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To determine the present-day community composition of siliceous Rhizaria (Radiolaria and Phaeodaria) in Norwegian fjords, plankton tows were conducted in south-western and northern Norwegian fjords in September 2016. The mean total abundance of radiolarians was 306 m–3 in the Sognefjord complex, which was the southern research site, and, in the north, 945 m–3 in Malangen and 89 m–3 in Balsfjord, both above the Arctic Circle. Sticholonche zanclea was the most abundant radiolarian in the Sognefjord complex and Malangen, accounting for 78–100% (mean 89%) of radiolarian abundance. The mean total abundance of phaeodarians was 1554 m–3 in the Sognefjord complex, 51 m–3 in Malangen and 11 m–3 in Balsfjord. Medusetta arcifera was the most abundant phaeodaria in the Sognefjord complex, accounting for >99% of phaeodarian abundance, but was absent in Malangen and Balsfjord, where Protocystis tridens accounted for >96% of phaeodarian abundance. The carbon biomass of S. zanclea and M. arcifera was 188 and 438 µg C m–3, respectively, which is similar to and 8.6 times higher than, respectively, that of phaeodarians >1 mm in the western North Pacific, suggesting that M. arcifera contributes to organic carbon transport in the Sognefjord complex. Amphimelissa setosa (Nassellaria, Radiolaria), which was a dominant species in the study area in 1982–83, was absent in the present study in all sampled fjords. This could have been caused by the approximately 2 °C increase in water temperature that has occurred since 1990 and can be taken as evidence of a climate-change-associated local temperature rise linked to the warming of advected Atlantic Water.

In 2011, a first comprehensive assessment of the footprints of climate change on Arctic marine ecosystems (such as altered distribution ranges, abundances, growth and body conditions, behaviours and phenologies, as well as community and regime shifts) was published. Here, we re-assess the climate-driven impacts reported since then, to elucidate to which extent and how observed ecological footprints have changed in the following decade (2011 to 2021). In total, 98 footprints have been described and analysed. Most of those impacts reported in the 2011 assessment are reconfirmed and can, hence, be assumed as continuing trends. In addition, novel footprints (behavioural changes, diet changes, altered competition and pathogen load) are described. As in 2011, most reported footprints are related to changes in distribution ranges, abundances, biomass and production. Range shifts have mostly been observed for fish species, while behavioural changes have mainly been reported for mammals. Primary production has been observed to further increase in Arctic seas. The footprints on pelagic herbivores, particularly the key species Calanus spp., are less clear. In comparison to 2011, more complex, cascading effects of climate change, such as increased bowhead whale body conditions due to increased primary production, have been reported. The observed footprints, and the trends that they indicate, strongly suggest that due to further northward range shifts of sub-Arctic and boreal species Arctic seas are likely to experience increasing species richness in the future. However, a tipping point may be reached, characterized by subsequent biodiversity decline, when Arctic-endemic species will go extinct as ocean warming and/or acidification will exceed their physiological adaptation capacity. Furthermore, as invading boreal species have a competitive advantage due to their wider physiological and trophic range, Arctic species abundances are predicted to decrease. Overall, the future Arctic Ocean will very likely experience increasing numbers and intensities of climate-change footprints.

The success of biotherapeutics is often challenged by the undesirable events of immunogenicity in patients, characterized by the formation of anti-drug antibodies (ADA). Under specific conditions, the ADAs recognizing the biotherapeutic can trigger the formation of immune complexes (ICs), followed by cascades of subsequent effects on various cell types. Hereby, the connection between the characteristics of ICs and their downstream impact is still not well understood. Factors governing the formation of ICs and the characteristics of these IC species were assessed systematically in vitro. Classic analytical methodologies such as SEC-MALS and SV-AUC, and the state-of-the-art technology mass photometry were applied for the characterization. The study demonstrates a clear interplay between (1) the absolute concentration of the involved components, (2) their molar ratios, (3) structural features of the biologic, (4) and of its endogenous target. This surrogate study design and the associated analytical tool-box is readily applicable to most biotherapeutics and provides valuable insights into mechanisms of IC formation prior to FIH studies. The applicability is versatile—from the detection of candidates with immunogenicity risks during developability assessment to evaluation of the impact of degraded or post-translationally modified biotherapeutics on the formation of ICs.

