Description: Contrasting models predict two different climate change scenarios for the Southern Ocean (SO), forecasting either less or stronger vertical mixing of the water column. To investigate the responses of SO phytoplankton to these future conditions, we sampled a natural diatom dominated (63%) community from today's relatively moderately mixed Drake Passage waters with both low availabilities of iron (Fe) and light. The phytoplankton community was then incubated at these ambient open ocean conditions (low Fe and low light, moderate mixing treatment), representing a control treatment. In addition, the phytoplankton was grown under two future mixing scenarios based on current climate model predictions. Mixing was simulated by changes in light and Fe availabilities. The two future scenarios consisted of a low mixing scenario (low Fe and higher light, low mixing treatment) and a strong mixing scenario (high Fe and low light, strong mixing treatment). In addition, communities of each mixing scenario were exposed to ambient and low pH, the latter simulating ocean acidification (OA). The effects of the scenarios on particulate organic carbon (POC) production, trace metal to carbon ratios, photophysiology and the relative numerical contribution of diatoms and nanoflagellates were assessed. During the first growth phase, at ambient pH both future mixing scenarios promoted the numerical abundance of diatoms (~75%) relative to nanoflagellates. This positive effect, however, vanished in response to OA in the communities of both future mixing scenarios (~65%), with different effects for their productivity. At the end of the experiment, diatoms remained numerically the most abundant phytoplankton group across all treatments (~80%). In addition, POC production was increased in the two future mixing scenarios under OA. Overall, this study suggests a continued numerical dominance of diatoms as well as higher carbon fixation in response to both future mixing scenarios under OA, irrespective of different changes in light and Fe availability.

Description: Contrasting models predict two different climate change scenarios for the Southern Ocean (SO), forecasting either less or stronger vertical mixing of the water column. To investigate the responses of SO phytoplankton to these future conditions, we sampled a natural diatom dominated (63%) community from today's relatively moderately mixed Drake Passage waters with both low availabilities of iron (Fe) and light. The phytoplankton community was then incubated at these ambient open ocean conditions (low Fe and low light, moderate mixing treatment), representing a control treatment. In addition, the phytoplankton was grown under two future mixing scenarios based on current climate model predictions. Mixing was simulated by changes in light and Fe availabilities. The two future scenarios consisted of a low mixing scenario (low Fe and higher light, low mixing treatment) and a strong mixing scenario (high Fe and low light, strong mixing treatment). In addition, communities of each mixing scenario were exposed to ambient and low pH, the latter simulating ocean acidification (OA). The effects of the scenarios on particulate organic carbon (POC) production, trace metal to carbon ratios, photophysiology and the relative numerical contribution of diatoms and nanoflagellates were assessed. During the first growth phase, at ambient pH both future mixing scenarios promoted the numerical abundance of diatoms (~75%) relative to nanoflagellates. This positive effect, however, vanished in response to OA in the communities of both future mixing scenarios (~65%), with different effects for their productivity. At the end of the experiment, diatoms remained numerically the most abundant phytoplankton group across all treatments (~80%). In addition, POC production was increased in the two future mixing scenarios under OA. Overall, this study suggests a continued numerical dominance of diatoms as well as higher carbon fixation in response to both future mixing scenarios under OA, irrespective of different changes in light and Fe availability.

Description: Polar Regions are facing rapid temperature increase. Combined with other factors temperature increase might have a strong impact on foundation species in Arctic shallow-water coastal ecosystems, such as the abundant kelp Saccharina latissima. We ran two short-term 2-factor experiments with field samples from Kongsfjorden (Svalbard) to reveal the impact of temperature increase in summer combined with hyposalinity (temperature × salinity) or nutrient enrichment (temperature × nutrients) and analyzed different biochemical and physiological parameters. The experiments were conducted with field samples at AWIPEV Station in Ny-Ålesund, Svalbard (Spitsbergen) in June/July 2019. As physiological parameter, size and the maximum photosynthetic quantum yield of photosystem II (Fv/Fm; Imaging-PAM, Walz GmbH Mess- und Regeltechnik, Effeltrich, Germany) were monitored every second day. For growth, the size of the algal discs was analyzed with ImageJ (Version 1.52a). For better comparison of the physiological parameters, Fv/Fm and growth the initial size of the different treatments was adjusted to 100% and size of each sample as % of initial was calculated. The C:N ratio, total nitrogen and total carbon content were analyzed with an elemental analyzer. Mannitol, as well as absolute pigment concentrations were analyzed using a HPLC. The de-expoxidation state of the xanthophyll cycle (DPS) and chlorophyll a : accessory pigment ratio calculated afterwards. Phlorotannins were analyzed using the photometric Folin-Ciocalteu method.

