Transient electromagnetic surveys with unimodal transverse magnetic field: ideas and results

The theory behind transient electromagnetic surveys can be well described in terms of transverse magnetic and transverse electric modes. Soundings using transverse magnetic and transverse electric modes require different source configurations. In this study, we consider an alternating transverse magnetic field excitation by a circular electric dipole. The circular electric dipole transmitter is a horizontal analogue of the vertical electric dipole. Offshore surveys using circular electric dipole might represent an alternative to the conventional marine controlled‐source electromagnetic method at shallow sea and/or for exploring relatively small targets. Field acquisition is carried out by recording either electric or magnetic responses. Electric responses bear information on the 1D structure of a layered earth and successfully resolve high‐resistivity targets in marine surveys. Land‐based circular electric dipole soundings are affected by induced polarisation. On the contrary, magnetic responses are absent on the surface of a 1D earth, and as a result, they are very sensitive to any and even very small 3D conductivity perturbations. In addition, they are sensitive to induced polarisation or some other polarisation effects in the subsurface. At present, circular electric dipole transmitters and magnetic receivers are successfully used in on‐land mineral and petroleum exploration.     

Frequent subgraph mining in oceanographic multi-level directed graphs

We present an adaptation and application of frequent subgraph mining (FSM) in a time series of spatial multi-level directed graphs depicting probabilistic transitions of water masses between neighboring sea areas within a given time interval. The directed graphs are created from the results of the numerical model, the Mediterranean Ocean Forecasting System. We assign unique labels (geographical locations) to vertices of the multi-level directed graphs. Then, we add the edge labels as discretized values of the probabilities of transitions between vertices. This modification allows the use of the established algorithm gSpan to search for frequently directed subgraphs in the sequence of such directed graphs. Thus, we obtain both general and specific subgraphs, such as convergences, divergences, and paths of the ocean currents in the numerical model. The resulting substructures, revealed by directed subgraphs, match oceanographic structures (gyres, convergences/divergences, and paths) deduced from field observations, and can also serve as a tool for the validation of the numerical model of circulation in the sea.     

Shock‐induced formation of wüstite and fayalite in a magnetite‐quartz target rock

Projectile–target interactions as a result of a large bolide impact are important issues, as abundant extraterrestrial material has been delivered to the Earth throughout its history. Here, we report results of shock‐recovery experiments with a magnetite‐quartz target rock positioned in an ARMCO iron container. Petrography, synchrotron‐assisted X‐ray powder diffraction, and micro‐chemical analysis confirm the appearance of wüstite, fayalite, and iron in targets subjected to 30 GPa. The newly formed mineral phases occur along shock veins and melt pockets within the magnetite‐quartz aggregates, as well as along intergranular fractures. We suggest that iron melt formed locally at the contact between ARMCO container and target, and intruded the sample causing melt corrosion at the rims of intensely fractured magnetite and quartz. The strongly reducing iron melt, in the form of μm‐sized droplets, caused mainly a diffusion rim of wüstite with minor melt corrosion around magnetite. In contact with quartz, iron reacted to form an iron‐enriched silicate melt, from which fayalite crystallized rapidly as dendritic grains. The temperatures required for these transformations are estimated between 1200 and 1600 °C, indicating extreme local temperature spikes during the 30 GPa shock pressure experiments.     

Observation of a 3d Magnetic Null Point in the Solar Corona

A saddle-like structure is clearly discerned in SOHO EIT images in the Fe wavebands in the active region NOAA 8113, from 6 to 10 December 1997, when the active region reached the solar limb. It appears after the emergence of a small patch of parasitic polarity near the footpoints of the loops forming the outer boundary of an arcade. There is a 3D null point in the center of the saddle. The height of the null is in good agreement with the relationship between the parasitic flux and the background magnetic field. In spite of the fact that a saddle-like or hyperbolic magnetic configuration is usually assumed as the necessary condition for magnetic field-line reconnection and magnetic energy release, no additional heating is observed inside the saddle structure. Moreover, interior parts of the saddle seem to be darker than the neighbouring loops of the arcade.     

