Norwegian Sea Research Articles

Sources of Material for Surface Bottom Sediments in Some Regions of the Nordic Seas (According to Geochemical Data)

The mineral, bulk chemical (main rock-forming oxides) composition and systematics of rare-earth elements, Sc, Cr, Zr and Th of surface bottom sediments taken in a number of cruises of the R/V Akademik Mstislav Keldysh in the Nordic Seas (Mona, Knipovich, Kolbeinsey and Aegir ridges, the basins of the Norwegian and Greenland seas, the continental slope of Svalbard, the western continental margin of the Barents Sea, etc.) are considered to determine the sources of fine-grained material of bottom sediments. If for coastal sediments the primary influence of terrigenous drift is obvious, then seaward sediments are affected by “relatively war-mer” Atlantic waters, leading to their dilution with calcium carbonate, the main producers of which are planktonic foraminifers. It is concluded that the source of fine-grained aluminosiliciclastics for most of the studied samples were both acidic and basic igneous rocks (volcanic rocks of Iceland) in different proportions.

Biological Features of Atlantic Cod <i>Gadus Morhua</i> L., 1758 (Gadiformes: Gadidae) of the Murmansk Coast: Race Composition and Fishing

The biological features of Atlantic cod in the coastal zones of the Murman for 1999–2006 were studied. The age composition, growth rate and maturation, feeding habits and structure of otoliths were analyzed. Histological and genetic studies were carried out. It was shown that young cod mainly lives and spawns in Western Murman bays. Older cod leaves the bays due to insufficient food supply. The growth rate of young coastal cod is comparable to that of cod in the open part of the Barents Sea. With age, the cod of open sea areas noticeably overtakes the cod that lives in the coastal zone in growth. It was noted that cod spawns in the bays with both coastal and Atlantic types of otoliths. Studies of genetic polymorphism indicate a high degree of genetic si-milarity between cod groups in the Norwegian and Barents Seas, which is evidenced under the influence of currents (branches of the Norwegian Atlantic Current, the Murmansk Coastal Current) and against the background of migrations at different stages of ontogeny of cod individuals from coastal and open water areas.

Over 20% of marine fishes shifting in the North and Barents Seas, but not in the Norwegian Sea.

Climate warming generally induces poleward range expansions and equatorward range contractions of species' environmental niches on a global scale. Here, we examined the direction and magnitude of species biomass centroid geographic shifts in relation to temperature and depth for 83 fish species in 9,522 standardised research trawls from the North Sea (1998-2020) to the Norwegian (2000-2020) and Barents Sea (2004-2020). We detected an overall significant northward shift of the marine fish community biomass in the North Sea, and individual species northward shifts in the Barents and North Seas, in 20% and 25% of the species' biomass centroids in each respective region. We did not detect overall community shifts in the Norwegian Sea, where two species (8%) shifted in each direction (northwards and southwards). Among 9 biological traits, species biogeographic assignation, preferred temperature, age at maturity and maximum depth were significant explanatory variables for species latitudinal shifts in some of the study areas, and Arctic species shifted significantly faster than boreal species in the Barents Sea. Overall, our results suggest a strong influence of other factors, such as biological interactions, in determining several species' recent geographic shifts.

Integrated assessment of biological responses to pollution in wild mussels (Mytilus edulis) from subarctic and arctic areas in the Norwegian sea

