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Over the satellite record, the Barents Sea winter maximum in sea ice extent has declined and was increasingly limited to areas north of the Polar Front after 2005 by warming Atlantic Water (AW) and Barents Sea Water (BSW). Sea ice extent here continues to garner interest, not least because it is associated with extreme winter weather in Europe and Asia. Previous model studies suggest there is a possibility that natural variability will cause southward re-expansion of the lost sea ice cover but reducing uncertainties requires a better understanding of the processes driving BSW variability. To address questions about BSW variability, we used a high-resolution model validated with observations over 1985-2014 to calculate the watermass transport, heat and freshwater budgets within the central Barents Sea, south of the Polar Front. The model shows BSW volume minima events in years centering at 1990 and 2004, meaning a reduction in the Barents Sea’s volume reservoir (also termed “memory”) of water that is consistent with historical BSW properties. Both events were preceded by extensive winter sea ice and substantial summer net sea ice melt. The event in 2004 was more extreme and led to warming AW occupying a greater volume in the Barents Sea after 2005. The reduced “memory” of BSW volume could impede a return to the more extensive winter sea ice regime and make further reduction in winter sea ice possible. Key Points We identify events of minimum dense water volume in the Barents Sea, with the 2002-2005 event being unique with large sea ice import During this event, a freshwater anomaly from sea ice melt enhanced the salinity gradient, reducing dense water formation and export After the event in 2006-2014, the proportion of dense water present in the southern Barents Sea remained smaller than during 1985-2002 Plain Language Summary Winter sea ice in the Barents Sea, in the eastern Arctic Ocean, has been in decline, particularly since 2000. The sea ice extent in this region is associated with atmospheric weather conditions during winter in Europe and Asia. An important factor in understanding the sea ice retreat is understanding the variability in Barents Sea temperature and salinity. Using a high-resolution simulation, the source of variability in Barents Sea Water properties has been quantified. This shows two events, 1990 and 2004, when Barents Sea Water volume reduced, giving less “memory” of previous conditions. The event in 2004 was larger and followed a large net sea ice melt. The volume of Barents Sea Water present in the Barents Sea did not fully recover after 2005. This could make it more difficult for winter sea ice to return to the region.

Monitoring marine primary productivity (PP) is crucial for understanding changes in the marine ecosystem. Based on satellite data and the vertically generalized production model (VGPM), this study investigated the spatiotemporal distribution and long-term trend of PP in the Yellow and Bohai Seas (YBSs) from 2003 to 2020. By using the calibrated satellite data and optimized parameterization scheme, the accuracy of the PP results in the YBSs was significantly improved compared to online PP products. The annual mean PP in the YBSs from 2003 to 2020 was 523.8 mgC/(m2·d), with significant seasonal and interannual differences. Seasonally, PP in the Yellow Sea and the Bohai Sea exhibited bimodal (two peaks in May and October) and unimodal (one peak in June) variation, respectively. The magnitude of mean PP in the YBSs was ranked as spring > summer > autumn > winter, with spring PP (~1000 mgC/(m2·d)) contributing more than 40% of the annual PP. The annual mean PP in the YBSs showed an overall decrease from 2003 to 2020, with a decrease rate of 5–6 mgC/(m2·d)/y. The interannual variation of the PP was mainly related to the variability of the chlorophyll-a concentration and was essentially inverse to the phases of the Pacific Decadal Oscillation and the El Niño-Southern Oscillation.

Understanding how gelatinous zooplankton communities are structured by local hydrography and physical forcing has important implications for fisheries and higher trophic predators. Although a large body of research has described how fronts, hydrographic boundaries, and different water masses (e.g., mixed vs. stratified) influence phytoplankton and zooplankton communities, comparatively few studies have investigated their influence on gelatinous zooplankton communities. In July 2015, 49 plankton samples were collected from 50 m depth to the surface, across five transects in the Celtic Sea, of which, four crossed the Celtic Sea Front. Two distinct gelatinous communities were found in this dynamic shelf sea: a cold water community in the cooler mixed water that mainly contained neritic taxa and a warm water community in the warmer stratified water that contained a mixture of neritic and oceanic taxa. The gelatinous biomass was 40% greater in the warm water community (∼ 2 mg C m−3) compared with the cold water community (∼ 1.3 mg C m−3). The warm water community was dominated by Aglantha digitale, Lizzia blondina, and Nanomia bijuga, whereas the cold water community was dominated by Clytia hemisphaerica and ctenophores. Physonect siphonophores contributed > 36% to the gelatinous biomass in the warm water community, and their widespread distribution suggests they are ecologically more important than previously thought. A distinct oceanic influence was also recorded in the wider warm water zooplankton community, accounting for a ∼ 20 mg C m−3 increase in biomass in that region.