Physical properties, spectral reflectance and thickness development of first year fast ice in Kongsfjorden, Svalbard

A ground truth study was performed on first year fast ice in Kongsfjorden, Svalbard, during spring 1997 and 1998. The survey included sea ice thickness monitoring as well as observation of surface albedo, attenuation of optical radiation in the ice, physical properties and texture of snow and sea ice. The average total sea ice thickness in May was about 0.9 m, including a 0.2 m thick snow layer on top. Within a few weeks in both years, the snow melted almost completely, whereas the ice thickness decreased by not more than 0.05 m. During spring, the lower part of the snow refroze into a solid layer. The sea ice became more porous. Temperatures in the sea ice increased and the measurable salinity of the sea ice decreased with time. Due to snow cover thinning and snow grain growth, maximum surface albedo decreased from 0.96 to 0.74. Texture analysis on cores showed columnar ice with large crystals (max. crystal lenght > 0.1 m) below a 0.11 m thick mixed surface layer of granular ice with smaller crystals. In both years, we observed sea ice algae at the bottom part of the ice. This layer has a significant effect on the radiation transmissivity.     

Mineral composition of the fine-dispersed fractions of loess and soil processes developed in them

Of the stable indications of elementary soil processes those are to be identified which are taking place in the fine-dispersed fractions of soil by transformations of layer silicates and primarily of interstratified formations.Instrumental detection of transformations in the fine-dispersed material and of its migration along paleosol profiles allows a comparison with changes in recent soils and a judgement about the conditions of paleosol formation. This presumption is supported by data on the mineral composition of the fine-dispersed fractions of the Mikulino interglacial soils as a product of the first phase of pedogenesis within the Mezin loess- paleosol complex (Morozova et al. 1979) and, in general, of the loess-paleosol sequence developed above the ground moraine of the Don glacier tongue containing paleosols formed in the Early, Middle and Late Pleistocene (Velichko et al. 1965).     

Role of the upper ocean structure in the response of ENSO-like SST variability to global warming

The response of El Niño and Southern Oscillation (ENSO)-like variability to global warming varies comparatively between the two different climate system models, i.e., the Meteorological Research Institute (MRI) and Geophysical Fluid Dynamics Laboratory (GFDL) Coupled General Circulation Models (CGCMs). Here, we examine the role of the simulated upper ocean temperature structure in the different sensitivities of the simulated ENSO variability in the models based on the different level of CO₂ concentrations. In the MRI model, the sea surface temperature (SST) undergoes a rather drastic modification, namely a tendency toward a permanent El Niño-like state. This is associated with an enhanced stratification which results in greater ENSO amplitude for the MRI model. On the other hand, the ENSO simulated by GFDL model is hardly modified although the mean temperature in the near surface layer increases. In order to understand the associated mechanisms we carry out a vertical mode decomposition of the mean equatorial stratification and a simplified heat balance analysis using an intermediate tropical Pacific model tuned from the CGCM outputs. It is found that in the MRI model the increased stratification is associated with an enhancement of the zonal advective feedback and the non-linear advection. In the GFDL model, on the other hand, the thermocline variability and associated anomalous vertical advection are reduced in the eastern equatorial Pacific under global warming, which erodes the thermocline feedback and explains why the ENSO amplitude is reduced in a warmer climate in this model. It is suggested that change in stratification associated with global warming impacts the equatorial wave dynamics in a way that enhances the second baroclinic mode over the gravest one, which leads to the change in feedback processes in the CGCMs. Our results illustrate that the upper ocean vertical structure simulated in the CGCMs is a key parameter of the sensitivity of ENSO-like SST variability to global warming.     

