Description: It is currently under debate whether organisms that regulate their acid-base status under environmental hypercapnia demand additional energy. This could impair animal fitness, but might be compensated for via increased ingestion rates when food is available. No data are yet available for dominant Calanus spp. from boreal and Arctic waters. To fill this gap, we incubated C. glacialis at 390, 1120 and 3000 µatm for 16 days with Thalassiosira weissflogii (diatom) as food source on-board RV Polarstern in Fram Strait in 2012. Every four days copepods were sub-sampled from all CO2 treatments and clearance and ingestion rates were determined. During the SOPRAN mesocosm experiment in Bergen, Norway, 2011, we weekly collected C. finmarchicus from mesocosms initially adjusted to 390 and 3000 µatm CO2 and measured grazing at low and high pCO2. In addition, copepods were deep frozen for body mass analyses. Elevated pCO2 did not directly affect grazing activities and body mass, suggesting that the copepods did not have additional energy demands for coping with acidification, neither during long-term exposure nor after immediate changes in pCO2. Shifts in seawater pH thus do not seem to challenge these copepod species.

Description: The sensitivity of copepods to ocean acidification (OA) and warming may increase with time, however, studies 〉10 days and on synergistic effects are rare. We therefore incubated late copepodites and females of two dominant Arctic species, Calanus glacialis and Calanus hyperboreus, at 0 °C at 390 and 3000 µatm pCO2 for several months in fall/winter 2010. Respiration rates, body mass and mortality in both species and life stages did not change with pCO2. To detect synergistic effects, in 2011 C. hyperboreus females were kept at different pCO2 and temperatures (0, 5, 10 °C). Incubation at 10 °C induced sublethal stress, which might have overruled effects of pCO2. At 5 °C and 3000 µatm, body carbon was significantly lowest indicating a synergistic effect. The copepods, thus, can tolerate pCO2 predicted for a future ocean, but in combination with increasing temperatures they could be sensitive to OA.

Description: About 50 Gt of carbon is fixed photosynthetically by surface ocean phytoplankton communities every year. Part of this organic matter is reprocessed within the plankton community to form aggregates which eventually sink and export carbon into the deep ocean. The fraction of organic matter leaving the surface ocean is partly dependent on aggregate sinking velocity which accelerates with increasing aggregate size and density, where the latter is controlled by ballast load and aggregate porosity. In May 2011, we moored nine 25 m deep mesocosms in a Norwegian fjord to assess on a daily basis how plankton community structure affects material properties and sinking velocities of aggregates (Ø 80–400 µm) collected in the mesocosms' sediment traps. We noted that sinking velocity was not necessarily accelerated by opal ballast during diatom blooms, which could be due to relatively high porosity of these rather fresh aggregates. Furthermore, estimated aggregate porosity (Pestimated) decreased as the picoautotroph (0.2–2 µm) fraction of the phytoplankton biomass increased. Thus, picoautotroph‐dominated communities may be indicative for food webs promoting a high degree of aggregate repackaging with potential for accelerated sinking. Blooms of the coccolithophore Emiliania huxleyi revealed that cell concentrations of ~1500 cells/mL accelerate sinking by about 35–40%, which we estimate (by one‐dimensional modeling) to elevate organic matter transfer efficiency through the mesopelagic from 14 to 24%. Our results indicate that sinking velocities are influenced by the complex interplay between the availability of ballast minerals and aggregate packaging; both of which are controlled by plankton community structure.

Description: This dataset contains energy content measurements performed on zooplankton collected in the Arctic Ocean during the MOSAiC expedition (PS122) from November 2019 untill September 2020. Energy content measurements were done on Apherusa glacialis, Themisto abyssorum, Chaetognatha, Thysanoessa longicaudata and Calanus hyperboreus. These species are all known prey of polar cod (Boreogadus saida), and their energy content was measured to be included in a bioenergetic model of the growth rate of this predator and to gain insight in the differences between prey species. The meaurements were performed on freeze-dried specimens using a 6725 semi-micro oxygen calorimeter (Parr, USA) connected to a 6772 calorimetric thermometer (Parr, USA).

Description: This dataset presents microplastics in water samples collected from the underway system and CTD alongside the August 2019 zooplankton samples presented in https://doi.pangaea.de/10.1594/PANGAEA.950296. These samples were initially digested using a homogenising solution and then filtered in preparation for Fourier Transform Infrared spectroscopy (FTIR) analysis in combination with an automated polymer identification approach (SIMPLE software) to identify polymer types, shape and size. Microplastics were also visualised using a microscope to further determine shape and size, particularly of fibres. Data collected on the microplastics found includes; polymer type, shape, size, species ingestion and location.

Description: This dataset contains energy content measurements performed on zooplankton collected in the Arctic Ocean during the MOSAiC expedition (PS122) from November 2019 untill September 2020. Energy content measurements were done on Apherusa glacialis, Themisto abyssorum, Chaetognatha, Thysanoessa longicaudata and Calanus hyperboreus. These species are all known prey of polar cod (Boreogadus saida), and their energy content was measured to be included in a bioenergetic model of the growth rate of this predator and to gain insight in the differences between prey species. The meaurements were performed on freeze-dried specimens using a 6725 semi-micro oxygen calorimeter (Parr, USA) connected to a 6772 calorimetric thermometer (Parr, USA).

Description: This dataset contains energy content measurements performed on zooplankton collected in the Arctic Ocean during the MOSAiC expedition (PS122) from November 2019 untill September 2020. Energy content measurements were done on Apherusa glacialis, Themisto abyssorum, Chaetognatha, Thysanoessa longicaudata and Calanus hyperboreus. These species are all known prey of polar cod (Boreogadus saida), and their energy content was measured to be included in a bioenergetic model of the growth rate of this predator and to gain insight in the differences between prey species. The meaurements were performed on freeze-dried specimens using a 6725 semi-micro oxygen calorimeter (Parr, USA) connected to a 6772 calorimetric thermometer (Parr, USA).