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Behaviour of anadromous brown trout (Salmo trutta) in a hydropower regulated freshwater system
Get PDFMany Norwegian rivers and lakes are regulated for hydropower, which afects freshwater ecosystems and anadromous fish species, such as sea trout (Salmo trutta). Lakes are an important feature of many anadromous river systems. However, there is limited knowledge on the importance of lakes as habitat for sea trout and how hydropower afects the behaviour of sea trout in lakes. To investigate this, we conducted an acoustic telemetry study. A total of 31 adult sea trout (532±93 mm total length) were captured by angling in river Aurlandselva, Norway, and tagged between July 20 and August 12, 2021. The tags were instrumented with accelerometer, temperature, and depth sensors, which provided information on the sea trout’s presence and behaviour in lake Vassbygdevatnet. Our results indicate that there was a large prevalence of sea trout in the lake during the spawning migration, and that the sea trout were less active in the lake compared to the riverine habitats. An increase in activity of sea trout in the lake during autumn might indicate that sea trout spawn in the lake. However, the discharge from the high-head storage plant into the lake did not afect the depth use or activity of sea trout in the lake. Furthermore, the large prevalence of spawners in the lake during autumn will likely cause an underestimation of the size of the sea trout population in rivers with lakes during annual stock assessment. In conclusion, our results could not fnd evidence of a large impact of the discharge on the behaviour of sea trout in the lake. Biologging, Anadromous brown trout, Hydropower, Lake ecology, AccelerationpublishedVersio
The hydrological cycle and ocean circulation of the Maritime Continent in the Pliocene: results from PlioMIP2
Get PDFThe Maritime Continent (MC) forms the western boundary of the tropical Pacific Ocean, and relatively small changes in this region can impact the climate locally and remotely. In the mid-Piacenzian warm period of the Pliocene (mPWP; 3.264 to 3.025 Ma) atmospheric CO2 concentrations were ∼ 400 ppm, and the subaerial Sunda and Sahul shelves made the land–sea distribution of the MC different to today. Topographic changes and elevated levels of CO2, combined with other forcings, are therefore expected to have driven a substantial climate signal in the MC region at this time. By using the results from the Pliocene Model Intercomparison Project Phase 2 (PlioMIP2), we study the mean climatic features of the MC in the mPWP and changes in Indonesian Throughflow (ITF) with respect to the preindustrial. Results show a warmer and wetter mPWP climate of the MC and lower sea surface salinity in the surrounding ocean compared with the preindustrial. Furthermore, we quantify the volume transfer through the ITF; although the ITF may be expected to be hindered by the subaerial shelves, 10 out of 15 models show an increased volume transport compared with the preindustrial. In order to avoid undue influence from closely related models that are present in the PlioMIP2 ensemble, we introduce a new metric, the multi-cluster mean (MCM), which is based on cluster analysis of the individual models. We study the effect that the choice of MCM versus the more traditional analysis of multi-model mean (MMM) and individual models has on the discrepancy between model results and data. We find that models, which reproduce modern MC climate well, are not always good at simulating the mPWP climate anomaly of the MC. By comparing with individual models, the MMM and MCM reproduce the preindustrial sea surface temperature (SST) of the reanalysis better than most individual models and produce less discrepancy with reconstructed sea surface temperature anomalies (SSTA) than most individual models in the MC. In addition, the clusters reveal spatial signals that are not captured by the MMM, so that the MCM provides us with a new way to explore the results from model ensembles that include similar models.publishedVersio
Deep-Reaching Global Ocean Overturning Circulation Generated by Surface Buoyancy Forcing