An important yet still not well documented aspect of recent changes in the Arctic Ocean is associated with the advection of anomalous sub-Arctic Atlantic- and Pacific-origin waters and biota into the polar basins, a process which we refer to as borealization. Using a 37-year archive of observations (1981–2017) we demonstrate dramatically contrasting regional responses to atlantification (that part of borealization related to progression of anomalies from the Atlantic sector of sub-Arctic seas into the Arctic Ocean) and pacification (the counterpart of atlantification associated with influx of anomalous Pacific waters). Particularly, we show strong salinification of the upper Eurasian Basin since 2000, with attendant reductions in stratification, and potentially altered nutrient fluxes and primary production. These changes are closely related to upstream conditions. In contrast, pacification is strongly manifested in the Amerasian Basin by the anomalous influx of Pacific waters, creating conditions favorable for increased heat and freshwater content in the Beaufort Gyre halocline and expansion of Pacific species into the Arctic interior. Here, changes in the upper (overlying) layers are driven by local Arctic atmospheric processes resulting in stronger wind/ice/ocean coupling, increased convergence within the Beaufort Gyre, a thickening of the fresh surface layer, and a deepening of the nutricline and deep chlorophyll maximum. Thus, a divergent (Eurasian Basin) gyre responds altogether differently than does a convergent (Amerasian Basin) gyre to climate forcing. Available geochemical data indicate a general decrease in nutrient concentrations Arctic-wide, except in the northern portions of the Makarov and Amundsen Basins and northern Chukchi Sea and Canada Basin. Thus, changes in the circulation pathways of specific water masses, as well as the utilization of nutrients in upstream regions, may control the availability of nutrients in the Arctic Ocean. Model-based evaluation of the trajectory of the Arctic climate system into the future suggests that Arctic borealization will continue under scenarios of global warming. Results from this synthesis further our understanding of the Arctic Ocean’s complex and sometimes non-intuitive Arctic response to climate forcing by identifying new feedbacks in the atmosphere-ice-ocean system in which borealization plays a key role.

Abstract Plankton respiration rate is a major component of global CO2 production and is forecasted to increase rapidly in the Arctic with warming. Yet, existing assessments in the Arctic evaluated plankton respiration in the dark. Evidence that plankton respiration may be stimulated in the light is particularly relevant for the high Arctic where plankton communities experience continuous daylight in spring and summer. Here we demonstrate that plankton community respiration evaluated under the continuous daylight conditions present in situ, tends to be higher than that evaluated in the dark. The ratio between community respiration measured in the light (Rlight) and in the dark (Rdark) increased as the 2/3 power of Rlight so that the Rlight:Rdark ratio increased from an average value of 1.37 at the median Rlight measured here (3.62 µmol O2 L−1 d−1) to an average value of 17.56 at the highest Rlight measured here (15.8 µmol O2 L−1 d−1). The role of respiratory processes as a source of CO2 in the Arctic has, therefore, been underestimated and is far more important than previously believed, particularly in the late spring, with 24 h photoperiods, when community respiration rates are highest.

Phytoplankton contribute half of the primary production (PP) in the biosphere and are the major source of energy for the Arctic Ocean ecosystem. While PP measurements are therefore fundamental to our understanding of marine biogeochemical cycling, the extent to which current methods provide a definitive estimate of this process remains uncertain given differences in their underlying approaches, and assumptions. This is especially the case in the Arctic Ocean, a region of the planet undergoing rapid evolution as a result of climate change, yet where PP measurements are sparse. In this study, we compared three common methods for estimating PP in the European Arctic Ocean: (1) production of 18O-labeled oxygen (GPP-18O), (2) changes in dissolved oxygen (GPP-DO), and (3) incorporation rates of 14C-labeled carbon into particulate organic carbon (14C-POC) and into total organic carbon (14C-TOC, the sum of dissolved and particulate organic carbon). Results show that PP rates derived using oxygen methods showed good agreement across season and were strongly positively correlated. While also strongly correlated, higher scatter associated with seasonal changes was observed between 14C-POC and 14C-TOC. The 14C-TOC-derived rates were, on average, approximately 50% of the oxygen-based estimates. However, the relationship between these estimates changed seasonally. In May, during a spring bloom of Phaeocystis sp., 14C-TOC was 52% and 50% of GPP-DO, and GPP-18O, respectively, while in August, during post-bloom conditions dominated by flagellates, 14C-TOC was 125% of GPP-DO, and 14C-TOC was 175% of GPP-18O. Varying relationship between C and O rates may be the result of varying importance of respiration, where C-based rates estimate net primary production (NPP) and O-based rates estimate gross primary production (GPP). However, uncertainty remains in this comparison, given differing assumptions of the methods and the photosynthetic quotients. The median O:C ratio of 4.75 in May is within the range of that observed for other regions of the world’s ocean. However, the median O:C ratio for August is

The northern Svalbard shelf region is part of the Atlantic advective contiguous domain along which nutrients, phyto- and mesozooplankton are advected with Atlantic Water from the Norwegian Sea along the Norwegian shelf break and into the Arctic Ocean. By applying the SINMOD model, we investigated how much mesozooplankton may be advected into the northern Svalbard shelf region. We also compared this supply with the local mesozooplankton production. To achieve this, we selected a box north of Svalbard and calculated the in- and outflux of Atlantic Calanus finmarchicus and Arctic Calanus glacialis. The average biomass inside the box ranged between 0.5 and 3.0 g C month–2 in March and August, respectively. Annually, 18.8 g C month–2 of advected (and locally produced) mesozooplankton would be available for predators inside the box before it is advected out. The advection of mesozooplankton reached 12 times more than the average biomass within the box. The model projects significance variability in mesozooplankton advection which may be explained by the hitherto non-quantified recirculation in the northern Fram Strait and differences in the geographic origin of the mesozooplankton source population. The results imply that grazing upon mesozooplankton in the Atlantic advective contiguous domain north of Svalbard is greatly advantageous for pelagic predators. It could represent an important food source for fish, birds, and whales. It is suggested that mesozooplankton encountered on the shelf north of Svalbard may derive from populations along the North Norwegian shelf break, in some years as far south as the Lofoten/Vesterålen region. This illustrates the extent and significance of the Atlantic advective contiguous domain for the European shelf of the Arctic Ocean which apparently depends on significant food supply through expatriates. Primary production on the shelf is lower than C consumption and thus the European shelf of the AO is presumably net-heterotrophic.