North Atlantic and Arctic Oceans contain large amount of undiscovered oil and gas reserves. Therefore threat of oil spills and its hazardous ecological consequences are of great importance to the marine environment. Although mussels (Mytilus sp.) respond clearly to contaminants, biomarkers have shown variability linked to biological and environmental changes. In order to help avoiding misinterpretation of biological responses the aim of this study was to reveal the effect of natural variability in the responsiveness to pollution of a battery of cell and tissue-level biomarkers in mussels. Mussels were collected in relatively non-impacted and potentially impacted sites at ports and the vicinity of a waste water treatment plant in Trondheim and Tromsø in autumn of 2016. Although the battery of biomarkers used herein proved to be useful to discriminate impacted and non-impacted mussel populations, some confounding factors altering the biological responses were identified. Geographical/latitudinal factors seemed to be critical regarding the reproductive cycle, reserve material storage and the prevalence of parasites such as Gymnophallus cf. Bursicola trematodes. Mussels from the reference site in Tromsø displayed general stress responses at different levels, which could be influenced by the pathogenic effect of the Gymnophallus cf. Bursicola trematode and by a more advanced gametogenic developmental stage compared to the mussels from Trondheim, which could lead to misinterpretation of the reasons behind the measured stress levels in those mussels. Despite these confounding effects, the use of integrative tools such as IBR index helped to discriminate mussel populations from chemically impacted and non-impacted sites. Overall, this work serves as an anchor point both as a reference of the baseline level values of the analyzed endpoints in the studied geographical area and time of the year, and as an indication of the potential extent of the environmental confounding factors in monitoring programs causing stress on the analyzed mussel populations.

Rapid glacial sedimentation and overpressure in oozes causing large craters on the mid-Norwegian margin: integrated interpretation of the Naust, Kai and Brygge formations

Abstract Along continental margins with rapid sedimentation, overpressure may build up in porous and compressible sediments. Large-scale release of such overpressure has major implications for fluid migration and slope stability. Here, we study if the widespread crater-mound-shaped structures in the subsurface along the mid-Norwegian continental margin are caused by overpressure that accumulated within high-compressibility oozes sealed by low-permeability glacial muds. We interpret 56 000 km 2 of 3D and 150 000 km 2 of 2D-cubed seismic data in the Norwegian Sea, combining horizon picking, well ties and seismic geomorphological analyses of the crater-mound landforms. Along the mid-Norwegian margin, the base of the glacially influenced sediments abruptly deepens to form 28 craters with typical depths of c. 100 m, areal extents of up to 5130 km 2 and volumes of up to 820 km 3 . Mounds are observed in the vicinity of the craters at several stratigraphic levels above the craters. We present a new model for the formation of the craters and mounds where the mounds consist of remobilized oozes evacuated from the craters. In our model, repeated and overpressure-driven sediment failure is interpreted to cause the crater-mound structures, as opposed to erosive megaslides. Seismic geomorphological analyses suggest that ooze remobilization occurred as an abrupt energetic and extrusive process. The results also suggest that rapidly deposited, low-permeability and low-porosity glacial sediments seal overpressure that originated from fluids being expelled from the underlying high-permeability and high-compressibility biosiliceous oozes.

Estimation of long-term changes in thermal conditions and distribution of Atlantic and Subarctic water in the XXI Century in the Norwegian Sea on area surveys data

Purpose of the work: assessing the spatial and temporal variability of thermal conditions in waters of various origins in the Norwegian Sea in the first decades of the 21st century. Materials: oceanographic data collected during the International Ecosystem Surveys in the Norwegian Sea in 2000–2021. Methods used: comparative data analysis, descriptive statistics methods, correlation analysis. Results: the “boxes”, temperature in which most fully describes the change in the temperature of the Atlantic and Subarctic waters of the Norwegian Sea, were identified. This is confirmed by the high correlation coefficients of temperature in the “boxes” with the water temperature over a wide area of distribution of waters of various origins. The interannual temperature variability in the “boxes” was studied with the separation of warm and cold periods. An assessment of the interannual variability of the distribution boundaries of the Atlantic and subarctic waters is made by the position of isotherms at different horizons. A statistically significant relationship is shown between changes in the temperature of Atlantic and Subarctic waters according to the “boxes” data and changes in the boundaries of the distribution of water masses and the position of the frontal zone between them. Practical significance: the results of the analysis of in situ data from annual areal surveys make it possible to estimate the interannual variability of the thermal state of waters of various origins in the Norwegian Sea in the absence of standard sections and can be used to predict the distribution of pelagic fish in the sea area depending on oceanographic conditions.