Get PDFIn contrast with the atmosphere, which is heated from below by solar radiation, the ocean is both heated and cooled from above. To drive a deep-reaching overturning circulation in this context, it is generally assumed that either intense interior mixing by winds and internal tides, or wind-driven upwelling is required; in their absence, the circulation is thought to collapse to a shallow surface cell. We demonstrate, using a primitive equation model with an idealized domain and no wind forcing, that the surface temperature forcing can in fact drive an interhemispheric overturning provided that there is an open channel unblocked in the zonal direction, such as in the Southern Ocean. With this geometry, rotating horizontal convection, in combination with asymmetric surface cooling between the north and south, drives a deep-reaching two-cell overturning circulation. The resulting vertical mid-depth stratification closely resembles that of the real ocean, suggesting that wind-driven pumping is not necessary to produce a deep-reaching overturning circulation, and that buoyancy forcing plays a more important role than is usually assumed.publishedVersio
Quantifying prior model complexity for subsurface reservoir models
Get PDFIn Bayesian approaches to history matching for subsurface inference, the prior model specifies the uncertain model parameters and the joint probability of those parameters before incorporating production-related data. A good prior model is generally complex enough to capture the future reservoir behavior in the long term, realistic enough to be plausible, consistent with geologic knowledge, and simple enough to allow calibration for data matching. Model complexity is often associated with the number of model parameters, thus the focus on finding the sufficient number of parameters needed for history matching and quantifying future uncertainty. This work explores model choice based on concepts of complexity and informativeness of models for subsurface reservoir models. It focuses on the effect of the misspecification of prior models for assimilating flow data and their predictive accuracy. The concept of the effective number of parameters is used to investigate the suitability of various types of prior models with different levels of complexity, ranging from a highly simplified polynomial trend model to a more realistic multipoint statistical model(MPS) and a family of isotropic Gaussian models and explore the effect of level of model complexity on the robustness of forecasting. The numerical experiments were performed with different combinations of data type, prior informativeness, forecast type, and model type to compare the effect of different prior models on the robustness of the results. The effective number of parameters was computed for each prior model and their accuracy for predicting future reservoir behavior was analyzed. The results suggest that effective model dimension is a useful measure of model complexity for history matching problems, although it is not independent of the data used for model calibration and the number of effective model parameters is generally much smaller than the number of model parameters. In a data-rich problem, realism of a model is much less important than the complexity of a model, while for a problem with few data, realism was beneficial for reliable forecasts.publishedVersio
Acute management of fractures in primary care - a cost minimisation analysis
Get PDFBackground In Norway, primary healthcare has first-line responsibility for all medical emergencies, including traumas and fractures. Normally, patients with suspected fractures are referred to specialist care in hospitals. However, the cooperating municipalities of Bykle and Valle have X-ray facilities and handle minor fractures locally. The aim of this study was to estimate the costs of X-ray diagnosis and initial treatment of fractures at the local primary care centre compared with initial transport and treatment in hospital. Methods We conducted a cost minimisation analysis by comparing expected costs of initial examination with X-ray and treatment of patients with fractures or suspected fractures at two possible sites, in the local municipality or at the hospital. A cost minimisation analysis is an economic evaluation based on the assumption that the outcomes of the two treatment procedure regimens are equal. Costs were estimated in Euros (EUR) using 2021 mean exchange rates. Results In 2019, we identified a total of 403 patients with suspected fractures in the two municipalities. Among these, 12 patients bypassed the primary care system as they needed urgent hospital care. A total of 391 injured patients were assessed with X-ray at the primary health care centres, 382 received their initial treatment there, and nine were referred to hospital. In an alternative hospital model, without X-ray and treatment possibilities in the municipality, the 382 patients would have been sent directly to hospital for radiological imaging and treatment. The total cost was estimated at EUR 367,756 in the hospital model and at EUR 69,835 in the primary care model, a cost saving of EUR 297,921. Conclusion Based on cost minimisation analysis, this study found that radiological diagnosis of suspected fractures and initial treatment of uncomplicated fractures in primary care cost substantially less than transport to and treatment in hospital.publishedVersio
