Fatigue crack growth in mooring chain steel at different mean load levels

The fatigue crack growth rates of R4 mooring chain steel at different R-ratios are investigated. Crack growth experiments are performed at three different R-ratios, 0.1, 0.3 and 0.7, utilizing compact tension specimens in air environment. Huang and Moan’s driving force parameter ΔKE, which relates the growth rates at different R-ratios to those obtained at R = 0, is explored and adapted for R4 steel. A full-scale fatigue experiment involving a chain assembly with an identified crack is presented, where the observed crack growth was successfully modelled by the proposed crack growth model. Case studies with different mean loads are explored where the crack growth model is utilized to predict the fatigue life of D = 145 mm chain links with a crack at the crown location. The crack growth simulations are compared and discussed against published S–N curves for chain links with varying mean load. The S–N curves may give very inaccurate results when extrapolated outside of the underlying test data. The crack growth model predicts longer lives at low stress ranges and low mean loads compared to the S–N curves, indicating that current guidelines may be overly conservative in these conditions.publishedVersio

Energy content of krill and amphipods in the Barents Sea from summer to winter: variation across species and size

Arctic zooplankton develop large energy reserves, as an adaptation to strong seasonality, making them valuable prey items. We quantified the energy content (kJ g−1 dry weight) of abundant krill (arcto-boreal, Thysanoessa inermis and boreal, Meganyctiphanes norvegica) and amphipods (Arctic, Themisto libellula and sub-Arctic-boreal, Themisto abyssorum) in the Barents Sea in late summer (August) and early winter (December). Variation in energy content was attributed to species-specific traits and body size categories, the latter in part as a proxy for ontogeny. T. inermis had the highest energy content, (Aug: 26.8 ± 1.5 (SD) kJ g−1) and remained similar from summer to winter. Energy content increased in M. norvegica and decreased in both amphipod species, with the lowest energy content being in T. abyssorum (Dec: 17.8 ± 0.8 kJ g−1). The effect of body size varied between species, with energy content increasing with size in T. inermis and T. libellula, and no change with size in M. norvegica and T. abyssorum. The reproductive stages of T. libellula differed in energy content, being highest in gravid females. Energy content varied with species’ dependence on energy storage. Our findings highlight how phylogenetically and morphologically similar prey items cannot necessarily be considered equal from a predator´s perspective. Energetically, the northern T. inermis was higher quality compared to the more southern M. norvegica, and mostly so during summer. Ecological models and management strategies should consider such variation in prey quality, especially as Arctic borealization is expected to change species composition and the energetic landscape for predators.publishedVersio

Analysis of S–N data for new and corroded mooring chains at varying mean load levels using a hierarchical linear model

Results from full scale fatigue tests of offshore mooring chains are analyzed. The data set includes new and used chains, tested at a variety of mean load levels. The used chains have been retrieved after operation offshore and include samples with varying surface conditions, ranging from as-new to heavily corroded. Based on a parameterized S–N curve intercept parameter, the effects of mean load and chain condition are estimated empirically by regression analysis. A hierarchical linear model is used, to account for and quantify correlations within subsets of the data. The choice of grouping criterion for the hierarchical model is discussed, and assessed based on the current data. Results show that the mean load and corrosion effects are both significant. Differences in the fatigue performance of new versus used chains are quantified and discussed.publishedVersio

Livestock-Associated MRSA CC1 in Norway; Introduction to Pig Farms, Zoonotic Transmission, and Eradication

Farm animals have been identified as an emerging reservoir for transmission of livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) to humans. The low incidence of MRSA in humans and farm animals in Norway has led to the implementation of a national strategy of surveillance and control of LA-MRSA aiming to prevent livestock becoming a domestic source of MRSA to humans. In 2015, MRSA clonal complex 1 spa-type t177 was identified in nine Norwegian pig herds in two neighboring counties. An outbreak investigation was undertaken, and measures of control through eradication were imposed. We performed a register-based cohort study including pig herds and MRSA-positive persons in Norway between 2008 and 2016 to investigate the livestock-association of MRSA CC1, the transmission of the outbreak strain to humans before and after control measures, and the effect of control measures imposed. Data from the Norwegian Surveillance System of Communicable Diseases were merged with data collected through outbreak investigations for LA-MRSA, the National Registry and the Norwegian Register for Health Personnel. Whole-genome sequencing was performed on isolates from livestock and humans identified through contact tracing, in addition to t177 and t127 isolates diagnosed in persons in the same counties. It is likely that a farm worker introduced MRSA CC1 to a sow farm, and further transmission to eight fattening pig farms through trade of live pigs confirmed the potential for livestock association of this MRSA type. The outbreak strain formed a distinct phylogenetic cluster which in addition to the pig farms included one sheep herd and five exposed persons. None of the investigated isolates from possible cases without direct contact to the MRSA positive farms were phylogenetically related to the outbreak strain. Moreover, isolates of t177 or t127 from healthcare and community-acquired cases were not closely related to the outbreak cluster. Eradication measures imposed were effective in eliminating MRSA t177 from the positive pig holdings, and the outbreak strain was not detected in the national pig population or in persons from these counties after control measures

Aggregations of foraging black guillemots (Cepphus grylle) at a sea-ice edge in front of a tidewater glacier

