growth rates remained high in all treatments and biomass production increased strongly with light. Even under low irradiances cells maintained a high-light acclimated state, allowing them to opportunistically utilize high irradiances by means of a highly plastic photosynthetic machinery and carbon uptake. The ice-associated M. arctica proved to be less plastic and more specialized on low-light. Its acclimation to high irradiances was characterized by minimizing photon harvest and photosynthetic efficiency, which led to lowered growth. Comparably low growth rates and strong silification advocate a strategy of persistence rather than of fast proliferation, which is also in line with the observed formation of resting stages under low-light conditions. In both species, responses to elevated pCO2 were comparably minor. Although both diatom species persisted under the applied conditions, their competitive abilities and strategies differ strongly. With the anticipated extension of Arctic pelagic habitats, flexible high-light specialists like T. hyalina seem to face a brighter future.

Description: We performed a temperature incubation experiment on board the RV Polarstern with a unicellular microbial community sampled from the Hausgarten station IV in Fram Strait during the campagin PS126 on June 1st, 2021 (Soltwedel et al., 2021). The community was sampled with CTD-bound niskin bottles (SBE 32 Carousel Water Sampler attached to a Seabird SBE911+ CTD-system; Seabird Scientific, Bellevue, WA, USA) from a depth of 15 m (Hoppmann et al., in review) and, after filtering the seawater through a 150 µm net, incubated in triplicate on plankton wheels in three temperature-controlled containers for ten days. To mimick todays and potential future temperature conditions of the Arctic ocean, we chose a control temperature of 2 °C, an intermediate warming scenario of 6 °C, and an extreme warming scenario of 9 °C. The goal was to investigate the effects of concurrent warming and Atlantification and therefore we chose an Arctic-Atlantic mixed water mass as community origin. This dataset comprises the chlorophyll, particulate nutrients, dissolved nutrients, carbonate chemistry, and flow cytometric measurements of the starting as well as the final communities. A total 300 mL of sample water for chlorophyll a, and 200 mL for particulate organic carbon and nitrogen (and the same volumes of ultrapure water for blank corrections), were vacuum-filtered (〈−200 mbar) onto pre-combusted glass-fiber filters (GF/F Whatman, Maidstone, UK). These were put into 2 mL cryovials (Sarstedt, Nümbrecht, Germany) and kept at −80 °C until processing. Filters for chlorophyll a were manually shredded in 6 mL of 90% acetone and extracted for 20 h at 8 °C according to the EPA method 445.0 (Arar et al., 1997). The extract was centrifuged to remove residual filter snips, and Chlorophyll a was determined on a Trilogy fluorometer (Turner Designs, San Jose, CA, USA) after correcting for phaeopigments via acidification (1 M HCl). Filters for particulate nutrients were also acidified (0.5 M HCl) and dried for 12 h at 60 °C. Analysis was performed using a gas chromatograph CHNS-O elemental analyzer (EURO EA 3000, HEKAtech, Wegberg, Germany). pH was measured with a pH meter (EcoScan pH 5, ThermoFisher Scientific, Waltham, MA, USA) including a glass electrode (Sentix 62, Mettler Toledo, Columbus, OH, USA) that was one-point calibrated with a technical buffer solution (pH 7, Mettler Toledo, Columbus, OH, USA). Samples for total alkalinity and dissolved nutrients were filtered through a 0.22 µm cellulose-acetate syringe filter (Nalgene, Rochester, NY, USA) and stored at 4 °C in 125 mL borosilicate bottles and 15 mL polycarbonate tubes. Total alkalinity was measured by duplicate potentiometric titration using a TitroLine alphaplus autosampler (Schott Instruments, Mainz, Germany) and corrected with certified reference materials from A. Dickson (Scripps Institution of Oceanography, San Diego, CA, USA). The full carbonate system was calculated for tfin using the software CO2sys (Pierrot et al., 2011) with dissociation constants of carbonic acid by Mehrbach et al. (1973), refitted by Dickson and Millero (1987). Dissolved nutrients were measured colorimetrically at on a continuous-flow autoanalyzer (Evolution III, Alliance Instruments, Freilassing, Germany) following standard seawater analytical methods for nitrate and nitrite (Armstrong et al., 1967), phosphate (Eberlein et al., 1987), silicate (Grasshoff et al., 2009), and ammonium (Koroleff et al. 1970). For flow cytometric measurements, 3.5 mL of the sample were preserved with hexamine-buffered formalin (0.5% final concentration) and stored at −80 °C after dark incubation for 15 min. For analysis, samples were thawed at room temperature, vortexed, and measured at a fast speed for three minutes using an Accuri C6 flow cytometer (BD Sciences, Franklin Lakes, NJ, USA) after setting the threshold of the FL-3 channel to 900. Phenotypic diversity (D2) was calculated for each sample based on the flow cytometric fingerprint according to Props et al. (2016), using the values of FSC-H, SSC-H, FL-2, FL-3, and FL-4. Parts of the metadata as well as calculations from it were used in the publication of Ahme et al. (2023). All scripts can be found on GitHub (https://github.com/AntoniaAhme/PS126CommunityExperiment). The sequence data are available at the European Nucleotide Archive (ENA).

Description: The potential for adaptation of phytoplankton to future climate is often extrapolated based on single strain responses of a representative species, ignoring variability within and between species. The aim of this study was to approximate the range of strain-specific reaction patterns within an Arctic diatom population, which selection can act upon. In a laboratory experiment, we first incubated natural communities from an Arctic fjord under present and future conditions. In a second step, single strains of the diatom Thalassiosira hyalina were isolated from these selection environments and exposed to a matrix of temperature (38C and 68C) and pCO 2 levels (180 latm, 370 latm, 1000 latm, 1400 latm) to establish reaction norms for growth, production rates, and elemental quotas. The results revealed interactive effects of temperature and pCO 2 as well as wide tolerance ranges. Between strains, however, sensitivities and optima differed greatly. These strain-specific responses corresponded well with their respective selection environments of the previous com- munity incubation. We therefore hypothesize that intraspecific variability and the selection between coexist- ing strains may pose an underestimated source of species’ plasticity. Thus, adaptation of phytoplankton assemblages may also occur by selection within rather than only between species, and species-wide inferences from single strain experiments should be treated with caution.