Constrained optimization of offshore wind turbine positions under uncertain wind conditions with correlated data
Get PDFOffshore wind power production is subject to substantial uncertainty due to variability in wind conditions. Planning of new wind parks should take these uncertainties into account by means of stochastic modeling and uncertainty quantification. Wind speed and wind direction exhibit dependence that needs to be properly modeled to yield reliable uncertainty estimates. In particular, the dependence is strong when data are averaged over a short time-horizon, e.g., on a monthly rather than an annual basis. In this work we introduce a stochastic model for wind speed and wind direction using Rosenblatt transformation and an empirical model. This allows efficient numerical quadrature that replaces thousands of Monte Carlos samples by a few tens of model evaluations at quadrature points in parametric space. A robust design formulation for maximizing power production honoring dependent data is proposed and demonstrated on data from the North Sea site Sørlige Nordsjø II.Constrained optimization of offshore wind turbine positions under uncertain wind conditions with correlated datapublishedVersio
The development of ocean currents and the response of the cryosphere on the Southwest Svalbard shelf over the Holocene
Get PDFWhile general trends in the inflow of Atlantic Water (AW) to the European Arctic over the present interglacial (the Holocene) are well known, regional changes in climate and the AW current and subsequent environmental responses are less well established. In particular, there is only limited knowledge on the development of ocean currents after the last deglaciation. Here, to better understand past water mass dynamics and their effects on sea ice cover and the environment throughout the Holocene, we present a multiproxy record from core OCE2019-HR7-GC retrieved from the southwestern Svalbard inner shelf, a highly dynamic frontal area influenced by different ocean currents and local water masses. For sea ice reconstructions, we focus on the specific sea ice biomarker IP25 in combination with the phytoplankton biomarkers dinosterol and brassicasterol. We further reconstruct surface and bottom water temperatures using alkenones and Mg/Ca and prevailing water masses using foraminifera assemblages. Finally, we compare our sea ice and temperature records with published marine sediment and ice core data from the area. We observe extensive sea ice cover between 11 and 10.2 kyr BP, which was likely linked to the Preboreal Oscillation. Based on our reconstructions, the period between 10 and 7 kyr BP was characterized by the warmest Holocene conditions on the SW Svalbard shelf. This interval is also associated with high surface water productivity and an enhanced AW influx that drove strong erosive activity at the bottom. After 6.5 kyr BP, the SW Svalbard shelf was characterized by a dynamic environment with cold and unstable conditions that lasted until 3.5 kyr BP. After 3.5 kyr BP, we observed an increase in sea ice cover and iceberg rafting over our site once more, which likely indicated seasonally fluctuating ice margins, with low AW influx, which lasted until 2.2 kyr BP. A brief warm period accompanied by strong bottom currents occurred between 2.2 and 1.8 kyr BP. The environment returned to a colder state with the presence of sea ice until 1.5 kyr BP, which was followed by warmer conditions between 1.5 and 1 kyr BP.publishedVersio
The Relative Stability of Planktic Foraminifer Thermal Preferences over the Past 3 Million Years
Get PDFStationarity of species’ ecological tolerances is a first-order assumption of paleoenvironmental reconstruction based upon analog methods. To test this and other assumptions used in quantitative analysis of foraminiferal faunas for paleoceanographic reconstruction, we analyzed paired alkenone unsaturation ratio (′37) sea surface temperature (SST) estimates and relative abundances of planktic foraminifera within Late Pliocene assemblages. We established Pliocene temperature preferences for nine species in the North Atlantic: Dentoglobigerina altispira, Globorotalia menardii, Globoconella puncticulata, Neogloboquadrina atlantica, Neogloboquadrina incompta, Neogloboquadrina pachyderma, Trilobatus sacculifer, Globigerinita glutinata, and Globigerina bulloides. We compared these to the temperature preferences of the same extant species, and in the three cases where the species are now extinct (Dentoglobigerina altispira, Neogloboquadrina atlantica, and Globoconella puncticulata), comparisons were made to either the descendant species or other modern species commonly used as analogs. In general, the taxa tested show similar temperature responses in both Late Pliocene and present-day (core-top) distributions. The data from these comparisons are mostly encouraging, supporting past paleoceanographic conclusions, and are otherwise valuable for testing previous taxonomic grouping decisions that are often necessary for interpreting the paleoenvironment based upon Pliocene foraminiferal assemblages.publishedVersio
