Transient electromagnetic modelling of an isolated wire loop over a conductive medium

A large closed wire loop is generally used in field experiments for testing airborne electrical exploration equipment. Thus, methods are required for the precise calculation of an electromagnetic response in the presence of a closed wire loop. We develop a fast and precise scheme for calculating the transient response for such a closed loop laid out at the surface of a horizontally layered conductive ground. Our scheme is based on the relationship between the magnetic flux flowing through a closed loop and the current induced in it. The developed scheme is compared with 2D and 3D finite‐element modelling for several positions of an airborne electromagnetic system flying over a closed loop. We also study the coupling effect between the current flowing in the closed loop and the current flowing in the horizontally layered conductive medium. The result shows that for the central position of the transmitter, the difference between axisymmetrical finite‐element modelling and our scheme is less than 1%. Moreover, for the non‐coaxial transmitter–receiver–loop system, the solution obtained by our scheme is in good agreement with full 3D finite‐element modelling, and our total simulation time is substantially lower: 1 minute versus 120 hours.     

Correlations between fatty acid composition of seston and zooplankton and effects of environmental parameters in a eutrophic Siberian reservoir

During two sampling seasons we analyzed on weekly basis fatty acid (FA) composition of seston fraction <130 μm and zooplankton fraction >130 μm, and compared them using a multivariate canonical correlation analysis (CCA). Besides, we evaluated a possible impact of water temperature and inorganic nutrients on FA composition of the seston and the zooplankton.In spite of significant differences in percentages of several individual FAs, we found very strong canonical correlation (cross-correlation, 1-week lag) between FA composition of the seston and the zooplankton. The most important factor, providing the overall canonical cross-correlation between FA profiles of the seston and the zooplankton fractions was eicosapentaenoic acid (20:5ω3, EPA). FA composition of the zooplankton fraction had comparatively poor correlations with taxonomic composition of the zooplankton. Thus, seasonal variations of FA composition of the zooplankton were determined primarily by seasonal changes in FA composition of the seston, rather than by taxonomic differences of FA profiles between rotifers, cyclopoids and cladocerans. FA composition of the seston was strongly affected by its taxonomic composition, namely by that of phytoplankton. According to CCA, the highest factor loadings pertained to diatoms interacting with their marker acids, including EPA, and cyanobacteria and greens, interacting with their marker acids. Ciliates and small rotifers composed considerable and sometimes major part of the seston biomass, but according to CCA their contributions to seasonal variations of the total FA profile of the seston were insignificant. This finding indirectly support the conclusion of the other authors, that the main source of FAs presented in ciliates and rotifers must be sought in algae and that they do not modify FA composition of food consumed, apart from repackaging it.Water temperature was the principal environmental parameter which drove the overall variations of FA composition. Factor loadings for the inorganic nutrients were comparatively negligible. The main contribution in the seasonal variation of FA composition of the seston was given by negative interaction between water temperature and percentage of EPA in the seston.     

Deep currents in the central part of the Drake Passage based on the data of the 2008 hydrographic survey

The currents within the junction of the Shackleton and West-Scotia ridges in the central part of the Drake Passage are studied using the data of the hydrographic survey carried out in October–November of 2008. The absolute geostrophic currents were computed by matching the CTD and LADCP data. As a result, the complicated system of deep currents conditioned by the ocean bottom’s topography was revealed and described. A new path of propagation of the Antarctic Bottom Water has been revealed.     

Determination of the equatorial velocity and inclination of the equatorial plane of an astrophysical object in space

N. É. Bauman Scientific-Research Institute of Applied Mathematics and Mechanics. Translated from Astrofizika, Vol. 34, No. 2, pp. 227–232, March–April, 1991.     

The role of the Spitsbergen shear zone in determining morphology,segmentation and evolution of the Knipovich Ridge