The Barents and Norwegian Seas beaked redfish (Sebastes mentella): stock assessment and fishery management

An analytical review of the stock assessment and fishery regulation of the Barents and Norwegian Seas beaked redfish is presented. Model estimates of stock dynamics are characterized by uncertainty associated with incomplete coverage of the beaked redfish distribution in surveys, age determination problems, and assumptions made in the model. The regulation of fishing mortality is based on the precautionary approach, and the main management aim is achievement of the maximum sustainable yield. Technical measures include limiting the minimum mesh size in the trawl, establishing a minimum fish length for fishery, temporal fishery closures and limiting by-catch in multi-species fisheries. The unregulated fishery of the Norwegian-Barents Sea beaked redfish in the 1970s was one of the reasons for the decline in its stock and appearance of poor recruitment, which led to the ban on its targeted fishing in the Norwegian Economic Zone and in the fish protection area of the Svalbard. In 2014, the fishing was reopened. At present, the stock of beaked redfish of the Norwegian-Barents Sea population is in a safe state and further growth of the catch is expected.

Some Results of Direct FR Technology Applied to Study Methane Seepage Areas in the Arctic Region

The experimental study of the seepage processes' sources formation in structures of the Arctic Region was carried out using modified methods of frequency-resonance (FR) processing and decoding of satellite images and photographs with the vertical scanning of the cross-sections. The newly obtained results show that the intensity and dynamics of the methane seeps and pockmarks fields’ formation depend on active deep degassing processes in the continental margin structures. The use of direct FR-sounding technologies allows for determining the probable origin and depth of geological sources of gas migration at marginal migration centers in Greenland, and Norwegian and Barents Seas. New results confirm the crust-mantle gas fluids’ influence on the nature and degassing processes features in the scan points of polar marginal structures. These data are important arguments in favor of the “volcanic model” of various structural elements formation in this and other regions. The FR technologies data also showed a possibility of seeps use as shallow and deep hydrocarbon field indicators in gas emission areas. These independent data can be used in compiling models of the deep lithosphere structure and possible mechanisms of abiogenetic hydrocarbon formation in Arctic margin structures. The authors suppose that hydrocarbons through deep channels migrate (from 57 km deep) to the upper crustal horizons where their fields can form. During this migration, gas seeps and pockmarks are formed on the sea bottom and part of the gas can migrate into the atmosphere. Data show that basaltic volcanoes in Greenland scan points can be the real channels through which hydrogen migrates to the upper crustal horizons and further into the atmosphere. Active gas migration in Arctic seepage areas can be an important factor in the global climate change processes.

Spatial Variability of the Frontal Zones and its Eddies Generated in the Norwegian Sea

The Norwegian Sea is the meeting place of warm and salty Atlantic waters with cold and fresh Arctic waters. The thermal and haline frontal zones (FZs) formed as a result of this interaction are areas of increased horizontal gradients of physical, chemical, and biological parameters, and have a significant impact on regional circulation. Many mesoscale eddies are generated in the FZs which are actively involved in the eddy dynamics of the Norwegian Sea. The aim of this work is to analyze the spatio-temporal variability of the vertical structure of FZs in the Norwegian Sea, as well as the eddies that form within their boundaries. The work uses data from the oceanic reanalysis GLORYS12V1, as well as the Atlas of Mesoscale Eddies "Mesoscale Eddy Trajectory Atlas product META 3.2 DT" for the period 1993--2021. We analyze the average depth and thickness of FZs, the vertical distribution of their thermohaline gradients and areas. The work examines the seasonal and interannual variability of the volumes of thermal and haline FZs, the seasonal and interannual variability of mesoscale eddies, their spatial distribution, trajectories, and main parameters. In some areas, deepening of FZs has been established, and their thickness can reach 900 m. The presence of significant haline gradients in the layer of 250--750 m has been found, while thermal FZs can be traced vertically up to 1000 m compared with haline FZs. In some FZs, the interannual variability may exceed the seasonal one. The greatest variability of haline FZs can be traced in the autumn period, and the smallest -- in the winter--spring. It is noticeable in the summer period that thermal FZs weaken. Eddies can leave the boundaries of the FZs and move away from the place of origin for hundreds of kilometers. The number and lifetime of cyclones exceed similar estimates for anticyclones, while anticyclones travel long distances compared to cyclones.