Arctic Ocean simulations in the CMIP6 Ocean Model Intercomparison Project (OMIP)
Get PDFArctic Ocean simulations in 19 global ocean–sea-ice models participating in the Ocean Model Intercomparison Project (OMIP) of the Coupled Model Intercomparison Project Phase 6 (CMIP6) are evaluated in this paper. Our findings show no significant improvements in Arctic Ocean simulations from the previous Coordinated Ocean-ice Reference Experiments phase II (CORE-II) to the current OMIP. Large model biases and inter-model spread exist in the simulated mean state of the halocline and Atlantic Water layer in the OMIP models. Most of the OMIP models suffer from a too thick and deep Atlantic Water layer, a too deep halocline base, and large fresh biases in the halocline. The OMIP models qualitatively agree on the variability and change of the Arctic Ocean freshwater content; sea surface height; stratification; and volume, heat, and freshwater transports through the Arctic Ocean gateways. They can reproduce the changes in the gateway transports observed in the early 21st century, with the exception of the Bering Strait. We also found that the OMIP models employing the NEMO ocean model simulate relatively larger volume and heat transports through the Barents Sea Opening. Overall, the performance of the Arctic Ocean simulations is similar between the CORE2-forced OMIP-1 and JRA55-do-forced OMIP-2 experiments.Arctic Ocean simulations in the CMIP6 Ocean Model Intercomparison Project (OMIP)publishedVersio
Interaction of temperature and feed ration on male postsmolt maturation of Atlantic salmon (Salmo salar L.)
Get PDFEarly maturation of Atlantic salmon male postsmolts is undesirable in aquaculture due to its negative impact on growth, welfare and seawater adaptation, however it is an increasing problem under intensive rearing conditions. The effect of temperature and feeding ration on sexual maturation during the induction of smoltification was tested with a 3 × 2 factorial design including three temperatures (8, 12.5 and 18 °C) and two feeding rations (100% and 67%), from 28 October 2018 to 30 May 2019. Fish in the six resulting treatments (1800 parr, initial mean weight 23.1 ± 7.2 g) were reared in flow-through under continuous light (LD24:0) except for a 5-week winter signal (LD12:12) introduced on 4 February 2019 to induce smoltification. A major effect of temperature determining the life history pattern of each group was observed. At 18 °C, a majority of the males were maturing in May under both rations (100% males in 18–100% and 88.9% males in 18–67%). Fish at 18 °C experienced an early activation of the BPG (Brain-Pituitary-Gonad) axis and displayed very poor signs of smoltification. At 12.5 °C, early maturation was also present, although at lower proportion than at 18 °C and more dependent upon feed ration (40% of males maturing in 12.5–100%, 8.6% in 12.5–67%). Salmon at 12.5 °C displayed the best growth within each feed regime, some early signs of smolting but subsequent low Na+, K+- ATPase activity after the winter signal. At 8 °C, salmon showed best signs of smoltification and lowest growth, while no males matured. The feed restriction had a minor effect on maturation at 18 °C but a greater impact at 12.5 °C, evidenced by significant differences between 12.5–100% and 12.5–67% in gonadosomatic index, plasma 11-ketotestosterone, insulin-like growth factor-I, and pituitary fshb (follicle stimulating hormone β-subunit gene) transcription. Onset of maturation was associated with the photoperiod change from short to long daylength, which probably also induced a slight activation of the BPG axis in non-maturing groups. Our results suggest that postsmolt producers must be cautious when using sustained high water temperatures, or the risk of early maturation and poor hypo-osmoregulatory performance will increase significantly. In addition, reducing the feeding ration will not help decrease incidence of maturation without significantly affecting growth.publishedVersio