Despite concerns about rapid changes in Arctic Ocean physical forcing and ecosystem function, quantitative knowledge and time series are scarce. The number of reliable physical-biological coupled models and models based on remote sensing is small. To improve our comprehension of carbon flux in the most prominent Arctic Ocean feature, the seasonal ice zone, a possible first step is to evaluate how biogeochemical cycling might develop in the future by examining conceptual models that address climate warming and seasonality in ecosystem development. Here we present three conceptual models of biogeochemical cycling and climate warming in the seasonal ice zone of the Arctic Ocean. They are designed to enhance, in a conceptual and semiquantitative manner, understanding of the possible temporal sequence of future primary production development, its spatial variation, and food availability in the most productive part of the future Arctic Ocean, including pelagic-benthic coupling. We speculate that the largest changes will take place in (a) the northern portions of today's seasonal ice zone, which will expand to cover the entire Arctic Ocean, and (b) the southern portions, which will be exposed to more thermal stratification. The former change increases and the latter change decreases productivity and supply to the bottom. Lack of nutrient availability means that new production in the central Arctic Ocean will remain low. Blooms of ice and plankton algae may start earlier, depending on snow cover, providing more continuity in food supply for grazers in the upper water column. Weakening of today's highly episodic primary production in the seasonal ice zone will result in lower average food concentrations for pelagic heterotrophs. We suggest that more of the available energy will be recycled in the pelagic zone, and that vertical export of biogenic matter will be less variable and of reduced quality.

An experiment with eight vertically stratified seawater enclosures of 27 m3 (depth 9.3 m, diameter 2 m, 90% penetration of PAR) was run in order to test whether pulsed addition of nutrients may cause: 1, higher primary production; 2, higher build-up of phytoplankton biomass; 3, larger temporal mismatch between herbivores and phytoplankton biomass; and 4, higher sedimentation rates, distinguishing in each case between silicate and non-silicate fertilised systems. Nitrate and phosphate were added to all enclosures (NP), while silicate was added to four of the enclosures (NPS). Each enclosure received the same total amount of nutrients, but the nutrients were supplied at four different intervals ranging from one single load to continuous additions. Spring bloom-like systems developed where nutrients were added in one or two pulses as they were characterised by high primary production, high suspended biomass of chlorophyll a (Chl a) and particulate organic carbon (POC) and high sedimentation rates. In contrast, the seawater enclosures receiving nutrients about every third day or in a continuous supply resembled regenerated systems with low concentrations of suspended Chl a and POC and with low and stable loss rates. Due to a typical autumn inoculum with dominance of dinoflagellates and flagellates, diatoms did not dominate the NPS enclosures. The only significant effect of the silicate addition was higher vertical flux of particulate organic nitrogen in the NPS enclosures, and higher microzooplankton biomass. The mesozooplankton did not show responses to the different frequencies of nutrient additions. However, accumulation of mesozooplankton biomass was higher in the NP-mesocosms, probably reflecting better feeding conditions. We conclude that the frequency of nutrient additions had a stronger influence on the development of the phytoplankton and vertical flux of carbon than the +/- silicate treatment in this experiment.

The proportion in which carbon and growth-limiting nutrients are exported from the oceans' productive surface layer to the deep sea is a crucial parameter in models of the biological carbon pump. Based on >400 vertical flux observations of particulate organic carbon (POC) and nitrogen (PON) from the European Arctic Ocean we show the common assumption of constant C:N stoichiometry not to be met. Exported POC:PON ratios exceeded the classical Redfield atomic ratio of 6.625 in the entire region, with the largest deviation in the deep Central Arctic Ocean. In this part the mean exported POC:PON ratio of 9.7 (a:a) implies c. 40% higher carbon export compared to Redfield-based estimates. When spatially integrated, the potential POC export in the European Arctic was 10-30% higher than suggested by calculations based on constant POC:PON ratios. We further demonstrate that the exported POC:PON ratio varies regionally in relation to nitrate-based new production over geographical scales that range from the Arctic to the subtropics, being highest in the least productive oligotrophic Central Arctic Ocean and subtropical gyres. Accounting for variations in export stoichiometry among systems of different productivity will improve the ability of models to resolve regional patterns in carbon export and, hence, the oceans' contribution to the global carbon cycle will be predicted more accurately.