Вертикальная изменчивость интенсивности фронтальных зон Норвежского моря

The Norwegian Sea is the meeting place of warm and salty Atlantic waters with cold and fresh Arctic waters. The thermal and haline frontal zones (FZs) formed as a result of this interaction are areas of increased horizontal gradients of physical, chemical, and biological parameters, and have a significant impact on regional circulation. Many mesoscale eddies are generated in the FZs which are actively involved in the eddy dynamics of the Norwegian Sea. The aim of this work is to analyze the spatio-temporal variability of the vertical structure of FZs in the Norwegian Sea, as well as the eddies that form within their boundaries. The work uses data from the oceanic reanalysis GLORYS12V1, as well as the Atlas of Mesoscale Eddies "Mesoscale Eddy Trajectory Atlas product META 3.2 DT" for the period 1993--2021. We analyze the average depth and thickness of FZs, the vertical distribution of their thermohaline gradients and areas. The work examines the seasonal and interannual variability of the volumes of thermal and haline FZs, the seasonal and interannual variability of mesoscale eddies, their spatial distribution, trajectories, and main parameters. In some areas, deepening of FZs has been established, and their thickness can reach 900 m. The presence of significant haline gradients in the layer of 250--750 m has been found, while thermal FZs can be traced vertically up to 1000 m compared with haline FZs. In some FZs, the interannual variability may exceed the seasonal one. The greatest variability of haline FZs can be traced in the autumn period, and the smallest -- in the winter--spring. It is noticeable in the summer period that thermal FZs weaken. Eddies can leave the boundaries of the FZs and move away from the place of origin for hundreds of kilometers. The number and lifetime of cyclones exceed similar estimates for anticyclones, while anticyclones travel long distances compared to cyclones.

Some patterns of formation of extreme surface air temperature in the area of the Spitzbergen (Svalbard) archipelago during the cold period

The article presents research findings of meteorological conditions during the formation of extreme surface air temperature (SAT) in the cold period from October to May in the Barentsburg area, the Spitzbergen (Svalbard) archipelago. Six extremely cold periods and six extremely warm periods for the weather sequence from 1912 to 2022 are considered. Correlation coefficients of extreme SAT in Barentsburg with extreme SAT in the points of Longyearbyen, Hornsund, Isfjord Radio, Pyramiden, Nu-Alesund, located in the west of Spitzbergen (Svalbard), were calculated. Also, characteristics of atmospheric circulation at the surface level, the level of the geopotential surface 500 hPa and 700 hPa and air temperature anomalies are analyzed, the results of comparing atmospheric circulation indices NAO and AO in the formation of extreme SAT are presented. Characteristic localizations of the polar vortex were found during the formation of negative and positive anomalies of SAT. For cold periods with extremely low temperatures, the localization of the polar vortex in the northeast of the Kara Sea and Severnaya Zemlya archipelago is observed. At the surface level the baric trough from the Atlantic depression is shifted to the coast of Scandinavia and the southern part of the Barents Sea. The Svalbard region is under the influence of the periphery of the anticyclonic field over the Arctic basin, Greenland, over the western Arctic Seas, conditions are formed for the deviation of SAT by 3–4 degrees below normal. In the case of extremely high SAT, the polar vortex is shifted to the eastern part of the Canadian Arctic Archipelago and the Baffin Sea. At the surface level, the baric trough from the Icelandic depression develops over the Greenland, Norwegian and Barents Seas, which leads to the moving of warm air masses from the Atlantic to polar latitudes and the formation of average SAT in the Spitzbergen (Svalbard) region above long-term values by 1–2 degrees. The estimates of macroprocesses obtained can be used for preparing long-term forecasts for the northern polar region and detailing them for the Spitzbergen (Svalbard) region.