Description: Kelps act as ecosystem engineers and foundation species on many polar rocky shore coastlines. The main driver for their vertical and latitudinal distribution is the underwater light climate and temperature. Both are changing drastically in the Arctic in the course of global climate change. It was the aim of this study to analyse the effects of rising temperature and deteriorating underwater light climate on the potential habitat of kelps in the Arctic. The analyses of the underwater light climate in Arctic Kongsfjorden, Svalbard in July 2021. We divided Kongsfjorden in three areas, which are influenced by the run-off of sea-terminating glaciers (station A–J), the run-off of a land-terminating glacier (station K–O) and mostly clear water (control, station P–Q). In each area, we measured the spectrally resolved underwater light climate in the UV-B radiation (280-320 nm), UV-A radiation (320-400 nm) and photosynthetically active radiation (PAR, 400-700 nm) with a RAMSES-ACC-UV/VIS radiometer (TriOS Optical Sensor, Oldenburg, Germany) from 0–12.5 m. UV-B, UV-A and PAR were calculated by integrating the irradiance over the respective wavelengths.

Description: The Arctic is one area that has been affected by rising temperatures, leading to an increase in meltwater in the water column. During the months of June/July 2019, fronds of the red seaweed Palmaria palmata in Kongsfjorden, Svalbard (78°55'56.0N 11°55'59.6E) were colected in the intertidal zone. For 21 days at 0ºC, P. palmata was subjected to variations of irradiance cycles and three different salinities SA 34 (control), 28 and 18 in laboratory conditions. Subsequently, measurements in triplicate (n=3) were made of photosynthetic parameters such as maximal quantum yield of PSII (Fv/Fm), non-photochemical quenching (NPQ), biochemical parameters such as quantification of pigments chlorophyll a (Chl a), lutein (Lut), zeaxanthin (Zeax), β-carotene (β-Car), and antioxidant activity 2,2-diphenyl-1-picrylhydrazyl (DPPH).

Description: Broadly distributed seaweeds, such as the boreal-temperate kelp species Saccharina latissima, contain a multitude of metabolites supporting acclimation to environmental changes, such as temperature and salinity. In Europe, S. latissima occurs along the coasts from Spitsbergen to Portugal, including the Baltic Sea, exhibiting great morphological plasticity. We investigated the morphological and biochemical traits of field-collected sporophytes from 16 different locations across the species entire European distributional range in relation to local abiotic conditions (sea surface temperature, sea surface salinity, sampling depth). By statistically linking morphological (frond length:width), biochemical (mannitol, phlorotannins, C:N), and genetic data of the mitochondrial cytochrome-c-oxidase I gene (COI-5P) to the geographic abiotic information, we aimed to obtain first insights into the site-specific adaptive features of this species. Mannitol concentrations were analyzed using a HPLC. The molar C:N ratio was analyzed with an elemental analyzer. Phlorotannins were analyzed using the photometric Folin-Ciocalteu method.

Description: Kelps act as ecosystem engineers and foundation species on many polar rocky shore coastlines. The main driver for their vertical and latitudinal distribution is the underwater light climate and temperature. Both are changing drastically in the Arctic in the course of global climate change. It was the aim of this study to analyse the effects of rising temperature and deteriorating underwater light climate on the potential habitat of kelps in the Arctic. A laboratory experiment, in which we determined temperature-related changes in the light-use characteristics of two temperate kelp species (Alaria esculenta, Saccharina latissima) at 3, 7, and 11 °C. Therefore, grown sporophytes were sampled in the field from a sampling depth of 6–9 m. Meristematic discs (Ø 2 cm) were cut and distributed between temperature treatments and replicates. The experiment ran for seven days, during which the treatment temperature was increased every two days by 4 °C until treatment temperature was reached, allowing for successive acclimation. The photosynthesis vs. irradiance curves were measured with a 4-channel optode set-up (FireStingO2 Fibre-Optic Oxygen Meter FSO2-01, PyroScience Sensor technology, Aachen, Germany) by analysing the oxygen evolution in response to different light intensities within a 25 mL Schott bottle, each containing three meristematic discs. Maximum photosynthetic quantum yield was measured using a pulse amplitude modulated fluorometer (Portable Chlorophyll Fluorometer PAM-2100, Heinz Walz GmbH, Effeltrich, Germany). Pigment analysis was analysed with a High-Performance Liquid Chromatograph (HPLC, LaChromElite® system, L-2200 autosampler (chilled), DA-detetctor L-2450; VWR-Hitachi International GmbH, Darmstadt, Germany).