The object of this article is to define the facilities construction for the Avaldsnes section of the Johan Sverdrup field in the North Sea. Based on the experiences of oil and gas companies, the applicability of various offshore oil and gas field structures will be analyzed. According to the results, the most relevant field facilities scenarios were formed. Each scenario was technically and economically assessed. The technical assessment consisted of the evaluation of loads under the different climate conditions on the offshore oil and gas facility, along with resistance against overturning and sliding. The economic assessment included the calculation of the key economic indicators of various scenarios and comparing them. The integrated assessment indicated that the combination of several subsea production modules is the most cost-effective field facilities scenario to implement in the Avaldsnes area of the Johan Sverdrup field in the North Sea.

Phuket Marine Biological Center Research Bulletin, 77, 1, 77–87

A three dimensional hydrodynamic model with a coupled carbonate speciation sub-model is used to simulate large additions of CO2 into the North Sea, representing leakages at potential carbon sequestration sites. A range of leakage scenarios are conducted at two distinct release sites, allowing an analysis of the seasonal, inter-annual and spatial variability of impacts to the marine ecosystem. Seasonally stratified regions are shown to be more vulnerable to CO2 release during the summer as the added CO2 remains trapped beneath the thermocline, preventing outgasing to the atmosphere. On average, CO2 injected into the northern North Sea is shown to reside within the water column twice as long as an equivalent addition in the southern North Sea before reaching the atmosphere. Short-term leakages of 5000 tonnes CO2 over a single day result in substantial acidification at the release sites (up to -1.92 pH units), with significant perturbations (greater than 0.1 pH units) generally confined to a 10 km radius. Long-term CO2 leakages sustained for a year may result in extensive plumes of acidified seawater, carried by major advective pathways. Whilst such scenarios could be harmful to marine biota over confined spatial scales, continued unmitigated CO2 emissions from fossil fuels are predicted to result in greater and more long-lived perturbations to the carbonate system over the next few decades.

Thermohaline fronts are present globally and have been identified as biodiversity hotspots, encouraging enhanced primary productivity and attracting dense aggregations of higher trophic level organisms. The Celtic Boundary Front (CBF) sits in an important zone of economic activity yet no contemporary studies describing the meso-zooplankton community exist for this region. High-frequency sampling during June 2009 revealed three distinct areas on the mixed (Irish Sea) and stratified (Celtic Sea; Celtic Deep) sides of the front, each exhibiting distinct physical and biological characteristics. Low zooplankton abundance was found above the Celtic Deep, despite apparent optimal phytoplankton conditions, conflicting with observations made at other frontal locations. Although zooplankton assemblages were generally distinct within areas, the copepod Acartia clausii was ubiquitous across all three areas and accounted for almost 60% of all counted individuals. The long-term variation of zooplankton during the seasonal front development was examined using samples from the Continuous Plankton Recorder. The results of this analysis suggest that low abundance is a recurring feature over the Celtic Deep. Possible explanations for the observed patterns may be top-down effects on zooplankton from pelagic fish; alternatively, these patterns may be a consequence of the strong density and stratification gradients in the Celtic Deep.

The seafloor in shallow coastal and shelf seas is a highly dynamic system providing plenty of natural resources and important ecosystem services. Driven by energetic physical forcing, biological activity and intense anthropogenic use, its mobile sediments are constantly overturned. The reworking processes mediate the exchange of abundant organic matter and pollutants across the benthic interface. Coherent in situ measurements of forcing and morphodynamic response help to identify relevant reworking mechanisms, to outline their spatial and temporal scales, and to quantify their impacts on the benthic ecosystem. New high-resolution observation techniques enable also the assessment of small-scale processes that, due to their ubiquity, are yet of shelf-wide importance. This thesis explores three mechanisms in the southeastern North Sea: The morphology and dynamics of small scale-bedforms, the relation of physical and biogenic sediment reworking by bedform migration and bioturbation, and the effect of submarine fluid expulsion. The analysis of these processes reveals new links between physical and biological drivers and illustrates their complex interactions at the benthic interface.