Vertical Structure of Clouds and Precipitation During Arctic Cold‐Air Outbreaks and Warm‐Air Intrusions: Observations From COMBLE

AbstractThe Arctic is marked by deep intrusions of warm, moist air, alternating with outbreaks of cold air down to lower latitudes. The typical vertical structure of clouds and precipitation during these two synoptic weather extremes is examined at a coastal site at 69°N in Norway. The Norwegian Sea is a corridor for warm‐air intrusions (WAIs) and frequently witnesses cold‐air outbreaks (CAOs). This study uses data from profiling radar, lidar, and microwave radiometer, radiosondes and other probes that were collected during the CAOs in the Marine Boundary Layer Experiment (COMBLE) between 1 December 2019 and 31 May 2020. Marine CAOs are defined in terms of thermal instability relative to the sea surface temperature, and WAIs in terms of equivalent potential temperature stratification between the surface and 850 hPa. Cloud structures in CAOs are convective, driven by strong surface heat fluxes over a long fetch of open water, with cloud tops rarely exceeding 6 km above sea level. The mostly open‐cellular convection produces intermittent moderately‐heavy precipitation at the observational site, notwithstanding the low precipitable water vapor (PWV). In contrast, WAIs are marked by high values of PWV and integrated vapor transport. WAI clouds are synoptically driven, stratiform, with cloud tops often exceeding 5 km, sometimes layered, and generally producing persistent precipitation that can be heavier than in CAOs.

Using multivariate autoregressive state‐space models to examine stock structure of Greenland halibut in the North Atlantic

AbstractAccurate information on population structure is essential for effective fisheries management. Greenland halibut (Reinhardtius hippoglossoides) in the North Atlantic is managed as four separate offshore stocks. We use Multivariate Autoregressive State‐Space (MARSS) models to assess population structure by means of abundance and biomass trends in four regions (Norwegian Sea, Iceland, Southeast Greenland, and Northwest Atlantic) where three offshore stocks are recognized: (1) Baffin Bay–Davis Strait (Northwest Atlantic stock), (2) Southeast Greenland and Iceland (West Nordic stock (WNS)), and (3) the Barents and Norwegian Seas (Northeast Arctic stock). We formulated model alternatives, using bottom trawl survey data from each region for 1996–2019, to evaluate support for different population structures. Abundance and biomass observations from each region were linked to growth rate parameters in MARSS models and the impact of climate (North Atlantic Oscillation Index) and fishing (commercial catches) on stock dynamics was investigated. Top models identified the Northwest Atlantic as an independent population. Best‐fit models treated Greenland halibut in the WNS as two independent populations (east and west), with potential connections between eastern Iceland and the western Barents Sea. These results suggest a mismatch between current stock perception and management boundaries in the Northeast Atlantic.

Poleward spawning of Atlantic mackerel (Scomber scombrus) is facilitated by ocean warming but triggered by energetic constraints

Abstract The Northeast Atlantic mackerel is an income breeder with indeterminate fecundity, spawning in multiple batches at optimal temperatures around 11°C in the upper water column during February–July along the continental shelf from 36–62°N. Based on macroscopic staging of gonads (N ∼62000) collected in 2004–2021, we detected an on-going extension of spawning activities into the Norwegian Sea feeding area (62–75°N), reaching stable levels around 2012 onwards. This poleward expansion increased as more fish entered the area, whilst the maximum proportions of spawners concurrently dropped from about 75 to 15% from May to July. Detailed histological examinations in 2018 confirmed the macroscopic results but clarified that 38% of the spawning-capable females in July terminated their spawning by atresia. We suggest that increased access to suitable spawning areas (≥10°C), following ocean warming from 2002 onwards, functions as a proximate cause behind the noticed expansion, whereas the ultimate trigger was the historic drop in body growth and condition about 10 years later. Driven by these energetic constraints, mackerel likely spawn in the direction of high prey concentrations to rebuild body resources and secure the future rather than current reproduction success. The ambient temperature that far north is considered suboptimal for egg and larval survival.