In 1989–1990 the SeaMARC II side-looking sonar and swath bathymetric system imaged more than 80 000 km² of the seafloor in the Norwegian-Greenland Sea and southern Arctic Ocean. One of our main goals was to investigate the morphotectonic evolution of the ultra-slow spreading Knipovich Ridge from its oblique (115° ) intersection with the Mohns Ridge in the south to its boundary with the Molloy Transform Fault in the north, and to determine whether or not the ancient Spitsbergen Shear Zone continued to play any involvement in the rise axis evolution and segmentation. Structural evidence for ongoing northward rift propagation of the Mohns Ridge into the ancient Spitsbergen Shear Zone (forming the Knipovich Ridge in the process) includes ancient deactivated and migrated transforms, subtle V-shaped-oriented flank faults which have their apex at the present day Molloy Transform, and rift related faults that extend north of the present Molloy Transform Fault. The Knipovich Ridge is segmented into distinct elongate basins; the bathymetric inverse of the very-slow spreading Reykjanes Ridge to the south. Three major fault directions are detected: the N-S oriented rift walls, the highly oblique en-echelon faults, which reside in the rift valley, and the structures, defining the orientation of many of the axial highs, which are oblique to both the rift walls and the faults in the axial rift valley. The segmentation of this slow spreading center is dominated by quasi stationary, focused magma centers creating (axial highs) located between long oblique rift basins. Present day segment discontinuities on the Knipovich Ridge are aligned along highly oblique, probably strike-slip faults, which could have been created in response to rotating shear couples within zones of transtension across the multiple faults of the Spitsbergen Shear Zone. Fault interaction between major strike slip shears may have lead to the formation of en-echelon pull apart basins. The curved stress trajectories create arcuate faults and subsiding elongate basins while focusing most of the volcanism through the boundary faults. As a result, the Knipovich Ridge is characterized by Underlapping magma centers, with long oblique rifts. This style of basin-dominated segmentation probably evolved in a simple shear detachment fault environment which led to the extreme morphotectonic and geophysical asymmetries across the rise axis. The influence of the Spitsbergen Shear Zone on the evolution of the Knipovich Ridge is the primary reason that the segment discontinuities are predominantly volcanic. Fault orientation data suggest that different extension directions along the Knipovich Ridge and Mohns Ridge (280° vs. 330°, respectively) cause the crust on the western side of the intersection of these two ridges to buckle and uplift via compression as is evidenced by the uplifted western wall province and the large 60 mGal free air gravity anomalies in this area. In addition, the structural data suggest that the northwards propagation of the spreading center is ongoing and that a `normal' pure shear spreading regime has not evolved along this ridge. This revised version was published online in November 2006 with corrections to the Cover Date.     

Anomalously deep convection in the Irminger Sea during the winter of 2014–2015

The anomalous thermohaline properties of the core of the Labrador Sea water (LSW), a product of winter convection resulted from the ocean–winter interaction, which were recorded in the Irminger Sea in 2014 and 2015, are discussed. It is found that, in the summer of 2015, the LSW filled the entire deepwater basin in the south of the sea down to a depth of 1300 m over the periphery of the Irminger gyral, and down to a depth of 1800 m, in the anticyclone eddy formed in early June of 2015. The maximum density of the LSW core here was 27.75 σ_θ. Such deep and intense winter convection in the Irminger Sea was last recorded 20 years ago. As a result, the temperature of the LSW dropped to values observed in the years 2002 and 2007, but its average salinity remained high. The LSW that have been formed in recent years are reported to have great amplitude and nonmonotonic variability of the properties.     

The Arctic Coastal Dynamics Database: A New Classification Scheme and Statistics on Arctic Permafrost Coastlines

Arctic permafrost coasts are sensitive to changing climate. The lengthening open water season and the increasing open water area are likely to induce greater erosion and threaten community and industry infrastructure as well as dramatically change nutrient pathways in the near-shore zone. The shallow, mediterranean Arctic Ocean is likely to be strongly affected by changes in currently poorly observed arctic coastal dynamics. We present a geomorphological classification scheme for the arctic coast, with 101,447?km of coastline in 1,315 segments. The average rate of erosion for the arctic coast is 0.5?m? year^?1 with high local and regional variability. Highest rates are observed in the Laptev, East Siberian, and Beaufort Seas. Strong spatial variability in associated database bluff height, ground carbon and ice content, and coastline movement highlights the need to estimate the relative importance of shifting coastal fluxes to the Arctic Ocean at multiple spatial scales.     

Upper layer structure and variability of the Antarctic Circumpolar Current in the Drake Passage

The spatiotemporal variability of the Antarctic Circumpolar Current (ACC) structure in the upper 100–800 m layer is analyzed at two sections in the Drake Passage. The existence of the Subantarctic and Polar Current superjets, formed due to the confluence of a few jets together, is confirmed. Peak eddy activity at the periphery of all the ACC jets is revealed, which demonstates intensive meridional eddy exchange of properties across the Passage. The ACC jets are strongly coherent in the vertical direction. The ACC upper layer transport intensifies over bottom relief rises because of jet acceleration during their crossing.     

Subpolar mode water classes in the northeast Atlantic: Interannual and long-term variability

Doklady Earth Sciences - We distinguish the classes of Subpolar Mode Waters (SPMWs), calculate their long-term characteristics, and analyze their interannual and long-term variability based on data...