Influence of Biogenic Secondary Organic Aerosol Formation Approaches on Atmospheric Chemistry

Global secondary organic aerosol formation (SOA) is currently assumed to be between 11.2 and 270 Tg/yr. This range of uncertainty is reflected in the gas-phase chemistry. In this study, we focus on the feedback of SOA formation on the concentrations of most important trace gases such as ozone, and compare it to the impact of monoterpene gas-phase chemistry with a newly developed reduced monoterpene mechanism (MMM) for either α- or β-pinene in the global chemistry transport model MATCH-MPIC. With this set-up an uncertainty range of 3.5–4.0% increase in annually averaged tropospheric ozone was found to be caused by the gas-phase chemistry of the investigated monoterpenes. Moreover, a strong feedback has been observed for NO_x, HCHO, HNO₃ and PAN. These observations are affected remarkably by different SOA formation approaches like partitioning or saturation vapour pressure limitation and by the structure of the monoterpene used, e.g. reducing the impact on tropospheric ozone to 1.2–1.9% by using the partitioning approach versus the simulation with gas-phase chemistry only. Therefore, a consideration of the individual processes associated with SOA formation seems to be necessary to reduce the uncertainty in SOA formation and to understand the impact of VOCs on atmospheric chemistry. An erratum to this article is available at .     

Insight into the Last Glacial Maximum climate and environments of the Baikal region

This study presents a multi‐proxy record from Lake Kotokel in the Baikal region at decadal‐to‐multidecadal resolution and provides a reconstruction of terrestrial and aquatic environments in the area during a 2000‐year interval of globally harsh climate often referred to as the Last Glacial Maximum (LGM). The studied lake is situated near the eastern shoreline of Lake Baikal, in a climatically sensitive zone that hosts boreal taiga and cold deciduous forests, cold steppe associations typical for northern Mongolia, and mountain tundra vegetation. The results provide a detailed picture of the period in focus, indicating (i) a driest phase (c. 24.0–23.4 cal. ka BP) with low precipitation, high summer evaporation, and low lake levels, (ii) a transitional interval of unstable conditions (c. 23.4–22.6 cal. ka BP), and (iii) a phase (c. 22.6–22.0 cal. ka BP) of relatively high precipitation (and moisture availability) and relatively high lake levels. One hotly debated issue in late Quaternary research is regional summer thermal conditions during the LGM. Our chironomid‐based reconstruction suggests at least 3.5 °C higher than present summer temperatures between c. 22.6 and 22.0 cal. ka BP, which are well in line with warmer and wetter conditions in the North Atlantic region inferred from Greenland ice‐cores. Overall, it appears that environments in central Eurasia during the LGM were affected by much colder than present winter temperatures and higher than present summer temperatures, although the effects of temperature oscillations were strongly influenced by changes in humidity.     

http://www.sciencedirect.com/science/article/pii/S1674987111000806

Zoned tourmaline（schorl-dravite） in the matrix of hydrothermal explosive breccia and ore veins in gold deposits,Chita region.Eastern Transbaikalia.Russia,are associated with Na- and K-rich porphyry-type subvolcanic intrusives.δ¹⁸O values of tourmaline from three gold deposits（Darasun. Talatui,Teremkinskoye） are +8.3‰,+7.6‰,and +6.0‰and calculatedδ¹⁸O values of fluids responsible for the tourmalinization are +7.3‰,+7.7‰,and +4.2‰,respectively.These data imply an igneous fluid source,except at the Teremkin deposit where mixing with meteoric water is indicated.Wide ranges of Fe³⁺/Fe_tot,and the presence of vacancies characterize the Darasun deposit tourmaline indicating wide ranges of f（O₂） and pH of mineralizing fluids.Initial stage tourmalines from the gold deposits of the Darasun ore district are dravite or high mg schorl.Second stage tourmaline is characterized by oscillatory zoning but with Fe generally increasing towards crystal rims indicating decreasing temperature.Third stage tourmaline formed unzoned crystals with x_Mg（mole fraction of Mg） close to that of the hrst stage tourmaline,due to a close association with pyrite and arsenopyrite.From Fe³⁺/Fe_tot values,chemical composition and crystallization temperatures.logf（O₂） of mineralizing fluids ranged from ca.—25 to—20. much higher than for the gold-bearing beresite—listvenite association,indicating that tourmalinization was not related to gold mineralization.