Recent marine growth declines in wild and ranched Atlantic salmonSalmo salarfrom a western European catchment discovered using a 62-year time series

AbstractTo address population declines, many salmon populations are supplemented with hatchery-bred fish. Little is known about how growth performance of hatchery-bred and wild salmon compare during critical periods such as the first summer at sea. This study compares scale growth measurements between 1725 ranched and 1976 wild salmon from the Burrishoole catchment (western Ireland) over 62 years (1956–2017). Post-smolt growth (PSG) was greater in wild than ranched fish; this difference was consistent with compensatory growth rather than size-dependant growth. Temporal trends in marine growth of wild and ranched fish were similar, with a marked decline in PSG and return size after the early 2000s. The decline in PSG was significantly related to freshwater growth and autumn sea surface temperature in the Norwegian Sea. Temporal changes in the pattern of intercirculi spacings along the PSG growth trajectory were also identified; circuli deposited during the first summer at sea were narrower in the 2000s and 2010s compared to earlier decades, while circuli from the first winter were wider. The recent decline in growth affects both populations similarly, is associated with increasing temperature and is manifested as a change in growth pattern as well as overall growth.

Future Winter Precipitation Decreases Associated With the North Atlantic Warming Hole and Reduced Convection

AbstractClimate projections in the North Atlantic region suffer from great uncertainties, and projections of precipitation are given with a large spread. Some of this uncertainty is related to projections of the North Atlantic warming hole (NAWH). The Community Earth System Model version 2 (CESM2) projects a relatively strong and extensive NAWH, with future sea surface cooling extending to Northern Scandinavia. This study investigates the relatively large winter precipitation decrease projected by CESM2 in the northeastern North Atlantic region, reinforced in a regional model. Three future scenarios from CESM2 are dynamically downscaled with the Weather Research and Forecast model. A methodology to separate convective and orographic from stratiform precipitation is applied to explore the physical mechanisms. Changes in stratiform precipitation closely relate to storm‐track changes, which varies between the scenarios. Convective precipitation decreases by up to 50% over the Norwegian Sea at the end of the century, which is robust across the scenarios. This is explained by the underlying reduced sea surface temperatures of the NAWH, leading to reduced evaporation and reduced convective activity and intensity. The orographic precipitation maximum over the Scandinavian mountains is shifted upstream, likely affected by increased static stability and flow blocking, which also relates to the NAWH. This shift is possibly also explained by more frequent rain versus snow, as well as reduced cross‐barrier wind speeds. This study contributes to highlight the importance of focusing future research efforts on the NAWH, in order to constrain future climate projections in this region.

Arctic Edible Brown Alga Fucus distichus L.: Biochemical Composition, Antiradical Potential and Human Health Risk.

Fucus distichus L. is the dominant canopy-forming macroalga in the rocky intertidal areas of the Arctic and Subarctic. In the present study, the impact of the geographic location of F. distichus collected in the Baffin Sea (BfS), Norwegian Sea (NS), White Sea (WS), and Barents Sea (BS) on the variations in biochemical composition, antiradical properties, and health risk was evaluated. The accumulation of main carbohydrates (fucoidan, mannitol, and alginic acid) varied from 335 mg/g dry weight (DW) in NS to 445 mg/g DW in BS. The highest level of the sum of polyphenols and flavonoids was found in samples of F. distichus from WS and was located in the following ranking order: BS < BfS < NS < WS. The 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity of seaweed is correlated with its phenolic content. It is notable that in most Arctic F. distichus samples, Cd, Cr, Pb, and Ni were not detected or their concentrations were below the limit of quantification. According to calculated targeted hazard quotient and hazard index values, all studied samples of Arctic F. distichus are safe for daily consumption as they do not pose a carcinogenic risk to the health of adults or children. The results of this study support the rationale for using Arctic F. distichus as a rich source of polysaccharides, polyphenols, and flavonoids with important antiradical activity. We believe that our data will help to effectively use the potential of F. distichus and expand the use of this algae as a promising and safe raw material for the food and pharmaceutical industries.

