The performance of Arctic charr (Salvelinus alpinus) was monitored following transfer from low-salinity water (LSW, 3.6 ppt) to brackish water (BW, 20 ppt) at two juvenile stages. The early-entry group (EE) was transferred at ∼8 g, whereas the late-entry group (LE) entered BW 151 days later at 176 g. Mortality did not differ between groups. Growth was initially slower in BW than in LSW, but after the LE group was transferred, the EE group gradually caught up, and from day 328 to harvest on day 502 no differences in body length were detected, although the LE group had significantly higher final weight. Length growth was relatively stable, whereas weight growth followed cyclical patterns of reduced and accelerated growth. At harvest, the LE group showed a significantly higher incidence of skeletal deformities, suggesting that the timing of transfer to BW may influence bone health. Fish with elevated gonadosomatic index (GSI) at harvest showed contrasting growth trajectories between sexes. Males with slightly elevated GSI (Mean GSI ≈ 0.13%) were heavier than males with lower GSI (< 0.1%), whereas females with slightly elevated GSI (mean GSI ≈ 0.47%) exhibited reduced somatic growth during the latter part of the production cycle. Overall, the study suggests that Arctic charr juveniles of the Hólar strain can be transferred to BW earlier than is currently practiced, without compromising welfare.
Lake Mývatn experiences remarkable fluctuations in the populations of many of its 37 midge species. Here, we analyzed data from four adult traps from 1977 to 2023, and nine traps from 1999 to 2023, to characterize the annual dynamics of individual midge species, patterns of trends and cyclicity, synchrony among their fluctuations, and changes in community composition. Eighteen of the 20 common species from the 1977–2023 dataset showed quasi-periodic dynamics with periods of either 3–4 or 6–8 years. Furthermore, 12/20 species showed significant declines in abundance, while only one showed a significant increase. Although many pairs of species fluctuated in synchrony, synchrony was not greater for taxonomically related species. However, species that were more likely to have high adult abundances at the same locations (traps) were more likely to show synchrony. Finally, at the community level, a single species, Tanytarsus gracilentus, was associated with changes in the species composition of midges in Mývatn through time, while another common species, Cricotopus sylvestris, was primarily responsible for differences in community composition in space; differences occurred among traps from the two basins of Mývatn and along the Laxá outlet river. The prevalence of quasi-periodicity and synchrony in the dynamics among species suggests that many species share the same drivers of population fluctuations. We discuss the possible drivers, and although we can use the data to exclude some possible explanations of midge population dynamics, the data do not reveal a single explanation as best. Our results show the value of high-quality, long-term data on communities of organisms for revealing the existence of species-species and species-environment interactions that link the dynamics of species within the community and generate spatiotemporal changes in community composition.
This work presents a comprehensive compilation of cold-water coral records from within Iceland’s exclusive economic zone (EEZ). The resulting database includes 2,710 records across two classes, Octocorallia (orders Malacalcyonace and Scleralcyonacea) and Hexacorallia (orders Scleractinia and Antipatharia). Data sources include records from the Danish Ingolf expedition (late 19th to early twentieth century), specimens held at the Natural Science Institute of Iceland (NSII), the BIOICE project (1991–2004), bycatch data from groundfish trawl surveys conducted by the Marine and Freshwater Research Institute (MFRI, 2015–2020), underwater images from MFRI’s Benthic Habitat Mapping programme (2004–2021), and records from published literature. Cold-water corals are distributed widely within Icelandic waters, with a taxonomic diversity of 77 species across 27 families. Records were obtained at locations with mean temperature ranging from -1.0 to 9.0 °C and at depths of 15 to 2,710 m., with most observations recorded in waters deeper than 600 m. Three distinct species assemblages were identified: group A, consisting of a few species present both north and south of Iceland and including species predominantly located in the cold waters north of Iceland; group B and group C, comprising species found in the warmer waters south and west of Iceland. The Icelandic coral fauna displays mixed geographic affinities. Scleractinia show significant similarities to coral faunas of the Shetland, Faroe, Orkney, New Hebrides Islands and Rockall Bank, as well as to those of the western North Atlantic from Canada to the Gulf of Maine. The geographic affinity of octocorals aligns more closely with the boreal eastern Atlantic and northern Mid-Atlantic Ridge, as well as the western North Atlantic fauna from east off Canada to Cape Hatteras.
Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere in a changing climate is critical to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe and synthesise datasets and methodologies to quantify the five major components of the global carbon budget and their uncertainties. Fossil CO2 emissions (EFOS) are based on energy and cement production data. Emissions from land-use change (ELUC) are estimated by bookkeeping models based on land-use data. The global atmospheric CO2 growth rate (GATM) is computed from changes in concentration measured at surface stations. The global net uptake of CO2 by the ocean (SOCEAN) is estimated with global ocean biogeochemistry models and observation-based fCO2-products. The global net uptake of CO2 by the land (SLAND) is estimated with dynamic global vegetation models. Additional lines of evidence are provided by atmospheric inversions, atmospheric oxygen measurements, ocean interior observation-based estimates, and Earth System Models. This year, we introduced corrections on the ELUC, SOCEAN and SLAND estimates. The sum of all sources and sinks results in the carbon budget imbalance (BIM), a measure of imperfect data and incomplete understanding of the contemporary carbon cycle. All uncertainties are reported as ± 1σ. For the year 2024, EFOS increased by 1.1 % relative to 2023, with fossil emissions at 10.3 ± 0.5 GtC yr−1 (including the cement carbonation sink, 0.2 GtC yr−1), ELUC was 1.3 ± 0.7 GtC yr−1, for total anthropogenic CO2 emissions of 11.6 ± 0.9 GtC yr−1 (42.4 ± 3.2 GtCO2 yr−1). Also, for 2024, GATM was 7.9 ± 0.2 GtC yr−1 (3.73 ± 0.1 ppm yr−1), 2.2 GtC above the 2023 growth rate. SOCEAN was 3.4 ± 0.4 GtC yr−1 and SLAND was 1.9 ± 1.1 GtC yr−1, leaving a large negative BIM (−1.7 GtC yr−1), suggesting that the total sink or GATM is strongly overestimated in 2024. The global atmospheric CO2 concentration averaged over 2024 reached 422.8 ± 0.1 ppm. Preliminary data for 2025 suggest an increase in EFOS relative to 2024 of +1.0 % (0.2 % to 1.7 %) globally, and atmospheric CO2 concentration increasing by 2.1 ppm reaching 425.6 ppm, 53 % above the pre-industrial level (around 278 ppm in 1750). Overall, the mean and trend in the components of the global carbon budget are consistently estimated over the period 1959–2024, with a near-zero overall budget imbalance, although discrepancies of up to around 1 GtC yr−1 persist for the representation of annual to decadal variability in CO2 fluxes. Comparison of estimates from multiple approaches and observations shows: (1) a persistent large uncertainty in the estimate of land-use change emissions, (2) a low agreement between the different methods on the magnitude of the land CO2 flux in the northern extra-tropics, and (3) a discrepancy between the different methods on the mean ocean sink. This living data update documents changes in methods and datasets applied to this most-recent global carbon budget as well as evolving community understanding of the global carbon cycle. The data presented in this work are available at https://doi.org/10.18160/GCP-2025 (Friedlingstein et al., 2025c).
Northern bottlenose whales (Hyperoodon ampullatus) are echolocating, deep-diving beaked whales found primarily in arctic and sub-arctic offshore waters. In the eastern North Atlantic, the species has been suggested to undergo seasonal north–south migrations, however, previous whaling data and more recent sighting surveys insufficiently covered the winter months. To address this data gap, bottom-moored hydrophone deployments (n = 8) were conducted at three locations in the Nordic Seas: off Jan Mayen (Norway; 2015–2017), north-east Iceland (2020–2022) and east Iceland (2020–2023). Automated click detection allowed identification of species-specific clicks. Detector precision and recall were manually evaluated using subsets of the data and precision was used to correct the weekly proportion of snapshots that contained clicks. Generalized additive mixed models were used to investigate whether environmental variables associated with prey availability explained occurrence patterns. Results revealed near year-round presence of northern bottlenose whales in the Nordic Seas with a gradual northward shift in spring between Iceland and Jan Mayen. The lowest numbers of detections occurred from July into September, contradicting the long-standing hypothesis of north–south migrations to enable overwintering at lower latitudes. The observed seasonal occurrence patterns were stable across years and associated with higher sea surface height variation, indicative of eddy activity. We interpreted this as support of a prey-driven distribution, as eddies characterize the spawning grounds of northern bottlenose whales’ main squid prey in the Nordic Seas, Gonatus fabricii. The observed occurrence patterns can inform planning of future anthropogenic activities in these waters to avoid habitat degradation and reduce stressors on this species.