Seabirds in cold biomes sometimes aggregate near glacier fronts and at sea-ice edges to forage. In this note, we report on large aggregations of black guillemots (Cepphus grylle) at the edge of sea ice in front of the tidewater glacier Kongsbreen (Kongsfjorden, Svalbard). During several days in the second half of June 2011, we observed 49–155 individuals of black guillemots at this ice edge. They foraged actively, and many of the dives were directed underneath the sea ice. The outflow of glacial meltwater and resulting upwelling generated opportunities for the black guillemots to feed, likely on zooplankton or fish. The black guillemots used the sea ice as a resting platform between dives or diving sessions, and whilst on the ice, they interacted socially. On our last visit, the sea ice was gone, and the black guillemots had left the bay. At the neighbouring tidewater glacier Kronebreen, there was no sea ice connected to the glacier. Surface-feeding seabirds, particularly black-legged kittiwakes (Rissa tridactyla), were numerous at the plumes generated by meltwater from Kronebreen. Black guillemots were not seen at these plumes, but some individuals were seen scattered in the fjord system. Our observations add to the natural history of black guillemots and enhance our knowledge of ecological interactions and seabird habitat use shaped by tidewater glaciers

Keeping track of samples in multidisciplinary fieldwork

We here present methods, tools and results for efficiently collecting metadata and tracking samples collected in the field. The samples and metadata were collected during scientific cruises conducted by amongst others marine biologists, oceanographers, geochemists and marine geologists in the Nansen Legacy project. It is here reported on the successful development and implementation of a system for labeling, tracking and openly publishing metadata from the cruises. The results and tools have been made openly available, as they are suitable for a range of situations, from the individual scientist working in the field to large research missions

Nutrient fuxes from an Arctic seabird colony to the adjacent coastal marine ecosystem

Seabirds are important vectors for nutrient transfer across ecosystem boundaries. In this seasonal study, we evaluate the impact of an Arctic colony (Alkhornet, Svalbard) of Black-legged Kittiwakes (Rissa tridactyla) and Brünnich’s Guillemots (Uria lomvia) on stream nutrient concentrations and fuxes, as well as utilization by coastal biota. Water samples from seabird-impacted and control streams were collected regularly throughout the melt season (June–September) for nutrient and organic carbon analysis. Stable carbon and nitrogen isotope analysis (δ13C and δ15N) was used to assess whether seabird derived nitrogen (N) could be traced into flamentous stream algae and marine algae as well as consumers (amphipods). Concentrations of nitrate (NO3−) and nitrite (NO2) peaked in July at 9200 µg N L−1 in seabird-impacted streams, 70 times higher than for control streams. Mean concentrations of phosphate (PO4 3−) in seabird-impacted streams were 21.9 µg P L−1, tenfold higher than in controls. Areal fuxes from seabird-impacted study catchments of NO3− + NO2− and PO4 3− had estimated ranges of 400–2100 kg N km−2 and 15–70 kg P km−2, respectively. Higher δ15N was found in all biota collected from seabird-impacted sites, indicating utilization of seabird-derived nitrogen. Acrosiphonia sp. from seabird-impacted sites had higher δ15N values (20–23‰ vs. 3–6‰) and lower C:N ratios (10.9 vs. 14.3) than specimens collected from control sites, indicating reliance on seabird-derived nitrogen sources and potentially higher N-availability at seabird-impacted nearshore sites. Our study demonstrates how marine nutrients brought onshore by seabirds also can return to the ocean and be utilized by nearshore primary producers and consumers. Cross-ecosystem fuxes · Runof · Svalbard · Seabird guano · Rissa tridactyla · Uria lomvia · Macroalga

Nutrient fuxes from an Arctic seabird colony to the adjacent coastal marine ecosystem

Seabirds are important vectors for nutrient transfer across ecosystem boundaries. In this seasonal study, we evaluate the impact of an Arctic colony (Alkhornet, Svalbard) of Black-legged Kittiwakes (Rissa tridactyla) and Brünnich’s Guillemots (Uria lomvia) on stream nutrient concentrations and fuxes, as well as utilization by coastal biota. Water samples from seabird-impacted and control streams were collected regularly throughout the melt season (June–September) for nutrient and organic carbon analysis. Stable carbon and nitrogen isotope analysis (δ13C and δ15N) was used to assess whether seabird derived nitrogen (N) could be traced into flamentous stream algae and marine algae as well as consumers (amphipods). Concentrations of nitrate (NO3−) and nitrite (NO2) peaked in July at 9200 µg N L−1 in seabird-impacted streams, 70 times higher than for control streams. Mean concentrations of phosphate (PO4 3−) in seabird-impacted streams were 21.9 µg P L−1, tenfold higher than in controls. Areal fuxes from seabird-impacted study catchments of NO3− + NO2− and PO4 3− had estimated ranges of 400–2100 kg N km−2 and 15–70 kg P km−2, respectively. Higher δ15N was found in all biota collected from seabird-impacted sites, indicating utilization of seabird-derived nitrogen. Acrosiphonia sp. from seabird-impacted sites had higher δ15N values (20–23‰ vs. 3–6‰) and lower C:N ratios (10.9 vs. 14.3) than specimens collected from control sites, indicating reliance on seabird-derived nitrogen sources and potentially higher N-availability at seabird-impacted nearshore sites. Our study demonstrates how marine nutrients brought onshore by seabirds also can return to the ocean and be utilized by nearshore primary producers and consumers. Cross-ecosystem fuxes · Runof · Svalbard · Seabird guano · Rissa tridactyla · Uria lomvia · Macroalga