Analysis of the Development Mechanisms of a Polar Low over the Norwegian Sea Simulated with the Canadian Regional Climate Model

Polar lows (PLs) are maritime mesoscale cyclones associated with severe weather. They develop during marine cold air outbreaks near coastlines and the sea ice edge. Unfortunately, our knowledge about the mechanisms leading to PL development is still incomplete. This study aims to provide a detailed analysis of the development mechanisms of a PL that formed over the Norwegian Sea on 25 March 2019 using the output of a simulation with the sixth version of the Canadian Regional Climate Model (CRCM6/GEM4), a convection-permitting model. First, the life cycle of the PL is described and the vertical wind shear environment is analysed. Then, the horizontal wind divergence and the baroclinic conversion term are computed, and a surface pressure tendency equation is developed. In addition, the roles of atmospheric static stability, latent heat release, and surface heat and moisture fluxes are explored. The results show that the PL developed in a forward-shear environment and that moist baroclinic instability played a major role in its genesis and intensification. Baroclinic instability was initially only present at low levels of the atmosphere, but later extended upward until it reached the mid-troposphere. Whereas the latent heat of condensation and the surface heat fluxes also contributed to the development of the PL, convective available potential energy and barotropic conversion do not seem to have played a major role in its intensification. In conclusion, this study shows that a convection-permitting model simulation is a powerful tool to study the details of the structure of PLs, as well as their development mechanisms.

Estimating Surface Concentrations of Calanus finmarchicus Using Standardised Satellite-Derived Enhanced RGB Imagery

Calanus finmarchicus is a keystone zooplankton species that is commercially harvested and is critical in sustaining many important fisheries in the North Atlantic. However, due to their patchy population distributions, they are notoriously difficult to map using traditional ship-based techniques. This study involves the use of a combined approach of standardized ocean colour imagery and radiative transfer modelling to identify reflectance anomalies potentially caused by surface swarms of C. finmarchicus in the northern Norwegian Sea. Here, we have standardized satellite eRGB imagery that depicts a distinct ‘red’ patch, which coincides with in situ measurements of high surface concentrations of C. finmarchicus. Anomaly mapping using a novel colour matching technique shows a high degree of anomaly within this patch compared to the surrounding waters, indicating the presence of something other than the standard bio-optical model constituents influencing the optics of the water column. Optical closure between modelled and satellite-derived reflectance signals is achieved (and the anomaly is significantly reduced) through the addition of C. finmarchicus absorption into the model. Estimations of the surface concentrations of C. finmarchicus suggest between 80,000 and 150,000 individuals m−3 within the extent of the identified red patch. Furthermore, analysis of the impact of C. finmarchicus absorption on the OC3M algorithm performance points to the potential for the algorithm to over-estimate chlorophyll concentrations if C. finmarchicus populations are present in the surface waters.

Bidimensional climatology and trends of Northern Hemisphere blocking utilizing a new detection method

AbstractIn this article, the meridional gradient of daily potential vorticity (PV) on the 330 K isentropic surface is used to identify atmospheric blocking events for the period 1979–2019. The associated two‐dimensional index considers not only Rossby wave breaking, but also energy dispersion and nonlinearity of blocking systems, and thus has a solid theoretical foundation. It also has the advantage of automatically excluding subtropical high‐pressure systems in summer and autumn. The index reveals that the Northern Hemisphere exhibits high blocking frequency over Euro‐Atlantic, North Pacific and Greenland in winter, spring and autumn, and over two wide‐extended bands at high latitudes in summer. Two prominent blocking episode (BE) intensity centres are found over the eastern Atlantic and eastern Pacific in all seasons, while the long‐lived BE is primarily situated in regions with high BE frequency. There is more frequent and longer‐lived BE in the Euro‐Atlantic sector than in the North Pacific, whereas the BE in the North Pacific is more intense. Notably, with the same poleward criterion for the four seasons, the BE frequency and duration are supposed to be overestimated in summer. Comparing our blocking detection method with previous blocking indices provides additional information about the long‐term trends for blocking frequency and intensity, which can be useful to our understanding of future extremes on climate time‐scales. It is found that both blocking frequency and intensity exhibit upward linear trends in the Ural region and Barents–Kara Sea in winter, Europe, northern North Pacific and East Siberia in spring, western Greenland in summer, as well as Norwegian Sea, Europe and North Atlantic in autumn, which point to increases in high‐impact weather events in these regions.